Meeting Abstract
Many marine organisms have complex life histories, having limited mobility as adults and relying on the plankontic larval period for dispersal. Larval life stages thus play a significant role in determining population and community dynamics. Larvae swim and disperse in a complex fluid environment and the effect of ambient flow conditions on larval behaviour remains a question of interest. In this study, we examine how local flow and ontogeny influence swimming behaviour in pre-competent sea urchin (Arbacia punctulata) larvae. We exposed larvae to grid-stirred turbulence and recorded their behaviour during two life stages (four and six-armed plutei). Using particle image velocimetry to quantify and subtract local flow, we tested the hypothesis that larvae respond to turbulence by increasing swimming speed, and that the increase varies with ontogeny. Contrary to our hypothesis, and to prior studies of larval molluscs, changes in local flow properties (acceleration, vorticity, and deformation) did not induce a significant change in larval swimming velocities. Increased turbulence intensity, however, decreased the relative time that larvae spent in the typical upright orientation. Larger, older 6-armed larvae were tilted more frequently in turbulence, in contrast to younger 4-armed larvae. This observation suggests that as larvae increase in size and add pairs of arms they are more likely to be passively re-oriented by moving water, despite the increase in weight (ballast), potentially leading to differential transport. Our results show that turbulence plays an important role in the larval life history, not just during settlement but also in earlier stages through morphology-flow interactions.
