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

Abstract

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 dragminimizing 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.

Slow-moving predatory gastropods track prey odors in fast and turbulent flow

“…In our flume experiments, whelks routinely displayed digging and plowing behaviors rather than merely gliding across the sediment surface. This partially submerged movement should allow whelks to maintain their body position lower in the sediments to reduce the drag imposed on their shell, a physical constraint that has clear ramifications for foraging blue crabs (Weissburg et al, 2003). It was difficult to interpret these behaviors, however, because we provided only a 1·cm layer of sand for animals to move through.…”

Dual antennular chemosensory pathways can mediate orientation by Caribbean spiny lobsters in naturalistic flow conditions

“…(See Webster and Weissburg, 2001;Weissburg et al, 2003;Keller et al, 2003 for descriptions of the flume and its use in examining chemosensory behavior of other animals.) The flume measured 12.5·m long, 0.75·m wide and 0.35·m high, and the 2·m working section for this study began 10·m downstream of the entry way and ended 0.5·m upstream of the reservoir (Fig.·2).…”

Behavioral responses of free-ranging blue crabs to episodic hypoxia. I. Movement

“…whether DO is increasing or decreasing); however, additional information from another stimulus, such as current direction, is required to decide in which direction to move. Blue crabs and other crustaceans orient up-current when detecting a favorable chemical stimulus (Herrnkind 1983, Weissburg & Zimmerfaust 1993, Nevitt et al 1995, Weissburg & Dusenbery 2002, Weissburg et al 2003. Conversely, we would expect that when a drop in DO to hypoxic concentrations is detected, blue crabs would orient and move down-current to avoid hypoxia.…”