Macroalgal feeding characteristics of the sea urchin Diadema antillarum Philippi at Discovery Bay, Jamaica

Food choice of Diadema antillarum Philippi was investigated in 1995 at Disc overy Bay, Jamaica, using a variety of laboratory experiments. In two food choice experiments, D. antillarum was offered five species of macroalgae co mmon on shallow fore-reefs away from resident populations. The urchin was a ttracted towards water passing over heavily calcified Halimeda opuntia and also over less-calcified species such as Lobophora variegata. Sargassum sp. and Galaxaura sp. provoked no response when tested against pure seawater. The urchin was not selective when offered a variety of algae for consumptio n. However, when offered H. opuntia or Galaxaura sp. alone over a 24-hour p eriod, it consumed more of the heavily calcified alga. During six-week expe riments, D. antillarum consumed considerably more Galaxaura sp. than any ot her species. For D. antillarum to gain enough nutrition to live, it seems t hat it must feed on heavily calcified species at a greater rate than fleshi er brown algal species. However, prolonged consumption of the heavily calci fied H. opuntia led to spine loss and test decay in half of the test animal s. Implications for community development are significant because D. antill arum consumed macroalgae previously considered unfavourable to other coral reef herbivores. With the slow rise of D. antillarum numbers over the Carib bean region, there is the potential for these animals to reduce the cover o f macroalgae from coral reefs.