RESPONSES OF THE RIBBED MUSSEL, GEUKENSIA DEMISSA, TO THE HARMFUL ALGAE AUREOCOCCUS ANOPHAGEFFERENS AND HETEROSIGMA AKASHIWO

The ribbed mussel (Geukensia demissa) is a keystone species in the salt marshes of the North American Atlantic coast. We investigated the clearance rates (CRs) and pathology of ribbed mussels exposed to cul-tures of two toxic algae, Aureococcus anophagefferens andHeterosigma akashiwo, for 5 d and contrasted the results with mussels fed the nontoxic alga Tetraselmis chui. We also conducted a separate, in vitro experiment in which we exposed extracted mussel haemocytes to the three different algae, their respective media and sea water, as a toxicity bioassay. Results show that mussels exposed to either of the toxic algae had significantly decreased CRs during the entire exposure period. Histopathology revealed thinner digestive tubules, gonad reabsorption and a decrease in gill ciliates in response to both toxic algal species. There was a significant in-crease in mortality of haemocytes exposed in vitro to both toxic algae compared with seawater controls. Results suggest that ribbed mussel feeding behaviour and physiology can be impacted in several ways by harmful algae, which could undermine their contribution to pelagic-benthic coupling processes