Expansion of coral communities within the Northern Gulf of Mexico via offshore oil and gas platforms

Approximately 4000 oil and gas platforms exist in the northern Gulf of Mexico. These platforms provide hard substratum that extends throughout the euphotic zone, in a region where such has been rare in recent geological time. Major exceptions to this are coral reefs of the Flower Garden Banks (FGB), ~200 km S-SE of Galveston, Texas, USA. We determined whether extensive scleractinian coral populations had colonized these platforms, quantified them, and determined their population and community characteristics. We also examined the relationship between these variables and distance from the FGB, platform age and depth. Surveys were performed on 13 oil or gas production platforms down to 36 m depth, encompassing an ellipse around the FGB. Corals occurred in abundance on most of the platforms. We found 11 species, comprising 8 hermatypic scleractinians, 2 ahermatypic scleractinians and 1 hydrozoan coral. The most abundant corals were Madracis decactis, Diploria strigosa and Tubastraea coccinea. Distance from the FGB was not related to the coral community variables measured, including total coral abundances of the dominant 3 species in shallow water (<14 m), deep water (14 to 36 m), or both depths combined. Total coral abundance increased significantly with increasing platform age, and the community was best developed on platforms >12 to 15 yr old. Abundance of M. decactis increased significantly with increasing platform age in deeper water and both depths combined, as did coral species diversity (S). This was not the case with D. strigosa, indicating that it may not be associated with any particular successional sere. Neither was T. coccinea abundance associated with platform age, except in shallow water, where it decreased in abundance with increasing age, indicating that this species may be an opportunistic pioneer species. All corals combined exhibited a significantly non-uniform depth distribution, with total coral abundance peaking at ~20 and 28 m depths. M. decactis exhibited a similar bimodal depth distribution, with a disproportionately high peak at depths > 27 m. D. strigosa exhibited peaks at ~10 and 23 m depth and was not found at depths > 27 m. T. coccinea exhibited a near-normal distribution, with a mode at ~17 m depth. Platforms have facilitated the expansion of coral populations in the GOM. Such platforms possess an intrinsic environmental value through the presence of coral populations, and this may influence future decisions regarding their removal.