Habitat impacts of offshore drilling, eastern Gulf of Mexico

Abstract

In this survey six offshore exploratory drill sites in a variety of environments and water depths were examined using a small research submersible. Sites varied from locations off northwest Florida to as far west as offshore Alabama. Water depths ranged from 21 m (70 ft) to 149 m (489 ft), and bottom sediments ranged from carbonate mud to Shelly quartz sand and silt to hard limestone. The age of the sites (the time between cessation of drilling activities and our observations) ranged from 15 months to 17 years . In a previous MMS-funded study, Shinn et al. (1989) and Dustan et al . (1991) examined eight sites off South Florida, where the age of the sites ranged from 2 to 29 years. The study documented repeatedly variability of impact from site to site . In the present study, we note a similar wide divergence of impacts . Using the concentration of barium (the major component of drill mud), cuttings, and trace metals as a basis, we found that time is the single most important factor determining the nature of habitat recovery. Older sites, particularly the 17-year-old site, were relatively pristine. At a 7-year-old site, two hurricanes did far more damage than drilling . At other sites, we documented a significant amount of discarded debris, and at two 5-year-old sites, large concentrations of barium and cuttings. Impacts, such as the extent of debris and cuttings, affected the bottom ranging in area from almost negligible (17-year-old site) to as much as 3 acres (4-year-old site) . As suspected, those sites with the most debris and/or open boreholes attracted the most abundant and diverse fish fauna.