Multiscale effects of wind‐induced hydrodynamics on lake plankton distribution

Abstract

AbstractIn this study, we used a combination of high‐intensity sampling technologies, and a 3D hydrodynamic model of a medium‐sized lake in southern Ontario, Canada to investigate physical–biological relationships at spatial scales from 100 m to 6 km and temporal scales from hours to months. At the scale of the whole study basin, we predicted that stronger winds would lead to higher zooplankton biomass downwind relative to upwind. The hydrodynamic model suggests rapid downwind displacement of progressively deeper surface mixed layers with increasing winds, and we found a statistically higher downwind biomass of small‐bodied zooplankton on windy days, but not large zooplankton. At a fine spatial scale (hundreds of meters), we predicted that zooplankton patchiness would decrease with increasing wind mixing of the upper water column and confirmed this for small‐bodied but not large‐bodied zooplankton. At this fine‐scale cross‐correlations of zooplankton biomass with water temperature and chlorophyll fluorescence suggested that zooplankton are not simply moved passively by water masses. We also found a clear change in the cross‐correlation between large‐ and small‐bodied zooplankton biomass, with out‐of‐phase spatial distributions during calm periods becoming in‐phase with increasing winds. Overall these results indicate that the response of zooplankton to wind‐driven physical forces is strongly dependent on an interaction between their body size, which determines their swimming speed and capacity to position themselves vertically in the water column, and the spatial scale and intensity of the wind‐generated physical forces. We discuss the implications for food web interactions.