Testing the turbulence avoidance hypothesis

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This project will evaluate species-specific responses of copepods to turbulence via laboratory experiments and computer simulations. Field studies strongly suggest that oceanic turbulence affects the vertical position of copepods primarily by changing their behavior, and only secondarily by physically altering their position. The hypothesis to be tested is that fine-scale turbulence alters copepod behavior via directed movements and changes in swimming kinematics. The specially-designed laboratory apparatus enables comparison of plankton kinematic patterns in response to fine-scale turbulent flow features. The apparatus creates turbulent flows with dissipation rates, length scales, velocity scales, and fluctuating strain rate levels that are appropriate for zooplankton studies. Recent advances in 3D velocity measuring techniques make this an opportune time to quantify the flow field around frees-wimming zooplankton at high spatial and temporal resolution. To correlate specific behavior responses to specific instantaneous 3D flow patterns, the velocity field must be quantified in a 3D volume surrounding the animal. The experiments will facilitate a quantitative correlation between copepod behavior and hydrodynamic conditions and will provide new insight to the balance of biological versus physical forcing. Further, the rules of copepod response to a spatially-explicit physical environment will be entered into an individual-based model (IBM) to provide a context to assess the ecological significance of zooplankton behavior. The IBM simulations will test the influence of micro-scale behavior on fine-scale copepod distributions, and hence allow the turbulence-avoidance hypothesis question to be addressed: Do individual copepods react to fine-scale turbulent features with a species-specific response that results in a population distribution that does not overlap with the turbulent region?Collaborative interactions are essential to extending understanding of the biological, physical, and chemical processes that create and maintain fine-scale plankton distribution patterns. This interdisciplinary effort relies on combining expertise in fluid mechanics and biological oceanography to advance understanding of copepod ecology and sensory systems. This project will increase our understanding and ability to model the effects of turbulence on zooplankton distributions. Further, the data will be used by NOAA personnel towards developing long-term indices of secondary production as a function of wind-generated mixed-layer turbulence as part of NOAA's FATE (Fisheries And The Environment) program. Training will be provided for a graduate student in the specific areas of advanced laser measurement systems, copepod mechanosensory systems, and biological-physical interactions in the ocean. The student will experience a rich interdisciplinary research environment and develop skills to be a leader in her/his field. The project connects well with on-going educational efforts, in particular NSF IGERT and REU programs to educate in the area of aquatic chemical and hydromechanical signaling. Further, the investigators plan to work with staff members at the Georgia Aquarium and Zoo Atlanta to set up exhibits of invertebrate behavior and the role of underwater perception in mediating behavior.