Meiofauna response to the Agip Abruzzo oil spill in subtidal sediments of the Ligurian Sea

The effects of the Agip Abruzzo oil spill (10 April 1991) on meiobenthic assemblages of the Ligurian Sea were investigated using samples collected from January 1991 to January 1992. Meiofauna appeared to be highly sensitive to hydrocarbon stress since the oil spill determined an observable decline in density, relative to the pre-pollution conditions. Such patterns were unusual since reported in a period in which, because of the usual seasonality of Mediterranean meiofauna, we would expect an increase in density. In particular, clear decreases in nematode, turbellarian and foraminiferan densities were observed. Oil-induced disturbance had no influence on copepods, which slightly increased after the oil spill, probably because they were dominated by epibenthic forms which were able to escape from the toxic effects of hydrocarbon pollution. The results of classification and ordination analyses as well as the univariate indices indicated that the level of the major meiofaunal groups was not sufficient for detecting oil-induced disturbance, but nematodes at the genus level proved to be highly efficient. The oil spill determined evident changes in terms of a decrease in N1 diversity. Changes were also observed in richness and in the k-dominance curves of nematode genera, showing a decrease in overall community diversity. One month after the oil spill, diversity patterns were similar to pre-pollution conditions. In contrast, the nematode: copepod ratio and its modifications were not sensitive to the induced stress and proved to be inadequate for detecting hydrocarbon pollution. Similarly, no significant variations were observed when analysing the index of trophic diversity. However, the nonselective deposit feeding nematodes (1B) declined after the oil spill thus indicating possible changes in the functional characteristics of the meiobenthic assemblages. Meiofaunal response to oil pollution was extremely rapid. Meiofaunal structure was significantly affected only immediately after the oil spill (22 April 1991). Univariate and multivariate analyses indicated that the structural characteristics of meiobenthos recovered after only 2 weeks and were almost indistinguishable from pre-pollution conditions a few weeks later, indicating the high resilience of these meiobenthic assemblages.