Evaluation of mussel immune responses as indicators of contamination in San Francisco Bay

Several immune parameters were evaluated in two species of mussels (Mytilus californianus and M. galloprovincialis/M. trossulus) as bioindicators of contaminant effects. The mussels were deployed in San Francisco Bay Estuary and a control site at Bodega Marine Laboratory. Assays for phagocytosis and phagocytic index (average number of particles engulfed per hemocyte) were conducted with hemocytes in their own hemolymph—the “Serum” method. The responses were compared with contaminant concentrations in those mussels. For both species, the contaminated South Bay Dumbarton Bridge and Redwood Creek sites had elevated phagocytosis relative to the Bodega control site, indicating contaminant stress. The results also showed that M. californianus had higher percentages of phagocytosis (74%) and a higher phagocytic index (4.6 particles per cell) than those of M. galloprovincialis/M. trossulus (60% phagocytosis and 3.5 particles per cell). As there is a difference in immune response to contaminants, it is suggested that future San Francisco Estuary monitoring should be conducted with endemic M. galloprovincialis/M. trossulus rather than with the currently utilized M. californianus, which is not found in the estuary.