Hopkins Marine Station Student Paper

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Title: Whelk predation on Balanus glandula in Monterey Bay
Student Author(s): Fleischman, Forrest D.
Faculty Advisor(s): Watanabe, Jim
Pages: 21
Location: Final Papers Biology 175H
Date: June 2001
Abstract: Traditional ecological models developed in rocky intertidal systems state that species ranges are determined primarily by physical stress in upper tidal zones and biotic interactions in lower tidal zones. Studies of the barnacles Balanus and Chthamalus show that smaller chthamaloids are able to persist in a larger range of habitats than balanoids because of their greater tolerance to physical stress and lower susceptibility to predation. I tested this model on the barnacles Balanus glandula and Chthamalus spp. at two sites in Monterey Bay which differed in wave exposure and abundance of the common predatory snail, Nucella emarginata. I ran lab experiments to determine prey preferences of N. emarginata, and then measured densities of both species of barnacles and of the whelk along transects in the field. B. glandula and Chthamalus spp. distributions were positively correlated, indicating that competition between the two species did not play an important role in determining distribution. Nested ANOVA's of barnacle densities revealed significant differences between sites and among replicate transects within each site for both species. Although whelks were abundant in the exposed site, they did not play a major role in determining barnacle abundance. Lab experiments showed that Nucella emarginata had a strong preference for B. glandula over Chthamalus spp. As this difference did not manifest itself in differential distributions in the field, I conclude that factors other than whelk predation alone regulate the distribution of these species. A strong recruitment event in spring 2001 of B. glandula enabled me to compare distributions of B. glandula adults and recruits. No strong difference was detected. The very high variance in barnacle density in both sites may indicate that barnacle distributions in Monterey Bay are regulated by multiple complex factors. Further research is needed to understand these interactions.