Assessing and conserving groundwater biodiversity: synthesis and perspectives

Summary 1. This paper is a synthesis of a special issue on groundwater biodiversity with a focus on obligate subterranean species, the stygobionts. The series of papers constitutes a great leap forward in assessing and understanding biodiversity patterns because of the use of large quantitative data sets obtained over a broad geographic scale. They also represent a conceptual shift, away from a purely taxonomic and phylogenetic focus to the analysis of whole groundwater assemblages. 2. The general patterns emerging for groundwater fauna are: very high levels of endemism, low local diversity relative to regional diversity, a limited number of lineages, occurrence of many relicts, and truncated food webs with very few predators. 3. β‐Diversity is at least as important as α‐diversity in determining total richness at different scales (aquifer, basin and region) and overall taxa richness increases across spatial scales. 4. Advances in understanding groundwater biodiversity patterns further include identification of several important factors related to geology and hydrology that determine the composition of European stygobiotic assemblages. 5. Important challenges for future research include improving sampling strategies, filling gaps in sampling coverage, intensifying research on theoretical and statistical models, and including functional and genetic diversity components in biodiversity assessments. 6. Strategies are proposed for protecting groundwater biodiversity and an argument is made to integrate biodiversity in groundwater management. Applying principles such as complementarity and flexibility for groundwater biodiversity conservation is a major step toward delineating a reserve network that maximise species representation at the European scale.