Harlequinmania

Click through to see the images. There have been many debates about symbiotic flatworms, especially about their effect on corals. Aquarists have long regarded flatworms as a nuisance, possibly due to their unaesthetic appearance when present in large numbers. To keep flatworm populations under control, aquarists use a variety of methods, both chemical and biological (Carl 2008). Flatworms, here Waminoa sp. on a Goniopora sp., are usually considered a nuisance in home aquaria. Flatworms are found on many coral species, including Catalaphyllia jardinei. The presence of two lobes on the posterior ends of these flatworms could suggest they are members of the genus Waminoa. Without the presence of natural predators, flatworm populations are difficult to control in aquaria. A small Euphyllia colony can easily host hundreds of flatworms. Scientists, on the other hand, have regarded flatworms with much interest over the years. Marine biologists have long wondered whether flatworms should be regarded as mutualistic, parasitic or commensal coral symbionts. It is now clear that many polyclad (from Greek; polýs=many, klados=branch) flatworms are coral predators, or corallivores, which can devour complete Acropora colonies in short periods of time (Nosratpour 2008; Rawlinson 2010). The nature of acoelomorph (from Greek; a=not, coelom=body cavity, morph=form) flatworms, distant relatives of polyclads, has been elusive however. These gutless flatworms are commonly found in aquaria and on coral reefs, and are suspected to reduce photosynthesis rates of coral zooxanthellae through light shading; as acoelomorph flatworms host zooxanthellae themselves, high worm densities on coral tissue may act as sunscreens, reducing the amount of available light for corals (Barneah et al. 2007). Recent evidence published by Naumann et al. (2010) has shown that these so-called epizoic (from Greek; epi=on, zoon=animal) acoelomorph flatworms feed on coral mucus. By labeling Fungia and Ctenactis mucus with a stable nitrogen isotope, they were able to retrieve its isotopic signature from the flatworms (Waminoa sp.). By feeding on coral mucus, the flatworms may render the corals more sensitive to sedimentation, desiccation after air exposure, UV radiation and bacterial infections. Although corals infested with flatworms may look healthy, Naumann et al. (2010) stated that "the association of epizoic Waminoa worms with scleractinian corals will require further investigation to fully resolve its potential function, including the possible role of Waminoa as a pest in corals." A year later, members of our coral lab at Aquaculture and Fisheries (Dept. of Animal Sciences, Wageningen University and Research Centre) demonstrated that acoelomorph flatworms compete with their coral host for zooplankton (Wijgerde et al. 2011a). These flatworms, tentatively identified as Waminoa sp., were found to capture Artemia by rising from the polyp surface and encapsulating their prey (see video below). Although the flatworms only captured moderate amounts of zooplankton compared to their coral host, we theorized that competition between corals and flatworms for prey could be highly disadvantageous to corals under low prey concentrations, as flatworms seem to be more efficient zooplanktivores compared to their host. This may be especially true in the wild, where ambient zooplankton concentrations are generally low: three zooplankters per liter of water is not uncommon (Palardy et al. 2006). This video shows flatworms capturing Artemia nauplii. Prey is rapidly immobilized after which ingestion and digestion are likely to occur. The effect of flatworms on coral feeding Based on our preliminary findings, we decided to determine to what extent flatworms affect the feeding rates of their coral host. To this end, we used solitary polyps of the scleractinian coral Galaxea fascicularis. Individual polyps were removed from a large parent colony using pincers, and mounted onto PVC plates with epoxy resin. Solitary polyps (N=9) were either used for experiments together with their epizoic acoelomorph worms, or dewormed completely (N=9) with the anthelminthic levamisole hydrochloride. Levamisole is commonly used in the aquarium industry (Carl 2008), and induces spasms in flatworms while corals seem unaffected, at least at a concentration of 25 mg L-1 (Leewis et al. 2009). As acoelomorph flatworms produce eggs that may be insensitive to chemical agents, the worm-free corals were exposed to levamisole again after one week. After the last levamisole treatment, we allowed all corals to recover for two weeks. With the help of professor Ulf Jondelius of the Naturhistoriska riksmuseet (Stockholm, Sweden), we identified the flatworms hosted by our corals using DNA analysis. This revealed that the worms belonged to the genus Waminoa (family Convolutidae), which is found on many coral species (Barneah et al. 2007; Haapkylä et al. 2009; Naumann et al. 2010).The flatworm tissue contained high densities of symbiotic algae, possibly Symbiodinium or Amphidinium sp. Photomicrograph of an epizoic acoelomorph flatworm (Waminoa sp.) isolated from Galaxea fascicularis. Note the abundant symbiotic dinoflagellates in the worm's tissue. Scale bar: 100 m. After the recovery period, we incubated the polyps individually in a flow cell for 30 minutes together with newly hatched Artemia nauplii (brine shrimp larvae), during which their feeding activities were recorded (for details see Wijgerde 2011b). To determine whether the negative effect of flatworms, if any, would increase at lower prey availability, we incubated each polyp at three different prey concentrations (250, 500 and 1,000 Artemia nauplii L-1). These concentrations were chosen as they reflect aquaculture conditions, and to ensure that sufficient feeding events would occur during the short incubations. As each coral polyp was exposed to three concentrations, we randomized these treatments for each polyp to minimize the effect of time (for example, corals could learn from the first experimental run, resulting in more feeding during the second and third experiments). Each coral polyp was allowed to rest for one week between experiments. Several variables were scored during video analysis; capture, release and retention (capture minus release) of prey by coral polyps; capture and release of prey by flatworms; prey stolen from the coral by flatworms; total number of flatworms present on the disc of the coral; and cumulative flatworm time spent on the disc of the coral. During all treatments, G. fascicularis polyps were active and well expanded. All polyps captured, released and retained zooplankton prey by mucus entrapment. Nauplii were either ingested or digested externally by mesenterial filaments, which were expelled through the mouth and temporary openings in the ectoderm of the disc. Capture rates at prey concentrations of 250 and 500 nauplii L-1 were similar for worm-free and worm-hosting corals. In contrast, dewormed polyps captured significantly more prey at the highest prey concentration of 1,000 nauplii L-1. The same pattern was found for prey release and retention, where worm-free polyps released and retained more prey compared to worm-hosting polyps at 1,000 nauplii L-1. Statistical analysis of the data revealed that higher prey concentrations led to higher feeding rates, with an approximate linear relationship between the two variables. This linear effect of prey density on coral feeding has been reported frequently in the literature (Clayton and Lasker 1982; Ferrier-Pagès et al. 1998; Houlbrèque et al. 2004a; Lasker 1982; Lewis 1992) and is due to the fact that at higher prey densities, corals encounter and capture more prey (up to a certain point, after which satiation occurs). However, this linear effect was only found for worm-free polyps. Corals hosting flatworms did not exhibit higher feeding rates when the prey concentration was elevated. In addition, we only detected a negative effect of flatworms on coral feeding rates at the highest prey concentration. At 250 and 500 nauplii L-1, negative trends were visible, but these were not significant. Galaxea fascicularis feeding rates, with and without flatworms, at different prey concentrations. (A) Captured, ( released and © retained prey by single polyps, expressed as nauplii polyp-1 30 min-1, at three different prey concentrations; 250, 500 and 1,000 nauplii L-1, without (black bars) or hosting (grey bars) epizoic flatworms. Values are means + s.d. (N=9). *Indicates significant difference (P<0.050, simple effects analysis). Prey capture and kleptoparasitism by epizoic flatworms Not only the corals were found to capture prey; flatworms captured nauplii by raising themselves from the coral surface and encapsulating their prey, like a cloth thrown over a table. Subsequent paralysis of prey was observed, which was possibly followed by ingestion and digestion in the worm's syncytial digestive system (a network of interconnected cells that serve as a primitive intestine). Some flatworms captured additional prey whilst holding on to previously captured prey, with a maximum of two prey items per worm, although this behaviour was rare. We did not observe any release of prey. Interestingly, flatworms stole prey from their host, by removing nauplii from the polyp surface after capture by the coral. This regularly occurred within several minutes after the corals captured nauplii. In relative terms, these stealing rates were equal to 50.0±2.1, 5.3±3.3 and 22.2±2.8% of prey previously captured by the corals at the three prey concentrations, respectively. No translocation of nauplii or organic material from the flatworms to the coral host was observed. We also did not find any significant effect of prey concentration on prey capture by flatworms or the number of prey stolen from the host coral. Again, a trend was visible, but this was not significant. Overview of an epizoic flatworm capturing a single Artemia nauplius. Upper left: a flatworm (Waminoa sp.) hosted by G. fascicularis. Upper right: the flatworm raises its anterior edge from the polyp surface. Lower left: the worm folds itself over its prey. Lower right: the worm presses its prey onto the coral surface. Scale bar: 1 mm. Prey capture and kleptoparasitism by epizoic flatworms. (A) Total captured prey from the water column and ( stolen prey from the host coral by epizoic flatworms inhabiting a single coral polyp, expressed as nauplii 30 min-1, at three different prey concentrations; 250, 500 and 1,000 nauplii L-1. Values are means + s.d. (N=9). How do flatworms impair coral feeding? Based on our findings, it is clear that epizoic acoelomorph flatworms impair the ability of their coral host to feed on zooplankton. However, flatworms only seem to reduce coral feeding rates at high prey concentrations. What could the explanation? Flatworms may reduce feeding of the coral host due to several mechanisms; competition with the host coral for zooplankton prey (prey which come in close proximity to the coral polyp are regularly captured by epizoic flatworms instead of the coral); physical blocking of the disc of the host; mucus removal from the disc; and finally kleptoparasitism. At different prey concentrations, these four mechanisms may contribute to feeding impairment of the coral host to varying degrees. As flatworm feeding rates were moderate when compared to the worm-free coral host (3.2±4.0 versus 16.9±10.3 nauplii 30 min-1 at 1,000 nauplii L-1), a competition effect does not account for the total reduction of coral prey capture by flatworms, which was 14.2±10.9 nauplii polyp-1 30 min-1 at 1,000 nauplii L-1. Hence, physical blocking of the disc, mucus removal from the disc and kleptoparasitism remain as the potential mechanisms by which flatworms impair a coral's ability to feed on zooplankton. Physical blocking of the disc by flatworms is likely to reduce feeding effectiveness as not all tentacles are able to respond to incoming prey. However, as we found that flatworm presence and cumulative time spent on the disc did not differ between prey concentrations, this does not satisfactorily explain the absence of a flatworm effect at 250 and 500 nauplii L-1. Grazing on coral mucus by flatworms, as demonstrated for Waminoa sp. (Naumann et al. 2010), could result in prey capture impairment due to the reduced adhesive properties of the polyp. Indeed, at an ambient concentration of 1,000 nauplii L-1, prey were observed to interact with flatworm-hosting coral polyps without adhering to their tentacles on a number of occasions. Such lack of adherence was not observed for polyps that had their symbiotic flatworms removed. This suggests that the observed impairment of prey capture and retention at 1,000 nauplii L-1 was due to mucus grazing by flatworms, limiting the capacity of polyps to capture and retain more nauplii at higher prey concentrations. Finally, the stealing of prey by flatworms clearly contributed to a reduction of coral feeding. This behaviour is known as kleptoparasitism (from Greek; klepto=to steal), a specific form of parasitism where the parasite steals resources from another species. This behaviour is beneficial to the parasite, as it saves time and energy spent on resource gathering, and obviously disadvantageous to the host. An common example of marine kleptoparasites are seagulls, which regularly steal prey from diving birds. Waminoa sp. lurk in between the tentacles of this Galaxea fascicularis colony, where they steal prey previously acquired by their coral host. The camera flash reveals these obscure worms with their brown spotted tissue, a feature resulting from their symbiotic algae. Implications for corals Next to having reduced prey capture abilities, flatworm-hosting corals lose a significant portion of their captured prey (5.3±3.3 to 50.0±2.1%) to their epizoic flatworms. This loss of prey translates into a substantial loss of nutrients for corals. This could lead to nutritional deficiencies in terms of amino acids and fatty acids, which are taken up through zooplankton predation and are essential to coral growth (Houlbrèque and Ferrier-Pagès 2009). Thus, corals hosting high flatworm densities may experience a growth retardation, both in aquaculture and in the wild. In the latter situation, flatworms may be especially harmful as coral feeding rates on reefs are limited by a low prey availability. On reefs, corals could lose up to 100% of their daily acquired prey to epizoic flatworms. Given the fact that significant coral-associated flatworm populations have been found in the Red Sea and the Indo-Pacific (Barneah et al. 2007; Haapkylä et al. 2009; Naumann et al. 2010), epizoic flatworms may limit coral growth by impairing both photosynthesis and feeding. At this time, we have to conclude that the coral-associated Waminoa sp. in our lab is an epizoic parasite. Future studies may reveal that most, if not all, Waminoa spp. compromise the growth and health of corals when present in high densities. The same may hold true for members of the genus Convolutriloba, which are also commonly found on corals. Recent field evidence suggests that Waminoa spp. induce tissue loss in scleractinian corals, which, according to the authors, may be caused by reduced coral respiration, feeding and sediment shedding capacities (Hoeksema and Farenzena 2012). Implications for aquarists For aquarists, limiting captive flatworm populations may be appropriate after all to prevent harmful long-term effects on corals. To reduce the potential negative impact of acoelomorph flatworms on coral feeding and growth, natural predators may be introduced to keep flatworm numbers under control. There is evidence that certain wrasses (e.g. Halichoerus spp.), dragonets (e.g. Synchiropus splendidus) and nudibranchs (Chelidonura varians) actively prey on flatworms (Carl 2008; Nosratpour 2008; seaslugforum.net). Chemical treatment of corals with anthelmintics such as Levamisole works well, but this is laborious and could negatively affect long-term coral health. I would like to end this article by stating that the negative view people have on flatworms is not entirely justified. These interesting animals are a natural part of the reef ecosystem, and serve as a food source for predatory fish and nudibranchs. It is even possible that flatworms secrete wastes that are absorbed by their coral host. If this were true, our view of the symbiosis between flatworms and corals would change yet again. When flatworm populations are kept in check, they can be an interesting addition to the aquarium. Flatworms are a natural part of the reef ecosystem, and are not necessarily detrimental to corals if their numbers are kept low. Download the paper from the Biology Open website. References Barneah O, Brickner I, Hooge M, Weis VM, LaJeunesse TC, Benayahu Y (2007) Three party symbiosis: acoelomorph worms, corals and unicellular algal symbionts in Eilat (Red Sea). Mar Biol 151:1215-1223 Carl M (2008) Predators and pests of captive corals. In: Leewis RJ, Janse M (Eds) Advances in Coral Husbandry in Public Aquariums - Public Aquarium Husbandry Series, Volume 2, Burgers' Zoo, Arnhem, 31-36 Clayton WS, Lasker H (1982) Effects of light and dark treatments on feeding by the reef coral Pocillopora damicornis. J Exp Mar Biol Ecol 63:269-279 Ferrier-Pagès C, Allemand D, Gattuso JP, Jaubert J, Rassoulzadegan F (1998) Microheterotrophy in the zooxanthellate coral Stylophora pistillata: Effects of light and ciliate density. Limnol Oceanogr 43:1639-1648 Haapkylä J, Seymour AS, Barneah O, Brickner I, Hennige S, Suggett D, Smith D (2009) Association of Waminoa sp. (Acoela) with corals in the Wakatobi Marine Park, South-East Sulawesi, Indonesia. Mar Biol 156:2021-1027 Hoeksema BW, Farenzena ZT (2012) Tissue loss in corals infested by acoelomorph flatworms (Waminoa sp.). Coral Reefs 31:869 Houlbrèque F, Ferrier-Pagès C (2009) Heterotrophy in tropical scleractinian corals. Biol Rev Camb Philos 84:1-17 Houlbrèque F, Tambutté E, Richard C, Ferrier-Pagès C (2004) Importance of a micro-diet for scleractinian corals. Mar Ecol Prog Ser 282:151-160 Lasker HR, Syron JA, Clayton WS (1982) The feeding response of Hydra viridis: effects of prey density on capture rates. Biol Bull 162:290-298 Leewis RJ, Wijgerde T, Laterveer M, Osinga R (2009) Working with aquarium corals - A book of Protocols for the Breeding and Husbandry of Scleractinian Corals. Rotterdam Zoo, Rotterdam Lewis JB (1992) Heterotrophy in corals: Zooplankton predation by the hydrocoral Millepora complanata. Mar Ecol Prog Ser 90:251-256 Naumann MS, Mayr C, Struck U, Wild C (2010) Coral mucus stable isotope composition and labeling: experimental evidence for mucus uptake by epizoic acoelomorph worms. Mar Biol 157:2521-2531 Nosratpour F (2008) Observations of a polyclad flatworm affecting acroporid corals in captivity. In: Leewis RJ, Janse M (Eds) Advances in Coral Husbandry in Public Aquariums - Public Aquarium Husbandry Series, Volume 2, Burgers' Zoo, Arnhem, 37-46 Palardy JE, Grottoli AG, Matthews KA (2006) Effect of naturally changing zooplankton concentrations on feeding rates of two coral species in the Eastern Pacific. J Exp Mar Biol Ecol 331:99-107 Rawlinson KA, Gillis JA, Billings RE, Borneman EH (2011) Taxonomy and life history of the Acropora-eating flatworm Amakusaplana acroporae nov. sp. (Polycladida: Prosthiostomidae). Coral Reefs 30:693-705 The Sea Slug Forum, www.seaslugforum.net Wijgerde T (2011b) Aquarium corals: Zooplankton feeding by corals underestimated. Advanced Aquarist 10(10) Wijgerde T, Schots P, van Onselen E, Janse M, Karruppannan E, Verreth JAJ, Osinga R (2012) Epizoic acoelomorph flatworms impair zooplankton feeding by the scleractinian coral Galaxea fascicularis. Biol Open x:xx-xx Wijgerde T, Spijkers P, Verreth J, Osinga R (2011a) Epizoic acoelomorph flatworms compete with their coral host for zooplankton. Coral Reefs DOI: 10.1007/s00338-011-0781-z View the full article

