Longterm Change in a Large River Fish Assemblage: Food Webs

We identified a major change in the fish assemblage of the Wabash River using a long-term dataset of electrofishing data from 1974-2008. The fish assemblage changed in approximately 1992 from a planktivore-omnivore dominated community to benthic invertivore dominated. We sampled stomachs of planktivores from archival collections, as a representation of historical phytoplankton in the river. Our analyses showed phytoplankton communities of the 1960s that were dominated by green algae, a relatively high quality food source to fishes. The current community is dominated by blue-greens and diatoms that have less nutritional quality to fishes. The carbon and nitrogen isotope ratios of consumers were used to reconstruct historical food webs for comparison to recent food webs, using fishes and mussel specimens from recent and archival natural history collections. C and N isotope ratios in historical food webs were different from recent food webs.