Crab inhabitant of a coral colony (photo 10A)

This small (about 3/4 inch long) unidentified spider crab appears to have a rough exoskeleton, because it has attached tiny bits of sponges and other material as part of its disguise. Crabs which do this are often referred to as "decorator crabs". The green branch of coral has some of its flower-like polyps extended and some retracted. This hermatypic coral has algae called zooanthellae living within the tissues of the polyps; the algae use sunlight and carbon dioxide (through photosynthesis) to produce organic compounds which provide most of the nutrition needed by the coral.

The limestone coral skeletons deposited by countless generations of corals form the underlying structure of the reef. The complex structures offered by coral colonies provide hiding places and breeding ground for thousands of species of reef animals. When a reef's waters become excessively polluted, such as by soil runoff due to deforestation, the corals receive insufficient light needed for the symbiotic zooanthellae, because the suspended particles filter the sunlight. In addition, the excess nutrients in the water caused by soil runoff and pollution often cause algae suspended in the reef's waters to suddenly bloom uncontrollably, which in turn upsets the delicate measure of light reaching the corals. These factors combined cause the coral colonies to die, stopping the normal filtration of the reef's waters by healthy coral colonies, and robbing the residents of the reef of their habitat.

Coral identification:
Tubastraea micrantha

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