Click through to see the images. Last year I blogged about a new prototype jellyfish aquarium from Cubic in the UK and now it is coming to the states in a matter of months via the new UK distributor Reef-Eden International. Currently US residents only have two options for tanks specifically designed to keep jellyfish: either Jellyfish Art's tank or Sunset Marine Labs' aquarium. Jellyfish Arts tank is a 6-gallon mini-kreisel design whereas Sunset Marine Labs' 10-gallon aquarium is more of your traditional boxy aquarium look but specifically designed to provide optimum flow for jellies. Cubic's jellyfish aquarium is also a kreisel, and features a rounded-corner rectangular system design, which gives it more of a traditional aquarium-like look but with smooth corners to keep jellies from becoming trapped in low-flow areas like traditional square-cornered aquariums. Rendering of how the Cubic aquarium in a household environment. According to Cubic and Reef-Eden International, the aquarium is made out of 10mm acrylic and measures 26" long x 10.2" wide x 23.6" tall yielding a net water volume of 21 gallons. This makes it the largest of the three available jellyfish aquariums on the market and the larger water volume may help with system stability as well. The aquarium comes with: builtin Biomatrix filtration which includes a removable coarse filter media tower and sponge media that is easy to replace. hard plumbed tank outlets ready for attachment to chillers and other devices. a CE-approved electrical system for lighting and filtration, which sits in its own dedicated dry compartment and incorporates water tight connectors where needed. a inbuilt fully functional remote controlled LED lighting system that allows the user to infinitely adjust the lighting using a range of settings yielding any color they wish. Settings includebrightness, static color, color auto transition and translation. Top-down photo of the filtration chamber highlighting the biomedia tower and sponge filtration. A top photo of the multi-color LEDs and remote for the aquarium. When someone purchases one of these aquariums, they will also receive a multi-language instructional CD which contains information about maintaining the aquarium itself in addition to information ranging from jellyfish biology, feeding, to handling advice. They will also have full access to Cubic's jellyfish forum where other Cubic jellyfish keepers can obtain support and advice from Cubic and from other jelly keepers. The price (subject to change) is around 807.23 euros or roughly $1039 according to Simon Garratt of Reef-Eden International. I encourage you to follow both Cubic Aquarium Systems and Reef-Eden International on Facebook (in addition to Advanced Aquarist) to keep up-to-date on this awesome aquarium. We definitely look forward to seeing this new addition to the aquarium market when it becomes available. Below are a couple videos from Cubic's Youtube channel highlighting the new jellyfish aquarium, some of which are from the Aquatics Live exhibition in London a few months back: View the full article

Click through to see the images. Kessil's A150W LED aquarium light packs a lot of photons into a small, compact package and is a great buy for anyone looking for a quality LED fixture for their tank. Indeed, Kessil has remained a popular light choice for reefkeepers based on Marine Depot's Aquarium Lighting listing with Kessil as one of the Top Selling Brands for many months running. The A150W light in combination with their pendant gooseneck clamp / mount make for a great way to hang the light without a lot of fuss. This $40 drop happened at a nice time of the year as reefkeepers begin making out their Christmas Wish Lists, and I am sure a lot of people will add them given this pricing adjustment. According to Kessil, this price drop covers the Deep Ocean Blue, Ocean Blue, Sky Blue, and Amazon Sun fixtures. Keep up with Kessil on Facebook, Twitter, and Youtube to stay on top of the latest company and product information. View the full article

Click through to see the images. The West African Seahorse, Hippocampus algiricus, is not well understood. Little is known about its habitat and lifecycle even though over 600,000 of these animals are traded annually on the market with most of them ending up in China for Chinese medicine. Kate West, a Masters student at the Imperial College London, wants to change that to better help the Senegalese and other governments better manage populations and maintain their CITES obligations for this species. Kate performed extensive field research into this species for her Masters Thesis, extensively documenting threats to this species, its wildlife trade, biology, distribution, habitat, and economic value. “Poor diving conditions and underwater visibility off the West African coast make it more difficult to conduct field studies than in other areas where seahorses are found,” Ms West said. “No research has been done on this species, and nothing is known about its habitat, life cycle, or population status, which is why this study is so vital for their conservation.” ... “In recent years, the West African seahorse has become highly sought after, along with many other seahorse species. Our fieldwork – the first ever study of this species – is revealing the fishing and trade pressures they face, and how populations can be sustained,” said Prof Amanda Vincent of the University of British Columbia, director of Project Seahorse. Below is a video that Kate shot of H. algiricus (the first ever!) while diving off the coast of Senegal, which is on the western coast of Africa: After studying a West African seahorse, researcher Kate West convinced the fishers to release the animal back into the wild. The seahorse swims away unharmed. Credit: Kate West / Project Seahorse (via Sci-News.com) View the full article

Click through to see the images. Vertex Aquaristic (Germany) worked with GlueTec GmbH to develop a two-part epoxy stick with the following aquarium-friendly characteristics: Reduced clouding in the water column Extended malleability period to allow aquarists longer working times to attach corals or rocks. Reduced impact on skimming performance pH netural Violet coloration to blend with coralline algae 4 ounce (114g) V-Collar Viola sticks are now available in Europe and should soon be available through authorized Vertex distributors worldwide. View the full article

Click through to see the images. The talk began shortly after Hurricane Sandy subsided. Reef organizations started mobilizing members to help out reefkeepers devastated by the massive storm. Many reefers were without power and heat for multiple days and many even lost entire households in the aftermath. Tanks were in multiple states of disrepair from not affected at all to complete losses. Hundreds if not thousands of reef tanks were probably lost during the storm and extended power outages. Posts began popping up on forums and Facebook mobilizing people to help and as of Saturday evening, the following reef clubs and vendors have pledged support to help get reefkeepers back on track: Atlanta Reef Club Manhattan Reefs Sexy Corals Rocky Mountain Frags If you, your reef club, or company would like to help, I would recommend contacting the Manhattan Reefs group to find out more information. View the full article

Since this method of filtration is rather new in our forum, i would just like to share this "Natural " filtration method which reefer might find useful and interesting to discuss about this. Below article written by :John Cunningham ( Link : http://www.aquaristsonline.com/blog/general/aquarium-filtration/cryptic-zones-another-filtration-possibility/ ) Cryptic Zones – Another Filtration Possibility There is a scientific term used which is called ‘the gradient concept’. This term basically describes how various marine organisms can be graded according to the amount of light which they receive. There are two zonal categories which are most commonly used, these are the exposed and the semi exposed zones. The exposed zone is an environment which is in shallow water and receives a lot of strong sunlight. This is the zone which is typical of the upper reef, otherwise known as a shallow reef. The water currents in this zone are normally quite fast and chaotic, therefore any organisms which live in this area have to be able to withstand such high currents. Due to the high currents there is normally a lot of suspended matter moving around in the water; however with the strong water current a lot of the filter feeding organisms struggle to extract these from the water. This zone is where the majority of the light loving high current SPS corals live and is effectively the environment which we attempt to replicate in the majority of our reef aquariums. The semi exposed zone is similar to the exposed zone but both the light and water currents are considerably less. Because of the lower water currents filter feeding organisms are able to extract the particulate matter from the water more easily. This zone is similar to that of deeper reef conditions, and is otherwise known as the back reef. In this zone there are still a huge range of photosynthetic organisms which can survive but this zone, because of the lower light conditions, also provides the non photosynthetic organisms with a place to thrive. Again this environment can easily be replicated in our reef aquariums. In the marine aquatic world there are effectively three more zones which are: 1. Semi Cryptic 2. Cryptic 3. Filter Feeding The semi cryptic zone is the zone which occurs in the sections of the reef which are either deeper down the face or in naturally occurring overhangs in the reef structures. This zone has a very low light level and can only support photosynthetic organisms which can survive in this type of area. The cryptic zone is the zone which occurs in the sections of the reef where light if any is far too weak to support any photosynthetic organisms in any way at all, and can only support non photosynthetic organisms. In the natural reef this occurs either within caves or deep into the overhangs of a reef structure. The filter feeding zone is effectively a combination of the semi cryptic zone and the semi exposed zone. The difference in this mixed zone is that there is little light but very strong water currents, therefore particulate matter in the water can be delivered and consumed via the various filter feeding organisms. This zone is normally where the non photosynthetic soft corals occur. Understanding the differences between the zones enables you to be able to see what zones you currently have in your aquarium – you will be surprised as to how many you actually have. You will probably find that you have many or even all of these types of zones in parts of your aquarium, however some may be quite small – e.g. small caves in the rock face. You need to consider these types of zones when setting up a new reef system and also when introducing corals into the aquarium. When purchasing a new coral you need to understand the requirements of the coral and ensure that you have an area of the correct zone available in your aquarium to support it. In your aquarium you will have various zones in various sizes, however one which is a valuable addition to the aquarium is the implementation of a designated cryptic zone. A designated cryptic zone can easily be implemented into an existing system by adding a new aquarium into the system, possibly next to the sump, in the sump etc. This aquarium is filled with aquarium water via an overflow from the main aquarium or a tee off from an existing overflow. A small amount of substrate needs to be added. On top of this substrate is placed some pieces of live rock, sponges, sea squirts, non photosynthetic corals etc – effectively any non photosynthetic organism which can survive in a cryptic zone. The aquarium should then be effectively covered up to prevent any light from entering. Dirty water (un-skimmed as DOC’s are a requirement in this area) is fed to this aquarium at a very slow pace and there is minimal water current. This un-skimmed water is best fed into the cryptic zone along the top of the water. What this does is allow the particulate matter in the water to slowly settle down onto the organisms so that it can be consumed. The matter also falls onto the substrate. This allows for the growth of the organisms and therefore more removal of particulate matter from the water. Water from the cryptic zone normally overflows down to the sump so that it can be skimmed therefore for this reason you will need to install the cryptic zone aquarium higher than the sump so that it can overflow. It is also advisable to add some types of cleanup crew into the cryptic zone aquarium so that they can deal with any particulate matter on the substrate, rock work etc. I have seen various designs of a designated cryptic zone in use. Some have even been combined with deep sand beds/plenums. Occasionally if you open up the covers and have a look you will be amazed at the life which is growing in there and how fast it grows. The thing I like about a cryptic zone is that sponges can quite easily grow. Sponges are a good filtration tool and utilising a cryptic zone will afford you the opportunity to grow some of them. Of course more than one zone can be implemented whether this is directly in the display aquarium or by using external aquariums.

Click through to see the images. #10: Stunning imagery of pelagic mesoplankton Photographer Solvin Zanki captures some of the most amazing photos of plankton we've ever seen. We share some of his amazing work. If these photos do not instill a sense of awe and wonder for the diversity of life in our oceans, we give up. Read more... #9: Videos of Acropora spawning in captivity Captive spawning of invertebrates is always an amazing and rewarding sight, and even more so for a coral once considered impossible to keep in captivity just a few decades ago. We share two videos of Acropora spawning in home aquariums. Read more... #8: Baby flying fish are all sorts of awesome There's no denying flying fish are incredible animals, and baby flying fish are really something else! Our friend Ned DeLoach of blennywatcher.com shares incredible photos of juvenile flying fish. Read more... #7: How NOT to frag zoanthids Fragging soft coral is easy. Slice it with a razor blade and glue it to a piece of live rock rubble or frag plug. However, this is not so with zoanthids and palythoa, where nitrile gloves (and possibly razor-proof gloves) and goggles must be worn while working with them. Read more... #6: A Classroom Dreams Are Made Of In 2011, the York Public School (Australia) began an extraordinary outreach program to educate and inspire local children about coral reefs. Through partnership with the Sydney Aquarium Conservation Fund and their LFS (Salt Aquariums), teacher and aquarist Benjamin Eggins set up a 240 gallon reef aquarium in his classroom ... and brought the living sea to his students. Read more... #5: Soft corals are underrated For the past two decades, SPS and LPS have stolen the spotlight with reefkeepers as the corals of choice. Stoney coral reef aquariums dominate the modern scene, so it's easy to forget just how alluring soft coral exhibits can be. This Dutch aquarium reminds us not to underestimate the beauty of soft corals. Read more... #4: Robo-clownfish, for the lazy reefkeeper near you A Japanese toymaker thinks it has the solution for the lazy freshwater and saltwater aquarium keepers: robotic aquarium fish! Read more... #3: HGTV to air special: "Ultimate Aquariums" Cable television network HGTV will premiere an one hour special on October 12, 2012 titled "Ultimate Aquariums." The new show will feature concept, design, and install of high-end custom installations built for "celebrities and the wealthy." Read more... #2: Palytoxin-containing zoanthids can temporarily - or possibly permanently - blind you Another reason why you should always wear proper personal protective equipment when working in and around your tank - simply rubbing your eye can infect it with palytoxin from stressed Palythoa sp. zoanthids. Read more... #1: Free Monster Aquarium If you're near Massachusetts and have 8 to 10 strong friends, this monster custom aquarium can be yours for FREE. The owner A.J. is looking to give away his aquarium by the end of October. Kid not included. Read more... View the full article

Click through to see the images. Reef Balls, for those of you who have not seen them before, are artificial concrete reef structures that are placed on damaged reefs in order to provide new habitat for coral, fish, and other aquatic life. They look artificial for years after but they do serve a purpose. An Australian company, Sustainable Oceans International, however, wants to impove on these structures by 3D printing them with more organic curves and shapes to make them look more realistic. In a recent blog post, I covered how one could print their own liverock (with the appropriate technology, of course). In it, I explained how architects Petr Novikov, Inder Shergill and Anna Kulik used Stone Spray technology to design a myriad of different shapes including ones that look very much like liverock. It appears that Sustainable Oceans International wants to do something similar but use it to build actual reef structures. Sustainable Oceans International actually has its roots in the Reef Ball project so they know quite a bit about reef remediation and restoration. Their Director, David Lennon and Team Leader Coral Reef Restoration, John Walch both utilized and served on the Reef Ball project in years past. David is the sole authorized contractor in Australia for Reef Ball artificial reef modules and John is on the Board of Directors for Reef Ball. A third team member, Mike Naugle, is also a qualified coral handler by the Reef Ball Foundation. The Australian-Bahraini team working on the new reef restoration project includes Sustainable Oceans International (SOI), a specialist reef design consultancy in Australia, James Gardiner an award winning architect, and Reef Arabia a reef construction company in the Arabian Gulf. One thing that Sustainable Oceans International does is issue annual Sustainable Ocean Innovation Awards to individuals or companies that are pushing ocean sustainability through innovative techniques and technology. The 2010 winner was James Gardiner for using 3D printing technology to print large, complex, structures that could mimic reef structures. “When we saw this project we immediately recognised the potential for this technology to move SOI one step closer to achieving our goal of constructing beautiful natural looking reefs” says David Lennon, Director of SOI. The first structures printed were 1 meter high and weighed up to 500 kg (~1100 lbs) and look much more natural than Reef Balls. Left: computer rendered 3D file used to create the 3D printed reef unit (right) from a patented sandstone material. Process allows infinite variations of each unit just as nature provides as well as the ability to replicate natural features or manmade objects. “We currently use one of the most natural looking concrete and mold systems available to build our reefs, but these 3D printed units are amazing in comparison. You can’t tell the difference from real rock and the advantage is that we can engineer them to have very specific features that suit target marine species” says David. Four prototypes were made (three pictured above) and two of these were purchased by Reef Arabia for a restoration project in Bahrain. Reef Arabia plans to deploy these two structures in and among 270 standard concrete precast reef units (presumably Reef Balls). These new 3D printed structures will be closely monitored and compared to the precast concrete structures to gauge their effectiveness. "This is very exciting and for us and it’s what I imagine it was like to watch the first plane take off in 1903 - witnessing the birth of a new era. It is a reflection of how advances in manufacturing technology can help us repair human impacts on the environment" said David. (via Sustainable Oceans International) View the full article

