Meeting Abstract

82.2  Sunday, Jan. 6  Fluid dynamics of antennule flicking of the blue crab, Callinectes sapidus WALDROP, L. D.*; REIDENBACH, M. A.; KOEHL, M. A. R.; Univ. of California, Berkeley; Univ. of California, Berkeley; Univ. of California, Berkeley

Sensing chemical signals (odors) in the surrounding fluid is an important way that organisms gather information about their environment. One mechanism used by malacostracan crustaceans to capture odors is to flick their olfactory antennules through the water. The lateral filament of a crab antennule is lexible and bears a toothbrush-like array of chemosensory hairs (aesthetascs). When the blue crab, Callinectes sapidus, flicks an antennule, the downstroke pushes the aesthetascs through water at an average velocity of 17 cm/s, while the return stroke in the opposite direction is slower (6.1 cm/s). The flexible aesthetascs are on the upstream side of the antennule during the downstroke, when they are splayed apart, increasing the distance between neighboring hairs. During the slower return stroke, the hairs are pushed back to a straight orientation and clump more tightly together. We used particle image velocimetry (PIV) to measure water flow fields around the aesthetasc arrays of dynamically scaled models of C. sapidus antennules to investigate the consequences of the differences in antennule configuration, orientation, and speed between the down and return strokes. Results show that during the downstroke, water flows into the spaces between the aesthetascs, whereas during the slower return stroke, water flows around the array of chemosensory hairs rather than through it. This change in water flow between the downstroke and upward return strokes allows for the exchange of water parcels held within the hair array, enabling the animal to take a discrete sample of fluid with each flick.