A cluster of the grazing echinoderm Diadema antillarum, one of the major controls on algal growth on reefs. The die off of this species in the 1980s contributed to the reduction of the coral reefs, as rapidly growing fleshy algae were uncontrolled and overgrew corals. These echinoids were hazardous to waders or snorkelers jumping into shallow water, as the spines would penetrate flesh and then break off.