The faunal Ponto-Caspianization of central and western European waterways

As alien invasive species are a key driver of biodiversity loss, understanding patterns of rapidly changing global species compositions depends upon knowledge of invasive species population dynamics and trends at large scales. Within this context, the Ponto-Caspian region is among the most notable donor regions for aquatic invasive species in Europe. Using macroinvertebrate time series collected over 52 years (1968–2020) at 265 sites across 11 central and western European countries, we examined the occurrences, invasion rates, and abundances of freshwater Ponto-Caspian fauna. We examined whether: (i) successive Ponto-Caspian invasions follow a consistent pattern of composition pioneered by the same species, and (ii) Ponto-Caspian invasion accelerates subsequent invasion rates. In our dataset, Ponto-Caspian macroinvertebrates increased from two species in 1972 to 29 species in 2012. This trend was parallelled by a non-significant increasing trend in the abundances of Ponto-Caspian taxa. Trends in Ponto-Caspian invader richness increased significantly over time. We found a relatively uniform distribution of Ponto-Caspian macroinvertebrates across Europe without any relation to the distance to their native region. The Ponto-Caspian species that arrived first were often bivalves (46.5% of cases), particularly Dreissena polymorpha, followed secondarily by amphipods (83.8%; primarily Chelicorophium curvispinum and Dikerogammarus villosus). The time between consecutive invasions decreased significantly at our coarse regional scale, suggesting that previous alien establishments may facilitate invasions of subsequent taxa. Should alien species continue to translocate from the Ponto-Caspian region, our results suggest a high potential for their future invasion success highly connected central and western European waters. However, each species’ population may decline after an initial ‘boom’ phase or after the arrival of new invasive species, resulting in different alien species dominating over time.
This study was supported by the Grant Agency of the University of South Bohemia, project number 065/2022/Z. R.N.C. acknowledges funding from the Leverhulme Trust Early Career Fellowship (ECF-2021-001). We also acknowledge Flanders Environment Agency for providing the publicy available data. P.H. and P.J.H. received funding from the EU Horizon 2020 project eLTER PLUS (Grant Agreement No. 871128). NB and MC were supported by the Serra-Hunter programme (Generalitat de Catalunya). MC was also supported by a Ramón y Cajal contract funded by the Spanish Ministry of Science and Innovation (RYC2020-029829-I). NB was also supported by the H2020 European Research and Innovation action Grant Agreement no. 869226 (DRYvER). The FEHM (Freshwater Ecology, Hydrology and Management) research group (to which NB and MC belong) was funded by the “Agència de Gestió d’Ajuts Universitaris i de Recerca” (AGAUR) at the "Generalitat de Catalunya” (2017SGR1643). BG was funded through the 2017–2018 Belmont Forum and BIODIVERSA joint call for research proposals, under the BiodivScen ERANet COFUND programme, funded through the Spanish State Research Agency (MCI/AEI/FEDER, UE, PCI2018-092986).