Fig. 2

Fully competent sand dollar larvae exposed to turbulence are less choosy about settlement substrate, and thus behave like ‘desperate’ larvae. We either exposed D. excentricus larvae 11 dpf (reared at ~ 20 °C) to 3 min of 6 W/kg turbulent shear or did not (“no turbulence”). Then, we transferred exposed and control larvae into one of two settlement conditions: 0% extract of sand from sand dollar aquaria (MFSW; no inducer) or 40% extract of sand from sand dollar aquaria (strong natural inducer), and counted the numbers settled at 1 and 16 h. We also exposed a separate set of control (no turbulence) larvae for 1 h to 40 mM excess KCl in MFSW, followed by recovery in MFSW (right side of graph). More than 95% of these latter larvae settled, confirming that the larvae in this experiment were indeed fully competent. Error bars are + s.e.m. Asterisks indicate comparisons within settlement medium at the indicated time point between turbulence exposed (6 W/kg) larvae and the corresponding controls (no turbulence): *p < 0.05; **p < 0.01; ***p < 0.001