Perception of inert particles by calanoid copepods: behavioral observations and a numerical model

High-resolution video showed freely swimming Diaptomus sicilis attacking and capturing inert 50 mu m polystyrene beads that were outside the influence of the copepod feeding current. The beads were frequently more than half a body length away and were attacked after the 'bow wake' of the moving copepod displaced the bead away from the copepod. To investigate the hypothesis that deformation of streamlines around the copepod and its first antennae stimulated the attack response, a finite element numerical model was constructed. The model described the fluid interactions between a large object approaching a smaller object in a laminar flow at Reynolds number 5, which is characteristic of the fluid regime experienced by foraging copepods. The model revealed that fluid velocity fluctuations and streamline deformations arose in the region between the two objects as separation distance between the objects decreased. The video observations and the model results support the hypotheses that chemoreception is not required for the detection and capture of large phytoplankton cells [Vanderploeg et al., in Hughes, R.N. (ed.), Behavioral Mechanisms of Food Selection. NATO ASI Series G20, 1990; DeMott and Watson, J. Plankton Res., 13, 1203-1222, 1991], and that swimming behavior plays an integral role in prey detection.