Potential abiotic and biotic impacts of zebra mussels on the inland waters of North America

SYNOPSIS. The expansion of zebra mussel distribution into inland wa-terways of North America portends significant abiotic and biotic changes mediated either directly or indirectly by Dreissena. Dreissena fouls a wide array of submerged substrates including rock surfaces, macrophytes, native molluscs, canal and dock walls, and watercraft and motor out-drives. Fouling of water intake pipes and associated installations can se-verely impair water delivery to hydroelectric, municipal and industrial users, necessitating proactive or reactive control measures. Mussels in-crease water clarity by removing suspended clay, silt, bacteria, phyto-plankton, and small zooplankton. Clear water phases associated with Dreissena grazing may exceed in magnitude and duration those generated by zooplankton grazing. Enhanced water clarity increases light transmit-tance and growth of benthic plants. Some benthic invertebrates {e.g., unionid molluscs) are adversely affected by Dreissena, whereas others, including amphipod crustaceans, exploit structure associated with or wastes generated by zebra mussels. Dreissena is exploited by a host of predators, most notably waterfowl, fish and crayfish. Waterfowl predators that consume contaminated Dreissena have elevated concentrations of organic pesticides and polychlorinated biphenyl compounds. Invasion of shallow lakes and ponds by Dreissena may divert production and biomass from pelagic to benthic foodwebs, shifting ecosystems to an alternative state. When new species arrive and spread, munity composition or structure (Mills et even if they do not have the appearance al., 1993). However, significant economic of the explosive invader, they may herald and ecological problems have been record-the onset of future changes in the balance ed in a diverse array of ecosystems invaded of populations by exotic species {e.g., see McCoid, 1991). —Charles Elton, 1958 In addition to affecting community com-position and species diversity, exotic spe