Sal noted to me that there seem to be more and more urchins in our touch pool, which is indeed correct. They are collector urchins, hawa'e maoli, Tripneustes gratilla.
Malia Rivera uses the urchins for their H.S. level Urchin Fertilization Lab - where students can explore the effects of water quality on sea urchin fertilization and embryonic development.
Urchins are broadcast spawners. Once one starts spawning (releasing eggs or sperm) all the nearby urchins tend to go off as well, until a cloud of eggs and sperm fills the water around them. Students can collect the results and watch cell division and embryonic development - very cool.
When the urchins are ripe/in season/with mature gonads/ etc., they can be induced to spawn through a variety of methods. Sometimes just raising the water temperature a degree or two will do it, or a non-lethal injection of potassium chloride will also suffice.
So Malia's group keeps a large number of urchins on hand - currently mostly in the lower tank, but some up above. For some nice animations of various parts of a standard sea urchin fertilization and development lab - check out this link from Stanford: http://www.stanford.edu/group/Urchin/ani-plus.htm
You can imagine how students discover that reduced water quality will lead to less success in fertilization or egg development. We typically think only about pollutant effects on adults, but on the reef where up to 80% of the reef life are broadcast spawners with a planktonic stage, the importance of clean water may be most significant at the beginning of the life cycle.
Aloha,
Mark
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