An experimental evaluation of the direct and indirect effects of endemic seaweeds, barnacles, and invertebrate predators on the abundance of the introduced rocky intertidal barnacle Balanus glandula
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The barnacle, Balanus glandula has recently invaded along the Pacific coast of eastern Hokkaido, Japan. To evaluate the direct and indirect effects of endemic seaweeds, barnacles, and invertebrate predators on the abundance of B. glandula on the rocky intertidal coast of eastern Hokkaido, we conducted a field experiment from June 2011 to October 2012 in which we manipulated the presence or absence of these factors. Seaweeds showed no significant effect on the abundance of B. glandula. The endemic barnacle Chthamalus dalli and the invertebrate predator Nucella lima reduced the abundance of B. glandula. However, the simultaneous influence of N. lima and C. dalli was compensative rather than additive, probably due to keystone predation. These findings suggest that competition by the endemic barnacle C. dalli and predation by the invertebrate predator N. lima decreased the abundance of B. glandula, but that N. lima predation on C. dalli weakened the negative influence of C. dalli on B. glandula. The implications of these findings are twofold: the endemic competitor and invertebrate predator may have played important roles in decreasing the abundance of B. glandula in natural habitats, and conservation of endemic invertebrate predators may be crucial to impede the establishment and survival of introduced barnacles in rocky intertidal habitats.
KeywordsCompetition Indirect effect Invasion success Macrobenthos Predation Rocky intertidal
We thank Masahiro Nakaoka for his assistance and advice regarding this experiment. We also thank Tomoaki Hagino, Keiichi Fukaya, and Mituho Iida for their help in setting up the field experiment. We are grateful to member of the Akkeshi Marine Laboratory for their assistance with transportation to the study site. This research was supported by the Akkeshi Waterfowl Observation Center. Financial support was provided to AKMRA in the form of a scholarship entitled “Special Grants Program for International Students to perform Doctoral Research” by Hokkaido University, and was partly supported by JSPS KAKENHI Grant (Nos. 24570012 and 15K07208 to TN).
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