Abstract

Understanding the mechanisms that determine invasion success requires evaluating both abiotic constraints and biotic interactions acting on introduced species. In this study we analyzed the role of environmental filtering, understood as the capacity of organisms to tolerate physical conditions such as temperature and oxygen availability, and biotic resistance, defined as the effects of native consumers in limiting establishment. These processes were evaluated in two solitary ascidians, Corella eumyota (Phlebobranchia: Corellidae) and Asterocarpa humilis (Stolidobranchia: Styelidae), collected from settlement plates deployed at approximately 1 m depth in Coliumo Bay (36 degrees 32 ' S, 72 degrees 56 ' W), central Chile. Both species exhibited broad thermal tolerance, maintaining survival between 12 and 20 degrees C, tolerating cooling to 4 degrees C, and showing mortality at 24 degrees C. They also displayed high resistance to hypoxic conditions, with critical oxygen tension (Pcrit) values of 0.64 +/- 0.35 kPa for Corella eumyota and 2.01 +/- 0.74 kPa for Asterocarpa humilis, indicating physiological capacity to persist in low oxygen environments. Predation assays conducted with native consumers observed in the plates revealed contrasting effects, as the crab Romaleon setosum consumed a high proportion of individuals, whereas the fish Hypsoblennius sordidus showed limited consumption. Adult ascidians were used in the experiments, allowing the assessment of local consumers to prey on settled organisms rather than early life stages. Overall, the results indicate that invasion success in these ascidians emerges from the combined action of broad physiological tolerance that enables persistence under broad environmental conditions and context dependent biotic resistance that may limit their expansion into adjacent natural habitats.