Assimilation of micro‐ and mesozooplankton by zebra mussels: A demonstration of thefood web link between zooplankton and benthic suspension feeders

We tested the hypothesis that rotifer species in the micro‐ and mesozooplankton are a potential food source for zebra mussels. We labeled phytoplankton with 14 C, fed them to two species of rotifers (140–210 µm length) that were previously found abundantly in the Hudson River and had declined following a zebra mussel invasion, and estimated the assimilation of carbon. Assimilation efficiencies were found to be ~37.47–54.0%. Combined with our feeding experiments, the data on rotifer densities before and after the invasion allowed us to calculate the energy budgets for zebra mussels. Before zebra mussels dominated the Hudson River in 1992, the absorption of energy from rotifers was about two to three times higher than that necessary to maintain its routine metabolic rate and contributed about 0.349–0.662 J h −1 to mussel growth and reproduction, conferring a positive scope for growth. Since the zebra mussels became abundant in the Hudson River, assimilation of rotifers is still sufficient to explain ~16.4–23.1% of the mussels' routine metabolic rate. Therefore, rotifers play a conceivably large role in the energy budget of zebra mussels, whether at high rotifer concentrations (before the invasion) or at low rotifer concentrations (after the invasion). This is the first quantitative evidence for a trophic link between benthic bivalve mollusks and larger micro‐ and mesozooplankton that might extend to marine systems where bivalves can derive nutrition from microzooplankton, including planktonic invertebrate larvae. Combined with other recent results, this study documents a benthos‐zooplankton trophic loop, demonstrating potentially strong top‐down control by dense bivalves on aquatic systems.