Diadema antillarum, also known as the lime urchin, black sea urchin, or the long-spined sea urchin, is a species of sea urchin in the family Diadematidae. 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. Anatomy Diadema antillarum has a "shell," similar to most other sea urchins. What distinguishes the Diadema is the length of its spines. Most sea urchin spines are 1–3 cm, but the spines in this species are usually 10–12 cm in length, and can grow as long as 30 cm in very large individuals. Life habits This species usually lives at 1–10 metres in depth on coral reefs. They will often lodge themselves in a crevice, so that only their spines can be seen, but individual urchins who can't find a suitable crevice will live in more exposed situations. Individuals that have been able to find a crevice usually will roam about one metre from their crevice at night during feeding. Diadema is very sensitive to light, and will often pick its crevice or resting place based on how much shade there is. Diadema mostly eat algae, and sometimes seagrass. Starving urchins have been known to become carnivorous. Ecological importance Diadema antillarum is still, in some tropical areas, one of the most abundant, widespread, and ecologically-important shallow-water sea urchins. It is found in the tropical Western Atlantic Ocean, including the Caribbean Sea, Gulf of Mexico and the northern and eastern coasts of South America (as far south as Brazil). It is also found in the East Atlantic at the Canary Islands and the Indian Ocean. This species is ecologically important because it consumes algae that can otherwise grow to such an extent that they can smother coral reefs. They live in holes that are in the reef. Die-off of urchins 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. This inhibits coral growth and has further compounded the ongoing decline of scleractinian corals. It also has an