Abstract
Zebra mussels established populations in Croton Pond, an impoundment on the Muskegon River in Michigan, between 1999 and 2000. Subsequently, declines in the filter feeding invertebrate communities downstream of the impoundment have occurred. Because of these changes, I investigated the impacts of zebra mussels on the production and downstream transport of phytoplankton in Croton Pond and the Muskegon River. Chlorophyll a concentrations were determined at multiple sites upstream, in the pond, and downstream. In addition, simulations were set up to predict algal biomass had zebra mussels not been introduced into the reservoir. Chlorophyll data indicates that the algal biomass in this portion of the river continually decreased with downstream flow. Clearance rates of zebra mussels were found to be 108 mLind.-1hr-1, immediately below Croton Dam while the incubations showed phytoplankton daily production rates to be 1.92 μgL-1 in the absence of zebra mussels. These data combined are a strong indication that the changes in chlorophyll a throughout the stream were a result of zebra mussel filtration. Decreased downstream transport of algal biomass may account for declines in other filter feeding invertebrate populations. In addition, zebra mussel filtering rates may directly limit the expansion of zebra mussel populations downstream due to food limitation.