Densities of reef-associated fish and corals on offshore platforms in the Gulf of Mexico

Abstract

The northern Gulf of Mexico possesses 1320 offshore oil/gas platforms, currently being removed at a rapid rate. Thirteen species of scleractinian corals inhabit these structures, and a positive association is known to exist between reef-associated fishes and coral. Here, we studied 22 platforms on the Mississippi River delta, an area devoid of natural reefs. We quantified the abundance of reef-associated fishes on platforms occurring in 19–334 m depths. We recorded 18 reef-associated fish species, most commonly Stegastes leucostictus (Muller and Troschel, 1848), Stegastes partitus (Poey, 1868), Abudefduf saxatilis (Linnaeus, 1758), Abudefduf taurus (Muller and Troschel, 1848), and Chromis multilineata (Guichenot, 1853). In water depths ≥25 m, average fish densities ranged from 1.0 to 15.3 m–2. No reef-associated fishes were observed on structures in 66 m depth, the fish densities dropped to zero. Average coral densities per platform in waters >30 m deep ranged from 0.4 to 173.0 colonies m–2. Individual sample densities ranged from 0 to 945.0 colonies m–2. There was a significant positive correlation between average reef-associated fish density and bottom water depth. There was also a positive correlation between average fish density and average coral density. The data indicated that coral and fish densities were lower in inshore waters. These waters are generally characterized by low salinity, low winter seawater temperatures, high turbidity, and high nutrient levels. Our data showed that the fish community is linked to the coral community, as is known to occur on natural reefs. We believe that these numerous organisms add environmental value to the platforms.