ABSTRACT
Comatulid crinoids are widely distributed on Western Atlantic reefs at low diversity and moderate abundance. Throughout the Caribbean and Bahamas, five species are commonly found on well-developed reefs; a maximum local diversity of seven species is known from the San Blas Islands of Panama. Variations in diversity and relative abundance suggest an onshore-offshore gradient. Onshore along the Panama Isthmus, one of four species is abundant, while three others are less common. In the San Blas, some 10 km offshore, several species are common. At San Andres Island, 190 km off Nicaragua, only two species occur in low abundance. Maximum crinoid richness is thus highest close to large landmasses, but directly onshore, richness is lower possibly as a result of runoff or high wave stress. At sites far removed from nearshore productivity, crinoid richness declines because of reduced food availability. However, where nearshore upwelling occurs, such as at Santa Marta, Colombia, crinoid richness is high, with six species. According to recent reports, a comatulid that was common at Barbados in the early 1970s, Tropiometra carinata, has disappeared altogether. As sessile, rheophilic suspension feeders, crinoids are sensitive to fluctuations of several environmental parameters, especially temporal and spatial patterns of water flow and modifications of available reef substrata. Monitoring of reef crinoids has been initiated at a unique site in the Bahamas as a potential indicator of environmental change.
