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The Journal of Experimental Biology 206, 171-180 (2003)
doi: 10.1242/jeb.00055

Fluid mechanics produces conflicting, constraints during olfactory navigation of blue crabs, Callinectes sapidus

M. J. Weissburg^1,*, C. P. James², D. L. Smee¹ and D. R. Webster²

¹ School of Biology, Georgia Institute of Technology, Atlanta, GA 30332-0230, USA
² School of Civil & Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0355, USA

^* Author for correspondence (e-mail: marc.weissburg{at}biology.gatech.edu)

Accepted 1 October 2002

Foraging blue crabs must respond to fluid forces imposed on their body while acquiring useful chemical signals from turbulent odor plumes. This study examines how blue crabs manage these simultaneous demands. The drag force, and hence the cost of locomotion, experienced by blue crabs is shown to be a function of the body orientation angle relative to the flow. Rather than adopting a fixed orientation that minimizes the drag, blue crabs decrease their relative angle (increase drag) when odor is present in low speed flow, while assuming a drag-minimizing posture under other conditions. The motivation for crabs to adopt an orientation with larger drag appears to relate to their ability to acquire chemical signal information for odor tracking. In particular, when orienting at a smaller angle relative to the flow direction, more concentrated odor filaments arrive at the antennules to mediate upstream movement, allowing a more useful bilateral comparison between the appendage chemosensors to be made. Blue crabs respond to conflicting demands by weighting the degree of drag minimization in proportion to the potential magnitude of the drag cost and the potential benefit of acquiring chemosensory cues. Higher flow velocity magnifies the locomotory cost of a high drag posture, thus in swift flows crabs minimize drag and sacrifice their ability to acquire olfactory cues.

Key words: chemosensation, drag, fluid dynamics, optimal foraging models, predation, sensory systems, olfaction, Callinectis sapidus, crab

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