Ellrich, Yorisue & Momota 2020 ESA Poster.pdf

Biotic resistance against introduced barnacles on the Pacific coast of Hokkaido, Japan

Introduced species are a major threat to coastal ecosystems worldwide. Therefore, invasion biology seeks to understand biotic resistance, which is the ability of native species to limit introduced species. In this study, we investigated effects of native dogwhelks (Nucella lima, predatory snails) and limpets (Lottia cassis, herbivorous snails) on introduced barnacles (Balanus glandula) on the Pacific coast of Hokkaido (northern Japan). Balanus glandula is native to the North American Pacific coast and was introduced, most likely by shipping, to Honshu (central Japan) where B. glandula replaced several native barnacle species. More recently, B. glandula spread to Hokkaido. Dogwhelks are often the main predators of barnacles and predator nonconsumptive effects (NCEs), mediated by dogwhelk mucus cues, can limit barnacle cyprid settlement and recruitment. Limpets are important grazers that not only control algae but also influence barnacles. For instance, grazing limpets ingest settling cyprids and push barnacle recruits off the substrate. Such limpet disturbance effects (LDEs) can limit barnacle recruitment. Working in Akkeshi Bay (Hokkaido), we conducted two manipulative lab experiments that examined dogwhelk feeding preferences for barnacles and two manipulative field experiments that examined NCEs and LDEs on barnacle recruitment to evaluate mechanism underlying biotic resistance against B. glandula.

We found that dogwhelks prefer B. glandula over native barnacles (Chthamalus dalli) and that dogwhelks prefer large over small B. glandula individuals. These preferences are likely driven by prey profitability as previous work in congeneric North American dogwhelks indicated that B. glandula-fed dogwhelks grow faster than C. dalli-fed dogwhelks and that dogwhelks fed large B. glandula individuals grow the fastest. Our results suggest that dogwhelk preferences for B. glandula may slow down the B. glandula spread, especially as large B. glandula individuals are of high reproductive potential. Furthermore, we found that dogwhelk NCEs limited C. dalli recruitment by 33 % and B. glandula recruitment by 56 %, presumably as cyprids moved away from dogwhelk mucus cues to reduce future predation risk. Finally, we detected that LDEs limited C. dalli recruitment by only 10 % but B. glandula recruitment by 81 %. These differential LDEs on C. dalli and B. glandula recruitment are related to recruitment intensity. As C. dalli recruitment was 12 times higher than B. glandula recruitment, we propose that the higher C. dalli recruitment compensated for LDEs on C. dalli recruitment. Overall, our study shows how native dogwhelks and limpets contribute to biotic resistance against introduced barnacles.