Measurement of the attachment strength of brachiolaria larvae and metamorphic individuals of the sea star Asterina gibbosa by a centrifugation method

Abstract

Two methods are generally used to measure the adhesive strength of invertebrate larvae: direct measurement with a force transducer connected to the organisms and indirect measurement with a water flow used to dislodge the organisms. Each of these methods, however, has its drawbacks. The present study aimed to design a simple and straightforward method to measure the adhesion strength of marine invertebrate larvae based on centrifugation. This centrifuge technique works in immersed conditions and applies forces acting at 45° to the substratum, therefore mimicking natural conditions. It was tested with three different substrata on two developmental stages of the sea star Asterina gibbosa: the brachiolaria larvae, which use temporary adhesion, and the metamorphic individuals which use permanent adhesion. Measurements were completed by SEM and TEM observations of the larval adhesive organs. The critical detachment force (force required to detach 50% of the larvae) of brachiolaria larvae attached to glass (36 ±9 µN) and rough PMMA (43 ± 16 µN) were equivalent and both significantly higher than the critical detachment force measured on smooth PMMA (11 ± 8 µN). Most metamorphic individuals, on the other hand, resisted to the highest centrifugation speed used, corresponding to a force of 2.13 mN. For the hydrodynamics of larval settlement and metamorphosis, force is the ecologically relevant factor, and adhesion forces obtained by centrifugation are strikingly similar to forces measured for other marine invertebrate larvae with other methods. This indicates the usefulness of the centrifugation technique to compare adhesion of larvae between different species or development stages, or between different treatments.