I think it would be difficult to propagate mangrove trees in captivity, due to the large size of the trees and the way the seeds mature.
In the wild, "red mangrove trees are viviparous,meaning the seeds mature while they are still on the tree, and only afterwards do they fall in to the water. For the seed to reach its full level of maturity, it needs to spend about a month in the water. During this time, the seed collects the water in its lower portion of the body and floats vertically, with the bud facing skyward, and roots facing down. These seeds will be floating in the salt water for months until they are washed on the shore. One of the conditions needed for the seed to start growing, is absence of disturbances. This is the way nature makes sure that the plant will grow in good conditions."
http://toptropicals.com/html/aqua/plants/m...angrove_eng.htm