Data for Euryhalinity of Ponto-Caspian invaders in their native and introduced regions

In the past decades, Ponto-Caspian species established in freshwater and brackish habitats of the North and Baltic Sea and Great Lakes-St. Lawrence River region in much higher numbers than expected based on introduction effort (i.e. shipping frequency) and environmental conditions between these regions. Several studies suggested that Ponto-Caspian taxa are euryhaline and might be able to adapt rapidly to changing salinity conditions, and therefore might be more successful colonizers than species from other regions. To determine the realized niche in the native and introduced habitats of Ponto-Caspian invaders and to assess whether they expanded their salinity tolerance during the invasion process, we conducted a literature search to assess the salinity ranges of 55 Ponto-Caspian species in their native and introduced region. Our results confirmed that the majority of those species occupied a wide range of salinity in their native and introduced habitats. Approximately 50 % of the species were reported from both freshwater and brackish habitats (0-18 PSU) in their native region, occupying a salinity range of at least 10 PSU difference. In general, the number of species tended to decline as salinity increased in both native and introduced habitats. More than 90 % of the Ponto-Caspian invaders occupied freshwater (0-0.5 PSU) habitats, while 18 % did not occur above 18 PSU. Due to the limitation of our dataset, we were not able to confirm shifts in salinity tolerance during the invasion process. However, as our results suggest that the majority of the Ponto-Caspian invaders occupy freshwater and brackish habitats in their native region, the recent numerous invasions of freshwater and brackish areas by those species should not be a surprise. Therefore, managers and policy makers should take into account that the majority of Ponto-Caspian invaders originate from fresh water or low salinities and develop new regulations to prevent future invasions from the Ponto-Caspian region, as well as from areas highly invaded by Ponto-Caspian taxa such as Northern Europe.