Relationship between duration of cyprid attachment and drag forces associated with detachment ofBalanus amphitrite cyprids

Abstract

Relationships between the duration of antennular attachment of cyprids ofBalanus amphitrite and forces associated with detachment were assessed in a small flume. For six of twelve sets of measurements obtained on separate dates between 27 January and 2 June 1989, drag forces associated with detachment were significantly and positively correlated with duration of attachment within the range 100 to 103 s. In general, the instantaneous drag force exerted on cyprids at detachment was more strongly correlated with duration of attachment than was either the maximum or mean force exerted prior to detachment. Our indirect method of estimating drag forces from shear velocities measured ≤0.5 cm from cyprids (i.e., ≤10 body lengths) probably underestimated the true association between detachment force and attachment time since the spatial coherence of shear velocities characterizing turbulent flows in the flume was not strong at these scales. The relationship between attachment time and drag force at detachment suggests that spatial and temporal variability in fluid forces in situ may contribute to stochastic variations in intensities of settlement ofB. amphitrite. Stresses sustained by the antennular adhesive of cyprids ofB. amphitrite were calculated to standardize forces to the area of antennular contact and permit comparisons with similar measurements made onSemibalanus balanoides by other investigators. Stresses sustained by the adhesive ofB. amphitrite were an order of magnitude lower than those reported for the adhesive of the larger cyprids ofS. balanoides. This difference may reflect differences in the stress sustainable by the adhesive secreted onto antennular pads when loaded purely in tension (measured previously) rather than in a combination of shear and tension (calculated here). Alternatively, there may be interspecific differences in the adhesive used for reversible attachment or in behavioral responses of exploring cyprids to strong flow.