Does the native predator Trophon geversianus exert top-down control on the invasive barnacle Balanus glandula on Patagonian rocky shores?

Abstract

Trophic interactions between the native gastropod predator Trophon geversianus and the invasive barnacle Balanus glandula may have facilitated the successful expansion of the barnacle along rocky intertidal coastlines in Argentina. In this study, through field observations and a stable isotope reconstruction of the diet of T. geversianus, we assessed whether and how frequently this drilling muricid gastropod consumes the invasive B. glandula on a Patagonian rocky shore. Field observations indicated that B. glandula and T. geversianus co-occur in the middle intertidal. Feeding observations and stable carbon and nitrogen isotope dietary reconstructions showed that T. geversianus readily and successfully consumes B. glandula, but at low rates (4% of diet) relative to native mussel prey, which compete with B. glandula for space. This study shows that T. geversianus exerts little top-down control on this invasive barnacle on Patagonian rocky shores. The success of B. glandula on these shores is plausibly enhanced directly by this weak interaction and indirectly by the preference of T. geversianus for native prey rather than the absence of predators or invader immunity from predation. The results of this study complement previous studies that have shown that tolerance to extreme desiccation stress in harsh intertidal environments is crucial for the establishment of B. glandula.