The abundance and distribution of free-living marine nematodes of the Piltun-Astokhskoye oil and gas field (North-East Sakhalin)

Although offshore oil and gas production platforms are a potential source for a number of toxic compounds, their impact on the meiofauna is insufficiently studied. In the vicinity of the oil and gas production platform MOLIKPAQ (North-East Sakhalin, the Sea of Okhotsk), the relative abundance of meiofauna assemblages ranged from 23.5 to 406.0 ind. 10 cm(-2). The dominant group, nematodes, ranged from 6 to 385 ind. 10 cm(-2). The maximum nematode density was at the distance of 250 in from the platform coupled with the highest petroleum hydrocarbons concentration (6.52 mg g(-1)) and the lowest values of the Shannon-Wiener diversity and Pielou's evenness indices (1.25 and 0.33, respectively). In total, 69 nematode species were found. Disturbance in the structure of nematocenes, decrease of number species, drop of biological diversity indices, as well as increase in dominance of some nematode species of occurred in response to the introduction of PHCs as a stress factor. CLUSTER, MDS and SIMPER analyses clearly distinguished site groupings related to the different concentrations of PHC and sediment granulometry. The significant differences of nematode assemblages occurred in the response to the appearance of even low-level PHC contamination sediment. These results suggest that nematode assemblages can be used to detect non-catastrophic levels of oil contamination.