Freshwater conservation assessments in (semi-)arid regions: Testing river intermittence and buffer strategies using freshwater mussels (Bivalvia, Unionida) in Morocco

Abstract

The IUCN Red List assessments are essentially based on population trends and range, namely Area of Occupancy (AOO) and Extent of Occupancy (EOO). Range estimations are based on fixed grids, but this is likely inappropriate for species living in river networks. Furthermore, AOO and EOO are measured using the whole hydrographic network, therefore disregarding temporary sections, which is particularly problematic in arid and semi-arid regions. Here we mapped the permanent hydrographic network of Morocco using satellite imagery, complemented with field surveys to collect samples for molecular analyses of the five freshwater mussel species present and assess their distribution. The phylogeographic patterns are described for each species and used to identify priority areas and evolutionary significant units for conservation. Permanent hydrographic river sections represent only 18.3% of the whole hydrographic network. A north-to-south gradient of genetic diversity, species richness and distribution range was found, being coherent with water availability and river intermittence. Isolated evolutionary units were detected in southern basins that should also receive particular attention in conservation planning. We propose the mean river width multiplied by the extent of the river network as the best and the most adequate way to estimate both EOO and AOO. Given the worldwide degradation of freshwater systems and biodiversity, an accurate (re)assessment of species conservation status supported with maps of intermittent water bodies will be essential for prioritizing and guiding conservation actions and management plans, especially in arid and semi-arid regions.