ARRIVAL, SPREAD, AND EARLY DYNAMICS OF A ZEBRA MUSSEL (DREISSENA-POLYMORPHA) POPULATION IN THE HUDSON RIVER ESTUARY

The zebra mussel (Dreissena polymorpha) population of the Hudson River estuary grew and spread rapidly following its first detection in May 1991. The population reached 550 billion animals (4000/m(2), mean over the freshwater tidal river) by the end of 1992, constituting >70% of zoobenthic biomass, and filtered a volume equivalent to the entire wat er column in 1 day. Over 95% of the population lived on subtidal rocks . Following the period of rapid population growth in 1991-1992, reprod uctive success (young of the year per adult) fell by four orders of ma gnitude in 1993-1994. Furthermore, at the end of the 1993-1994 growing seasons, young of the year were only 20-30% as large as in 1991. Adul t zebra mussels may have been outcompeting the larvae for food. We pro pose that such food-limited zebra mussel populations may be especially frequent in rivers and estuaries, where the ratio of food supply to a vailable substratum is small.