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Pulsing Xenia mystery solved By Brian Blank on Apr 30, 2013 Read more: http://reefbuilders.com/2013/04/30/pulsing-xenia-mystery-solved/#ixzz2S2kA3eGV The pulsing Xenia has been a scientific mystery for that last 200 years since it was first discovered by Jean-Baptiste Lamarck (1744-1829). Why does this particular coral spend so much energy pulsating? Corals are extremely efficient organisms and do not waste energy unless there is compelling enough benefit — in this case nutrients. Why does the Heteroxenia fuscescens go through all that fuss? Seems like a lot of wasted energy doesn’t it? Recent research by a team of scientists from the Hebrew University of Jerusalem and the Technion-Israel Institute of Technology finally have a few answers released in a recent issue of the Proceedings of the National Academy of Sciences. The team discovered the motion of the polyps helps with binding of carbon dioxide to the photosynthetic enzyme RuBisCo (Ribulose-1,5-bisphosphate carboxylase oxygenase), while also decreasing photorespiration. This led the team to the conclusion that in the case of H. fuscescens, the benefit overcomes the cost. Because of the pulsation, the ratio between photosynthesis to respiration in this Xenia is the highest ever measured in stony and non-pulsating soft corals. We know corals rely on water flow to deliver nutrients and organisms also alter the flow around them as well. By studying the flow around Xenia colonies, the team used an underwater measuring device called PIV (particle imaging velocimetry). This allowed the team to record highly accurate measurements of the flow field around the Xenia in their natural habitat at night. Through the data provided, the team discovered the motion of the polyps sweeps water up and away from the coral tissues and into the surrounding water. If you’ve ever been entranced with the pulsing motion of the Xenia, you’ll recall that the polyps do not pulse in a synchronized motion. Despite this, the overall result for the colony is significantly enhanced flow that helps reduce the chance of refiltering the same water. Armed with new data and the hypothesis that the pulsation motions enhance the coral’s photosynthesis rate, the team was able to get clearance from the government to harvest a few colonies for experiments in the lab. The zooxanthellae in corals requires CO2 during the day and oxygen at night as well as other nutrients (like phosphate and nitrogen) all day. Now it makes sense that coral colonies would want to increase the concentration of these essential commodities around them by being able to mix the ambient water. But again, why would the Xenia use so much energy just to mix the water? The team measured the photosynthesis rate of the pulsating Xenia colony was found to be an order of magnitude higher than when it is at rest. The researchers increased the oxygen levels in the tank so as the corals pulsated and mixed the water, instead of pulling in CO2-rich water they were pulling oxygen-rich water into the colony. The team found out that when the higher oxygen levels led to low photosynthesis rates — just as if the coral was at rest — proving their hypothesis. One other interesting observation was the pulsing Xenia pump continually only taking a daily half-hour break in the afternoon. This is still one mystery the team was unable to unlock.

Read more: http://reefbuilders.com/2007/01/14/new-coral-xenia-corla/#ixzz2S2jL1y9S on Xenia Coral : Hardiness: Xenia is an interesting family of coral as far as hardiness is concerned. Some hobbyist cannot seem to keep this coral alive and others find it to be a fast growing ‘weed’ coral. Although there are some guidelines which can be followed to improve the chance of success, no one fully understands what will guarantee success with this coral. Even a colony that has been thriving in a tank for an extended period of time can quickly go into decline and die for no obvious reason. Lighting: Requires moderate to strong lighting. Usually, brighter is better although some hobbyist appear to have very good success with lower light levels. Water Current: Xenia require at least moderate water flow. They are one of the few corals that seem content to be right against the strong output of a powerhead. In still waters the pumping usually diminishes and the coral goes into decline. Temperature: Does well within a range of at least 75º to 83º F. Temperatures around 84º can sometimes appear to cause stress and Xenia appears to be more stable at lower temperatures of 76º – 78º. Aggressiveness: Low. Xenia does not possess any apparent stinging capability and will not bother other corals, but can tend to grow over and shadow its neighbors. When happy, the coral can reproduce by division at an alarming rate and may require frequent pruning to keep it from crowding out other corals. Feeding: Xenia is photosynthetic and does not accept any known foods. It is thought that they absorb some of their nutrients directly from the water. In fact, some hobbyist keep large colonies of Xenia as filter beds where the xenia is regularly pruned for nutrient export. It is unclear if this is very effective. Xenia may do better in tanks that are not heavily skimmed. Supplements: The main supplement normally associated with successfully keeping Xenia is Iodine. Many authors state categorically that iodine supplements are critical to success and lack of iodine supplements will cause xenia to crash. I have keep Xenia with and without iodine supplementation and have observed no difference, so I am more skeptical of the iodine connection. Low Alkalinity levels can cause Xenia pulsing to decrease or cease altogether, so alkalinity levels should be monitored and kept above a minimum of 2.5meq/l. Tank Positioning: Usually kept high up on the reef for strong water flow and highest possible lighting. Xenia will reproduce in the tank by attaching its stalk against adjacent surfaces it contacts and splitting into two colonies. In this way, Xenia colonies tend to ‘walk’ in the direction that water movement bends their stocks, so you may want to consider this in your placement. Xenia can usually be coaxed to grow up the back glass of the tank and forms a nice background display.

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