Reef Urchin

The reef urchin has an elliptical reddish brown test (shell) covered with medium length spines. These are greenish in colour with paler bases and darker, often violet, tips. This urchin grows to a diameter of 5 centimetres (2.0 in) with the longest spines being 3 centimetres (1.2 in). It looks very similar to the rock-boring urchin Echinometra lucunter, but the dark tips and the greater length of the spines are distinctive.

The reef urchin is found on reefs in the Caribbean Sea from southern Florida to Venezuela at depths down to about 15 metres (49 ft). It is not as common as the rock-boring urchin and seems to be absent from the West Indies to the east of the Virgin Islands.

The reef urchin is an important grazer on fleshy algae in the Caribbean area. Its abundance is reduced by predation by fish, especially the jolthead porgy (Calamus bajonado), the queen triggerfish (Balistes vetula), the ocean triggerfish (Canthidermis sufflamen) and the hogfish (Lachnolaimus maximus). Because of this predation, the reef urchin avoids open reef flats and in these locations there is an overgrowth of fleshy algae. It is unable to take over the algal controlling role of the black sea urchin (Diadema antillarum) which is subject to great fluctuations in population.

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