Interactive effects of temperature and copper on immunocompetence and disease susceptibility in mussels (Mytilus edulis).

The interactive effects of temperature and copper on immune function and consequently disease susceptibility of the marine mussel, Mytilus edulis were investigated. Two studies were carried out, the first involved sequential exposure to copper at 0.02 and 0.05 ppm followed by the bacterium Vibrio tubiashii. In the second study, mussels were simultaneously exposed to copper and V. tubiashii. Both studies were carried out at 10 and 15 degrees C, to ascertain whether temperature had an additional effect on immunocompetence. A multi-assay approach was used to obtain an overall view of immune function in the mussels. Assays carried out included total and differential haemocyte counts, production of intracellular superoxide and phagocytosis by haemocytes. Data are presented showing significant effects on immune parameters of sequential and simultaneous exposure to copper and V. tubiashii at 10 and 15 degrees C. Each of the factors considered were shown to have a significant effect on at least one of the immune parameters measured. There were also significant effects due to the interaction of these factors. The response of total and differential blood cell counts to copper were shown to alter, if mussels were exposed in a sequential manner as opposed to simultaneous exposure. The results confirmed that the immune system of M. edulis is susceptible to copper at relatively low concentrations. Furthermore, the effects of copper alter with environmental variables, including temperature and the presence of a potential pathogen. The complexity of the interactions demonstrate that extrapolation of data obtained from single stressor studies into field situations could give a misleading picture.