Award: OCE-1537284

Copepods are the most abundant multi-cellular organisms on earth and play a critically-important function in the food web of the world’s oceans. They provide an important conduit for the flow of energy from primary producers (algae) to the higher trophic levels including commercially-important fish species, seabirds, and marine mammals. Turbulent processes have been shown to alter metabolic rates, predator-prey encounter rates, grazing rates, egg production, swimming behavior, and population dynamics of marine copepods. It has been hypothesized that copepods detect and respond to turbulent features by aggregating within the turbulent eddies. These aggregates may enhance mating success but also may increase their chance of being eaten. The purpose of this project was to examine the capability of copepods to detect turbulent fluid motion in the ocean. This project tested the hypothesis that the copepods Acartia tonsa, Temora longicornis, and Calanus finmarchicus detect hydrodynamic cues related to vortices in turbulent flows and actively respond via changes in their swimming motion. A turbulent-like flow is mimicked in a laboratory aquarium as a small vortex (i.e., swirling motion like a tornado) with characteristics corresponding to typical turbulent vortices that copepods are likely to encounter in their habitats, and copepod swimming behavior was observed in and around the vortex. The three copepod species were chosen due to the differences in the geographical location at which they are found, their swimming and mating behaviors, and differences in their sensory architecture. Acartia tonsa is a hop-sinker with a 3D sensor array and shows significant changes in swimming kinematics and an increase in relative swimming velocity and hop frequency with increasing vortex strength. Furthermore, in moderate-to-strong vortices, A. tonsa follows circular trajectories around the vortex, which would increase encounter rates with other similarly behaving copepods. While changes in swimming kinematics depend on vortex intensity, orientation of the vortex axis shows minimal effect. Hop and escape motions were most common in the vortex core, which is spatially coincident with the peak in vorticity, a measure of fluid rotation, suggesting that vorticity is the hydrodynamic cue that evokes these behaviors. The responses to the Burgers vortex flow are species specific. While all three species followed circular trajectories around the vortex (which would lead to aggregations and increase encounter rates), T. longicornis (a cruise swimmer with a planar setal array) demonstrates a mild behavioral response to the vortex (compared to the A. tonsa response). Calanus finmarchicus (a swim-sink mode copepod with a planar setal array) demonstrates a stronger reaction to the orientation of the vortex compared to the other species. In sum, these results provide insight to the ecological consequences of the behavior and may help to explain their horizontal and vertical distribution in the water column. The project also had a strong education and outreach effort. This work brought together and provided training for two women pursuing a Ph.D., two M.S. students, and 11 undergraduate students (8 at Georgia Tech and 3 at Bigelow Laboratory for Ocean Sciences) in STEM related fields such as engineering, biology, and computational sciences. Further, research results were presented to the scientific community and provided context for outreach efforts to educate the general public and students at local high schools. Last Modified: 09/17/2020 Submitted by: Donald R Webster