Oil pollution and plankton dynamics

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Abstract
The responses of some marine microplankters to oil, oil/nutrients, and oil/dispersant were tested during summer using enclosed water columns (20 m long, 0.78 m2 surface). Addition of 0.5 litre crude oil to the surface in one bag caused the heterotrophic ciliates at 0.5 and 2 m depths to disappear after 3 and 10 days in samples with concentrations of oil-derived material of 0.207 and 0.728 mg per litre, respectively. Myrionecta rubra (LOHMANN) JANKOWSKI appeared to be more sensitive to oil-derived material than the heterotrophic ciliates. The disappearance of the ciliates from the surface layer in the oil bag was probably due to migration to deeper strata. Compared to the effects from oil alone, addition of oil and dispersant (Corexit 9527) caused a faster depopulation of ciliates in the surface layer and the affected layer was deeper. As judged by the concentrations of the oil-derived material, however, the dispersed oil appeared less harmful to the ciliates and the dinophysids than the oil alone. M. rubra appeared to be less sensitive to the dispersed oil than the heterotrophic ciliates. As the heterotrophic ciliates never reappeared at 0.5 m in either the oil bag or the oil/dispersant bag but reappeared at the end of the experiment in the oil/nutrient bag, it is assumed that the nutrients ameliorated the negative effects from the oil.