Black Sea Urchin, Diadema antillarum

Diadema antillarum, known also as the Lime Urchin, the Long-Spined Sea Urchin, or the Black Sea Urchin, is a species of sea urchin belonging to the family Diadematidae.

It is characterized by its extremely long black spines.

This species is the most plentiful and significant herbivore on the coral reefs of the western Atlantic and Caribbean basin. Then the population of these sea urchins is at a healthy level, they’re the main grazers which prevent algae overgrowth of the reef.

This urchin has a test or “shell” much like most other sea urchins. What distinguishes it is the length of its spines. The majority of sea urchin spines are 1 to 3 centimeters, but the spines of this species are usually 10 to 12 centimeters long, and can grow as long as 30 centimeters in very large individuals.

It usually lives at 1 to 10 meters deep on coral reefs. They will frequently lodge themselves in a crevice so that only their spines can be seen, but individual urchins who cannot find a suitable crevice will live in more exposed situations. Individuals that have been able to find a crevice will normally wander about one meter from their crevice at night during feeding. Diadema is very sensitive to light, and will frequently pick its crevice or resting place based on how much shade there is.

This species mainly consumes algae, and occasionally sea grass. Urchins that are starving have been known to become carnivorous.

These urchins are still, in some areas, one of the most abundant, widespread, and ecologically significant shallow-water genera of tropical sea urchins. It’s found in the tropical Western Atlantic Ocean, including the Gulf of Mexico, Caribbean Sea and the northern and eastern coasts of South America. It’s also found in the East Atlantic at the Canary Islands.

Image Caption: Diadema antillarum (black spiny Caribbean sea urchin). Credit: Dpbsmith/Wikipedia (CC BY-SA 3.0)