Comparative study of sea urchins Strongylocentrotus purpuratus and S. droebachiensis adhesive performance

Abstract

The marine intertidal is subject to challenging hydrodynamic forces. Organisms that reside within these zones; such as purple (Strongylocentrotus purpuratus) and green (Strongylocentrotus droebachiensis) sea urchins, must have strong attachment to prevent dislodgement, ambulate, and feed in intense environmental conditions. Sea urchins attach to the substrate via their podia (tube feet). The disc found in the distal part of tube feet has a duo-gland that releases specialized adhesive compounds and de-adhesive enzymes to achieve adhesion. Adhesive performance was evaluated to determine if purple sea urchins, that are predominantly found in high wave exposure areas, have better adhesive performance than green sea urchins, which are abundantly found in areas protected from wave action. We evaluated the following adhesive performance variables, stem mechanical properties, tube foot disc tenacity, attachment area, speed of detachment and whole animal adhesive force. We found that for most adhesive performance metrics, purple urchins performed better than greens, except for detachment speed. These results suggest that, in the field, behavioral changes may play an important role in determining risk of detachment for sea urchins. Understanding how morphology, behavior and mechanical properties of tube feet work in conjunction to provide strong attachment, is critical to predict sea urchin fitness in challenging environmental conditions.