Click through to see the images. The video quality may not be the best we've shared, but it's more than sufficient to show both the elevated reef aquascape as well as the health and beauty of this 120 gallon walk-around reef tank. The practical benefit of this type of aquascaping is that corals are placed closer to the lights. But the shaded lower portion also creates a striking aesthetic counterbalance - an yin-yang duality if you will (yes, I am fully aware this is a Chinese Taoist concept!). Also, much of the biological activity on natural coral reefs actually occurs below the rock and coral cover. An aquarium with an elevated reef structure may better simulate a slice of natural reef in your home. It's a concept worth considering for your next reef aquarium aquascape. " height="383" type="application/x-shockwave-flash" width="680"> "> "> View the full article

Click through to see the images. Fresh on the heels of their new XR30W Pro announced at MACNA 2012 just a couple months ago, Ecotech Marine announces the replacement for their Radion XR30W. The Gen 2 XR30W will feature Ecotech's TIR lens as many predicted (read our hand-on review on the TIR). In addition, the G2 now uses the more efficient, higher output Cree XT-E for the white and royal blue LEDs, further increasing the XR30Ws PAR output. How much more will this improved performance cost aquarists? Nothing. In fact, the XR30W G2 will see a price drop from the first generation. The G2 will ship in late November at the price of $649 USD. Ecotech will also offer current Radion XR30W a path to upgrade their lights, with details to be announced in the coming weeks. For those wondering about the main difference between the new XR30W G2 and the XR30W Pro, the Pro features 10 more LEDs (42 versus the 32 found on the G2) for 25 watts more light output. The Pro's extra LEDs are comprised of four UV, four Indigo, and two yellow diodes. In order to control the additional LEDs, the Pro also features one additional control channel (six vs five on the standard XR30W). Last but not least, the price of the XR30W pro is $949 while the XR30W G2 is $649. For more information, visit Ecotech Marine's website (just updated today with the new G2). Specifications* Model – Radion XR30w G2 LEDs • White: 8 Cree XT-E Cool White (5W each) • Red: 4 Osram Oslon SSL Hyper Red (3W each) • Green: 4 Cree XP-E Green (3W each) • Blue: 8 Cree XP-E Blue (3W each) • Royal Blue: 8 Cree XT-E Royal Blue (5W each) Dimensions Length: 11.8 inches (30 cm) Width: 7 inches (18 cm) Thickness: 1.5 inches (3.9 cm) Wattage Max Wattage of Radion Fixture: 140 Watts Max Wattage of LED Channels: 130 Watts *Specifications are subject to change. View the full article

Click through to see the images. From the National Science Foundation: Small Marine Organisms' Big Changes Could Affect World Climate In the future, warmer waters could significantly change ocean distribution of populations of phytoplankton, tiny organisms that could have a major effect on climate change. Reporting in this week's online journal Science Express, researchers show that by the end of the 21st century, warmer oceans will cause populations of these marine microorganisms to thrive near the poles and shrink in equatorial waters. "In the tropical oceans, we are predicting a 40 percent drop in potential diversity, the number of strains of phytoplankton," says Mridul Thomas, a biologist at Michigan State University (MSU) and co-author of the journal paper. "If the oceans continue to warm as predicted," says Thomas, "there will be a sharp decline in the diversity of phytoplankton in tropical waters and a poleward shift in species' thermal niches--if they don't adapt." Thomas co-authored the paper with scientists Colin Kremer, Elena Litchman and Christopher Klausmeier, all of MSU. "The research is an important contribution to predicting plankton productivity and community structure in the oceans of the future," says David Garrison, program director in the National Science Foundation's (NSF) Division of Ocean Sciences, which funded the research along with NSF's Division of Environmental Biology. "The work addresses how phytoplankton species are affected by a changing environment," says Garrison, "and the really difficult question of whether adaptation to these changes is possible." The MSU scientists say that since phytoplankton play a key role in regulating atmospheric carbon dioxide levels, and therefore global climate, the shift could in turn cause further climate change. Phytoplankton and Earth's climate are inextricably intertwined. "These results will allow scientists to make predictions about how global warming will shift phytoplankton species distribution and diversity in the oceans," says Alan Tessier, program director in NSF's Division of Environmental Biology. "They illustrate the value of combining ecology and evolution in predicting species' responses." The microorganisms use light, carbon dioxide and nutrients to grow. Although phytoplankton are small, they flourish in every ocean, consuming about half of the carbon dioxide emitted into the atmosphere. When they die, some sink to the ocean bottom, depositing their carbon in the sediment, where it can be trapped for long periods of time. Water temperatures strongly influence their growth rates. Phytoplankton in warmer equatorial waters grow much faster than their cold-water cousins. With worldwide temperatures predicted to increase over the next century, it's important to gauge the reactions of phytoplankton species, say the scientists. They were able to show that phytoplankton have adapted to local temperatures. Based on projections of ocean temperatures in the future, however, many phytoplankton may not adapt quickly enough. Since they can't regulate their temperatures or migrate, if they don't adapt, they could be hard hit, Kremer says. "We've shown that a critical group of the world's organisms has evolved to do well under the temperatures to which they're accustomed," he says. But warming oceans may significantly limit their growth and diversity, with far-reaching implications for the global carbon cycle. "Future models that incorporate genetic variability within species will allow us to determine whether particular species can adapt," says Klausmeier, "or whether they will face extinction." View the full article

Click through to see the images. All that is required is a valid military ID or proof of service presented at the main entrance to gain free entry. Family members of servicemen are not eligible for the promotion but can purchase discounted tickets in advance at military bases. Children under the age of 3 are free. View the full article

