Free space availability and larval substratum selection as determinants of barnacle population structure in a developing rocky intertidal community

Variation in settlement and recruitment of Semibalanus balanoides was investigated in the high, mid and low intertidal zones at adjacent sites (A and B) on a rocky shore in Nova Scotia, following a rare occurrence of ice-scouring. In the high intertidal zone of Site A, density of settler was greater in treatments with ephemeral algae (wetter quadrats) than in those without. In general, early post-settlement mortality in treatments where algae had been removed increased with intertidal height, whereas in treatments where algae were present it remained relatively constant among heights. Post-recruitment mortality did not differ significantly among treatments in the high intertidal zone, suggesting that factors which influence selection of the substratum by cyprid larvae and promote early post-settlement survival may be particularly important in determining subsequent population structure of barnacles in this zone. Post-recruitment mortality, mainly due to predation by whelks, was highest in the low intertidal zone at both sites and did not differ significantly between treatments. In the mid intertidal zone at Site B, whelk foraging appeared to be constrained by desiccation stress and post-recruitment mortality was highest in treatments with Fucus spp. Where predation is intense, initial selection of the substratum by cyprid larvae may have little effect on the subsequent population structure of barnacles. -from Authors