Bivalves, Tributyltin and Green Tides: Ecosystem‐Level Impact?

Filter feeders such as bivalves are increasingly being shown to control phytoplankton blooms in eutrophic estuaries. The possibility of such a top‐down effect on macroalgae, however, has not been considered previously even though most green tide algal species reproduce by pelagic swarmers that are equivalent to phytoplankton. This work presents circumstantial evidence from an oyster‐culturing French embayment where, despite eutrophication since the mid‐1970s, macroalgae did not proliferate until 1982. This was also the year when tributyltin pollution from antifouling paints dropped substantially following a world‐wide prime ban that was implemented to save the shellfish industry. From the recorded evolution of the oyster stock, it is shown how tributyltin reduced the bivalve filter capacity within those years and resulted in Enteromorpha swarmers being much more likely to germinate and bloom. This suggests that the green tides had been successively contained by the biological activity and the chemical pressure. The effects of the latter on the former would thus have cascaded to ecosystem‐level changes, and so the functional role of bivalves should be evaluated and preserved wherever relevant.