Towards a nanomechanical basis for temporary adhesion in barnacle cyprids (Semibalanus balanoides)

Cypris larvae of barnacles are able to use a rapidly reversible temporary adhesion mechanism for exploring immersed surfaces. Despite decades of research interest, the means by which cyprids maintain attachment with surfaces prior to permanent settlement remain poorly understood. Here, we present novel observations on the morphology of 'footprints' of a putative adhesive secretion deposited by cyprids during surface exploration. Atomic force microscopy (AFM) was used to image footprints at high resolution and to acquire measurements of interaction forces. R-CH3- and R-NH2-terminated glass surfaces were used for comparison of footprint morphology, and it was noted that on R-NH2 each footprint comprised three times the volume of material deposited for footprints on R-CH3. Direct scaling of adhesion forces derived from AFM measurements did not adequately predict the real attachment tenacity of cyprids, and it is suggested that a mixture of 'wet' and 'dry' adhesive mechanisms may be at work in cyprid adhesion. High-resolution images of cyprid footprints are presented that correlate well with the known morphology of the attachment structures.