First record of the non-native colonial ascidian Botrylloides diegensis (Ascidiacea, Stolidobranchia) in the Southwestern Atlantic

A simultaneous and periodical sampling for non-native species was carried out in two ports of Argentina, Mar del Plata and Puerto Madryn. In this context, the first record of genus Botrylloides for Argentina and the species Botrylloides diegensis Ritter & Forsyth, 1917 for the Southwestern Atlantic is reported, identified by morphological and molecular analyses. Based on our results and previous studies, it is confirmed that B. diegensis is a recently introduced species, which might have been introduced from the English Channel or Japan according to the mitochondrial cytochrome oxidase I haplotype found in the specimens studied. Moreover, mature zooids and larvae were observed during summer in and outside the port area. These observations and the diversity of one- and two-color morphotypes found in both sites confirmed that it is an established species in Argentina. The sampling performed here allows the simultaneous identification of the species in two of the most important ports of Argentina and, because of the 50 years of knowledge of the fouling communities of the area, its classification as a non-native established species. Further studies are needed to predict the risk of expansion of B. diegensis along the coast of the Southwestern Atlantic and to other regions in the Southern Hemisphere.