Changes in immune parameters of natural mussel Mytilus edulis populations following a major oil spill ('Sea Empress', Wales, UK)

Abstract

In February 1996, the oil tanker 'Sea Empress' spilt over 70 000 t of crude oil which contaminated ca 200 km of coastline (Milford Haven, Wales, UK). The effects of the oil on immunity in mussels Mytilus edulis were investigated in parallel with the measurement of hydrocarbon contamination in the tissues. Initially, severe immunosuppression occurred in oiled mussels, corresponding with very high polycyclic aromatic hydrocarbon (PAH) levels. The haemocytes of mussels from oiled sites showed significantly reduced superoxide generation and phagocytic activity, effects likely to have deleterious consequences for successful disease resistance. As contaminant levels decreased, the immunosuppression became less extreme and recovery was evident by May 1996. Between October 1996 and March 1997, immune activity in the haemocytes of the previously oiled mussels was again significantly reduced, coinciding with increased PAH levels. During this latter period, certain high molecular mass PAHs (characteristically derived from combustion processes) were primarily responsible for the increase, occurring at similar concentrations in the mussel tissues to those observed just after the spill. A subsequent reduction of hydrocarbons in June 1997 was followed by another, but less marked, increase in PAHs between October 1997 and March 1998, coupled with only minimal changes in immunity. The results show that immunosuppression following the oil spill was severe, but that recovery followed a few months later and the initial effects were not therefore permanent. The results also suggest that seasonal peaks in combustion-derived PAHs may occur in the region and that these would have been greatly exacerbated early in 1996 by oil released from the 'Sea Empress'.