Barnacle population dynamics and recruitment regulation in southcentral Alaska

The role of recruitment in regulating population dynamics of three intertidal barnacle species was investigated by examining sources and scales of variation in recruitment and determining the nature of the relationship between recruitment density and resultant adult population size. The study was conducted in Kachemak Bay, Alaska (USA) from 1991 to 1993 to determine the extent to which recruitment influences population dynamics of species near their geographic limit. Year-to-year variation in recruitment was highly significant, with average maximum recruitment between 1991 and 1993 ranging from 0.85 to 8.71 cm(-2). Recruitment densities on individual test surfaces ranged from 0-71 cm(-2). Inter-site variation in recruitment was significant and the ranking of sites by recruitment density was consistent between years. Recruitment of Semibalanus cariosus (Pallas) in the low intertidal was 7-162 times greater than of S. balanoides (L.) and Balanus glandula Darwin in the upper intertidal. Predation significantly affected the survival of recruits during 1991, a year of comparatively low overall recruitment. Also, 1991 was a year during which there was a linear relationship between initial recruitment and subsequent adult density for all species. In 1992 and 1993, years when initial larval settlement of S. cariosus was much greater, recruits commonly exceeded adult saturation density in the lower intertidal, resulting in intense intra-specific competition for space and leading to decoupling of recruit and adult density. Despite high recruitment in 1992 and 1993, recruit survival to adulthood of all species was actually greatest in the low recruitment year (1991), suggesting that even comparatively low recruitment provides enough new individuals to maintain populations. Consequently, at sites near their geographic limit, recruitment is not the primary process limiting S. cariosus populations in the low intertidal, although its influence was evident for high intertidal S. balanoides and B. glandula populations.