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

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.