Click through to see the images. Perhaps every reef hobbyist is willing to provide the "right" light to his corals - both correct spectrum and sufficient intensity are important. Before we consider how to implement this "right light," we shall first try to understand what kind of light marine organisms get in their natural environment. As our starting point, consider the spectral distribution of solar energy in Fiji in July, Fig. 1: Fig. 1 Spectral distribution of sunlight energy at the level of the sea The horizontal axis of the graph is wavelength, in nanometers, and the vertical axis is spectral irradiance, in W/m2·nm. The human eye is sensitive to radiation in the range between approximately 400 and 700nm, therefore we marked the wavelength ranges shorter than 400nm (ultraviolet light) or longer than 700nm (infrared radiation) in black, whereas visible wavelengths are colored as they are perceived by the eye. The chart in Fig. 1 has been obtained from the solar spectrum at the boundary of the earth atmosphere using the SMARTS 2.9.5 scientific simulation software. This simulator takes into account light absorption by various components of the atmosphere as well as scattered light from the sky. Let us now try to find out what kind of light spectrum is available to marine organisms in their natural environment. In our attempt to build an ideal light fixture for our reef tanks we shall try to generate a similar spectral distribution at certain depths underwater. Different coral species live on various depths: some live in very shallow waters, whereas deep water corals, such as Bathypates spp., can be found on the depths of up to 8000 meters (about 5 miles). About 20% of all coral species are non photosynthetic; they do not require any light as a food source. Most corals, however, are photosynthetic, and these are the species which are kept most often at home aquaria. We shall try to figure out what kind of light they prefer. Consider the graph of solar light penetration into marine water, depending on wavelength, compiled by the Institute for Environment and Sustainability of the European Commission [4] (Fig. 2): Fig. 2 Penetration of light into seawater, depending on wavelength The horizontal axis is the light wavelength, in nanometers, and the vertical axis is depth, in meters, at which the intensity of that wavelength is equal to one percent of the intensity at the surface. It is clear from this graph that wavelengths between approximately 370 and 500nm best penetrate into the depth. In other words, violet and blue parts of the spectrum penetrate best into seawater, whereas green light is much worse at that, yellow-orange is even worse, and red light with wavelengths longer than 600nm is only capable of penetrating very shallow waters. The light spectrum on the surface can be defined as a function I0(λ), where λ is the wavelength and I0 is the intensity for corresponding wavelength at zero depth. Hence the adsorption spectrum Ia(λ) at the depth D can be determined as Ia(λ) = I0(λ) · K(λ) · D (1) where K(λ) is the adsorption by marine water as a function of wavelength. The spectrum at the depth D will be equal to the spectrum on the surface I0(λ) minus the adsorption spectrum Ia(λ): I(λ) = I0(λ) - Ia(λ), or, by substituting (1) into this expression, we shall derive: I(λ) = I0(λ) · (1 - K(λ) · D) (2) From this expression we can derive the graph of light penetration into seawater d(λ): d(λ) = (1 - I(λ) / I0(λ)) / K(λ)) (3) Providing that the graph in Fig. 2 is based on the assumption that light intensity on the specified depth is equal to 1% of the intensity on the surface, i.e. I(λ) = 0,01 · I0(λ), we can simplify (3): d(λ) = 0.99 / K(λ) This function d(λ) is our graph of light penetration into seawater, which is pictured in Fig. 2. Using this graph we can determine light adsorption in seawater as a function of wavelength K(λ): K(λ) = 0.99 / d(λ) (4) By substituting the expression (4) into (2), we can derive the spectral distribution of light at a given depth D: I(λ) = I0(λ) · (1 - 0.99 · D / d(λ)) (5) where I0(λ) is the light spectrum on the surface and d(λ) is the graph of light penetration into seawater (Fig. 2). Using the expression (5) and the data from graphs in Fig. 1 and Fig. 2, we can obtain the diagram of light energy distribution vs. wavelength at a given depth. As an example, on the same graph (Fig. 3) we pictured light's relative spectral distribution at the surface and at the depths of 5m (about 16.4 feet) and 15m (49 feet). Note: 15m is the maximum depth at which we can still find many light-demanding corals in nature. At the depths below 20m, the number of light demanding species sharply decreases. Fig. 3 Light spectral distribution vs. wavelength on the surface (light blue), at 5m (blue) and 15m (dark blue) depths The light-blue graph corresponds to irradiation on the surface, the blue graph - to 5m depth, and the dark-blue - to 15m depth. Note that with depth, the red part of the spectrum virtually disappears. During hundreds of millions years of evolution marine photosynthetic organisms adapted to best utilize mainly the violet and blue parts of the spectrum, which is more abundant in their environment, and are not very sensitive to the red spectrum (which, in contrast, is most actively utilized by terrestrial plants). Symbiotic zooxanthellae in marine photosynthetic organisms are primitive Pyrrophyta algae [5] containing mainly chlorophyll a and c and carotenoid pigments (peridinine, xanthins, etc) which exhibit strong absorption in the blue-green part of the spectrum. [6,7,22]. Fig. 4 [22] demonstrates light adsorption by zooxanthellae. Fig. 4 Light absorption by zooxanthellae The horizontal axis is the wavelength, in nanometers, and vertical axis is adsorption, in arbitrary units. You can see from the graph that violet and blue colors strongly prevail over red (note that for red spectrum, the 660-680nm range is preferable). Our main conclusion from the above is that violet and blue light are most important for marine photosynthetic organisms. Knowing what is naturally available to corals from the color spectrum, we shall now consider the next important issue: how irradiation by different spectral ranges affects coral coloration? Before we consider the influence of the light spectrum on coral coloration I would like to point out that even coloration of the same coral may vary significantly depending on conditions. Unfortunately, it is very difficult to provide exactly identical conditions for the corals, even in the same aquarium - and this is even harder for two different tanks. Without providing the right conditions for the corals, other attempts to improve their coloration, such as adjustments of the light spectrum, will be in vain. Experienced reef keepers well know how variable the coloration of the same coral can be in different conditions. There are three main factors which affect it most: light spectrum and intensity, the amount of food available in water (although coral polyps receive a significant portion of their energy from the zooxanthellae, they are also able to capture food particles from the water column), and from the purity of the water. This last factor is easiest to control: techniques to maintain pristine water in reef aquaria are well known. The second factor, too, can be solved easily since there are a number of quality coral foods readily available on the market. At the same time many aquarists believe that, if there are fish living in a reef aquarium, corals will get sufficient food from small particles which float around from feeding the fish (and fish poo too is consumed by corals). Light is the last important factor required for good health and the coloration of corals, and yet has not been studied sufficiently well in reef keeping. The situation is rather complex though, since corals can be very variable, and even the same species may contain different chromoproteins (proteins responsible for coloration) - their type and amount are also determined genetically, in the same way as, say, the color of human's eyes. Many of these proteins are fluorescent; i.e., they adsorb the light of a certain wavelength and radiate a different wavelength. Fig. 5 shows four specimens of the same species, Acropora millepora, in which different chromoproteins prevail: Fig. 5 The Acropora millepora specimens with different prevailing chromoproteins: (A) low concentration of chromoproteins, the color of zooxanthellae dominates; ( green fluorescent proteins; © red fluorescent proteins; (D) non-fluorescent chromoproteins. Image courtesy of Dr. C. D'Angelo and Dr. J. Wiedenmann, University of Southampton, UK, Coral Magazine, Nov./Dec. 2011 Fluorescence is witnessed not only in hard corals but, for example, in Zoanthidae and Palythoya polyps which exhibit much brighter coloration when irradiated with so-called short-wavelength "actinic" light. Coral fluorescence is very beautiful but it is not always easy to observe it. Have a look at the luminous function (spectral sensitivity chart) of the human eye (Fig. 6). Light sensitive elements of the eye are represented by two cell types - the so-called retinal cones and rods. The first are responsible for distinguishing between colors, and the second - for grey tones. The cones work best during daytime, the rods - at night. Remember the saying "all cats are grey in the dark." This is just because we mainly see with the rods in the dark, rather than with cones. The rods do not distinguish between colors: they only sense the relative brightness of an object. The rods are most sensitive to the emerald-green part of the spectrum, with the wavelength of about 510nm (of course, when seeing by the rods, this light is only perceived as a brighter shade of gray rather than green. There are three cell types in cones, each sensitive to a specific part of the spectrum. S-type cones are sensitive to violet and blue (S stands for Short wavelengths), M-type - for green and yellow (Medium wavelengths), and L-type - for orange and red (Long wavelengths). These three cone types, (along with the rods that are sensitive in the emerald-green part of the spectrum) are responsible for color vision in humans. The rods contain a color-sensitive pigment, rhodopsin, and their spectral characteristic depends on lighting conditions. For weak light, rhodopsin's adsorption peak is at about 510nm (the spectrum of the sky at twilight). And therefore the rods are responsible for twilight vision, when colors are hard to distinguish. At higher levels of illumination rhodopsin photo bleaches, and its sensitivity decreases, while the adsorption peak shifts into the blue region. As a result, under sufficient light, the human eye can use the rods as a shortwave (blue) light detector. S-cells are sensitive in the 400-500nm range with a maximum at 420-440nm; M-cells are sensitive in 460-630nm range, with a maximum at 534-555nm; L-cells are sensitive in the 500-700nm range with a maximum at 564-580nm [1]. Sensitivity ranges of long- and medium-wavelength cones are wide and overlapping. Therefore it is wrong to think that certain cone types only react to certain colors - they just more actively react to certain colors than to others [2]. The human eye is most sensitive in the range where sensitivities of M- and L-type cones add up: at 555nm (yellow-green light). The overall spectral sensitivity function [3] of human eye receptors is shown in Fig. 6: Fig. 6 Luminous function of the eye An important conclusion here is that the human eye sensitivity to light depends on the wavelength. For example, radiation of equal power is perceived 27 times brighter for the 555nm wavelength than for 450nm; this difference increases to 57 times for 420nm, and 135 times (!) for 410nm. Humans visually perceive any object as the sum of its reflected light and the object's intrinsic emission (an object is considered light emitting if its total emission at a certain wavelength range is higher than the falling light energy in that same region). Usually objects only reflect light, and their color is determined by the ratio, in which different wavelengths falling on its surface are adsorbed or reflected. For example, green leaves adsorb all visible wavelengths except for green, which is reflected - therefore we perceive it as green. When an object not only reflects but also emits its own light, the eye combines the emitted and reflected light spectrum into its perceived color. Yielding color depends on the ratio of the intensities and wavelengths of both reflected and emitted light. This color addition is best illustrated by the diagram shown in Fig. 7: Fig. 7 Additive color mixing When looking at the computer monitor, you witness the effects illustrated by this chart: every pixel on the screen consists of three sub pixels: red, green and blue, and all colors are obtained by combination of their intensities. Note that pure purple color and its tints, such as magenta or fuchsia, are unique in being non-spectral or extra-spectral: there is no specific wavelength associated with these colors, they are mixtures, and one of the required components is violet, with the wavelength around 400nm [13], and red. If a specific light source has no radiation in this range, up to 20% of the whole color palette is lost - and these are very bright colors and their shades! It is also interesting to note that by combining the yellow and blue colors the resulting color is visually perceived as pure white. Color vision is mainly inherited genetically. We are not talking about the defects of color vision, such as color blindness - but each person perceives colors in his own way, and this difference can be very significant. Apparently, it is very important to be able to adjust the spectral distribution of the light fixture, to find an individually suitable color distribution in the reef tank. To watch coral fluorescence we shall irradiate the fluorescent proteins with light of a specific wavelength. Look at the adsorption and radiation wavelengths chart for most common fluorescent pigments available in marine organisms [9], shown in Fig. 8: Fig. 8 Adsorption and emission wavelengths for fluorescent pigments available in marine organisms. The figure is courtesy of Dan Kelley The horizontal axis are the wavelengths which cause fluorescence in various chromoproteins; the vertical axis is the wavelength emitted as a result of fluorescence. You can see that virtually all pigments adsorb shorter wavelengths and emit longer wavelengths. As we have shown above, the eye is most susceptible to the 550nm range, and the closer the emitted light is to that wavelength, the brighter it will be perceived. Thus, specific proteins available in marine organisms adsorb the poorly visible to the eye short wavelengths and fluoresce with a color which looks much brighter to our eye. Under purely "actinic" light, which only contains shorter wavelengths, our fish tank will glow with bright colors, whereas the light from the fixture itself is almost invisible to the eye. This gives the impression of miniature light bulbs installed in each coral or polyp, which glow brightly in the dark! Color of a coral, as perceived by the eye, also depends on the color of falling light. The color of any object that we see represents the reflected portion of the falling light spectrum. As we have pointed out above, when illuminated by a full-spectrum light, the leaves of most terrestrial plants adsorb almost all parts of the visible spectrum, and reflect the green part - therefore we perceive them as green. However, if we irradiate the leaves by a light in which the green part of the spectrum is missing - by red light, for example - they will seem black to us, because all falling light is adsorbed. In a similar manner, white object looks white under full spectral light, because it uniformly reflects all parts of the spectrum, but will "take up" the color of any light that we throw at it: red, green, blue, or their combination. Back to corals - let us consider an organism containing a protein which, when irradiated by the 420nm light, will fluoresce by the 520nm wavelength. For reasons of simplicity, suppose that our light source radiates only at the 420nm wavelength, and the coral adsorbs this light completely, without reflection. The human eye has extremely low sensitivity to this wavelength (almost invisible), whereas it is most sensitive to the wavelength radiated by the coral as a result of fluorescence. We shall see this fluorescence very well in the "dark" pure actinic light. If the light source includes radiation at other wavelengths, the resulting color of the marine organism will be added up from fluorescence and reflected light. If the light source contains wavelengths, to which the eye is very sensitive (especially in close proximity to the 550nm sensitivity peak), we will mainly see the light from the fixture, and perception of coral fluorescence will be weak on this bright background. Our conclusion is that for best observation of fluorescence, we shall illuminate the tank with such light that its reflected portion would least hinder us in seeing the light radiated by corals. Wavelengths required for fluorescence of all chromoproteins are numerous, and there is no single wavelength that could be used for making an ideal actinic light. Based on Fig. 8, fluorescence is observed in quite wide a range of falling light wavelengths, mainly between 400 and 500nm, and different organisms have different fluorescent protein sets. For best fluorescence we need the capacity to adjust the light spectrum in the 400 to 500nm range, according to the needs of a particular aquarium. Note that the strongest fluorescence will be observed in 400-450nm range, particularly because the eye sensitivity in that range is very low. The light in this range is usually called "actinic light." Surely, coral fluorescence is one of the main factors to provide a reef tank's beauty, but the light in the 400-500nm range also has other importance: it is the most optimal light to promote marine photosynthesis. Therefore this part of the spectrum is of utmost importance for a reef tank. This conclusion matches well with the experimental research in this field [16]. Fragments of Acropora millepora colony were maintained for six weeks under comparable amounts of red, green, and blue light. The conclusion of the article is that "the enhancement of coral pigmentation is primarily dependent on the blue component of the spectrum and regulated at the transcriptional level," and "light-driven accumulation of GFP-like proteins observed upon green light exposure is likely due to residual blue light passing the green filter." The experiments also revealed that radiation in the 430nm range is most efficient in promoting the protective bright coloration of the corals:"Among the known FPs and CPs, only the absorption properties of CFPs spectrally match the major absorption band of chlorophyll a and c at ~430 nm, making them suitable for effective shielding of the photosynthetic system of the zooxanthellae." The intensity of light is also very important for growth and active production of fluorescent chromoproteins. A light source could be best characterized, perhaps, by spectral distribution of the optical radiation energy at different wavelengths. This characteristic is usually represented by the spectral curve. For most common light sources, however, the spectral characteristic is usually unavailable, and instead an estimated light flux is provided, in lumens. Light flux in lumens is the visible light radiation power, as perceived by the human eye - depending on the eye's sensitivity to different wavelengths. Note: One lumen is the total luminous flux emitted uniformly by a light source with luminous intensity of one candela across a solid angle of one steradian (a cone with the angle of approximately 65.5° at the apex). Candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of 555nm wavelength (i.e. the wavelength at the peak sensitivity of the human eye), and has a radiant intensity in that direction of 1/683 watt per steradian. One watt of optical power radiated at the 555nm wavelength corresponds to 683 lm. For any other wavelengths, it is equal to the optical power emitted at that wavelength multiplied by the luminosity function of the eye for the same wavelength. To determine total lumens emitted by a light source we need to sum up the lumens for all emitted wavelengths. It is evident that the intensity equal light energy in various parts of the spectrum will be perceived differently by the eye: a powerful source in the 400-450nm range will be perceived as very dim light, and a light source emitting in the infrared region will seem black. Therefore an estimate of the light flux in lumens is only valid when light's spectral distribution is unimportant and the only thing that matters is brightness, as perceived by the eye. In our case, a more appropriate parameter for determination of light radiation would be the number of photons per second, falling on each meter square: μmol·photons/m2/s. During the hundreds of millions years of evolution marine photosynthetic organisms adapted to different light power levels. For each photosynthetic organism three threshold values can be defined [14]. First (least intensive) determines the minimum light required for the maintenance of photosynthetic organism's biomass - it is the minimum required light which will not result in gain or loss of mass. The second threshold value concerns illumination at which the photosynthesis efficiency is highest. And finally the third, upper threshold is the maximum light which can be utilized -there is no improvement in photosynthesis rate above that threshold. These three thresholds, of course, depend on particular organisms, but we can use an estimate for marine photosynthetic organisms living in shallow waters. We can safely call 80-100 μmol·photons/m2/s low light, 150-200 - medium, and 300-400 - optimal. The saturation limit of photosynthesis is about 600-700μmol·photons/m2/s. In our reef tank, we shall achieve a significantly better illumination than the minimum threshold - preferably near the optimal threshold. Let us consider yet another experiment with Acropora millepora to illustrate the production of chromo proteins under less than optimal illumination, and when the light level is in optimal value for the species (Fig.9). Illumination 100 400 Red fluorescent Green fluorescent Daylight Fig.9 An experiment with Acropora millepora illustrating the production of chromo proteins insufficient for photosynthesis, and intensity for optimal illumination for this species. Regarding light intensity this work also states that chromo proteins are not formed under illumination levels below 100 μmol·photons/m2·s, and their number grows almost linearly along with the increase of light intensity up to about 700 μmol·photons/m2·s. However, it is not always a good idea to provide as much light in home aquaria, since a coral can become very demanding to its environment parameters under such high levels of illumination. Under less than perfect conditions such high levels of illumination can yield a contrary result: coral bleaching. The experiment illustrates that optimal light levels improve coral growth and coloration, both for ordinary and fluorescent chromoproteins. Concluding from the above, light in the 400-500nm range is most beneficial for marine photosynthetic organisms, and its shortwave portion (400-450nm) is most useful for their bright coloration. Let us consider the most popular actinic light sources for a reef tank. These are mostly fluorescent bulbs which mainly radiate in the 400-500nm range, such as Giesemann Actinic Plus, Fig. 10: Fig. 10 A typical actinic fluorescent tube: Giesemann Actinic Plus Looking at the spectral distribution of this bulb we can see that apart from the pure actinic spectrum, which is required for coral fluorescence, there are also distinct "parasitic" peaks around 550nm. As we have pointed out, the human eye is over 20 times more sensitive to the wavelengths in this range rather than to the "actinic" range which causes fluorescence (see Fig. 6). As a result, this bulb is visually perceived as quite bright, almost white, but with strong blue-violet tint. The resulting fluorescence will be partially "dimmed" as a result of this parasitic radiation in the well-to-see range. In recent years multiple attempts were made to create narrow-range "actinic" bulbs. One of the best is Giesemann POWERCHROME actinic plus, with significantly reduced 450-500nm portion (Fig. 11): Fig. 11 The spectrum of the POWERCHROME actinic plus bulb We can see that "parasitic" portion of this bulb's spectrum is smaller and the 420-430nm range is better represented. However, this bulb too, still looks quite bright to the eye, because of the still present peak at 550nm. So far, conventional fluorescent tubes are not so efficient for observation of fluorescence in a reef tank. Desperate? No! Quite recently, there was a breakthrough in the field of solid-state lighting, and many light fixtures for reef tanks are now constructed with the use of LEDs. The advantages of LED fixtures over the conventional light sources are many; we shall only consider the main factors. Advantage #1: Higher efficiency and less heat generation Higher efficiency has two components. First is that LEDs are about twice more efficient than conventional fluorescent tubes or Metal Halide bulbs in converting the electric energy into light. Second is that LEDs only radiate in one direction of the plane and hence are not apt to block their own light. By utilizing proper lenses, LED light can be easily concentrated in the desired region. Good LED lenses are compact in size and, at the same time, can help to transfer up to 90 percent of produced light through the water surface. For comparison, when using conventional bulbs with reflectors usually only 40% of light penetrates the surface. Best reflectors (often cumbersome) can yield up to 60% of light penetration, and the bulb itself partially blocks the light returning from the reflector. Resultant efficiency of best LED fixtures can be three times higher compared with the best light bulbs. Consequently, LEDs can generate over 4.5 times less heat. This practically means that by installing a LED fixture over a reef tank we can probably eliminate the need for an expensive chiller (which also consumes significant power). Thus, LED fixtures may achieve significant power savings; apart from the economic effect, their environmental impact is also significant!). Advantage #2: Extended life cycle As a solid-state light source, a light emitting diode does not have quickly wearing parts, such as an incandescent filament. When operated at or below rated current, and providing that they do not overheat, high quality LEDs degrade very slowly. But LEDs too have their specific needs which have to be considered when designing a fixture. Lifespan of the best LEDs available in the market today (Cree XT-E, LUXEON Rebel ES) is indeed very high, if sufficient heat removal and properly conditioned power are provided. Of course, these are new LEDs and their operation have been tested for tens of years, but using complex models their life term and luminosity drop in that period can be estimated. We shall refer to two types of such forecasts: based on Cree's model (which we call the "worst case scenario" or "pessimistic model"), and in parenthesis we provide figures based on the Philips model for their LUXEON Rebel ES (which we call the "optimistic model"). If all the required operation conditions are fulfilled, we will still be getting about 70% of LED's initial radiation power after 40 (150) thousand hours of operation. These figures translate to 10 (33) years of operation of a light fixture, providing 12 hours of operation daily! After this period the LEDs will continue to lose luminance, reaching about 50% of the initial value after 100 (200) thousand hours! The probability of a single LED failure on a fixture is quite low, about 1% during the period of 50 thousand hours of operation, and after this period the probability increases to 50% by 200 thousand hours. Several LEDs in a light fixture are usually connected in series, and therefore, if one LED dies, the whole string will be effected. If we look at these figures statistically, is likely that for a fixture with about 200 LEDs this can happen in 10 years. However a LED's death is a probabilistic event and it can happen that a particular light emitting diode may get "fried" during the very first hours of its life. In practice, if the conditions are good, lifespan of modern LEDs is quite long. In comparison, conventional fluorescent tubes need to be replaced once every four to six months. Based on our worst case scenario, it means that they will have to be replaced at least 20 times during the lifetime of a LED fixture. Providing that the cost of specialized tubes for reef lighting can be quite high, a LED fixture can provide significant savings; e.g., not only monetary, but also of the time that was to be spent for acquisition and replacement of light bulbs. Let us try to calculate the possible savings from using a LED fixture. A 300W LED fixture can replace a 900W T5 fixture used on a 160 gallon SPS reef tank. In 10 years the LED fixture will save ((900-300)/1000)*12*365*10=26280KWh of electric power. The cost of electricity depends on where you live, how much you use, and possibly when you use it and the rates from the same provider can range from 12c to 50c per kWh [17]. For our estimate we shall use a sample rate of 15c per kWh, which is a reasonable example (you can find out how much you are actually paying for electric power by looking at your bill). Based on the 15c per KWH example, the fixture will save you $3942 in power alone. If we take the average cost of a specialized 80W T5 bulb to be around $25, we shall additionally save $25*10*20=$5000 in bulb replacements. Your total savings in 10 years will be about $8942. This is a "best scenario" estimate and we did not consider many additional expenses - for example, the cost of an aquarium chiller to remove the excessive heat from the tanks, as well as energy costs related to its operation. Besides, there are non-monetary values - such as the comfort of not having to provide maintenance on a light fixture in 10 years! Thus far, direct savings during the operational period are quite a few times higher than the cost of even most expensive LED fixture. In other words, not only you are getting it free, but it will even bring you some profit in its lifetime! Advantage #3: Ability to adjust illumination and spectrum When using dimmable drivers, the light emitted by LEDs can be easily adjusted. Aquarists often use special controllers to imitate sunrises and sunsets, similar to natural illumination changes during the day. It is important to note, however, that sunsets and sunrises in the equatorial zone are much quicker compared with higher latitudes, and daytime is equal to night (i.e. there is always a 12 hour photoperiod). Look at the diagram shown in Fig. 12 [20]: Fig. 12 The illustration shows how the time of day (A-E) affects the angle of incoming sunlight. Image courtesy of NASA Earth Observatory Real irradiance at the surface depends on multiple factors, such as cloudiness, the amount of water vapors in the air, atmospheric turbulence, etc. The insolation measured at the Great Barrier Reef on a typical day is shown in Fig. 13[21]. Fig. 13 Irradiance and solar elevation for September 2, 1998 at One Tree Island, Great Barrier Reef (23°30'S, 152°06'E) (Image courtesy of A. Salih, unpublished data) Also note that the light is almost fully reflected when the sun rays touch the water surface at small angles. Reflection also depends on the wind speed. These dependences are illustrated by the diagram in Fig. 14 [21]. Fig. 14 Reflectance of sunlight in relation to solar radiation. Theoretical and measured percentage of sunlight reflected off a completely smooth water surface in relation to solar elevation (based on calculations of Weinberg, 1976; Grichenko in Weinberg, 1976) This means that natural illumination under water is not sufficient for photosynthesis until the sun rises approximately 15 degrees over the horizon. In approximately 30 minutes after this the illumination quickly increases to about half of the daily maximum value. Therefore actual photoperiod is about 9 hours. These are the factors an aquarist should consider if he is wishing to replicate natural light cycles. Now let us consider important characteristics of light, which are required for our further conclusions. First such characteristic is CCT - Correlated Color Temperature. CCT of a given light source characterizes the temperature of an absolutely black body that would radiate a similar spectrum. The hotter the black body, the higher will be the CCT and the more blue or "cold" will be the light. As an illustration, sunlight has a yellow tint, whereas blue giants - huge stars with high temperature of the surface: 10000K and above (Sirius, for example) - seem bluish even to the naked eye. Let us compare the radiation spectrums from two different absolute black bodies with different CCTs [10]. The diagrams also indicate the dominating wavelength. Fig. 15 pictures the spectrum of a light source with 5500K CCT, and Fig. 16 - with 6500K CCT: Fig. 15 The spectrum of a light source with CCT 5500K Fig. 16 The spectrum of a light source with 6500K You can see that the dominating wavelength increases with the increase of CCT: it is equal to 444nm for the relatively warm light of the 6500K CCT. For a 8000K CCT bulb the calculated wavelength is about 420nm. Practically speaking, CCTs over 20000K is senseless. However, light bulb manufacturers often "abridge" the spectrum to a particular range of special interest, offering light bulbs with the spectrum similar to the one shown in Fig. 17: Fig. 17 The spectrum of the Grassy glow super blue 25000K bulb Even though the dominating wavelength of this bulb is about 450nm, it has a CCT of 25000K! [11] Thus, CCTs cannot be used as a criterion for the comparison of particular light source spectra. Moreover, even high CCT values do not guarantee that we shall get the required "actinic" spectrum. Another important characteristic is CRI - the Color Rendition Index. Unfortunately this term is often interpreted wrongly. It characterizes the influence of light source on the perception of an object's color. This parameter shows how correctly a light source with a particular CCT will deliver the color of an illuminated object, compared with an ideal source - an absolutely black body with the same color temperature. To determine the CRI, a set of 8 standard color samples is illuminated with the source and with the light of a back body with the same color temperature. If none of the samples change their color, CRI is equal to 100. The index reduces in inverse proportion to the number of color changes in samples. It is usually believed that a CRI above 80 is good. It is important to know, however, that CRI is calculated for light sources with a particular color temperature. It is not appropriate to compare a 2700K, 82 CRI light source with a 5000K, 85 CRI source. Also note that CCT and CRI are only defined for full-spectrum light sources. The CRI of monochromatic light is close to zero, and its CCT cannot be calculated. Look at Fig. 15, Fig. 16 - you can see a wide spectrum, starting near 120nm and finishing around 3000nm. In this whole range a clear maximum is present, and most of energy is radiated in a narrow band of wavelengths. Radiation spectrum of a black body can never have the shape of a narrow-band spike, similar to the spectrum of a monochromatic light source, and therefore, calculation of CCT for such sources makes no sense. All fluorescent and MH bulbs have a discrete spectrum, whereas sunlight has a continuous spectrum. Discrete spectrum is a result of using a discharge in mercury (and other metal) vapors, with several peaks at different wavelengths, mostly in the ultraviolet range. Phosphors on the bulb convert this radiation into narrow bands of visible light. A discrete spectrum vs. continuous is shown in Fig. 18: Fig. 18 Continuous (above) and discrete (below) spectrum The gaps - wavelengths that are missing in a discrete spectrum - mean that certain tints of color cannot be correctly rendered under such illumination and, as a result, the light source will have a low color rendition index (CRI). Of course, light bulb manufacturers try to avoid deep gaps in the spectrum. Look at the spectrums of popular marine MH bulbs: BLV HIT 10000K and BLV HIT 14000K (Fig. 19). Fig. 19 The spectrum of Metal Halide bulbs BLV HIT 10000K (a). Fig. 19 The spectrum of Metal Halide bulbs BLV HIT 14000K (. These bulbs do not have deep gaps in their spectrum, so that the intensity at a certain wavelength would drop to zero, hence both are full-spectrum bulbs and their CRI can be determined. At the same time, they exhibit clear discrete peaks, meaning that when using these bulbs precise color rendition cannot be achieved. Note that bulbs with different CCT: 10,000 Kelvin - 14,000 Kelvin are used in this example. Their main difference is in the significant portion of 400-440nm radiation in the second bulb, whereas the 460nm peak is missing. This is logical and clear: the higher the temperature of an absolutely black body, the more its spectrum would shift into the short wavelength region. Since the 400-450nm range is most important for a reef aquarium, and because, in order to attract the customer, manufacturers often calculate the CCT to satisfy their interests, we can safely state that maximum radiation in the required range is only achieved when a CCT of approximately 20000K is declared. Have a look at the spectrum of a 400W Hamilton Metal Halide bulb with 20000K CCT (Fig. 20): Fig. 20 The spectrum of a 400W Hamilton Radium Metal Halide bulb with 20000K CCT This bulb radiates a significant portion of its power in the 400-450nm range, with a noticeable peak around 420-430nm. Only a small portion of radiated power in the longer wavelength range makes its light visible, rather than dark to the eye as violet-blue. High CCT bulbs are often characterized by a significant portion of radiation in the 420-430nm range. Experienced reef aquarists recommend 20000K bulbs for providing the best color for marine organisms. This advice, obtained through years of practice, matches well with the conclusions we derived above. Of course, there is an exception from any rule. In our case, such an exception is marine organisms which only live in shallow waters in their natural habitat, in the tidal zone for example. This is an important reservation: there are species which can live both in shallow waters and at medium depth, and they are quite tolerant of the light spectrum. Certain species, however, can only live close to the surface, and cannot survive even at small depths. Such species do not adapt well, not only to the weaker illumination but also to a different spectrum. Certain species of colonial polyps of the Zoantidae genus are an example of this. Let us now consider the spectrum radiated by various LEDs. The spectrum of a cool-white LED with CCT around 7000K is shown in Fig. 21. Fig. 21 The spectrum of a white LED This spectrum is not discrete, but has a significant sag in the 470-500nm range. This gap can be compensated easily by adding a blue LED to the fixture. Have a look at the spectral power distribution for different color LEDs of Philips LUXEON Rebel ES series (Fig. 22). Fig. 22 Spectral power distribution of Philips LUXEON Rebel ES color LEDs Radiation of the Blue LED is most suitable to compensate for the required 470-490nm range. Even a better match could be achieved by using a LED with a 475nm peak - fortunately, such LEDs exist! To better explain this, let us consider the term bin, which manufacturers use to characterize their LEDs. A bin is a group of LEDs that have been selected according to a certain parameter. There are efficiency bins, CCT and CRI bins, and dominating wavelength (DWL) bins are available for monochromatic (single color) LEDs. DWL bins for blue LUXEON Rebel color LEDs are shown in Table 1. Table 1 LUXEON LED bin distribution by wavelength Adding a LED with the DWL bin code 4, we can flatten the white LED's spectral curve in the 430 to 600nm wavelength range. We shall now turn to actual implementation of LED fixtures for the reef aquaria. Using just two types of LEDs (white and blue) is not sufficient, because such a fixture will miss a significant amount of light in the 400-450nm range - much less than it is measured in the ocean, at the depth of just a few meters. The 450nm spectral range can be easily scaled up by using Royal Blue LEDs with a corresponding peak. Apart from that, the white LED spectrum quickly diminishes in the dark-red range, around 650-660nm. According to the model shown in Fig. 4, this part of the spectrum is also required for shallow-water photosynthetic organisms and adding this range can be beneficial -it will also help to emphasize the red color in the reef tank. What kind of spectrum shall we attain as a result? Answer: Something very close to the spectrum of the best light fixtures that are commercially available today. As an illustration, Fig. 23 shows the spectrum of Ecotechmarine Radion, ReefBuilders 2011 LED showdown winner [18]. Fig. 23 Output spectrum graph of Ecotechmarine Radion LED fixture As you can see, the gap in the 480nm range is properly filled (this fixture uses Cree's blue LEDs). Besides, a small peak in the 660nm range is available. However, any wavelengths in the 400-430nm range, which could promote the fluorescence of many marine organisms, are virtually missing. This range is missing in the majority of reef LED fixtures. Until recently, no LEDs of proper quality were available in the market for the 420nm range. For the few available offerings the prices were quite high, along with short operation time and poor efficiency. At the same time, the required total radiation in this wavelength range is quite significant, and adding the appropriate number of LEDs seriously affected the total cost of the fixture. As a result, manufacturers installed a tiny fraction of the required number of pure actinic LEDs, at best. In the beginning of 2012 this situation has the potential to change quickly since the introduction of efficient and relatively inexpensive 420nm LEDs [15]. By using these new generation LEDs in pure actinic wavelength range, it is possible to create an affordable LED fixture with proper spectrum required for the reef tank. Many hobbyists tried to use inexpensive no-brand Chinese LEDs in the pure actinic range. However, their efficiency is low and, as a result, the crystal deteriorates quickly due to overheating. Worst of all, this deterioration is hard to estimate visually, since the eye's sensitivity in 420nm range is very poor. Besides, spectral distribution of such low-quality LEDs can be very wide (from 350nm in the ultraviolet range, and up to green light): these longer wavelengths affect the visibility of coral fluorescence. At the same time the research conducted by the European Commission Joint Research Center [12] shows that UV light with shorter wavelengths may cause unsightly phosphorescence of small particles suspended in water (Fig. 24). Fig. 24 Phosphorescence of small particles in water under UV illumination The diagram contains several graphs for the phosphorescence of differently sized particles. We are mostly interested in particles sized around 60 μm, which are abundant in a reef tank. When irradiated with wavelengths shorter than 370-380nm, this phosphorescence can be quite significant. Wide spectral diagrams of previous generation LEDs contained a significant portion of 370nm radiation which caused noticeable phosphorescence of suspended particles in the aquarium, hence many DIY LED fixture builders recommended the use very few pure actinic LEDs. Fortunately, the newest generation of LEDs has an efficient bandwidth of about 30nm [15], and by using LEDs in the 400-430nm range we can avoid the phosphorescence of suspended particles, even though total radiation power can be quite high. We shall now try to estimate the amounts of light at selected wavelength ranges: 400-440nm, 440-480nm, 480-520nm, and 520-700nm. Each range will correspond to one color channel in a LED fixture and can be achieved by using one type or a combination of several types of LEDs. Insolation at the ocean surface depends on the presence of clouds, position of the sun, and other factors. For our estimates we shall assume an average monthly insolation of 1789 J/cm2, based on 3 months statistics for Fiji [20]. Assuming a 12 hours photoperiod, this translates to 413 W/m2. By integration of solar radiation power in accordance with Fig.3, we shall obtain the distribution of visible light power in the above sub-ranges for different depths (Table 2): Table 2 Average light power (in W per sq.m.) for the defined spectral ranges during the day Spectral sub-ranges, nm Depth, m (feet). 400-440 440-480 480-520 520-700 Total power 0 (0) 55 64 62 232 413 5 (16.4) 54 63 60 163 340 10 (32.8) 53 61 57 94 266 15 (49.2) 52 60 55 26 193 Although the table is based on naturally available spectral distribution at specified depths, note that the 400-500nm range is the most required, since it provides the best coloration and fluorescence in corals; whereas, the longer wavelength radiation in 500-700nm range is poorly utilized by marine photosynthetic organisms. At the same time, the human eye is very sensitive to the 520-600nm range and therefore we do not need very much radiation power in that range: even small amounts of illumination will be sufficient for the eye to perceive the tank as brightly lit. Meanwhile, supplementation of 660nm LEDs can be beneficial for shallow-water organisms. At the same time, this wavelength, in combination with the 400-420nm range, will promote correct rendition of the purple color. As we have shown, the 400-480nm range is most important for marine photosynthetic organisms. In their natural environment corals are getting 52 to 55W/m2 of optical power in the 400-440nm range and 60 to 64W/m2 in the 440-480nm range. If only these wavelengths are used in the fixture, using the empirical expression Watts/m2 = 0.21*L [19], we can achieve illumination levels between 528 and 567 μmol·photons/m2/s. As it was shown above, this is sufficient for proper growth and coloration of light-demanding corals. However, we do not recommend using that much radiation power all the time over the reef tank, and the following factors should be considered: Apart from the mentioned wavelength ranges, for an improved visual effect most hobbyists will also utilize LEDs in other ranges. These LEDs will also contribute to total radiated optical power. Radiation power over 400μmol·photons/m2/s can be too high. Production of chromoproteins stops below 100 μmol·photons/m2/s; i.e., at an illumination level 4 times smaller. Many aquarists are using controllers to imitate sunrises/sunsets and other effects, and radiated power may change significantly during the day. Mean power during the photoperiod is less than the maximum power. Marine photosynthetic organisms most efficiently utilize radiation with the wavelengths around 430nm, and this range also stimulates their most intensive coloration. We believe that the most reasonable maximum radiation power should be about 45W/m2 for the 400-440nm range and about 40W/m2 for the 440-480nm range. Note: Here and above we mention optical radiation power rather than the electrical power consumed by the LEDs. To determine the number of LEDs required in a fixture and their rated current these figures must be converted into electrical power, which depends on the efficiency of the LEDs actually used. These calculations, selection of particular LEDs and other matters concerning the actual construction of a LED fixture will be considered in our next article. If the reef tank is only illuminated in these wavelength ranges for 12 hours, with short sunrises and sunsets specific to the equatorial zone, we will obtain an average radiation power of 400μmol·photons/m2/s, which is sufficient for optimal production of chromoproteins. Since the light fixture is likely to also include LEDs in other wavelength ranges, we can safely assume that these figures include some power margin. Also note that although 400μmol·photons/m2/s radiation power is optimal for coloration of corals, such high illumination requires pristine water conditions in the tank. Radiation power 4 times below this level is already sufficient to start production of chromoproteins in corals. We recommend starting slowly, with initial lighting levels close to the lower boundary of about 100μmol·photons/m2/s. Within several months you can gradually increase the illumination, while closely monitoring water parameters and the corals' reaction. If the system is stable and all parameters are in the optimal range, optical power can be gradually increased up to 400μmol·photons/m2/s. As we have seen, formal parameters such as CRI and CCT are not very useful for determining whether a particular light fixture is suitable for a reef tank. At the same time we need to point out again that sufficient power in the 400-480nm wavelength range is critically important. If this condition is fulfilled, other parameters of the light fixture may be selected based on the owner's individual preferences (just make sure that the total radiated power does not exceed the recommended values). We have to admit, unfortunately, that most of the commercially available light fixtures today are only utilizing the 450nm range and above, whereas an ultimately important range between 400 and 440nm is usually left out, or is inadequately represented. References http://en.wikipedia.org/wiki/Color_vision David H.Hubel, Eye, Brain and Vision. 256p., 1995, ISBN/ASIN: 0716760096 http://www.ecse.rpi.edu/~schubert/Light-Emitting-Diodes-dot-org/Sample-Chapter.pdf http://ies.jrc.ec.europa.eu/uploads/fileadmin/Documentation/Reports/Global_Vegetation_Monitoring/EUR_2006-2007/EUR_22217_EN.pdf http://rybafish.umclidet.com/zooksantella-%E2%80%93-nevolnica-korallov.htm http://afonin-59-bio.narod.ru/4_evolution/4_evolution_self/es_13_algy.htm http://medbiol.ru/medbiol/botanica/000a984c.htm http://batrachos.com/node/442 http://reefcentral.com/forums/showpost.php?p=20296037&postcount=27 http://www.photo-mark.com/notes/2010/nov/19/plancks-despair/ http://reefbuilders.com/2010/06/17/grassy-glow-25000-k-metal-halide-bulb-from-volx-japan-hits-the-mark-for-blue-light-addicts/ http://ies.jrc.ec.europa.eu/uploads/fileadmin/Documentation/Reports/Global_Vegetation_Monitoring/EUR_2006-2007/EUR_22217_EN.pdf - 26p. R.W.Burnham, R.M.Hanes, C.J.Bartleson Color: A Guide to Basic Facts and Concepts. New York: John Wiley, 1953 Thai K. Van, William T Haller, and George Bowes Comparison of the Photosyntetic Characteristics of Three Submersed Aquatic Plants. www.plantphysiol.org/content/58/6/761.abstract http://www.led-professional.com/products/leds_led_modules/semileds-achieves-40-external-quantum-efficiency-for-ultraviolet-uv-led-chips C.D'Angelo, J.Wiedenmann, Blue light and its importance for the colors of stony corals, Coral Magazine, Nov./Dec. 2011 How much electricity costs, and how they charge you Ecotech Marine's Radion XR30w wins the 2011 Reef Builders LED showdown http://www.onsetcomp.com/support/knowledgebase/unit-conversion http://earthobservatory.nasa.gov/Features/EnergyBalance/page2.php http://reefkeeping.com/issues/2002-09/atj/feature/index.php Leletkin V.A., Popova L.I., Light absorption by carotenoid peridinin in zooxanthellae cell and setting down of hermatypic coral to depth, Zh. Obshch. Biol. 2005 May-Jun;66 (3) View the full article

