RESPONSE OF A SUBTIDAL SEDIMENT COMMUNITY TO LOW LEVELS OF OIL HYDROCARBONS IN A NORWEGIAN FJORD

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Abstract
During a nine-month field experiment, an artificially enclosed portion of the community on a subtidal sandy bottom was exposed to low levels of oil hydrocarbons (peak values between 25 and 50 µg/l in the water) for periods of two weeks at six week intervals. An adjacent portion of the community acted as a control. The oil input did not result in significant accumulation of aromatic hydrocarbons in the sediment, presumably due to biodegradation and loss to the enclosure walls. The fluctuation in numbers of sediment bacterial cells did not correlate with the oil stress. Generally, the sediment chlorophyll a content was significantly higher in the oiled sediment than in the control, which indicates decreased grazing by the sediment fauna and/or increased primary production under the oil stress. The nematode abundance decreased progressively in the oiled sediment compared to a seemingly steady state in the control, whereas the harpacticoid copepods showed no response to the oil stress. No significant short term fluctuations during the exposure periods were observed in any of the groups of organisms studied. The pollution level, although chemically significant, was not considered ecologically significant with respect to the benthos.

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