Chemical orientation of lobsters, Homarus americanus, in turbulent odor plumes

Abstract--The lobster, Homarus americanus, relies upon its lateral anten-nules to make initial directional choices in a turbulent odor plume. To deter-mine whether chemical signals provide cues for source direction and distance during orientation, we studied the search patterns of the lobster orienting within a turbulent odor plume. In an odor plume, animals walked signifi-cantly more slowly and most often up the middle of the tank; control animals (no odor present) walked rapidly in straight lines, frequently along a wall. Search patterns were not stereotyped ither for the population of experimental animals or for individuals. Three different phases of orientation were evident: an initial stage during which the animals increased their walking speeds and decreased their heading angles; an intermediate stage where both the walking speed and headings were constant; and the final stage close to the source, where heading angles increased while walking speed decreased. During this last stage the animals appear to be switching from a distance orientation (mediated by the antennules) to a local food search (mediated by the walking legs) as evidenced by a great increase in leg-raking behavior. Key Words--Chemotaxis, chemoreception, orientation, lobster, Homarus americanus, odor plume