Click through to see the images. Perhaps every reef hobbyist is willing to provide the "right" light to his corals - both correct spectrum and sufficient intensity are important. Before we consider how to implement this "right light," we shall first try to understand what kind of light marine organisms get in their natural environment. As our starting point, consider the spectral distribution of solar energy in Fiji in July, Fig. 1: Fig. 1 Spectral distribution of sunlight energy at the level of the sea The horizontal axis of the graph is wavelength, in nanometers, and the vertical axis is spectral irradiance, in W/m2·nm. The human eye is sensitive to radiation in the range between approximately 400 and 700nm, therefore we marked the wavelength ranges shorter than 400nm (ultraviolet light) or longer than 700nm (infrared radiation) in black, whereas visible wavelengths are colored as they are perceived by the eye. The chart in Fig. 1 has been obtained from the solar spectrum at the boundary of the earth atmosphere using the SMARTS 2.9.5 scientific simulation software. This simulator takes into account light absorption by various components of the atmosphere as well as scattered light from the sky. Let us now try to find out what kind of light spectrum is available to marine organisms in their natural environment. In our attempt to build an ideal light fixture for our reef tanks we shall try to generate a similar spectral distribution at certain depths underwater. Different coral species live on various depths: some live in very shallow waters, whereas deep water corals, such as Bathypates spp., can be found on the depths of up to 8000 meters (about 5 miles). About 20% of all coral species are non photosynthetic; they do not require any light as a food source. Most corals, however, are photosynthetic, and these are the species which are kept most often at home aquaria. We shall try to figure out what kind of light they prefer. Consider the graph of solar light penetration into marine water, depending on wavelength, compiled by the Institute for Environment and Sustainability of the European Commission [4] (Fig. 2): Fig. 2 Penetration of light into seawater, depending on wavelength The horizontal axis is the light wavelength, in nanometers, and the vertical axis is depth, in meters, at which the intensity of that wavelength is equal to one percent of the intensity at the surface. It is clear from this graph that wavelengths between approximately 370 and 500nm best penetrate into the depth. In other words, violet and blue parts of the spectrum penetrate best into seawater, whereas green light is much worse at that, yellow-orange is even worse, and red light with wavelengths longer than 600nm is only capable of penetrating very shallow waters. The light spectrum on the surface can be defined as a function I0(λ), where λ is the wavelength and I0 is the intensity for corresponding wavelength at zero depth. Hence the adsorption spectrum Ia(λ) at the depth D can be determined as Ia(λ) = I0(λ) · K(λ) · D (1) where K(λ) is the adsorption by marine water as a function of wavelength. The spectrum at the depth D will be equal to the spectrum on the surface I0(λ) minus the adsorption spectrum Ia(λ): I(λ) = I0(λ) - Ia(λ), or, by substituting (1) into this expression, we shall derive: I(λ) = I0(λ) · (1 - K(λ) · D) (2) From this expression we can derive the graph of light penetration into seawater d(λ): d(λ) = (1 - I(λ) / I0(λ)) / K(λ)) (3) Providing that the graph in Fig. 2 is based on the assumption that light intensity on the specified depth is equal to 1% of the intensity on the surface, i.e. I(λ) = 0,01 · I0(λ), we can simplify (3): d(λ) = 0.99 / K(λ) This function d(λ) is our graph of light penetration into seawater, which is pictured in Fig. 2. Using this graph we can determine light adsorption in seawater as a function of wavelength K(λ): K(λ) = 0.99 / d(λ) (4) By substituting the expression (4) into (2), we can derive the spectral distribution of light at a given depth D: I(λ) = I0(λ) · (1 - 0.99 · D / d(λ)) (5) where I0(λ) is the light spectrum on the surface and d(λ) is the graph of light penetration into seawater (Fig. 2). Using the expression (5) and the data from graphs in Fig. 1 and Fig. 2, we can obtain the diagram of light energy distribution vs. wavelength at a given depth. As an example, on the same graph (Fig. 3) we pictured light's relative spectral distribution at the surface and at the depths of 5m (about 16.4 feet) and 15m (49 feet). Note: 15m is the maximum depth at which we can still find many light-demanding corals in nature. At the depths below 20m, the number of light demanding species sharply decreases. Fig. 3 Light spectral distribution vs. wavelength on the surface (light blue), at 5m (blue) and 15m (dark blue) depths The light-blue graph corresponds to irradiation on the surface, the blue graph - to 5m depth, and the dark-blue - to 15m depth. Note that with depth, the red part of the spectrum virtually disappears. During hundreds of millions years of evolution marine photosynthetic organisms adapted to best utilize mainly the violet and blue parts of the spectrum, which is more abundant in their environment, and are not very sensitive to the red spectrum (which, in contrast, is most actively utilized by terrestrial plants). Symbiotic zooxanthellae in marine photosynthetic organisms are primitive Pyrrophyta algae [5] containing mainly chlorophyll a and c and carotenoid pigments (peridinine, xanthins, etc) which exhibit strong absorption in the blue-green part of the spectrum. [6,7,22]. Fig. 4 [22] demonstrates light adsorption by zooxanthellae. Fig. 4 Light absorption by zooxanthellae The horizontal axis is the wavelength, in nanometers, and vertical axis is adsorption, in arbitrary units. You can see from the graph that violet and blue colors strongly prevail over red (note that for red spectrum, the 660-680nm range is preferable). Our main conclusion from the above is that violet and blue light are most important for marine photosynthetic organisms. Knowing what is naturally available to corals from the color spectrum, we shall now consider the next important issue: how irradiation by different spectral ranges affects coral coloration? Before we consider the influence of the light spectrum on coral coloration I would like to point out that even coloration of the same coral may vary significantly depending on conditions. Unfortunately, it is very difficult to provide exactly identical conditions for the corals, even in the same aquarium - and this is even harder for two different tanks. Without providing the right conditions for the corals, other attempts to improve their coloration, such as adjustments of the light spectrum, will be in vain. Experienced reef keepers well know how variable the coloration of the same coral can be in different conditions. There are three main factors which affect it most: light spectrum and intensity, the amount of food available in water (although coral polyps receive a significant portion of their energy from the zooxanthellae, they are also able to capture food particles from the water column), and from the purity of the water. This last factor is easiest to control: techniques to maintain pristine water in reef aquaria are well known. The second factor, too, can be solved easily since there are a number of quality coral foods readily available on the market. At the same time many aquarists believe that, if there are fish living in a reef aquarium, corals will get sufficient food from small particles which float around from feeding the fish (and fish poo too is consumed by corals). Light is the last important factor required for good health and the coloration of corals, and yet has not been studied sufficiently well in reef keeping. The situation is rather complex though, since corals can be very variable, and even the same species may contain different chromoproteins (proteins responsible for coloration) - their type and amount are also determined genetically, in the same way as, say, the color of human's eyes. Many of these proteins are fluorescent; i.e., they adsorb the light of a certain wavelength and radiate a different wavelength. Fig. 5 shows four specimens of the same species, Acropora millepora, in which different chromoproteins prevail: Fig. 5 The Acropora millepora specimens with different prevailing chromoproteins: (A) low concentration of chromoproteins, the color of zooxanthellae dominates; ( green fluorescent proteins; © red fluorescent proteins; (D) non-fluorescent chromoproteins. Image courtesy of Dr. C. D'Angelo and Dr. J. Wiedenmann, University of Southampton, UK, Coral Magazine, Nov./Dec. 2011 Fluorescence is witnessed not only in hard corals but, for example, in Zoanthidae and Palythoya polyps which exhibit much brighter coloration when irradiated with so-called short-wavelength "actinic" light. Coral fluorescence is very beautiful but it is not always easy to observe it. Have a look at the luminous function (spectral sensitivity chart) of the human eye (Fig. 6). Light sensitive elements of the eye are represented by two cell types - the so-called retinal cones and rods. The first are responsible for distinguishing between colors, and the second - for grey tones. The cones work best during daytime, the rods - at night. Remember the saying "all cats are grey in the dark." This is just because we mainly see with the rods in the dark, rather than with cones. The rods do not distinguish between colors: they only sense the relative brightness of an object. The rods are most sensitive to the emerald-green part of the spectrum, with the wavelength of about 510nm (of course, when seeing by the rods, this light is only perceived as a brighter shade of gray rather than green. There are three cell types in cones, each sensitive to a specific part of the spectrum. S-type cones are sensitive to violet and blue (S stands for Short wavelengths), M-type - for green and yellow (Medium wavelengths), and L-type - for orange and red (Long wavelengths). These three cone types, (along with the rods that are sensitive in the emerald-green part of the spectrum) are responsible for color vision in humans. The rods contain a color-sensitive pigment, rhodopsin, and their spectral characteristic depends on lighting conditions. For weak light, rhodopsin's adsorption peak is at about 510nm (the spectrum of the sky at twilight). And therefore the rods are responsible for twilight vision, when colors are hard to distinguish. At higher levels of illumination rhodopsin photo bleaches, and its sensitivity decreases, while the adsorption peak shifts into the blue region. As a result, under sufficient light, the human eye can use the rods as a shortwave (blue) light detector. S-cells are sensitive in the 400-500nm range with a maximum at 420-440nm; M-cells are sensitive in 460-630nm range, with a maximum at 534-555nm; L-cells are sensitive in the 500-700nm range with a maximum at 564-580nm [1]. Sensitivity ranges of long- and medium-wavelength cones are wide and overlapping. Therefore it is wrong to think that certain cone types only react to certain colors - they just more actively react to certain colors than to others [2]. The human eye is most sensitive in the range where sensitivities of M- and L-type cones add up: at 555nm (yellow-green light). The overall spectral sensitivity function [3] of human eye receptors is shown in Fig. 6: Fig. 6 Luminous function of the eye An important conclusion here is that the human eye sensitivity to light depends on the wavelength. For example, radiation of equal power is perceived 27 times brighter for the 555nm wavelength than for 450nm; this difference increases to 57 times for 420nm, and 135 times (!) for 410nm. Humans visually perceive any object as the sum of its reflected light and the object's intrinsic emission (an object is considered light emitting if its total emission at a certain wavelength range is higher than the falling light energy in that same region). Usually objects only reflect light, and their color is determined by the ratio, in which different wavelengths falling on its surface are adsorbed or reflected. For example, green leaves adsorb all visible wavelengths except for green, which is reflected - therefore we perceive it as green. When an object not only reflects but also emits its own light, the eye combines the emitted and reflected light spectrum into its perceived color. Yielding color depends on the ratio of the intensities and wavelengths of both reflected and emitted light. This color addition is best illustrated by the diagram shown in Fig. 7: Fig. 7 Additive color mixing When looking at the computer monitor, you witness the effects illustrated by this chart: every pixel on the screen consists of three sub pixels: red, green and blue, and all colors are obtained by combination of their intensities. Note that pure purple color and its tints, such as magenta or fuchsia, are unique in being non-spectral or extra-spectral: there is no specific wavelength associated with these colors, they are mixtures, and one of the required components is violet, with the wavelength around 400nm [13], and red. If a specific light source has no radiation in this range, up to 20% of the whole color palette is lost - and these are very bright colors and their shades! It is also interesting to note that by combining the yellow and blue colors the resulting color is visually perceived as pure white. Color vision is mainly inherited genetically. We are not talking about the defects of color vision, such as color blindness - but each person perceives colors in his own way, and this difference can be very significant. Apparently, it is very important to be able to adjust the spectral distribution of the light fixture, to find an individually suitable color distribution in the reef tank. To watch coral fluorescence we shall irradiate the fluorescent proteins with light of a specific wavelength. Look at the adsorption and radiation wavelengths chart for most common fluorescent pigments available in marine organisms [9], shown in Fig. 8: Fig. 8 Adsorption and emission wavelengths for fluorescent pigments available in marine organisms. The figure is courtesy of Dan Kelley The horizontal axis are the wavelengths which cause fluorescence in various chromoproteins; the vertical axis is the wavelength emitted as a result of fluorescence. You can see that virtually all pigments adsorb shorter wavelengths and emit longer wavelengths. As we have shown above, the eye is most susceptible to the 550nm range, and the closer the emitted light is to that wavelength, the brighter it will be perceived. Thus, specific proteins available in marine organisms adsorb the poorly visible to the eye short wavelengths and fluoresce with a color which looks much brighter to our eye. Under purely "actinic" light, which only contains shorter wavelengths, our fish tank will glow with bright colors, whereas the light from the fixture itself is almost invisible to the eye. This gives the impression of miniature light bulbs installed in each coral or polyp, which glow brightly in the dark! Color of a coral, as perceived by the eye, also depends on the color of falling light. The color of any object that we see represents the reflected portion of the falling light spectrum. As we have pointed out above, when illuminated by a full-spectrum light, the leaves of most terrestrial plants adsorb almost all parts of the visible spectrum, and reflect the green part - therefore we perceive them as green. However, if we irradiate the leaves by a light in which the green part of the spectrum is missing - by red light, for example - they will seem black to us, because all falling light is adsorbed. In a similar manner, white object looks white under full spectral light, because it uniformly reflects all parts of the spectrum, but will "take up" the color of any light that we throw at it: red, green, blue, or their combination. Back to corals - let us consider an organism containing a protein which, when irradiated by the 420nm light, will fluoresce by the 520nm wavelength. For reasons of simplicity, suppose that our light source radiates only at the 420nm wavelength, and the coral adsorbs this light completely, without reflection. The human eye has extremely low sensitivity to this wavelength (almost invisible), whereas it is most sensitive to the wavelength radiated by the coral as a result of fluorescence. We shall see this fluorescence very well in the "dark" pure actinic light. If the light source includes radiation at other wavelengths, the resulting color of the marine organism will be added up from fluorescence and reflected light. If the light source contains wavelengths, to which the eye is very sensitive (especially in close proximity to the 550nm sensitivity peak), we will mainly see the light from the fixture, and perception of coral fluorescence will be weak on this bright background. Our conclusion is that for best observation of fluorescence, we shall illuminate the tank with such light that its reflected portion would least hinder us in seeing the light radiated by corals. Wavelengths required for fluorescence of all chromoproteins are numerous, and there is no single wavelength that could be used for making an ideal actinic light. Based on Fig. 8, fluorescence is observed in quite wide a range of falling light wavelengths, mainly between 400 and 500nm, and different organisms have different fluorescent protein sets. For best fluorescence we need the capacity to adjust the light spectrum in the 400 to 500nm range, according to the needs of a particular aquarium. Note that the strongest fluorescence will be observed in 400-450nm range, particularly because the eye sensitivity in that range is very low. The light in this range is usually called "actinic light." Surely, coral fluorescence is one of the main factors to provide a reef tank's beauty, but the light in the 400-500nm range also has other importance: it is the most optimal light to promote marine photosynthesis. Therefore this part of the spectrum is of utmost importance for a reef tank. This conclusion matches well with the experimental research in this field [16]. Fragments of Acropora millepora colony were maintained for six weeks under comparable amounts of red, green, and blue light. The conclusion of the article is that "the enhancement of coral pigmentation is primarily dependent on the blue component of the spectrum and regulated at the transcriptional level," and "light-driven accumulation of GFP-like proteins observed upon green light exposure is likely due to residual blue light passing the green filter." The experiments also revealed that radiation in the 430nm range is most efficient in promoting the protective bright coloration of the corals:"Among the known FPs and CPs, only the absorption properties of CFPs spectrally match the major absorption band of chlorophyll a and c at ~430 nm, making them suitable for effective shielding of the photosynthetic system of the zooxanthellae." The intensity of light is also very important for growth and active production of fluorescent chromoproteins. A light source could be best characterized, perhaps, by spectral distribution of the optical radiation energy at different wavelengths. This characteristic is usually represented by the spectral curve. For most common light sources, however, the spectral characteristic is usually unavailable, and instead an estimated light flux is provided, in lumens. Light flux in lumens is the visible light radiation power, as perceived by the human eye - depending on the eye's sensitivity to different wavelengths. Note: One lumen is the total luminous flux emitted uniformly by a light source with luminous intensity of one candela across a solid angle of one steradian (a cone with the angle of approximately 65.5° at the apex). Candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of 555nm wavelength (i.e. the wavelength at the peak sensitivity of the human eye), and has a radiant intensity in that direction of 1/683 watt per steradian. One watt of optical power radiated at the 555nm wavelength corresponds to 683 lm. For any other wavelengths, it is equal to the optical power emitted at that wavelength multiplied by the luminosity function of the eye for the same wavelength. To determine total lumens emitted by a light source we need to sum up the lumens for all emitted wavelengths. It is evident that the intensity equal light energy in various parts of the spectrum will be perceived differently by the eye: a powerful source in the 400-450nm range will be perceived as very dim light, and a light source emitting in the infrared region will seem black. Therefore an estimate of the light flux in lumens is only valid when light's spectral distribution is unimportant and the only thing that matters is brightness, as perceived by the eye. In our case, a more appropriate parameter for determination of light radiation would be the number of photons per second, falling on each meter square: μmol·photons/m2/s. During the hundreds of millions years of evolution marine photosynthetic organisms adapted to different light power levels. For each photosynthetic organism three threshold values can be defined [14]. First (least intensive) determines the minimum light required for the maintenance of photosynthetic organism's biomass - it is the minimum required light which will not result in gain or loss of mass. The second threshold value concerns illumination at which the photosynthesis efficiency is highest. And finally the third, upper threshold is the maximum light which can be utilized -there is no improvement in photosynthesis rate above that threshold. These three thresholds, of course, depend on particular organisms, but we can use an estimate for marine photosynthetic organisms living in shallow waters. We can safely call 80-100 μmol·photons/m2/s low light, 150-200 - medium, and 300-400 - optimal. The saturation limit of photosynthesis is about 600-700μmol·photons/m2/s. In our reef tank, we shall achieve a significantly better illumination than the minimum threshold - preferably near the optimal threshold. Let us consider yet another experiment with Acropora millepora to illustrate the production of chromo proteins under less than optimal illumination, and when the light level is in optimal value for the species (Fig.9). Illumination 100 400 Red fluorescent Green fluorescent Daylight Fig.9 An experiment with Acropora millepora illustrating the production of chromo proteins insufficient for photosynthesis, and intensity for optimal illumination for this species. Regarding light intensity this work also states that chromo proteins are not formed under illumination levels below 100 μmol·photons/m2·s, and their number grows almost linearly along with the increase of light intensity up to about 700 μmol·photons/m2·s. However, it is not always a good idea to provide as much light in home aquaria, since a coral can become very demanding to its environment parameters under such high levels of illumination. Under less than perfect conditions such high levels of illumination can yield a contrary result: coral bleaching. The experiment illustrates that optimal light levels improve coral growth and coloration, both for ordinary and fluorescent chromoproteins. Concluding from the above, light in the 400-500nm range is most beneficial for marine photosynthetic organisms, and its shortwave portion (400-450nm) is most useful for their bright coloration. Let us consider the most popular actinic light sources for a reef tank. These are mostly fluorescent bulbs which mainly radiate in the 400-500nm range, such as Giesemann Actinic Plus, Fig. 10: Fig. 10 A typical actinic fluorescent tube: Giesemann Actinic Plus Looking at the spectral distribution of this bulb we can see that apart from the pure actinic spectrum, which is required for coral fluorescence, there are also distinct "parasitic" peaks around 550nm. As we have pointed out, the human eye is over 20 times more sensitive to the wavelengths in this range rather than to the "actinic" range which causes fluorescence (see Fig. 6). As a result, this bulb is visually perceived as quite bright, almost white, but with strong blue-violet tint. The resulting fluorescence will be partially "dimmed" as a result of this parasitic radiation in the well-to-see range. In recent years multiple attempts were made to create narrow-range "actinic" bulbs. One of the best is Giesemann POWERCHROME actinic plus, with significantly reduced 450-500nm portion (Fig. 11): Fig. 11 The spectrum of the POWERCHROME actinic plus bulb We can see that "parasitic" portion of this bulb's spectrum is smaller and the 420-430nm range is better represented. However, this bulb too, still looks quite bright to the eye, because of the still present peak at 550nm. So far, conventional fluorescent tubes are not so efficient for observation of fluorescence in a reef tank. Desperate? No! Quite recently, there was a breakthrough in the field of solid-state lighting, and many light fixtures for reef tanks are now constructed with the use of LEDs. The advantages of LED fixtures over the conventional light sources are many; we shall only consider the main factors. Advantage #1: Higher efficiency and less heat generation Higher efficiency has two components. First is that LEDs are about twice more efficient than conventional fluorescent tubes or Metal Halide bulbs in converting the electric energy into light. Second is that LEDs only radiate in one direction of the plane and hence are not apt to block their own light. By utilizing proper lenses, LED light can be easily concentrated in the desired region. Good LED lenses are compact in size and, at the same time, can help to transfer up to 90 percent of produced light through the water surface. For comparison, when using conventional bulbs with reflectors usually only 40% of light penetrates the surface. Best