Diadema

Abstract

Diadema is a common and abundant sea urchin in the tropics with localized large influences on the grazing and benthic communities. There are six species, of which four are closely related morphologically and genetically; but only two species, D. setosum and D. savignyi, have frequently overlapping distributions. Diadema has long spines that allow it to graze in more open areas than most tropical sea urchins. Diadema has variable reproduction patterns with considerable differences in local environments in terms of their lunar patterns and in their reproduction in the presence of conspecifics. Recruitment patterns are also quite variable and only seldom associated with adult densities. Complex interactions between Diadema, its predators and competitors, as mediated by human fishing, are frequently a critical influence on the ecology of shallow coral reef and rocky habitats.