A comparative study of the behavioural responses to heavy metal pollution populations of the common mussel mytilus edulis L, collected from a polluted site(Teesmouth) and a relatively unpolluted site (Lindisfame)

Abstract

This study examined the ecological differences between two populations of the common blue mussel Mytilus edulis L. The project investigated the response to heavy metal pollution, administered in the form of metal salts, to individuals from populations inhabiting 'polluted' and 'relatively unpolluted' sites. First an assessment was made of morphological differences and the tissue content of copper, cadmium, lead and zinc. There were few differences in shell morphology, a slight difference in soft tissue weight, and surprisingly, a higher tissue concentration of copper and zinc at the 'unpolluted site'. Normal filtration behaviour was compared with that in the presence of solutions of salts of heavy metal, over a short time (up to 1 hour); this showed distinct differences in tolerance between the two populations in a way which was metal specific. When administered together, doses of metal salts which produced a 30% decrease in filtration rate individually, rarely showed additively; most seemed antagonistic. There was also a distinct variation in response to equivalent doses of the same metal, and investigation of filtration rate over three hours, both in clean seawater and in the presence of copper II sulphate, showed a fluctuation over time, in a manner which was altered in response to increasing concentration of metal. It was suggested that these variations in basal filtration rate were due to alternation between an aerobic phase and an anaerobic phase. Finally an assessment was made of the rates at which copper, lead, cadmium and zinc were accumulated in the tissues, over several weeks. Doses of single metal salts producing 30% decreases in filtration rate were chosen as the test concentration, though this proved to be fatal over a period of two weeks. This section was not completed for the 'polluted site' samples, as time did not permit further collection, but the experiment was repeated for mussels from the 'unpolluted site' using doses which resulted in a 10% decrease in filtration. While the two populations could not be compared for their bioaccumulation behaviour in this instance, it was shown conclusively that all four metals were uptaken. Overall, it seemed that there was evidence for development of tolerance at both collection sites, with Lindisfame mussels apparently able to detoxify and store zinc, and possibly copper. Due to the known high quantities of metals discharged from the Tees estuary, the suggestion was made that the Teesmouth mussel population have developed the ability to secrete metal from their bodies.