reflectors (often cumbersome) can yield up to 60% of light penetration, and the bulb itself partially blocks the light returning from the reflector. Resultant efficiency of best LED fixtures can be three times higher compared with the best light bulbs. Consequently, LEDs can generate over 4.5 times less heat. This practically means that by installing a LED fixture over a reef tank we can probably eliminate the need for an expensive chiller (which also consumes significant power). Thus, LED fixtures may achieve significant power savings; apart from the economic effect, their environmental impact is also significant!). Advantage #2: Extended life cycle As a solid-state light source, a light emitting diode does not have quickly wearing parts, such as an incandescent filament. When operated at or below rated current, and providing that they do not overheat, high quality LEDs degrade very slowly. But LEDs too have their specific needs which have to be considered when designing a fixture. Lifespan of the best LEDs available in the market today (Cree XT-E, LUXEON Rebel ES) is indeed very high, if sufficient heat removal and properly conditioned power are provided. Of course, these are new LEDs and their operation have been tested for tens of years, but using complex models their life term and luminosity drop in that period can be estimated. We shall refer to two types of such forecasts: based on Cree's model (which we call the "worst case scenario" or "pessimistic model"), and in parenthesis we provide figures based on the Philips model for their LUXEON Rebel ES (which we call the "optimistic model"). If all the required operation conditions are fulfilled, we will still be getting about 70% of LED's initial radiation power after 40 (150) thousand hours of operation. These figures translate to 10 (33) years of operation of a light fixture, providing 12 hours of operation daily! After this period the LEDs will continue to lose luminance, reaching about 50% of the initial value after 100 (200) thousand hours! The probability of a single LED failure on a fixture is quite low, about 1% during the period of 50 thousand hours of operation, and after this period the probability increases to 50% by 200 thousand hours. Several LEDs in a light fixture are usually connected in series, and therefore, if one LED dies, the whole string will be effected. If we look at these figures statistically, is likely that for a fixture with about 200 LEDs this can happen in 10 years. However a LED's death is a probabilistic event and it can happen that a particular light emitting diode may get "fried" during the very first hours of its life. In practice, if the conditions are good, lifespan of modern LEDs is quite long. In comparison, conventional fluorescent tubes need to be replaced once every four to six months. Based on our worst case scenario, it means that they will have to be replaced at least 20 times during the lifetime of a LED fixture. Providing that the cost of specialized tubes for reef lighting can be quite high, a LED fixture can provide significant savings; e.g., not only monetary, but also of the time that was to be spent for acquisition and replacement of light bulbs. Let us try to calculate the possible savings from using a LED fixture. A 300W LED fixture can replace a 900W T5 fixture used on a 160 gallon SPS reef tank. In 10 years the LED fixture will save ((900-300)/1000)*12*365*10=26280KWh of electric power. The cost of electricity depends on where you live, how much you use, and possibly when you use it and the rates from the same provider can range from 12c to 50c per kWh [17]. For our estimate we shall use a sample rate of 15c per kWh, which is a reasonable example (you can find out how much you are actually paying for electric power by looking at your bill). Based on the 15c per KWH example, the fixture will save you $3942 in power alone. If we take the average cost of a specialized 80W T5 bulb to be around $25, we shall additionally save $25*10*20=$5000 in bulb replacements. Your total savings in 10 years will be about $8942. This is a "best scenario" estimate and we did not consider many additional expenses - for example, the cost of an aquarium chiller to remove the excessive heat from the tanks, as well as energy costs related to its operation. Besides, there are non-monetary values - such as the comfort of not having to provide maintenance on a light fixture in 10 years! Thus far, direct savings during the operational period are quite a few times higher than the cost of even most expensive LED fixture. In other words, not only you are getting it free, but it will even bring you some profit in its lifetime! Advantage #3: Ability to adjust illumination and spectrum When using dimmable drivers, the light emitted by LEDs can be easily adjusted. Aquarists often use special controllers to imitate sunrises and sunsets, similar to natural illumination changes during the day. It is important to note, however, that sunsets and sunrises in the equatorial zone are much quicker compared with higher latitudes, and daytime is equal to night (i.e. there is always a 12 hour photoperiod). Look at the diagram shown in Fig. 12 [20]: Fig. 12 The illustration shows how the time of day (A-E) affects the angle of incoming sunlight. Image courtesy of NASA Earth Observatory Real irradiance at the surface depends on multiple factors, such as cloudiness, the amount of water vapors in the air, atmospheric turbulence, etc. The insolation measured at the Great Barrier Reef on a typical day is shown in Fig. 13[21]. Fig. 13 Irradiance and solar elevation for September 2, 1998 at One Tree Island, Great Barrier Reef (23°30'S, 152°06'E) (Image courtesy of A. Salih, unpublished data) Also note that the light is almost fully reflected when the sun rays touch the water surface at small angles. Reflection also depends on the wind speed. These dependences are illustrated by the diagram in Fig. 14 [21]. Fig. 14 Reflectance of sunlight in relation to solar radiation. Theoretical and measured percentage of sunlight reflected off a completely smooth water surface in relation to solar elevation (based on calculations of Weinberg, 1976; Grichenko in Weinberg, 1976) This means that natural illumination under water is not sufficient for photosynthesis until the sun rises approximately 15 degrees over the horizon. In approximately 30 minutes after this the illumination quickly increases to about half of the daily maximum value. Therefore actual photoperiod is about 9 hours. These are the factors an aquarist should consider if he is wishing to replicate natural light cycles. Now let us consider important characteristics of light, which are required for our further conclusions. First such characteristic is CCT - Correlated Color Temperature. CCT of a given light source characterizes the temperature of an absolutely black body that would radiate a similar spectrum. The hotter the black body, the higher will be the CCT and the more blue or "cold" will be the light. As an illustration, sunlight has a yellow tint, whereas blue giants - huge stars with high temperature of the surface: 10000K and above (Sirius, for example) - seem bluish even to the naked eye. Let us compare the radiation spectrums from two different absolute black bodies with different CCTs [10]. The diagrams also indicate the dominating wavelength. Fig. 15 pictures the spectrum of a light source with 5500K CCT, and Fig. 16 - with 6500K CCT: Fig. 15 The spectrum of a light source with CCT 5500K Fig. 16 The spectrum of a light source with 6500K You can see that the dominating wavelength increases with the increase of CCT: it is equal to 444nm for the relatively warm light of the 6500K CCT. For a 8000K CCT bulb the calculated wavelength is about 420nm. Practically speaking, CCTs over 20000K is senseless. However, light bulb manufacturers often "abridge" the spectrum to a particular range of special interest, offering light bulbs with the spectrum similar to the one shown in Fig. 17: Fig. 17 The spectrum of the Grassy glow super blue 25000K bulb Even though the dominating wavelength of this bulb is about 450nm, it has a CCT of 25000K! [11] Thus, CCTs cannot be used as a criterion for the comparison of particular light source spectra. Moreover, even high CCT values do not guarantee that we shall get the required "actinic" spectrum. Another important characteristic is CRI - the Color Rendition Index. Unfortunately this term is often interpreted wrongly. It characterizes the influence of light source on the perception of an object's color. This parameter shows how correctly a light source with a particular CCT will deliver the color of an illuminated object, compared with an ideal source - an absolutely black body with the same color temperature. To determine the CRI, a set of 8 standard color samples is illuminated with the source and with the light of a back body with the same color temperature. If none of the samples change their color, CRI is equal to 100. The index reduces in inverse proportion to the number of color changes in samples. It is usually believed that a CRI above 80 is good. It is important to know, however, that CRI is calculated for light sources with a particular color temperature. It is not appropriate to compare a 2700K, 82 CRI light source with a 5000K, 85 CRI source. Also note that CCT and CRI are only defined for full-spectrum light sources. The CRI of monochromatic light is close to zero, and its CCT cannot be calculated. Look at Fig. 15, Fig. 16 - you can see a wide spectrum, starting near 120nm and finishing around 3000nm. In this whole range a clear maximum is present, and most of energy is radiated in a narrow band of wavelengths. Radiation spectrum of a black body can never have the shape of a narrow-band spike, similar to the spectrum of a monochromatic light source, and therefore, calculation of CCT for such sources makes no sense. All fluorescent and MH bulbs have a discrete spectrum, whereas sunlight has a continuous spectrum. Discrete spectrum is a result of using a discharge in mercury (and other metal) vapors, with several peaks at different wavelengths, mostly in the ultraviolet range. Phosphors on the bulb convert this radiation into narrow bands of visible light. A discrete spectrum vs. continuous is shown in Fig. 18: Fig. 18 Continuous (above) and discrete (below) spectrum The gaps - wavelengths that are missing in a discrete spectrum - mean that certain tints of color cannot be correctly rendered under such illumination and, as a result, the light source will have a low color rendition index (CRI). Of course, light bulb manufacturers try to avoid deep gaps in the spectrum. Look at the spectrums of popular marine MH bulbs: BLV HIT 10000K and BLV HIT 14000K (Fig. 19). Fig. 19 The spectrum of Metal Halide bulbs BLV HIT 10000K (a). Fig. 19 The spectrum of Metal Halide bulbs BLV HIT 14000K (. These bulbs do not have deep gaps in their spectrum, so that the intensity at a certain wavelength would drop to zero, hence both are full-spectrum bulbs and their CRI can be determined. At the same time, they exhibit clear discrete peaks, meaning that when using these bulbs precise color rendition cannot be achieved. Note that bulbs with different CCT: 10,000 Kelvin - 14,000 Kelvin are used in this example. Their main difference is in the significant portion of 400-440nm radiation in the second bulb, whereas the 460nm peak is missing. This is logical and clear: the higher the temperature of an absolutely black body, the more its spectrum would shift into the short wavelength region. Since the 400-450nm range is most important for a reef aquarium, and because, in order to attract the customer, manufacturers often calculate the CCT to satisfy their interests, we can safely state that maximum radiation in the required range is only achieved when a CCT of approximately 20000K is declared. Have a look at the spectrum of a 400W Hamilton Metal Halide bulb with 20000K CCT (Fig. 20): Fig. 20 The spectrum of a 400W Hamilton Radium Metal Halide bulb with 20000K CCT This bulb radiates a significant portion of its power in the 400-450nm range, with a noticeable peak around 420-430nm. Only a small portion of radiated power in the longer wavelength range makes its light visible, rather than dark to the eye as violet-blue. High CCT bulbs are often characterized by a significant portion of radiation in the 420-430nm range. Experienced reef aquarists recommend 20000K bulbs for providing the best color for marine organisms. This advice, obtained through years of practice, matches well with the conclusions we derived above. Of course, there is an exception from any rule. In our case, such an exception is marine organisms which only live in shallow waters in their natural habitat, in the tidal zone for example. This is an important reservation: there are species which can live both in shallow waters and at medium depth, and they are quite tolerant of the light spectrum. Certain species, however, can only live close to the surface, and cannot survive even at small depths. Such species do not adapt well, not only to the weaker illumination but also to a different spectrum. Certain species of colonial polyps of the Zoantidae genus are an example of this. Let us now consider the spectrum radiated by various LEDs. The spectrum of a cool-white LED with CCT around 7000K is shown in Fig. 21. Fig. 21 The spectrum of a white LED This spectrum is not discrete, but has a significant sag in the 470-500nm range. This gap can be compensated easily by adding a blue LED to the fixture. Have a look at the spectral power distribution for different color LEDs of Philips LUXEON Rebel ES series (Fig. 22). Fig. 22 Spectral power distribution of Philips LUXEON Rebel ES color LEDs Radiation of the Blue LED is most suitable to compensate for the required 470-490nm range. Even a better match could be achieved by using a LED with a 475nm peak - fortunately, such LEDs exist! To better explain this, let us consider the term bin, which manufacturers use to characterize their LEDs. A bin is a group of LEDs that have been selected according to a certain parameter. There are efficiency bins, CCT and CRI bins, and dominating wavelength (DWL) bins are available for monochromatic (single color) LEDs. DWL bins for blue LUXEON Rebel color LEDs are shown in Table 1. Table 1 LUXEON LED bin distribution by wavelength Adding a LED with the DWL bin code 4, we can flatten the white LED's spectral curve in the 430 to 600nm wavelength range. We shall now turn to actual implementation of LED fixtures for the reef aquaria. Using just two types of LEDs (white and blue) is not sufficient, because such a fixture will miss a significant amount of light in the 400-450nm range - much less than it is measured in the ocean, at the depth of just a few meters. The 450nm spectral range can be easily scaled up by using Royal Blue LEDs with a corresponding peak. Apart from that, the white LED spectrum quickly diminishes in the dark-red range, around 650-660nm. According to the model shown in Fig. 4, this part of the spectrum is also required for shallow-water photosynthetic organisms and adding this range can be beneficial -it will also help to emphasize the red color in the reef tank. What kind of spectrum shall we attain as a result? Answer: Something very close to the spectrum of the best light fixtures that are commercially available today. As an illustration, Fig. 23 shows the spectrum of Ecotechmarine Radion, ReefBuilders 2011 LED showdown winner [18]. Fig. 23 Output spectrum graph of Ecotechmarine Radion LED fixture As you can see, the gap in the 480nm range is properly filled (this fixture uses Cree's blue LEDs). Besides, a small peak in the 660nm range is available. However, any wavelengths in the 400-430nm range, which could promote the fluorescence of many marine organisms, are virtually missing. This range is missing in the majority of reef LED fixtures. Until recently, no LEDs of proper quality were available in the market for the 420nm range. For the few available offerings the prices were quite high, along with short operation time and poor efficiency. At the same time, the required total radiation in this wavelength range is quite significant, and adding the appropriate number of LEDs seriously affected the total cost of the fixture. As a result, manufacturers installed a tiny fraction of the required number of pure actinic LEDs, at best. In the beginning of 2012 this situation has the potential to change quickly since the introduction of efficient and relatively inexpensive 420nm LEDs [15]. By using these new generation LEDs in pure actinic wavelength range, it is possible to create an affordable LED fixture with proper spectrum required for the reef tank. Many hobbyists tried to use inexpensive no-brand Chinese LEDs in the pure actinic range. However, their efficiency is low and, as a result, the crystal deteriorates quickly due to overheating. Worst of all, this deterioration is hard to estimate visually, since the eye's sensitivity in 420nm range is very poor. Besides, spectral distribution of such low-quality LEDs can be very wide (from 350nm in the ultraviolet range, and up to green light): these longer wavelengths affect the visibility of coral fluorescence. At the same time the research conducted by the European Commission Joint Research Center [12] shows that UV light with shorter wavelengths may cause unsightly phosphorescence of small particles suspended in water (Fig. 24). Fig. 24 Phosphorescence of small particles in water under UV illumination The diagram contains several graphs for the phosphorescence of differently sized particles. We are mostly interested in particles sized around 60 μm, which are abundant in a reef tank. When irradiated with wavelengths shorter than 370-380nm, this phosphorescence can be quite significant. Wide spectral diagrams of previous generation LEDs contained a significant portion of 370nm radiation which caused noticeable phosphorescence of suspended particles in the aquarium, hence many DIY LED fixture builders recommended the use very few pure actinic LEDs. Fortunately, the newest generation of LEDs has an efficient bandwidth of about 30nm [15], and by using LEDs in the 400-430nm range we can avoid the phosphorescence of suspended particles, even though total radiation power can be quite high. We shall now try to estimate the amounts of light at selected wavelength ranges: 400-440nm, 440-480nm, 480-520nm, and 520-700nm. Each range will correspond to one color channel in a LED fixture and can be achieved by using one type or a combination of several types of LEDs. Insolation at the ocean surface depends on the presence of clouds, position of the sun, and other factors. For our estimates we shall assume an average monthly insolation of 1789 J/cm2, based on 3 months statistics for Fiji [20]. Assuming a 12 hours photoperiod, this translates to 413 W/m2. By integration of solar radiation power in accordance with Fig.3, we shall obtain the distribution of visible light power in the above sub-ranges for different depths (Table 2): Table 2 Average light power (in W per sq.m.) for the defined spectral ranges during the day Spectral sub-ranges, nm Depth, m (feet). 400-440 440-480 480-520 520-700 Total power 0 (0) 55 64 62 232 413 5 (16.4) 54 63 60 163 340 10 (32.8) 53 61 57 94 266 15 (49.2) 52 60 55 26 193 Although the table is based on naturally available spectral distribution at specified depths, note that the 400-500nm range is the most required, since it provides the best coloration and fluorescence in corals; whereas, the longer wavelength radiation in 500-700nm range is poorly utilized by marine photosynthetic organisms. At the same time, the human eye is very sensitive to the 520-600nm range and therefore we do not need very much radiation power in that range: even small amounts of illumination will be sufficient for the eye to perceive the tank as brightly lit. Meanwhile, supplementation of 660nm LEDs can be beneficial for shallow-water organisms. At the same time, this wavelength, in combination with the 400-420nm range, will promote correct rendition of the purple color. As we have shown, the 400-480nm range is most important for marine photosynthetic organisms. In their natural environment corals are getting 52 to 55W/m2 of optical power in the 400-440nm range and 60 to 64W/m2 in the 440-480nm range. If only these wavelengths are used in the fixture, using the empirical expression Watts/m2 = 0.21*L [19], we can achieve illumination levels between 528 and 567 μmol·photons/m2/s. As it was shown above, this is sufficient for proper growth and coloration of light-demanding corals. However, we do not recommend using that much radiation power all the time over the reef tank, and the following factors should be considered: Apart from the mentioned wavelength ranges, for an improved visual effect most hobbyists will also utilize LEDs in other ranges. These LEDs will also contribute to total radiated optical power. Radiation power over 400μmol·photons/m2/s can be too high. Production of chromoproteins stops below 100 μmol·photons/m2/s; i.e., at an illumination level 4 times smaller. Many aquarists are using controllers to imitate sunrises/sunsets and other effects, and radiated power may change significantly during the day. Mean power during the photoperiod is less than the maximum power. Marine photosynthetic organisms most efficiently utilize radiation with the wavelengths around 430nm, and this range also stimulates their most intensive coloration. We believe that the most reasonable maximum radiation power should be about 45W/m2 for the 400-440nm range and about 40W/m2 for the 440-480nm range. Note: Here and above we mention optical radiation power rather than the electrical power consumed by the LEDs. To determine the number of LEDs required in a fixture and their rated current these figures must be converted into electrical power, which depends on the efficiency of the LEDs actually used. These calculations, selection of particular LEDs and other matters concerning the actual construction of a LED fixture will be considered in our next article. If the reef tank is only illuminated in these wavelength ranges for 12 hours, with short sunrises and sunsets specific to the equatorial zone, we will obtain an average radiation power of 400μmol·photons/m2/s, which is sufficient for optimal production of chromoproteins. Since the light fixture is likely to also include LEDs in other wavelength ranges, we can safely assume that these figures include some power margin. Also note that although 400μmol·photons/m2/s radiation power is optimal for coloration of corals, such high illumination requires pristine water conditions in the tank. Radiation power 4 times below this level is already sufficient to start production of chromoproteins in corals. We recommend starting slowly, with initial lighting levels close to the lower boundary of about 100μmol·photons/m2/s. Within several months you can gradually increase the illumination, while closely monitoring water parameters and the corals' reaction. If the system is stable and all parameters are in the optimal range, optical power can be gradually increased up to 400μmol·photons/m2/s. As we have seen, formal parameters such as CRI and CCT are not very useful for determining whether a particular light fixture is suitable for a reef tank. At the same time we need to point out again that sufficient power in the 400-480nm wavelength range is critically important. If this condition is fulfilled, other parameters of the light fixture may be selected based on the owner's individual preferences (just make sure that the total radiated power does not exceed the recommended values). We have to admit, unfortunately, that most of the commercially available light fixtures today are only utilizing the 450nm range and above, whereas an ultimately important range between 400 and 440nm is usually left out, or is inadequately represented. References http://en.wikipedia.org/wiki/Color_vision David H.Hubel, Eye, Brain and Vision. 256p., 1995, ISBN/ASIN: 0716760096 http://www.ecse.rpi.edu/~schubert/Light-Emitting-Diodes-dot-org/Sample-Chapter.pdf http://ies.jrc.ec.europa.eu/uploads/fileadmin/Documentation/Reports/Global_Vegetation_Monitoring/EUR_2006-2007/EUR_22217_EN.pdf http://rybafish.umclidet.com/zooksantella-%E2%80%93-nevolnica-korallov.htm http://afonin-59-bio.narod.ru/4_evolution/4_evolution_self/es_13_algy.htm http://medbiol.ru/medbiol/botanica/000a984c.htm http://batrachos.com/node/442 http://reefcentral.com/forums/showpost.php?p=20296037&postcount=27 http://www.photo-mark.com/notes/2010/nov/19/plancks-despair/ http://reefbuilders.com/2010/06/17/grassy-glow-25000-k-metal-halide-bulb-from-volx-japan-hits-the-mark-for-blue-light-addicts/ http://ies.jrc.ec.europa.eu/uploads/fileadmin/Documentation/Reports/Global_Vegetation_Monitoring/EUR_2006-2007/EUR_22217_EN.pdf - 26p. R.W.Burnham, R.M.Hanes, C.J.Bartleson Color: A Guide to Basic Facts and Concepts. New York: John Wiley, 1953 Thai K. Van, William T Haller, and George Bowes Comparison of the Photosyntetic Characteristics of Three Submersed Aquatic Plants. www.plantphysiol.org/content/58/6/761.abstract http://www.led-professional.com/products/leds_led_modules/semileds-achieves-40-external-quantum-efficiency-for-ultraviolet-uv-led-chips C.D'Angelo, J.Wiedenmann, Blue light and its importance for the colors of stony corals, Coral Magazine, Nov./Dec. 2011 How much electricity costs, and how they charge you Ecotech Marine's Radion XR30w wins the 2011 Reef Builders LED showdown http://www.onsetcomp.com/support/knowledgebase/unit-conversion http://earthobservatory.nasa.gov/Features/EnergyBalance/page2.php http://reefkeeping.com/issues/2002-09/atj/feature/index.php Leletkin V.A., Popova L.I., Light absorption by carotenoid peridinin in zooxanthellae cell and setting down of hermatypic coral to depth, Zh. Obshch. Biol. 2005 May-Jun;66 (3) View the full article

