IMPACT OF THE POLYCHAETE CAPITELLA SP-I ON MICROBIAL ACTIVITY IN AN ORGANIC-RICH MARINE SEDIMENT CONTAMINATED WITH THE POLYCYCLIC AROMATIC HYDROCARBON FLUORANTHENE

Polychaetes belonging to the genus Capitella are often present in high numbers in organic-rich sediments polluted with, e.g., oil components , and Capitella spp. may have a great impact on the biogeochemistry of these sediments. We examined the influence of Capitella sp. I on micr obial activity in an organic-rich marine sediment contaminated with th e polycyclic aromatic hydrocarbon, fluoranthene. Capitella sp. I were added to microcosms (10 000 ind m(-2)) and the impact of a pulse-sedim entation of fluoranthene-contaminated sediment (3 mm layer) was studie d for a period of 12 d after sedimentation. The sediment oxygen uptake and total sediment metabolism (TCO2 production) increased in cores wi th worms (71 to 131%), whereas the anaerobic activity, measured as sul fate reduction rate 12 d after sedimentation, was lower compared to co res without worms. The effect of fluoranthene on sulfate reduction was most pronounced in the presence of worms, with a 34% reduction versus 16% in cores without worms. The reduced sulfur pools in cores with wo rms were smaller than in cores without worms, suggesting that the redu ced anaerobic activity was caused by increased oxidation of the sedime nt, which may favor O-2 and other electron-accepters (e.g. NO3-, Fe3+, Mn4+) in organic matter decomposition. The sediment oxygen uptake and TCO2 production did not show significant changes due to fluoranthene treatment, indicating that these parameters were either less sensitive to fluoranthene stress or recovered more rapidly (i.e. within 48 h) t han sulfate reduction rates. Bioturbation by Capitella sp. I altered t he depth profile of fluoranthene such that fluoranthene was found in d eeper sediment layers (down to 2 cm) where diffusional loss and microb ial breakdown probably are reduced relative to surface layers. In core s without worms, fluoranthene was found down to 1 cm, with 75% remaini ng in the upper 5 mm.