Impacts of fish predation on an Ohio River zooplankton community

Compared to lentic systems, much less is known about the factors that structure zooplankton communities in large liver environments. In this study, we used an in situ mesocosm system, the potamocorrals, to assess the impact of larval fish on the zooplankton community in the Ohio River (USA). The responses of zooplankton to increasing biomasses of fish were taxon-dependent. The population growth rates of the most common zooplankton, Diacylops thomasi, varied inversely with fish biomass, while other crustacean zooplankton showed no significant responses to the fish treatment. The reverse pattern was seen for the rotifer Poyarthra sp. whose population growth rates increased with increasing fish biomass. This is the first in situ evaluation of fish predation on zooplankton in a large liver system and demonstrates that predation as well as physical factors may influence riverine zooplankton densities and community structure.