Accelerating rates of freshwater invasions in the catchment of the River Thames

We identify a total of 96 freshwater non-indigenous species established in the River Thames catchment, England; of which 55 % were introduced intentionally. Our analysis shows that 53 % of the species became established in the last 50 years and invasion rates have significantly increased since 1800. Analysis of shipping activity and population size in the catchment area revealed a positive correlation with non-indigenous species discovery, suggesting that globalisation has facilitated many species invasions. Our calculated modern (post 1961) invasion rates reveal that one non-indigenous species is discovered every 50 weeks, despite legislation aiming to prevent introductions, making the Thames catchment among the most highly invaded freshwater systems in the world. Although sympatric invaders are expected to interact and alter one another's impact, most studies focus on individual conspicuous invaders. Our results indicate that it is essential to comprehend multiple invasions in future work.