Aim Non-indigenous species pose a significant threat to the environment and to global economies. Predictive and preventative measures are widely considered more effective in curtailing invasions than are eradication or control measures. Of key importance in the prediction of regional invasion risk are the environmental conditions that enable successful establishment.
Location We surveyed native and non-indigenous sessile invertebrate diversity in each of two commercial (600–1500 vessels per year) and two recreational estuaries (seven to nine marinas) in New South Wales, Australia.
Methods A nested hierarchical design was employed to investigate variation in sessile invertebrate diversity at the scales of site (1–3 km apart) and estuary (40–180 km apart). Settlement plates (15 × 15 cm) were used to sample invertebrates and background heavy metal loads were assessed using bioaccumulation in experimentally deployed oysters. Other physico-chemical variables were monitored monthly. Manipulative experiments were used to test the direct effects of exposure to copper and tributyltin (TBT) antifouling paints on sessile invertebrates.
Results Native and non-indigenous species richness differed at various spatial scales, but showed no consistent difference between commercial and recreational estuaries. Instead, individual species distributions were strongly related to metal contamination, temperature, turbidity and pH. In experimental studies, several species (mostly invaders) were more abundant on plates exposed to copper and/or TBT antifouling paints. We found higher levels of copper (and in some instances TBT) in recreational marinas than in commercial harbours.
Main conclusions Our results demonstrate the importance of metal pollution and physico-chemical variables in the establishment of invaders in new regions. We have identified several native Australian species that have been exported overseas and suggested mechanisms contributing to their transport and establishment. Combining physico-chemical information about donor and recipient regions with species tolerances could go some way to predicting where future invasions may occur.