ISLA ARENA, A HEALTHY CORAL FORMATION IN THE AREA INFLUENCED BY THE SEDIMENT PLUME OF MAGDALENA RIVER, COLOMBIAN CARIBBEAN CONTINENTAL SHELF

Abstract

The morphology, composition and structure of the coral community developed around Isla Arena, a tiny shingle cay located on the central area of Caribbean continental shelf of Colombia, are described. Based on aerial photographs from the area field surveys, maps of bottom relief, habitat units according to substrate type and cover of dominating biota, wave exposure, and patterns of wave dispersion and refraction were drawn. Employing underwater videocamera, 10 m-long transects chain were recorded and analized using the plotless method in order to characterize the sessile community structure. A total of 33 species compose the community. Of these, 14 species are stony corals, 5 zoanthids, 1 octocoral, 1 anemone, 10 macroalgae and 2 sea grasses. Ten ecological zones were identified, each of them dominated by one more species. The spatial distribution pattern of the zones is mainly controlled by substrate and wave energy. The few coral species found seemed to be particularly adapted to meet the prevailing sub-optimal conditions (high water turbidity and turbulence). Furthermore, their healthy condition suggests that scleractinians growing under chronic stress may also to cope with infestation by common coral diseases when they are continuously subjected to natural stress.