Wind on lakes brings predator and prey together in the pelagic zone

Abstract

Wind blowing over the pelagic zones of stratified lakes creates recirculating water currents. In Lake Opeongo, we observed the effects of these currents on four different trophic levels using a variety of methods (acoustic Doppler current profiler, optical plankton counter, hydroacoustics, telemetry, and netting programs). During windy events, (1) water currents were stronger than the known swimming speeds of small zooplankton (355 to 399 μm) but not larger species or fish, (2) large zooplankton (>542 μm) and schooling planktivores congregated at the thermocline at the downwind end of the basin, and (3) large piscivores directed their foraging towards areas exposed to wind, where they appeared to acquire the same meal as under calm weather conditions but with less effort. We propose that (i) the horizontal physical homogeneity of pelagic zones, (ii) the slow swimming ability of zooplankton relative to the speed of wind-induced water currents, and (iii) the likely growth benefits to predators of foraging on patches of prey lead to the downwind aggregation of pelagic organisms. We discuss this conceptual framework with examples from both lake and ocean ecosystems to suggest that this phenonenon occurs across a large range of spatial scales in aquatic ecosystems.