On the reorientation of non-spherical prey particles in a feeding current

Potentially, non-spherical prey can be re-oriented in a flow field and impact on the predator's feeding structures in a non-random manner. Herein, we quantify a process whereby this passive reorientation occurs, and present a model that predicts the orientation of a spheroidal prey as a function of its shape, size and the characteristics of the fluid flow For a radial flow field, elongated prey tend to align with their long axis parallel to streamlines. This theory is well supported by our results from a laboratory study of cylindrical particles in a siphon flow. The model is extended to a more realistic representation of copepod feeding currents. In this context, the spatial scale over which this process is active is proportional to epsilon (-1/4) where epsilon is the turbulent dissipation rate. For a range of natural turbulence levels, re-orientation efficiency can range from >90% (low turbulence) to <10% (high turbulence).