Copepod interaction with small-scale, dissipative eddies in turbulence: Comparison among three marine species

Abstract

A physical model of a Burgers vortex was created in the laboratory with characteristics corresponding to dissipative-scale eddies that copepods are likely to encounter in turbulent flows. The swimming behavior of three marine copepod species is assessed as a function of vortex strength in and around the flow structure with the vortex axis aligned vertically or horizontally in the water. The studied species are Acartia tonsa, an estuarine copepod with a hop-sink swimming style; Temora longicornis, a coastal copepod with a cruise swimming style; and Calanus finmarchicus, an open-ocean copepod with a cruise-sink swimming style. The results show that copepods change their swimming behavior with the intensity of the Burgers vortex and reveal species-specific responses in nearly all kinematic parameters. A. tonsa and C. finmarchicus exhibited the strongest behavioral response to increasing vortex strength and T. longicornis exhibited the weakest response. A. tonsa and T. longicornis showed no response to changes in vortex orientation, whereas the behavior of C. finmarchicus revealed some vortex orientation dependence. One common behavior among the species is that the swimming trajectory shape becomes increasingly curved and spiral around the vortex core with increasing vortex strength, which provides a means of local aggregation and increased encounter rate with food and mates. The results are interpreted in relation to differences in swimming style and setal morphology among the species.