The effects of hydrodynamics on the feeding of a freshwater grazer (Daphnia magna): The influence of particle size and shape

Goulet, Luc
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University of Guelph

The transfer of energy through the consumption of phytoplankton producers by zooplankton grazers is one of the most important interactions in aquatic ecosystems. There are many factors influencing these interactions such as the size and shape of the algae. Physical interactions between grazer and algae are dictated by hydrodynamic forces, and a unimodal relationship has been established for grazer clearance rates (CR) as turbulence increases. The goal of this study was to determine the effect of algae size and shape on the relationship between CR and turbulence by generating vorticity in a rotational cylinder to simulate increasing turbulence. The CR of Daphnia magna was examined for two algae species; the small, spherical Chlorella vulgaris and the larger, elongated and colonial Scenedesmus quadricauda. The CR of D. magna followed the unimodal trend as expected, with overall CR being higher on C. vulgaris likely due to lower handling time and higher concentration in the feeding radius. Importantly, the unimodal trend was best described by vorticity rather than Reynolds number. These results help further the understanding of grazer feeding interactions in ecologically relevant hydrodynamic conditions.

Daphnia, Zooplankton feeding, Hydrodynamics, effects of turbulence on feeding, clearance rate, rotating cylinder, vorticity in lakes