Coral Settlement on Oil/Gas Platforms in the Northern Gulf of Mexico: Preliminary Evidence of Rarity
Gulf of Mexico Science
In recent decades, there have been two areas of shallow hard substrate available for zooxanthellate coral colonization in the North Gulf of Mexico: the Flower Garden Banks (FGB) and oil and gas platforms. We assessed coral recruitment on platforms possessing adult corals around the FGB. In this preliminary experiment, we used terra cotta plates mounted on racks, deployed on six platforms at depths of 15-27 m for a duration of #1 yr in two consecutive years. Data on coral spat taxonomic
... taxonomic identification, distribution, and densities were collected. Platform spat densities on plates averaged ,1/450 cm 2 , a low value when compared with the East-FGB (E-FGB; data from earlier similar experiment), other Caribbean sites, or the Great Barrier Reef. Spat density was not significantly different between platforms, suggesting that distance between the platforms and the E-FGB, a potential larval source, was large enough (.0.6-1.2 km) to permit extensive larval diffusion. Total spat density also did not vary significantly between settlement racks, indicating that settlement at the spatial scale of meters was relatively homogeneous. Only three species of spat were found-Tubastraea coccinea, Madracis decactis, and Montastraea sp.; the taxonomic composition of coral spat varied from those observed earlier on the E-FGB-Agaricia and Porites. The dominant recruits matched the dominant adults on the platformsan unusual situation. Tubastraea and Madracis spat densities, respectively, did not vary significantly between platforms or between racks. Because of low recruitment levels, these artificial reef communities may be considered fragile in comparison to many natural ones because of the time required for recovery in the event of a mass coral mortality. These low recruitment levels, however, when integrated over ,30 yr, can result in the successful establishment of adult coral communities on the platforms.