Reorientation and Swimming Stability in Sea Urchin Larvae

Jeanette Wheeler1, Kit Yu Karen Chan2,3, Erik Anderson3,4, Karl Richard Helfrich5, Lauren S Mullineaux1, Anupam Sengupta6,7 and Roman Stocker6,7, (1)Woods Hole Oceanographic Institution, Biology Department, Woods Hole, MA, United States, (2)Hong Kong University of Science and Technology, Division of Life Science, Clear Water Bay, Kowloon, Hong Kong, (3)Woods Hole Oceanographic Institution, Applied Ocean Physics and Engineering Department, Woods Hole, MA, United States, (4)Grove City College, Department of Mechanical Engineering, Grove City, PA, United States, (5)Woods Hole Oceanographic Institution, Physical Oceanography Department, Woods Hole, MA, United States, (6)Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, Cambridge, MA, United States, (7)Swiss Federal Institute of Technology (ETH Zurich), Department of Civil, Environmental and Geomatic Engineering, Zurich, Switzerland
Abstract:
Many benthic marine invertebrates have two-phase life histories, relying on planktonic larval stages for dispersal and exchange of individuals between adult populations. The dispersal of planktonic larvae is determined by two factors: passive advection by the ambient flow and active motility. By modifying dispersal and ultimately settlement, larval motility influences where and when individuals recruit into benthic communities. Despite its ecological relevance, our understanding of larval motility and behavior in the plankton remains limited, especially regarding the interactions of larval motility and ambient turbulence. As most larvae are smaller than the Kolmogorov scale, they experience ocean turbulence in part as a time-changing viscous torque produced by local fluid shear. This torque causes larval reorientation, impacting swimming direction and potentially dispersal at the macroscale. It is therefore paramount to understand the mechanisms of larval reorientation and the stability of larvae against reorientation. Here we report on the larval reorientation behavior of the sea urchins Arbacia punctulata and Heliocidaris crassispina. Both species have life histories characterized by ontogenetic changes to internal density structure and morphology, which we hypothesized to impact stability. To test this hypothesis, we performed “flip chamber” experiments, in which larvae swim freely in a small chamber that is intermittently inverted, mimicking the overturning experienced by larvae in turbulence. We investigated the role of larval age, body size, species, morphology (number of arms), and motility (live versus dead) on the reorientation dynamics. Our work contributes to a more mechanistic understanding of the role of hydrodynamics in the motility and transport of planktonic larvae.
Back to: Ecological Fluid Mechanics: Interactions among Organisms and Their Fluid Environment I