The effect of strain rate on adhesion in the purple sea urchin (Strongylocentrotus purpuratus).

Sea urchins attach to intertidal substrates in the face of dynamic hydrodynamic forces using flexible, adhesive tube feet. Tube-foot-based adhesion varies between species and among populations with different habitats (i.e. temperature and hydrodynamic forces). While some sea urchin species have tube foot stem tissues (tested in anesthetized individuals) that better resist breaking under higher loading rates, it remains unclear whether this improves the whole-animal adhesive performance in unanesthetized animals. To test whether the loading rate and previous hydrodynamic exposure influence the adhesive performance of the intertidal purple sea urchin, Strongylocentrotus purpuratus, we measured the strain rate dependence of the tube foot disc, tube foot stem, and whole-animal adhesion, using three sets of sea urchins with different environmental histories. In unanesthetized S. purpuratus, strain rate influenced tube foot disc tenacity, but not the tube foot stem or whole-animal adhesion. Rather, sea urchins collected more recently had higher whole-animal adhesion, and reliance on the tube foot disc and the tube foot stem varied among animal sets. These results further support the hypothesis that hydrodynamic loading maintains adhesive performance in sea urchins and highlight the importance of investigating strain rate at levels of organization that impact organismal performance in situ.