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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