Patterns of substrata use by the invasive acorn barnacle Balanus glandula in Patagonian salt marshes

Balanus glandula is a native barnacle of the rocky shores in the west coast of North America. Forty years after its introduction in Argentina, this species is the only barnacle dominating the high intertidal of local rocky shores and more interesting, it was also reported successfully colonizing soft-bottom salt marshes. In this study, we identified and characterized the substrata most successfully colonized by B. glandula in Patagonian salt marshes through descriptive and experimental means. We surveyed and compared two Patagonian salt marshes and the substrata colonized by B. glandula. Our results show that barnacles utilize more than 10 types of different substrata. Mussel valves were the most frequent type of substrata utilized in Riacho marsh, whereas the dominant halophyte Sarcocornia perennis was the substratum most utilized in Fracasso marsh where mussels were mostly absent. When the five most utilized substrata were experimentally offered, the halophyte shrub Limonium brasiliense was the most densely colonized of the experimental substrata, with the largest sizes and the lowest proportion of dead barnacles. Density and size of the barnacles recruited on plants were similar to that observed in nearby invaded rocky shores. Our study strongly suggests that soft-bottom environments, where hard substrata are available, have to be seriously considered when designing early detection plans targeting B. glandula and other similar rocky shore invasive species.