Tolerance of native and non-native fish species to chemical stress: a case study for the River Rhine

Freshwater ecosystems can be impacted by invasive species. Non-native species can become invasive due to their high tolerance to environmental stressors (e.g., pollution and habitat modifications). Yet, tolerance of native and non-native fish species exposed simultaneously to multiple chemical stressors has not been investigated. To quantify tolerance of native and non-native fish species in the Delta Rhine to 21 chemical stressors we derived Species Sensitivity Distributions (SSDs). Differences in tolerance between the two species groups to these stressors were not statistically significant. Based on annual maximum water concentrations of nine chemical stressors in the Delta Rhine the highest contribution to the overall Potentially Affected Fraction (PAF) of both species groups was noted for ammonium, followed by azinphos-methyl, copper, and zinc. PAFs of both groups for metals and ammonium showed a significant linear decrease over the period 1978-2010. Deriving a PAF for each species group was a useful tool for identifying stressors with a relatively highest impact on species of concern and can be applied to water pollution control. Species traits such as tolerance to chemical stress cannot explain the invasiveness of some fish species. For management of freshwater ecosystems potentially affected by non-native species, attention should be given also to temperature, hydrological regimes, and habitat quality.