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

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 investiga ted in parallel with the measurement of hydrocarbon contamination in the ti ssues. Initially, severe immunosuppression occurred in oiled mussels, corre sponding with very high polycyclic aromatic hydrocarbon (PAH) levels. The h aemocytes of mussels from oiled sites showed significantly reduced superoxi de generation and phagocytic activity, effects Likely to have deleterious c onsequences for successful disease resistance. As contaminant levels decrea sed, the immunosuppression became less extreme and recovery was evident by May 1996. Between October 1996 and March 1997, immune activity in the haemo cytes of the previously oiled mussels was again significantly reduced, coin ciding with increased PAH levels. During this latter period, certain high m olecular mass PAHs (characteristically derived from combustion processes) w ere primarily responsible for the increase, occurring at similar concentrat ions in the mussel tissues to those observed just after the spill. A subseq uent reduction of hydrocarbons in June 1997 was followed by another, but le ss marked, increase in PAHs between October 1997 and March 1998, coupled wi th only minimal changes in immunity. The results show that immunosuppressio n following the oil spill was severe, but that recovery followed a few mont hs later ana the initial effects were not therefore permanent. The results also suggest that seasonal peaks in combustion-derived PAHs may occur in th e region and that these would have been greatly exacerbated early in 1996 b y oil released from the 'Sea Empress'.