. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. BEHAVIOR OF ALTERNATIVE LARVAL MORPHS 241 larvae had a strong directional bias resulting in rapid down- ward movement. By swimming towards the seabed, com- petent larvae can increase the probability of contacting an appropriate settlement site. Although similar in si/e and passive sinking speeds, lecithotrophic and competent planktotrophic larvae of Alde- rin modesta exhibited subtle differences in path trajectories and vertical swimming speeds. Lecithotrophic larvae were more uniform in their behavior, and swam downward in
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. BEHAVIOR OF ALTERNATIVE LARVAL MORPHS 241 larvae had a strong directional bias resulting in rapid down- ward movement. By swimming towards the seabed, com- petent larvae can increase the probability of contacting an appropriate settlement site. Although similar in si/e and passive sinking speeds, lecithotrophic and competent planktotrophic larvae of Alde- rin modesta exhibited subtle differences in path trajectories and vertical swimming speeds. Lecithotrophic larvae were more uniform in their behavior, and swam downward in faster, straighter paths that resulted in higher rates of verti- cal movement. In cultures, we observed these short-lived larvae making rapid excursions up into the water column and back down to the bottom, which may allow them to repeatedly sample the substratum during a brief dispersal period. Competent planktotrophic larvae were less consis- tent in their behavior, swimming with a significant down- ward bias but at a lower rate. This pattern may result from developmental variation during the month-long maturation period of planktotrophic larvae. Surprisingly, few studies have documented vertical com- ponents of swimming behavior for taxa other than bivalves and crustaceans (Mileikovsky. 1973: Chia et ai, 1984). Bivalve larvae typically swim in vertically oriented helical spirals (Mann and Wolf, 1983; Mann et«/., 1991; Wang and Xu. 1997), and can lower their sinking rate, without altering swimming speed, by changing rotational velocity (Jonsson ct nl., 1991). Downward swimming speeds were slower than rates of gravitational sinking in all bivalves examined, as in A. modesta and other taxa besides crustaceans (Chia et til., 1984; Young. 1995). These data suggest that live larvae rarely move downward through passive sinking alone, but rather through a combination of gravity and behavior. Prior studies have not measured rates of net vertical displacement for populations of larva
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
