ABSTRACT
Introduction In the shallow-water areas of the Florida Keys, particularly in the channels between the Lower Keys and along the smaller islands north of the Lower Keys, large expanses of eroded limestone are exposed within the sublittoral zone, usually at depths of 1-3 m. These heavily pitted carbonate rocks, with their microkarstic surfaces, are extensions of the islands themselves and are covered with a thin veneer of carbonate sand. This coarse surficial sediment layer, which constantly shifts with tidal movement, prevents the growth of sea grasses and macroalgae. As a result, only organisms that can attach themselves to the underlying solid rock surface can flourish in this type of environment. In other areas of the Keys, primarily along the seaward sides of the Upper and Middle Keys, these sublittoral rocky platforms are devoid of the thin carbonate sand layer. Here, rock-boring sea urchins have excavated large pits across the entire exposed rock surface, creating a unique hardbottom habitat of miniature caves and cavities.
