Spatial priorities for freshwater biodiversity conservation in light of catchment protection and connectivity in Europe

the match between priority and protection in three ways (classification of catchments into four groups of high/low priority and protection, calculation of residual priority from a regression of priority over protection, estimation of the deviation from an ideal perfect match between pri- ority and protection), our approach thus avoids arbitrary decisions on priority and protection levels, and potential biases arising from using only the top-priority or the best-protected areas. Finally, it provides bench-marked information on the correspondence between priority and protection in each catchment, which will be of interest for conservation policy and practice. In conclusion, our results draw attention to the high priority of catchments in southern Europe, particularly in the Balkans, and in eastern Europe, particularly in southern Ukraine and Russia, and to karst/limestone areas in the conservation of freshwater biodiversity of Europe. These results are directly applicable in European, regional and local conservation efforts and provide a basis for potential future refinements. Two such potential refinements include restricting the prioritization to protected areas designated specifically for freshwater biodiversity, and implementing a spatial constraint on the proportion of area that can be selected in each ecoregion or country to distribute conservation effort more evenly across Europe. Similar continental-scale assessments based on ecologically meaningful planning units and data from terrestrial and marine biodiversity can greatly improve the efficiency of

the allocation of international conservation effort. Supporting information S1 File. (DOC) Author Contributions Conceptualization: Ma´rton Szabolcs, Jo¨rg Freyhof, William R. T. Darwall, Szabolcs Lengyel. Formal analysis: Ma´rton Szabolcs, Szabolcs Lengyel. Funding acquisition: Jo¨rg Freyhof, William R. T. Darwall. Investigation: Ma´rton Szabolcs, Felı´cia Kapusi, Savrina Carrizo, Danijela Markovic, William R. T. Darwall, Szabolcs Lengyel. Methodology: Ma´rton Szabolcs, Felı´cia Kapusi, Danijela Markovic, Nu´ria Cid, Mathias Scholz, Hans D. Kasperidus, Szabolcs Lengyel. Project administration: Jo¨rg Freyhof, William R. T. Darwall. Resources: Savrina Carrizo, Jo¨rg Freyhof, Nu´ria Cid, Ana Cristina Cardoso. Visualization: Szabolcs Lengyel. Writing – original draft: Ma´rton Szabolcs, Szabolcs Lengyel. Writing – review & editing: Ma´rton Szabolcs, Felı´cia Kapusi, Savrina Carrizo, Danijela Mar- kovic, Jo¨rg Freyhof, Nu´ria Cid, Ana Cristina Cardoso, Mathias Scholz, Hans D. Kasperidus, William R. T. Darwall, Szabolcs Lengyel. References 1. Strayer DL, Dudgeon D. Freshwater biodiversity conservation: recent progress and future challenges. J N Am Benthol Soc. 2010; 29: 344–358. https://doi.org/10.1899/08-171.1 2. Postel SL Carpenter S. 1997. Freshwater ecosystem services In: Daily GC, editor. Nature’s Services. Washington DC: Island Press; 1997. pp.195–214. PLOS ONE Spatial priorities for freshwater biodiversity in Europe PLOS ONE | https://doi.org/10.1371/journal.pone.0267801 May 17, 2022 12 / 15