Effects of Different Oil Doses, Dispersant and Dispersed Oil on Macrofauna in Model Tidal Flat Ecosystems

Abstract

Artificial intertidal mudflats were used to study effects of ‘Forties’ oil, a dispersant (Finasol OSR5) and dispersed oil. Oil was added in a 0.5 and a 0.1 mm layer. In the latter treatment, two exposure times were used. The effects on the development of stocked macrobenthic infauna species are presented here. As the experiments lasted 10 months, both short and long-term effects and interactions could be investigated.

The most important effects of oil were instant mortality in Cerastoderma edule (at the high dose), and a dose dependent mortality in Macoma balthica. Dispersant-alone had limited effects, but the temporary appearance at the sediment surface of a high proportion of the bivalves is of potential importance in natural situations. Dispersion of oil had more severe shortterm effects (high mortality in C. edule, M. balthica and Arenicola marina) than mere presence of oil. Increased mortality of C. edule, due to frost at the end of the first experiment, was only observed in oil and dispersed-oil treatments. This is one of the ecotoxicological effects observed due to the large-scale and the long-term nature of the experimental set-up. Population development of the amphipod Corophium volutator was retarded, depending on oil or dispersed-oil dosage or exposure time. Negative effects of oil and dispersed oil on parameters like length growth and individual dry weight were compensated for by better growth of surviving specimens. Interspecific food competition may have been involved.