Turbulence exposure recapitulates desperate behavior in late-stage sand dollar larvae

Abstract

Background: A common life cycle pattern in benthic-dwelling taxa in the ocean is an obligate pre-competent dispersal period of microscopic propagules followed by their entry into a competent period, during which they are capable of transitioning back to the sea floor at settlement. The behavior of larvae during their competent periods varies: some taxa are characterized by discriminating larvae that will only accept high quality habitat in which to settle, whereas larvae from other taxa may initially be discriminating, but will become increasingly ‘desperate’ to settle as they age. Larvae in this latter class, if they fail to encounter optimal settlement habitat, are observed to accept increasingly sub-optimal habitat as their competent period progresses. Results: Here we show that a brief exposure of competent sand dollar larvae (Dendraster excentricus) to a high intensity of turbulent shear shifts larvae into less discriminating settlement behavior. Specifically, turbulence-exposed larvae will settle in response to a wider variety of settlement cues, and will do so more rapidly than will their unexposed siblings. We also report that turbulence causes larvae to sink to the bottom in greater numbers, presumably increasing their exposure to cues on the substrate. Conclusions: We conclude that fundamental aspects of larval life history and habitat selection are sensitive to short term environmental exposure. We discuss these findings in the context of how larvae might more generally utilize transient features of their environment to make key life history decisions. Such a perspective has implications for issues as diverse as aquaculture, population recovery following disturbance, and the sensitivity and response of marine organisms to climate change.