Navigating through space in turbulence tubes: copepod responses to Burgers vortex

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Elmi, Dorsa
Webster, Donald R.
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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 (and size) in and around the flow structure with the vortex axis aligned vertically and 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 kinematics 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 C. finmarchicus revealed some 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. The results provide insight to the habitats in which the copepods live as well as their vertical distribution in the water column relative to turbulence intensity. This comparative study between species highlights that variations in turbulence intensity in the ocean can influence the dynamics of copepods and the ecology of marine species.
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