Three-dimensional odorant concentration measurements around actively tracking blue crabs

Brian D. Dickman, Donald R. Webster, Jennifer L. Page, Marc J. Weissburg

Limnol. Oceanogr. Methods 7:96-108 (2009) | DOI: 10.4319/lom.2009.7.96

ABSTRACT: Blue crabs (Callinectes sapidus) and other aquatic organisms locate food and mates by tracking turbulent odorant plumes. The odorant concentration fluctuates unpredictably due to turbulent transport, and many characteristics of the fluctuation pattern have been hypothesized as useful cues for orienting to the odorant source. To make a direct linkage between tracking behavior and odorant signal properties, we developed a laser-induced fluorescence measurement system to quantify the instantaneous three-dimensional (3D) concentration field surrounding actively tracking blue crabs. The data suggest a connection between upstream walking speed and bursts of odorant concentration arriving at the antennule chemosensors, which are located near the mouth region. Specifically, we note rapid upstream walking speed when high concentration bursts arrive at the antennules location and a decrease in upstream walking speed in the absence of odorant filaments near the antennules. Additionally, we note transverse crab movements in apparent response to the transverse distribution of the odorant concentration field. Specifically, asymmetry of the odorant concentration distribution at the elevation of the leg chemosensors is associated with subsequent crab position adjustments in the transverse direction. The methods described here allow for powerful and direct tests of chemosensory navigation strategies in blue crabs, as well as other macroscopic aquatic animals.