MEPS 385:205-216 (2009)  -  DOI: https://doi.org/10.3354/meps08105

ABSTRACT: Larval delivery to benthic habitats strongly influences populations and communities. Daily larval settlement and weekly to monthly recruitment have been used to infer larval delivery mechanisms. Daily studies find that delivery varies with wind direction and the spring to neap tidal cycle while recruitment studies find variations related only to upwelling and downwelling. To resolve this dichotomy, the 2 types of observations were replicated simultaneously. ‘Safety Walk’ settlement plates were divided into quarters, placed in the intertidal zone, and censused daily, weekly, biweekly (i.e. every 2 wk) and monthly. Mortality of settlers on plates was very high; on average <10% of cyprids survived to recruit as juveniles. To investigate the high mortality, I sampled ceramic floor tile settlement plates, censused living and dead cyprids daily, and related mortality to weather and surface temperature of settlement plates. In the sun, surface temperature of plates reach 40 to 50°C within minutes, resulting in rapid desiccation of cyprids. Surface temperatures of floor tiles and natural rock were significantly lower and mortality on tiles was significantly lower. Settlement rate varied with recruit density; at densities <10 ind. cm^–2 settlement was enhanced, but above this density settlement was inversely related to recruit density. Due to high cyprid mortality and the effect of recruit density on settlement, barnacle recruitment could not be used to infer mechanisms of larval delivery to the shore.

KEY WORDS: Cyprid · Settlement · Recruitment · Safety Walk plates · Upwelling · Downwelling · Upwelling relaxation · Internal tides · Intertidal zone · Balanus glandula