A multi-criteria approach to identify priority regions for freshwater biodiversity conservation

Area-based conservation requires identifying priority areas, but guidance on which ecological criteria to use and how these criteria influence perceived conservation priorities is limited. To assess the sensitivity of spatial prioritization to such decisions, we used three ecological concepts (irreplaceability, taxonomic representativeness, and vulnerability) to create five conservation prioritization strategies (three proactive, one reactive, and one representative). We applied these to prioritize areas for freshwater fish and mussel diversity in Southwestern Ontario, a region with rich freshwater biodiversity and high anthropogenic pressures. Prioritization differed based on the strategies. The proactive 1 strategy, focusing only on vulnerability, identified sub-basins with the lowest diversity, offering limited biodiversity benefits. Conversely, high-priority sub-basins in reactive and proactive (2 and 3) strategies provided similar conservation value, containing similar richness of at-risk species. Sub-basin prioritization varied depending on whether a single-taxon or multi-taxon approach was used, yet overall biodiversity representation was similar. Current protected area coverage, protecting only 0.36% of the region, is inadequate to offer protection to freshwater species. Our findings suggest that implementing conservation measures in sub-basins identified by proactive strategies can maximize gains across multiple taxa, outperforming commonly used single-species strategies.