Sea urchins eat both plants and animals (omnivores). Their menu includes sea weed, algae, plankton and decaying organic matter.
It is one of the most abundant, widespread, and ecologically important shallow water genera of tropical sea urchins.
This sea urchin is characterized by its exceptionally long black spines.
It is the most abundant and important herbivore on the coral reefs of the western Atlantic and Caribbean basin. When the population of these sea urchins is at a healthy level, they are the main grazers which prevent algae overgrowth of the reef.
In 1983, throughout the Caribbean faunal zone as far south as South America and north to the Bahamas, Diadema antillarum underwent mass mortality, with more than 97% of the urchins dying. Since this time some Caribbean reefs have been overgrown by foliose macroalgae.