PATTERNS OF SPONGE (PORIFERA, DEMOSPONGIAE) DISTRIBUTION IN REMOTE, OCEANIC REEF COMPLEXES OF THE SOUTHWESTERN CARIBBEAN

Abstract

Sponge abundance data were obtained in depths from 2. 5 to 22 m at Albuquerque Cays, Serrana Bank and Roncador Bank, three remote ato lis of the Southwestern Caribbean Sea (San Andrés and Old Prov idence Archipelago, Colombi a). Although the number of sponge species (96 overall, 52 to 6 1 per atoll ) was comparable to that in reef areas in the continental shelves, the density (atoll means 22.5 to 58.3 ind.20m^-2) was noticeably lower, possibly due to lower amounts of suspended organic matter. Cluster and Correspondence Anal y ses of stations showed that sponge distribution patterns were apparently stochastic, both at small and large scale, and only weakly related to major environmental variables. Inverse Analysis, however, revealed that the majority of sponges had marked habitat preferences, but th at their within-habitat di stribution was patchy. Short-di stance di spersa! of free-living larvae and migration of adults by rafting, coupled to the remoteness of the atolls, implies that the identity and timing of arri val of propagules is a random event. Together, the local proliferation of founder populations and the haphazard effect of perturbations. give rise to a strong heterogeneity, in a se ale of tens of meters to hundreds of kilometers, in the do mi nance within the same habitat type.