Observations on geographical variations in population density of the echinoid Diadema antillarum within the western North Atlantic

In the last two decades, research on the biology of the geographically widespread sea urchin Diadema antillarum Philippi has been conducted entirely in the West Indian Marine Province (Randall et a!., 1964; Lewis, 1966; Odgen et at., 1973). The biology of three discrete populations in southern Florida was reported by Bauer (1976), The abundance of this urchin has been determined only for a few widely separated populations (Randall et a!., 1964; McPherson, 1968; Odgen et a!., 1973; Bak and Eys, 1975; Van den Hoek et a!., 1978). Population densities of Diadema are important in the ecology of both intertidal and coral reef communities, and there is nothing in the literature on biological variations between geographically distant populations. I undertook this survey to determine the relationships between population densities, depth, and the biological communities throughout the distribution of D. antillarum. In the western Atlantic this urchin ranges from Bermuda and Florida, through the West Indian area as far south as Surinam.