Benthic-Pelagic coupling over a zebra mussel reef in western Lake Erie

We conducted a field study including a series of cruises over an isolated o ffshore zebra mussel reef (7-11 m deep) in Western Lake Erie to examine the effect of zebra mussels (Dreissena spp.) on the water column. The horizont al currents over the reef were found to be primarily due to the hydraulic B ow and surface gravitational seiches. The turbulence generated by these cur rents was found to be too weak to fully mix the water column. Although seas onal stratification was not observed, solar heating during the day and intr usions of cold central basin water caused stable stratification of the wate r column 60% of the time. Results from the seston analysis taken at five de pths showed a statistically significant mussel-feeding signature in chlorop hyll a and organic seston concentrations measured within 2 m above the reef . Estimates of clearance rates based on field data were consistent with rat es measured in a flow chamber using water from the site, which indicated th at zebra mussels could remove up to 40% of the total seston. The detection of a zebra mussel-induced concentration boundary layer is due to: (1) reduc ed vertical mixing as a result of semidiurnal periodic stratification, (2) refiltration of bottom water in zebra mussel populations, and (3) in situ c learance rates that are lower than those observed in the laboratory. Thus, offshore zebra mussel colonies may have less of an effect on the water colu mn than had been previously estimated by simple stirred reactor models, and the role of zebra mussels in the clarification of Lake Erie should be inve stigated further.