Benthic infaunal long term response to offshore production platforms in the Gulf of Mexico

Meiofaunal and macroinfaunal communities around three gas platforms on the continental shelf (29-157 m water depths) in the Gulf of Mexico were assessed for sublethal or persistent effects of chronic exposure to contaminants associated with long-term production. Subsamples of boxcores were collected from five distances (30-3000 m) along five radii from each platform during winter and spring in two years. In contrast with platforms in the North Sea, effects were very localized, extending to 100 m from the platforms. Total polychaete and nonselective deposit-feeding nematode density increased near platforms. Amphipod and harpacticoid abundance and diversity and harpacticoid reproductive success declined near platforms. Organic enrichment, contamination by toxicants (e.g., heavy metals and hydrocarbons), and changes in sediment granulometry are confounded along the gradient of distance from platforms. However, the pattern of community change in both meiofauna and macrofauna around these gas production platforms follows an emerging paradigm of response in which density increases of deposit-feeding polychaetes and nematodes indicate organic enrichment, while density declines of harpacticoids and amphipods indicate toxicity.