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 pl anktivorous fish interact with the sediment-water interface to influen ce planktonic and benthic production. Experiment 1 used three fish tre atments (Ictalurus punctatus, Notemigonus crysoleucas, Lepomis macroch irus) and a fishless control in the presence or absence of a natural p ond 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 unaffecte d by the planktivorous Notemigonus. Experiment 2 compared Ictalurus ne bulosus with those of other benthivorous (Cyprinus carpio) and omnivor ous (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 h ad no effect on turbidity while Cyprinus and Ictalurus enhanced turbid ity but suppressed dissolved oxygen. Nitrogen concentrations in sedime nt tubs were enhanced by Cyprinus and Ictalurus but nitrogen concentra tions in sediment-free tubs were enhanced by Dorosoma. This would sugg est that the benthivores affected nutrient levels through resuspension of sediments while omnivores affected nutrient levels through physiol ogical processes.