SCOPE FOR GROWTH AND CONTAMINANT LEVELS IN NORTH-SEA MUSSELS MYTILUS-EDULIS

Mussels Mytilus edulis, collected from 26 coastal sites from the Shetland Islands to the Thames estuary and 8 offshore Light vessels, were used to monitor changes in environmental quality along the North Sea coastline of the UK (July 1990 and August 1991). The combined measurements of the stress response, scope for growth (SFG), and chemical contaminants in the tissues of mussels were able to detect, quantify and identify some of the major toxicants causing the observed pollution effects. SFG declined from north to south, reflecting both the major inflow of clean water from the North Atlantic via the north of Scotland, and the overall increase in environmental contamination with increasing urbanisation and industrialisation towards the south. There were coastal regions (e.g. Humber-Wash area and the Thames estuary) as well as specific sites (e.g. Ythan, Montrose, Blyth, Teesmouth, Whitby) which showed markedly reduced SFG. Using experimentally derived tissue concentration-response relationships it was shown that at over half the sites the reduced SFG could be entirely explained by the recorded concentrations of contaminants in the tissues. At the majority of sites, a large contribution towards the observed decline in SFG was caused by toxic (mainly polyaromatic) hydrocarbons, largely reflecting urbanisation and shipping activity. in addition, reductions in SFG appear to be partially explained by the accumulation of significant amounts of 'polar organic compounds' and tributyltin. At no sites were metals accumulated to concentrations that could cause a significant reduction in SFG. At those sites with a large 'unexplained component' to the very low SFG values, there was a significant correlation between this 'residual unexplained toxicity' and concentrations of organochlorines in the mussels. More research on the toxicity of these organochlorine compounds to mussels is needed.