STROTHER, J.A.; KOEHL, M.A.R.; REIDENBACH, M.; HADFIELD, M.G.; KOSEFF, J.R.; Univ. of California, Berkeley; Univ. of California, Berkeley; Stanford University; University of Hawaii; Stanford University: Which aspects of the response of marine larvae to dissolved chemical cues affects their settlement in turbulent, wave driven flow?

While the larvae of many benthic marine invertebrates are known to settle and undergo metamorphosis in response to waterborne chemical cues, it is debated whether behavioral responses to dissolved cues can affect larval transport to the substratum in the turbulent, wave-driven flow that characterizes many coastal habitats. We addressed this question using larvae of the sea slug, Phestilla sibogae, which stop swimming and sink in response to a waterborne species-specific metabolite of their prey, Porites compressa. P. compressa are abundant corals that form reefs in the shallow, wave-dominated habitats of Hawaii. In previous studies, we described both the turbulent flow and the filamentous cue distribution which develops above these reefs. Here we used a numerical model to simulate the swimming and sinking of larvae through this environment to determine the effect of specific aspects of larval behavior on settlement. In our model, a population of larvae was released into the turbulent flow above the reef and made to respond to the cue filaments they encountered with a sinking behavior which incorporated the larval sensitivity to cue and lag times to begin or stop responding to cue. We found that the sensitivity to cue and the sinking speed had strong, non-linear effects on the settlement rate. In contrast, we found that the lag time before a larva begins or ceases to respond to a cue filament had little effect on the settlement rate within a biologically realistic range. Our model showed that even in turbulent flow, simple behavioral responses to cue can play an important role in the rate at which larvae encounter the reef.