Orientation of hydrodynamic cues affects differential behavior responses in mud crab larvae

Donald R Webster, Georgia Institute of Technology, Civil & Environmental Engineering, Atlanta, GA, United States, Aaron C True, Georgia Institute of Technology Main Campus, Civil & Environmental Engineering, Atlanta, GA, United States and Marc J. Weissburg, Georgia Institute of Technology, Biology, Atlanta, GA, United States
Abstract:
The estuarine mud crab Panopeus herbstii navigates a complex hydrodynamic environment throughout its life history. During the dispersed, pre-benthic settlement larval stage of the megalopae, crabs experience a wide spectra of hydrodynamic cues during the search for suitable adult habitats. Two of the most spatiotemporally persistent cues encountered during this stage are vertical and horizontal shear associated with clines and fronts, respectively. To assess the effect of spatial orientation of hydrodynamic cues on swimming behavior, we exposed mud crab megalopae to horizontal and vertical shear layers in a laboratory Bickley jet flume. Particle image velocimetry (PIV) measurements of the flow produced by the laminar slot jet confirmed steady, continuously varying fluid shear fields in which peak shear strain rate values were selected to mimic in situ conditions. Cross-correlation analyses between larval swimming behavior (relative swimming speed and turning frequency) and hydrodynamic cue (velocity, shear strain rate, and convective acceleration) revealed differential swimming behaviors in shear layers driven by upwelling, downwelling, and horizontal jet flows. Orientation-specific behavioral responses enable larvae that are navigating complex estuarine hydrodynamics to balance the immediate need to forage and assess suitability of settlement habitat with the ultimate need to optimize dispersal trajectories via Selective Tidal Stream Transport behaviors.
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