Fig. 3

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 40 dpf (reared at ~ 14 °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 200% extract of sand from a beach without sand dollars (poor quality natural inducer), and counted the numbers settled at 1.5, 3, 7.5 and 19 h. We also exposed a separate set of control (no turbulence) larvae to a strong natural inducer (30% extract of sand from sand dollar aquaria; right side of graph). This treatment not only confirms that the larvae were fully competent (100% of larvae settled by 8 h), but indicates the expected rate of settlement response in a strong cue as a basis of comparison to the sub-optimal cues described above. Error bars are ± s.e.m. Asterisks as in Fig. 2. Dotted line and Asterisks above non-sand dollar sand data indicates an accelerated response to this cue in turbulence-exposed larvae (see the text)