Coexistence of reef organisms in the Abrolhos Archipelago, Brazil

The first study on coexistence of reef benthic organisms in Brazilian coral reefs was done in three localities of the Abrolhos Archipelago. Organisms were recorded in concentric circle samples (10 and 20 cm in diameter) rando mly laid on transects. Type and frequency of "coexistence events" between p airs of organisms were determined. Most frequent organisms (massive and bra nched coralline algae, Favia gravida, and Agaricia agaricites) also had man y significant positive coexistence events. These results might be related t o the abundances of these organisms. The most frequent coral (Siderastrea s tellata), however, exhibited only a few significant coexistence events (9% of 32 tests). Since the great majority of events were positive, and since t here was high variation in the species/groups involved in significant event s in different localities, benthic communities of Abrolhos Archipelago may well be structured primarily by abiotic rather than biotic factors.