Bubbles from the Naturalist Jerry's tank - by Jerry Ligon

September 2005: Coral spawning

Coral spawning is a spectacular event rarely viewed by divers who hope they have seen everything. It occurs during the night, usually one or two nights a year and one has to be in the right place on the reef and be on time. It does not wait for any human intervention to proceed. For September, 2005, full moon is on 18 Sept. Within 5 to 8 days after full moon a particular coral head will release its gametes and with very little preview of its intent. Within a short minute or two the coral polyps will show some swelling and the individual gamete packet can be seen protruding. This packed is primarily a mass of eggs that looks like the end of a pencil's erasure. Surrounding the egg packet are thousands of invisible sperm. All derived from the same identical coral head which doesn't seem proper if fertilization occurs within the same pairing of gametes from the same genetic parents then it would be impossible for the embryos to be other than identical.

Nature abhors self fertilization and goes to any extreme to ensure that it does not happen. For corals the packet of eggs, surrounded by sperm cells, float to the surface and the wave action there begins to separate the individual sex cells. Also, the egg cells will not be ready for fertilization until a period of time, perhaps 20 or 30 minutes has passed. By this time, many coral have spawned and thousands of egg packets are mixing with tens of thousands of sperm cells, all from a variety of genetic parents, so that variety of offspring can develop showing diverse characteristics which will lead to better adaptations to their environment, especially if it is changing.

Fertilization occurs and the young embryos float on the surface and begin to develop into a feeding larvae polyp which will eventually settle to the bottom and it will try to find a particular species of algae that only grows on the undersides of reef formations upon which to settle. Chemical recognition occurs and the polyp will settle and begin to grow into a coral head that, after 150 to 200 years can be the kind that are the signature coral heads that divers love to see here on their dives, those that are pyramidal in shape and with a base that could be 20 feet across. They resemble pagodas and, as I point out on my dives, they are hollow in their centers. Corals began to die and they die where the oldest cells are, and that is in the very center. Corals grow radially, in all directions. But on the outside, a layer of beautiful, vigorous coral is growing, all derived from that one tiny polyp by a process of budding, one vigorous-growing cell splitting to form two, add infinitum.

Following are some photos of coral spawning (photo credits: Sipke Stapert). By clicking on one of the thumbnails, the photo will be enlarged (opens in new window).

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