GORGONIAN COMMUNITIES IN 2 CONTRASTING ENVIRONMENTS ON OCEANIC ATOLLSOF THE SOUTHWESTERN CARIBBEAN

Gorgonian assemblages were surveyed on two oceanic atolls in the south western Caribbean Sea (Albuquerque Cays and Courtown Cays, Colombia). Classification analysis showed two well defined assemblages located in two contrasting environments, mid-depth (4-11 m) lagoonal patch reefs vs. deeper (10.5-20.5 m) leeward and windward fore-reef terraces. Cor respondence analysis ordination (COA) yielded a more gradual transitio n, locating the leeward terrace intermediate between the calm lagoonal patch reefs and the strongly wave-exposed windward fore-reef terrace. Bottom rugosity was significantly correlated to COA scores. Although the counts of gorgonian colonies per station were quite similar in bot h environments, species number, colony size and cover index values wer e significantly greater in the fore-reef terraces, suggesting that zon es with low relief bottoms exposed to surf and swell represent a more suitable habitat for the development of diverse and structurally more complex gorgonian communities than the calm lagoonal environment. A st riking difference between lagoonal and fore-reef terrace assemblages i s that each is dominated by closely related species of Pseudopterogorg ia, suggesting an important role of contrasting environmental conditio ns in their niche distribution.