Recruitment dynamics of the barnacle Semibalanus balanoides (L.) in rocky shore communities

Larval recruitment is an important factor in structuring populations and communities in the benthic marine environment. To capture the importance of recruitment patterns on benthic community structure it is imperative to consider factors influencing the transition from pelagic to sessile life stages in addition to influential factors occurring in both the water column and the adult habitat. The intertidal barnacle Semibalanus balanoides (L.) is ideal for studies encompassing the components of the recruitment process because both the cyprid larvae and the adults are easily identified and sampled. A series of experiments was conducted to examine the delivery S. balanoides cyprid larvae on the rocky shores of Swans Island, Maine, and the factors that affect their subsequent settlement and survival. The timing and intensity of S. balanoides settlement among eight sites on Swans Island corresponds to the delivery of cyprid larvae by tidal currents. Despite differential delivery on the northern and southern shores of the island, biological interactions affecting recruitment within sites were similar on both shores. Stands of macroalgae acted as a barriers to the settlement of cyprids and mucus left on the substrate by two common macroalgal species inhibited cyprid settlement. Barnacle settlement was dramatically higher on surfaces treated with the mucus of the herbivorous snail Littorina littorea (L.), but mucus of the predator snail Nucella lapillus (L.) had no effect on settlement. Post-settlement survival was high at all sites and slightly greater in the presence of L. littorea. However, artifacts of exclusion cages confound the effect of both macroalgae and L. littorea on early mortality.