Benthic-pelagic coupling in planktonic crustaceans:: the role of the benthos

The population dynamics of many species of zooplankton are strongly tied to the benthos through their dormant egg banks. As a result of this link, populations of planktonic organisms may be affected not only by the water-column community, but by benthic organisms as well. During investigations of egg bank dynamics in two lakes we observed a variety of ways in which dormant zooplankton may be impacted by the benthic assemblage. Our observations are representative of the diversity of possible interactions of this type. In Oneida Lake, NY, USA, the ability of invertebrates to consume Daphnia diapausing eggs was examined in laboratory experiments. Amphipods readily ingested the ephippia whereas gastropods, turbellarians, chironomids and zebra mussels did not. Gut analyses performed on amphipods collected from Oneida Lake indicate that these animals eat ephippia in the field as well. Tn Bullhead Pond, RT, USA, a large fraction of the diapausing eggs produced by the copepod Diaptomus sanguineus are retained on macrophytes for up to five months before either hatching or sinking to the sediment. Eggs that reach the nearshore sediment may be redistributed by sunfish as they build their nests. Larval caddisflies in both lakes were found to use dormant stages in the construction of their cases. Because the effects of benthic-pelagic coupling on zooplankton population dynamics are species and system specific, a consideration of the processes influencing both the active and dormant fractions is needed to understand fully zooplankton dynamics.