S4-1.2 Thursday, Jan. 5 Physical constraints on larval swimming and their implications for dispersal CHAN, K.Y.K.*; CLAY, T. W.; GRÜNBAUM, D. ; Univ. of Washington, Seattle firstname.lastname@example.org
Most planktonic larvae of marine invertebrates are denser than sea water and rely on swimming to locate food, navigate advective currents and avoid predators. Hence, larval swimming plays an important role in larval survival and dispersal. Larval swimming is biomechanically constrained by the morphologies of larval bodies, which are often complex and highly variable between developmental stages, and is strongly modulated by larval responses to environmental conditions. We combined a theoretical hydrodynamic model and experimental video observations to assess the functional constraints imposed by swimming on larval morphologies using larval sand dollars (Dendraster excentricus) as a model system. Larval sand dollars propel themselves with ciliated projections called arms, adding pairs of arms as they develop. In the hydrodynamic model, observed morphologies of larval sand dollars fell within a narrow range of key morphological parameters that minimized downward transport in shear flows, outperforming hypothetical alternative morphologies. The model further suggested that ontogenetic changes in larval morphologies could lead to different vertical larval movements, potentially resulting in stage-dependent vertical distributions and lateral transport. This tight coupling between larval swimming and morphology suggests the hypothesis that stress-induced morphological perturbations could compromise larval swimming. To test this hypothesis, we exposed larval sand dollars to elevated pCO2 level, which potentially reduces calcification and growth. Observed morphological changes included some predicted to enhance and some predicted to reduce swimming, suggesting compensation to preserve swimming performance. Consistent with the compensation hypothesis, observed swimming performance in still water was unchanged. These results support the importance of swimming as a driving factor in the evolution of larval morphology.