STROTHER, J.A.*; MCHENRY, M.J.; University of California, Irvine; University of California, Irvine: The effects of morphology and behavior on phototaxis in ascidian larvae.

A large diversity of marine invertebrate larvae influence their dispersal by orienting their swimming to light. Despite an abundance of research that has measured ontogenetic patterns of phototaxis, it remains unclear how marine invertebrate larvae modify their swimming with respect to light cues to orient their movement. To study this mechanism, we used the tadpole larvae of ascidians, which swim in a helix that exposes a single ocellus to a time-varying light intensity. We constructed a three-dimensional numerical model that evaluated the hydrodynamics and mass distribution of an ascidian larvae (Botrylloides sp.) and calculated helical trajectories. The model was validated by making comparisons with measured trajectories; we then used this model to test behavioral algorithms of phototaxis. Futhermore, we modified the larval morphology and tail kinematics to examine the rate at which various species could orient to a light source. Our results support the hypothesis that ascidian larvae orient by helical klinotaxis and therefore swim either towards or away from light by modifying the delay between light perception and a response in tail kinematics.