Once they digitized the images and measured these details, they created a mechanical lobster that flicked in the same way. The mechanical lobster, which they dubbed Rasta Lobsta, was simply the molted shell of a spiny lobster filled with epoxy. Fresh antennules from lobsters could be mounted on this mechanical lobster and moved by a computerized motor to reproduce the motion of a flicking antennule.
They placed the mechanical lobster downstream of an "odor" source in a large water flow tank in the Environmental Fluid Mechanics Laboratory at Stanford University. Since odors are invisible, instead of the aroma of a tasty item, such as a rotting fish, the researchers substituted a fluorescent dye. The tank, operated by Jeffrey R. Koseff, professor of civil and environmental engineering at Stanford, and his colleagues, simulated the degree of turbulence a lobster might encounter while strolling along the ocean bottom.
Because they needed to see only the narrow slice of the odor plume hitting the antennule, which is only one milllimeter wide, they shone a thin sheet of laser light through the plume. While flicking the antennule, they made high-speed, close-up videos of the eddies and filaments in the dye plume to determine if and how the dye penetrated the array of chemosensory hairs at the antennule's tip.
What they found is that, during the downstroke, the lobster pushes the antennule through the water just fast enough for the water and dye to penetrate into the brush of sensory hairs, maintaining much of the detail in the swirls of dye.
On the return stroke, however, it sweeps more slowly, and the water is unable to move between the hairs. The fine filaments of dye that penetrated between the hairs during the downstroke are trapped within the brush of hairs until the next rapid downstroke. The lobsters sniff when they flick, and with each flick their antennules capture a detailed map of the
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Contact: Robert Sanders
rls@pa.urel.berkeley.edu
510-643-6998
University of California - Berkeley
30-Nov-2001