The acorn barnacle, Semibalanus balanoides, is thought to release larvae in response to phytoplankton blooms, but there is evidence that another, unidentified cue for release may exist. We conducted high-frequency sampling in Little Harbor, Massachusetts, USA, to determine whether early-stage larval abundance was related to several environmental variables, and to characterize vertical distributions of the larvae. Larval concentrations peaked at 2.52 and 1.02 individuals l during two storms. Larvae were more abundant near the surface than near the bottom. We suggest the hypothesis that turbid conditions and upward-swimming behavior may protect newly-released larvae from predation and cannibalism. Future studies should test this hypothesis with barnacles and other invertebrates. [ABSTRACT FROM AUTHOR]