. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 1 2 Minutes D 16-day planktotrophic. MMH^^M 1-day I lecithotroph: I (competent) 1 2 3 Minutes Figure 2. Mean number (± 1 SE) of larvae observed swimming off the bottom in response to light and dark, within a x cm field of view. Shading indicates observations made in the dark. (A) 8-d-old (precompetent) planktotrophic larvae, in alternating light and dark regimes. (B) 16-d-old (precompetent) planktotrophic larvae. (C) Competent (32-d-old) planktotrophic larvae. (D) 1-d-old lecithotrophic larvae, which are competent up
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 1 2 Minutes D 16-day planktotrophic. MMH^^M 1-day I lecithotroph: I (competent) 1 2 3 Minutes Figure 2. Mean number (± 1 SE) of larvae observed swimming off the bottom in response to light and dark, within a x cm field of view. Shading indicates observations made in the dark. (A) 8-d-old (precompetent) planktotrophic larvae, in alternating light and dark regimes. (B) 16-d-old (precompetent) planktotrophic larvae. (C) Competent (32-d-old) planktotrophic larvae. (D) 1-d-old lecithotrophic larvae, which are competent upon hatching. ratio expected for a null-model of equal upward and down- ward movement. This significant bias in direction, com- bined with greater speeds and straighter paths, resulted in significant rates of downward displacement for lecithotro- phic larvae (one-tailed /-test: t = , df = 57, P < ) and competent planktotrophic larvae (one-tailed f-test: / = , df = 46. P ). and showed similar patterns of downward movement. After 4 d, lecithotrophic larvae sank at a significantly slower rate (Scheffe test, P < ), closer to that of empty lecithotrophic shells ( ± mm/s). Older nonfeeding larvae expended their yolk re- serves and lost tissue mass during their planktonic period, which likely lowered their density and hence sinking rate. Lecithotrophic larvae of both ages had a significantly faster rate of net vertical displacement than precompetent plank- totrophic larvae (one-way ANOVA: F, _195 == , P < ; Scheffe test, P < ). Competent planktotrophic larvae were intermediate in their rate of net vertical dis- placement, due to swimming behaviors that tended to keep live larvae suspended off the bottom despite a high sinking rate. For all larval classes, video observations revealed that larvae moving straight downward were actively swimming with the velum extended, as opposed to passively sinking with the velum withdrawn as in t
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
