Gulf of Mexico hydrocarbon seep communities: Part III. Aromatic hydrocarbon concentrations in organisms, sediments, and water.

Organism tissues from areas of natural oil seepage contain significant amounts of polynuclear aromatic hydrocarbons (PAH). Higher concentrations are found in sedentary organisms (ie., mussels and tube worms) than in more mobile species ( i.e. fish). The PAH distributions indicate that the seep organisms are exposed to sediment and/or water associated PAH. The concentration and composition of PAH in sedentary organisms are similar to that of an oyster from a coastal site indicating similar mechanisms of PAH uptake, depuration and accumulation. Tissue PAH concentrations indicate that these organisms are chronically exposed to high levels of petroleum in their environments and yet thriving communities are present at these locations. Microbial biomass in these seep areas is also substantially enhanced, and the carbon isotopic composition of tissues of organisms from higher trophic levels reflects the incorporation of bacterial biomass. The sedimentary sulfur cycle is heavily influenced by the process of natural oil and gas seepage and plays a key role in maintaining these communities. The primary source of isotopically light carbon to the system can be soley derived from chemosynthesis (H2S or CH4). The role of degraded oil as a partial source of light carbon to some organisms cannot be ruled out.