The effects of small-scale turbulence on the ingestion rate of fathead minnow (Pimephales promelas) larvae

Abstract

Small-scale turbulence increases encounter rates between planktonic predators and their prey. It has been hypothesized to lead to an increase in feeding by fish larvae, yet this has rarely been tested experimentally. We investigated the effects of turbulence on feeding by fathead minnow (Pimephales promelas) larvae to test the null hypothesis of no effect of turbulence on ingestion. In one experiment, larvae were exposed to four turbulent velocities from 0 to 2 cm∙s−1 at a single prey concentration. Data analysis led to a rejection of the null hypothesis. Moreover these data suggested a significant nonlinear response of ingestion to increasing turbulence. In a second experiment, we varied turbulence and prey concentrations (15, 50, and 500 prey/L) simultaneously. We rejected the null hypothesis of no effect of turbulence for all prey concentrations. Results differed among prey concentrations. We observed a negative linear response for the two lower prey concentrations, but a domed response at 500 prey/L. We conclude that turbulence does influence ingestion, but not as suggested by an extension of encounter models. Thus, turbulence may not always be beneficial in the field.