Reproductive activity of the invasive barnacle Balanus glandula at Cabo Dos Bahias, Chubut, Argentina

 Balanus glandula - a barnacle native of the Pacific Coast of North America – arrived to the South Atlantic Ocean in the mid-1970´s and has since spread from San Clemente del Tuyu (36º22’ S; 56º44’ W) to Puerto San Julian (49º 30´ S; 67º 69´ W). Patagonian rocky shores are unique in that they have no native intertidal barnacle. Beds of the mussel Perumytilus purpuratus cover wave-exposed headlands from mid to high intertidal, meaning B. glandula has limited bare substrate available within their preferred elevational range to colonize. Reproduction is a key process in driving the success of invasive species, so we quantified barnacle reproductive activity on the two substrate types (mussel vs. rock) throughout 2006 in Cabo Dos Bahias Park, Chubut, Argentina. To examine reproductive activity, 50 B. glandula individuals on each substrate type were randomly chosen each month and the number of individuals with mature eggs was recorded. We found significant differences in the number of individuals with mature eggs between seasons and settlement substrate. In Cabo Dos Bahías Park, B. glandula was reproductively active all year; more individuals with mature eggs were found in winter and spring than in summer and autumn. We also found that barnacles living on top of mussel beds had higher reproductive activity (in number and in time-length), than barnacles on bare rock. Other authors have hypothesized that reproduction is a phenotypically plastic trait in barnacles that can be influenced by several variables (water temperature, density, etc). In this study, barnacle densities were lower on mussel beds where reproductive activity was highest, suggesting that plasticity in reproductive activity of Balanus glandula may improve their success as invaders and contribute to their rapid expansion along new shores.