Click through to see the images. The Dutch have done it again! Granted, there are a few stoney corals in this 1200 liter (~310 gallon) reef aquarium, but it's the big and beautiful soft corals and gorganians that capture our attention. Their dramatic forms and gentle sway create an aquascape that is arguably more dynamic than stony coral exhibits. Makes you want to set up a large soft coral tank, doesn't it? " height="408" type="application/x-shockwave-flash" width="680"> "> View the full article

Click through to see the images. We have covered how potentially dangerous fragging zoanthids are to reef hobbyists. Certain species are loaded with palytoxin, a naturally occurring toxin that is one of the most deadly natural toxins known with an LD50 of 300ng/kg in mice. LD50 means that 50% of mice dosed with just 300ng/kg body weight died when subjected to palytoxin. It is very potent and is not something to toy with when fragging. Scientists noted in their PLoS ONE paper that a single zoanthid polyp contained 600ug palytoxin, which is enough to kill 1,000 mice. A simple slip of a razor blade or rubbing a mucous membrane like the nose or eye could lead to serious injury and hospitalization when working with zoanthids. Adrienne Longo-White recounted her experience with palytoxin in her first-hand account last year and recently we covered how a 3reef member became blinded in one eye simply by rubbing her eye after handling a rock containing zoanthids. Palytoxins from zoanthids are not something we should take lightly. That is why we wanted to mention this youtube video (below) by fishinaddict94. In his video "how to frag zoas," he demonstrates (obviously) how to frag zoanthids. In my opinion, however, this video actually serves as an example on how not to frag zoanthids. Here are the dangerous mistakes seen in his presentation: He is not wearing nitrile gloves He is not wearing razor-proof gloves, which is especially important given how close he potentially comes to cutting himself during his fragging session He is not wearing safety glasses It is not our intention to shame well-intentioned aquarists looking to help others, but it's extremely important that all reefkeepers learn the proper handling of potentially harmful organisms we keep. If you are going to work with potentially dangerous animals, you need to take the proper safety precautions. Some may say we are overly cautious, but our motto is: Safety first. You are given only ten fingers, two eyes, and one life. Don't chance any of them by not practicing safe animal handling. It takes just one mishap. View the full article

