Long-term decline (and recovery?) of native bivalves in the Hudson River.
Strayer, David*,1, Malcom, Heather1, 1 Institute of Ecosystem Studies, Millbrook, NY, USA
ABSTRACT- Conservationists fear that the invasion of the zebra mussel (Dreissena polymorpha) from Europe in 1985 may lead to the extinction of many populations and species of native North American bivalves. The invasion of the Hudson River estuary by zebra mussels was followed by steep declines (77 to >99.7%) in populations of all species of native bivalves between 1992 and 1999. Body condition of all unionids, and growth and recruitment of young unionids also declined significantly. Declines in population size and body condition were correlated primarily with the filtration rate of the zebra mussel population, not with fouling of native bivalves by zebra mussels. Samples taken since 2000, however, have shown that populations of all four common native bivalves have stabilized or even recovered, although the zebra mussel population has not declined. The mechanisms underlying this apparent reversal of fortune are not clear: recruitment and growth of young mussels have showed limited recovery, but body condition of adults has not. We found no evidence that spatial refuges contributed to this reversal of population declines. Simple statistical models project now that native bivalves may persist at population densities about an order of magnitude below their pre-invasion densities. These results offer a slender hope that long-term coexistence of zebra mussels and native bivalves may be possible at some sites.
Key words: invasive species, freshwater ecology, bivalves
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