Benthic foraminifera as bio-indicators of drill cuttings disposal
Résumé
We present a study of benthic foraminiferal faunas from the outer continental shelf off Congo, Gabon and Angola (West Africa), with the aim to determine the impact of the discharge of oily drill cuttings on the sea floor environment, to judge the regenerating capacity of the benthic ecosystem, and to investigate the possibility to develop an environmental monitoring method for open marine continental shelf environments, based on benthic foraminifera. We studied the spatial distribution and microhabitats of living and dead foraminiferal faunas. Our results describe a zonation of foraminiferal faunas around the former disposal sites. At the immediate vicinity of the discharge points, faunas are characterized by low foraminiferal densities followed by a very high foraminiferal densities, with high percentages (about 80%) of opportunistic taxa. Far away from the disposal site, foraminiferal densities decrease, and the percentages of opportunistic species are lower (40–60% of indicator species). We used these data to develop a quantitative pollution index, values of which are strongly correlated to distance to the disposal site. This foraminiferal index offers the possibility to quantify the impact of anthropogenic eutrophication in continental shelf environments, but its validity must be tested in other continental shelf environments.