FISH INTERACTIONS WITH THE SEDIMENT-WATER INTERFACE

In two mesocosm experiments of cross-classified design, using sixteen 900-liter containers, we measured how benthivorous, omnivorous, and planktivorous fish interact with the sediment-water interface to influence planktonic and benthic production. Experiment 1 used three fish treatments (Ictalurus punctatus, Notemigonus crysoleucas, Lepomis macrochirus) and a fishless control in the presence or absence of a natural pond sediment layer. The benthivorous Ictalurus enhanced turbidity but had no effects on dissolved oxygen, diel changes in dissolved oxygen, pH, or nutrient concentrations. All parameters measured were unaffected by the planktivorous Notemigonus. Experiment 2 compared Ictalurus nebulosus with those of other benthivorous (Cyprinus carpio) and omnivorous (Dorosoma cepedianum) fish, again in the presence or absence of a sediment layer but at a higher stocking density than experiment 1. In the second experiment, Dorosoma enhanced dissolved oxygen levels but had no effect on turbidity while Cyprinus and Ictalurus enhanced turbidity but suppressed dissolved oxygen. Nitrogen concentrations in sediment tubs were enhanced by Cyprinus and Ictalurus but nitrogen concentrations in sediment-free tubs were enhanced by Dorosoma. This would suggest that the benthivores affected nutrient levels through resuspension of sediments while omnivores affected nutrient levels through physiological processes.