Society of Integrative and Comparative Biology Annual Meeting
Coral reefs have long been valued as the most diverse marine ecosystem in the world, but their persistence is now threatened by multiple disturbances. In contrast to the high sensitivity of scleractinians to many of the agents of the recent changes on coral reefs - notably high temperatures, storms, and perhaps rising pCO2 − octocorals show signs of resistance to the same disturbances. Such signs come in the form of a flexible body plan that resists hydrodynamic stress, potentially a strong utilization of heterotrophic resources, and an internal support system isolated from the effects of seawater chemistry. In this study, we asked whether there were signs that octocorals are now unusually abundant on coral reefs in St. John, U.S. Virgin Islands. Population densities and colony sizes were measured for a suite of octocoral genera on shallow reef (7−10m) along the south shore of St. John, and the results contextualized by historic data from photoquadrats in the same location, together with published studies from other locations. Surveys conducted in 2012 in St. John revealed mean octocoral densities of 9.5 ± 0.4 colonies m−2, with colonies distributed among the common genera Plexuara (21% of colonies), Eunicea (20%), Gorgonia (15%), Pseudopterogoria (15%) and Pseudoplexaura (15%); overall, 40% of colonies were juveniles (<10 cm tall), suggesting the populations were growing. Preliminary analysis of photoquadrats taken in 1992 from the similar locations suggests population densities have increased in St. John, and relative to historic records from Carrie Bow Cay (Belize) and the Yucatán - where octocoral densities were 5.5 colonies m−2 in 1982 and 7.6 colonies m−2 in 1987, respectively - the present octocoral densities in St. John are high. Our preliminary analyses are consistent with the hypothesis that octocorals are becoming more abundant on Caribbean reefs.
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