Effect of ultrasound on cyprids and juvenile barnacles

Settlement inhibition of barnacle (Amphibalanus amphitrite) cypris larvae resulting from exposure to ultrasound was measured at three frequencies (23, 63, and 102 kHz), applied at three acoustic pressure levels (9, 15, and 22 kPa) for exposure times of 30, 150, and 300 s. The lowest settlement was observed for 23 kHz, which also induced the highest cyprid mortality. Cyprid settlement following exposure to 23 kHz at 22 kPa for 30 s was reduced by a factor of two. Observing surface exploration by the cyprids revealed an altered behaviour following exposure to ultrasound: step length was increased, while step duration, walking pace, and the fraction of cyprids exploring the surface were significantly reduced with respect to control cyprids. The basal area of juvenile barnacles, metamorphosed from ultrasound-treated cyprids was initially smaller than unexposed individuals, but normalised over two weeks' growth. Thus, ultrasound exposure effectively reduced cyprid settlement, yet metamorphosed barnacles grew normally.