Long-term changes in microphytobenthos in a Brittany estuary after the 'Amoco Cadiz' oil spill

Abstract

After the 'Amoco Cadiz' oil spill (Mar 1978), a 4 yr survey of the microphytobenthos (cell numbers and chlorophyll a content) was carried out on a mud flat polluted by petroleum hydrocarbons. There was an obvious peak of microphytic biomass 7 mo after the spill, a decrease during 1979-1980, and a slow increase again in 1981. Moreover an annual pattern in biomass variations, involving early spring and autumn maxima, was noticed for 1979-80-81. whereas this seasonal cycle did not appear in 1978. During the unexpected increase in chlorophyll a content in autumn and winter 1978, a bloom of Euglenophyta and small epipelic diatoms was observed. Results suggest that the hydrocarbons affected the long-term trend of the biocenosis.