Bed-Roughness Effects on Boundary-Layer Turbulence and Consequences for Odor-Tracking Behavior of Blue Crabs (Callinectes sapidus)

We employed laser-induced fluorescence (LIF) measurements of odorant plume structure and behavioral observations to examine how turbulence affects the three-dimensional structure of odorant plumes and subsequently mediates olfactory search efficiency and success in our model organism, the blue crab (Callinectes sapidus). The turbulent characteristics of two laboratory flumes (one for behavioral quantification, one for signal-structure quantification) were systematically varied by changing the bed substrate roughness to create smooth, transitional, and fully rough flow conditions. Generally, increasing bed roughness caused greater mixing, decreased the time-averaged odorant concentration and concentration variance, and increased the plume width and homogeneity. Foraging success and speed of blue crabs attempting to locate the odorant source both declined consistently with increasing bed roughness. The variation in signal structure at the height of the antennules among bed-roughness treatments explains the observed behavior differences in crab foraging speed. In contrast, steering (path linearity) appeared to be unaffected by bed-roughness-induced turbulence. The transverse correlation function for odorant concentration at sensors separated across the width of the plume was examined among bedroughness treatments, and, ultimately, the correlation function was found to be related to the spatial position of tracking blue crabs. The spatial arrangement of blue crab chemosensors combined with the three-dimensional structure of odor plumes account for the differential effects of turbulence on the speed and success of crabtracking behavior.