Evaluation of the attachment strength of individuals of Asterina gibbosa (Asteroidea, Echinodermata) during the perimetamorphic period

Abstract

A turbulent channel flow apparatus was used to determine the adhesion strength of the three perimetamorphic stages of the asteroid Asterina gibbosa, i.e. the brachiolaria larvae, the metamorphic individuals and the juveniles. The mean critical wall shear stresses (wall shear stress required to dislodge 50% of the attached individuals) necessary to detach larvae attached by the brachiolar arms (1.2 Pa) and juveniles attached by the tube feet (7.1 Pa) were one order of magnitude lower than the stress required to dislodge metamorphic individuals attached by the adhesive disc (41 Pa). This variability in adhesion strength reflects differences in the functioning of the adhesive organs for these different life stages of sea stars. Brachiolar arms and tube feet function as temporary adhesion organs, allowing repetitive cycles of attachment to and detachment from the substratum, whereas the adhesive disc is used only once, at the onset of metamorphosis, and is responsible for the strong attachment of the metamorphic individual, which can be described as permanent adhesion. The results confirm that the turbulent water channel apparatus is a powerful tool to investigate the adhesion mechanisms of minute organisms.

Keywords:

• Shear stress
• adhesion
• perimetamorphic period
• benthic boundary layer
• larva

Acknowledgements

This work was supported by a FRIA grant and a ‘credit pour bref séjour’ from the FNRS (Belgium) to DH, and by a travel grant from the “European Science Exchange Programme” to PF. PF is a Reasearch Associate of the FNRS. This study is a contribution from the ‘Centre Interuniversitaire de Biologie Marine’ (CIBIM; www.ulb.ac.be/sciences/biomar/index.html).