Preliminary analyses suggest that the number and impact of non-indigenous species (hereafter NIS) are lower in Chilean marine environments than on other shores in the northern and southern hemispheres. Three non-exclusive hypotheses have been proposed to explain the apparent low number of NIS on the coast of Chile: (1) low propagule pressure, (2) biotic resistance, and (3) abiotic resistance. In this study we use boring polychaete species in native and exotic hosts as a study model for evaluating the patterns and processes of exotic species introduction to Chile’s marine systems. We quantified the occurrence of native and exotic polychaete infestation in invertebrates with calcareous shells within aquaculture facilities of the exotic mollusks, Crassostrea gigas and Haliotis spp., as well as in natural environments near to these facilities. We use ANOVA to assess differences in polychaete richness and abundance in native assemblages inside and outside aquaculture centers. Null model analyses of co-occurrence and analyses of similarity were used to evaluate whether polychaete assemblages were structured by competitive interactions between native and NIS polychaetes. Abiotic resistance was examined by evaluating the effect of sea temperature (average, minimum, maximum and coefficient of variation) on the abundance of polychaetes in natural communities.
Results/Conclusions
Our results indicate that aquaculture centers are a source of NIS polychaetes to natural communities, where NIS polychaetes infest a variety of different native invertebrate species. Although abundance of NIS polychaetes is lower outside aquaculture centers, dispersal limitation was not observed at the spatial scale of this study (500 meters) given that even at the furthest analyzed distances NIS polychaetes were present in natural assemblages. In contrast, native polychaete abundance did not differ inside and outside centers. We found evidence of biotic resistance through competition between native and NIS polychaetes. Polychaete assemblages in native hosts near aquaculture facilities were highly structured by competition, while exotic oyster host assemblages were not structured. Although polychaete richness did not differ between host types, NIS polychaetes were more abundant in native hosts. We did not find evidence of abiotic resistance of NIS polychaetes in relation to temperature, rather NIS polychaetes appear to tolerate a wider range of thermal conditions than native polychaetes, and present greater abundances at higher temperatures. Contrary to initial findings, Chilean marine communities are susceptible to NIS introductions. Studies in more pristine environments will determine the extent of influence of anthropogenic activities on patterns of NIS introduction in native communities.
