Zebra Mussels and Benthic Macroinvertebrate Communities of Southwestern Lake Ontario and Selected Tributaries: Unexpected Results?

Abstract

Since the zebra mussel (Dreissna polymorpha) colonized the Great Lakes Ecosystem, ecologists and managers have expressed concern about potential impacts it would have on native benthic macroinvertebrate communities in lakes and streams. We compared post-Dreissena invasion data (1991-1992) with pre-invasion data (1983) from the same sites in Lake Ontario. Dreissena was the overwhelmingly dominant taxon in 1991-1992. Nevertheless, the overall abundance of other benthic macroinvertebrates, and the number of taxa collected, were greater following establishment of Dreissena. Our study failed to provide evidence that Dreissena had induced a population in any non-bivalve taxon that was present in 1983. The invasion of Dreissena and other recent environmental changes appear to have created conditions that are more favorable for most benthic macroinvertebrate taxa in the nearshore region of Lake Ontario. We also asked why zebra mussels have not colonized many creeks in Western New York, some with apparently ideal habitat, that are fed partially by water from the Erie Canal which is a source of Dreissena larvae. Counts of Dreissena larvae and counts of chlorophyll a were much higher in the canal than in out study creek, yet water quality, current velocity and particulate organic carbon concentrations in the creak and the canal were very similar. Four factors appear to limit colonization of creeks by the zebra mussel: 1) Retention of larvae by wetlands through which discharges from the canal often flow, 2) Filtering of phytoplankton and larvae by dense beds of adult zebra mussels often found at the beginning of channels connecting the canal to creeks, 3) Inappropriate food quality (e.g., lack of small0diameter phytoplankton with important fatty-acid constituents) reaching creeks from the canal, or 4) Muddy substrates inappropriate for attachment and filter-feeding by Dreissena.