Benthic metabolism in a natural coastal petroleum seep

The rates of 3 processes known to be mediated by microbial metabolic activity were measured in the sediments of a shallow-water (18 m depth) natural petroleum seep and a nearby non- seep area near Santa Barbara, California. Measurements of oxygen flux, hydrocarbon degradation, and sulfate reduction were made in the sediments of 3 stations wlth varying amounts of petroleum seepage. At the seep, 1 station was at the margin of active seepage while the 2nd station (20m away) had moderate seepage. A 3rd non-seep station was 2.4 km away from the petroleum seep area. Total oxygen flux was not staustically different among the 3 stations studied. Rates of sulfate reduction and hydrocarbon degradation were greater at seep than non-seep sites. Within the seep area, greater rates of sulfate reduction and hydrocarbon degradation were found at the station of moderate seepage than at the margin of active oil and gas seepage. The greater rates of metabolism at the seep correlate with previous findings of higher amounts of ATP and macrolnfauna at the seep. We hypothesize that the higher abundances of infauna and concentrations of ATP at the seep are sustained by heterotrophlc bacterial degradation of petroleum and the consumption of those bacteria by infauna.