Join us in the online facebook photo contest and win some cash prizes !! Prizes to be won : CASH $ 400.00 Contest Details; 1. Select ONE of the Best photo taken during the event day (07.12.2012 ~ 09.12.2012) and upload it to SRC Facebook page here latest by 09.12.2012 @ 1200 hrs . 2 . Category accepted : Any photos taken during the event day ( 07.12.2012 ~ 09.12.2012 ) , candid shot, marine fish, equipment, funny photos, reefer ect .... 3. The photo with the most " LIKE " on our page by 09.12.2012 ( 1200 hrs ) get to win the contest. Alternatively you may also invite your friends to "LIKE" your photo at SGREEFCLUB Facebook page after you have uploaded in order for them to vote for you during the contest period. The more "LIKE" you get, the higher chance for you to win. 4 . The lucky winner will be informed by email or facebook private PM / phone on the last day of the event . 5. Participation is open to all new and existing SRC ( Singapore Reef Club ) members only including SRC moderator . 6. Prize money can be collected after being notify on the last day at the event itself. Notes ; ** Our SRC page on facebook will only be open for public posting of photo from 06.12.2012 onward. ** you have to join our facebook page before you can be able to post photos on our facebook page. ** Please Invite your friends to Vote / Likes on your photo and not the link . ** The judge decision is final.

If you are a newbie in this hobby or a reefer whom always wanted to know more about the marine or fresh water aquarium. Please drop by on Saturday ( 08.12.2012 ) during the event to join in one of the talks below. Free to all to attend and get to talk to the speaker from both local & oversea speaker whom will be there . There will also be a short Q & A after the talk as well as a lucky draw for those who attended with attractive prizes to be won !! :yahoo: Some information of the talks held on the event as follows; Date : 08 .12. 2012 (Sat) From : 1330 to 1530 1330 - 1400 How to set up a Frog Terrarium (Basic) - Green Chapter - Green Chapter 1400 - 1430 How to set up a freshwater shrimp tank (Basic, Beginner) - Green Chapter 1430 - 1500 Salt versus natural seawater, and the importance of testing and supplementing in reef aquariums - By REDSEA 1500 - 1530 )How to set up a Frog Terrarium (Basic) - Green Chapter 1530 Onward - Lucky draw with attractive prizes to be won. Hope to see you all at the talk ..

Click through to see the images. The Philips Hue is a 8.5 watt light bulb that contains 11 colored LEDs housed in a compact glass globe that also includes a wireless transmitter. Users can remotely control and customize the color of their bulb from web-enabled devices such as iPhones, Android phones, and web browsers. Does this concept sound familiar? Ecotech Marine's upcoming EcoSmart Live control platform (for their color-adjustable Radion LED) operates on a similar principle. However, unlike the Radion, the Hue does not require an USB connection to a computer with internet access. Users simply screw in Hue bulbs into E26 incandescent sockets and set up the supplied wireless gateway to control multiple bulbs over the internet. Starting October 30, 2012, Philips will market the Hue in a $200 retail package that includes three LED bulbs and one wireless gateway (as shown in the photo above); The gateway can control up to 50 bulbs, and each additional bulb is sold for $60. Aquarists can theoretically build a multi-bulb array of Hues to illuminate larger aquariums. However, at $60 per bulb, this path is not cost effective compared to aquarium LED systems nor does the Hue have an aquarium-specific control interface. Still, the Hue presents an interesting choice for nano aquariums and could make an interesting "accent lighting" option for larger aquariums. Speaking of control interfaces: While the Hue's control application is no where near as advanced as those designed for aquarium lighting, it does have one interesting feature worth mentioning. Users can select an area of a photo to replicate a color. This feature has interesting potential if adopted for aquarium use. For example, if a reefkeeper wants to replicate the combined spectrum of his favorite aquarium which uses a mixture of metal halides, fluorescents, and/or LEDs, you could in theory take a photo of the aquarium light shone on a reference card (provided his photo device is calibrated to a specific white balance). View the full article

Click through to see the images. View the full article

i didn't off my skimmer when i dose the bacteria. Yes, i agreed it's a great product without all the hassle of daily "Pumping" of my old zeovit reactor

Click through to see the images. Coral specialist Dr. Bert W. Hoeksema of Naturalis Biodiversity Center in Leiden, The Netherlands, recently published the description of a new coral species that lives on the ceilings of caves in Indo-Pacific coral reefs. It differs from its closest relatives by its small polyp size and by the absence of symbiotic algae, so-called zooxanthellae. Its distribution range overlaps with theCoral Triangle, an area that is famous for its high marine species richness. Marine zoologists of Naturalis visit this area frequently to explore its marine biodiversity. Reef corals in shallow tropical seas normally need the symbiotic algae for their survival and growth. Without these algae, many coral reefs would not exist. During periods of elevated seawater temperature, most reef corals lose their algae, which is visible as a dramatic whitening of the reefs, a coral disease known as bleaching. Most reef corals generally do not occur over 40 m depth, a twilight zone where sunlight is not bright anymore, but some species of the genus Leptoseris are exceptional and may even occur much deeper. At greater depths, seawater is generally colder and corals here may be less susceptible to bleaching than those at shallower depths. Despite the lack of zooxanthellae and its small size, the skeleton structures of the new species indicate that it is closely related to these Leptoseris corals, although it has not been found deeper than 35 m so far. The species is named Leptoseris troglodyta. The word troglodyta is derived from ancient Greek and means "one who dwells in holes", a cave dweller. The discovery sheds new light on the relation of reef corals with symbiotic algae. The new species has adapted to a life without them. Consequently, it may not grow fast, which would be convenient because space is limited on cave ceilings. The species description is published in the open access journal ZooKeys. ### Original source Hoeksema BW (2012) Forever in the dark: the cave-dwelling azooxanthellate reef coral Leptoseris troglodyta sp. n. (Scleractinia, Agariciidae). ZooKeys 228: 21. doi: 10.3897/zookeys.228.3798 (press release EurekAlert) View the full article

Click through to see the images. Adam Reddon from McMaster University experimented on African daffodil cichlids (Neolamprologus pulche) by injecting them with isotocin, the fish version of oxytocin. He then observed their interactions with other fish following treatment; Reddon discovered the tropical fish became more responsive to social queues. The cichlids grew more aware of their tank-mate's sizes and actually became more aggressive towards perceived challengers (ie larger specimens or even their own reflections) compared to saline-treated control counterparts who were aggressive towards every fish regardless of size. On the other hand, when Reddon injected isotocin into "lesser' middle-of-the-social-heirarchy specimens, these fish became even more submissive in the group. Previous isotocin studies have shown that goldfish and zebrafish were more likely to approach one another after treatment. These findings demonstrate isotocin increases social sensitivity in fish and sheds insight on oxytocin's effects on mammals including humans. Fishkeepers all know some fish are incorrigible bullies who will pick a fight with any fish. Might isoticin treatment help them to better socialize with tank-mates? Granted, such treatments are impractical and unlikely, but it's still interesting food for thought! Journal Reference: Reddon, O’Connor, Marsh-Rollo & Balshine.2012. Effects of isotocin on social responses in a cooperatively breeding fish. http://dx.doi.org/10.1016/j.anbehav.2012.07.021 [via Discover's Not Exactly Rocket Science blog] View the full article

its a clear bottle with private label. Maybe you can PM aquafauna supplies if they still got stock. Alternatively, you can also tried this product call "Elho Prazi Gold " which can be found in east ocean .