Recruitment of Semibalanus balanoides at Robin Hood Bay, North Yorkshire, between 1969 and 1981 ranged from almost total failure to ca. 30 spat/cm2. A similar annual pattern over 100 km of adjacent coast appears to implicate climatic or hydrographic factors. Adult fecundity did not vary greatly, but as there was substantial variation in the number of cyprids reaching the shore, events during the planktonic phase (particularly wind-driven larval dispersion) appeared to be of prime importance.Thereafter, settlement density was modified by cyprid behaviour, except when larvae were very abundant, by the availability of space and the temporal pattern of the settlement. Mortality during early shore life was highly variable, photographic studies in 1981 showing between 1% and 92% of settlers dying within ten days. Under highly desiccating conditions 70% of a single day's input to the upper shore died in the first 24h. Such severe mortality could be compensated for by later inputs as settlement extended over 4 weeks or more, primarily as a result of unexpectedly long and asynchronous release.