Fine-scale determinants of conservation value of river reaches in a hotspot of native and non-native species diversity

Global freshwater biodiversity is declining at unprecedented rates while non-native species are expanding. Examining diversity patterns across variable river conditions can help develop better management strategies. However, many indicators can be used to determine the conservartion value of aquatic communities, and little is known of how well they correlate to each other in making diagnostics, including when testing for the efficacy of protected areas. Using an extensive data set (99,700km2, n=530 sites) across protected and unprotected river reaches in 15 catchments of NE Spain, we examine correlations among 20 indicators of conservation value of fish communities, including the benefits they provide to birds and threatened mammals and mussels. Our results showed that total native fish abundance or richness correlated reasonably well with many native indicators. However, the lack of a strong congruence led modelling techniques to identify different river attributes for each indicator of conservation value. Overall, tributaries were identified as native fish refugees, and nutrient pollution, salinization, low water velocity and poor habitat structure as major threats to the native biota. We also found that protected areas offered limited coverage to major components of biodiversity, including rarity, threat and host-parasite relationships, even though values of non-native indicators were notably reduced. In conclusion, restoring natural hydrological regimes and water chemical status is a priority to stem freshwater biodiversity loss in this region. A complementary action can be the protection of tributaries, but more studies examining multiple components of diversity are necessary to fully test their potential as fluvial reserves in Mediterranean climate areas.We are grateful to people who assisted in the field and to the laboratory of GIS and Remote Sensing at Doñana Biological Station (LAST-EBD) for providing data on protected areas. We also thank Josep EscribanoAlacid (The ‘Museu Blau’- Natural History Museum of Barcelona) and Dr. Francesc Oliva (Department of Statistics, UB) for useful discussion and two anonymous reviewers for their constructive review. AMV was funded by the Severo Ochoa Program for Centres of Excellence in R + D + I (SEV-2012-0262). We also thank ‘Agència Catalana de l'Aigua (ACA)’ and ‘Confederación Hidrográfica del Ebro (CHE)’ for funding support. This study was also partially supported by 'la Fundació Barcelona Zoo i l'Ajuntament de Barcelona', the Spanish Ministry of Economy and Competitiveness and FEDER projects (CGL2013-43350-P and CGL2015-65346-R).