Atlantic blue crab Callinectes sapidus Rathbun, 1896 (Portunidae, Malacostraca) could lead to local extinction of few endemic freshwater species in the Eastern Morocco

The protected area of the Moulouya River mouth, also known as a SIBE (Site of Biological and Ecological Interest), is one of the most important and vulnerable freshwater reserves in the southern Mediterranean. This site is characterized by a wide variety of habitats that support rich aquatic biodiversity with a high degree of endemism. It was also one of the first wetlands in Morocco to be invaded by the marine and invasive American blue crab, Callinectes sapidus Rathbun, 1896, following its initial establishment in the Marchica Lagoon. Since its first detection in 2019, the blue crab has been expanding its range upstream in the Moulouya River, now reaching areas home to some of the last populations of endemic and patrimonial species in Eastern Morocco. In this paper, we compare the abundance of certain patrimonial species in the Moulouya SIBE before and after the arrival of the blue crab, focusing on the Moroccan endemic freshwater mussel Unio foucauldianus Pallary, 1936, and the freshwater crab Potamon algeriense Bott, 1967. We observed a complete disappearance of these species in certain areas of the lower Moulouya, which could likely be attributed to predation by the blue crab. The predation and migration behaviour of the blue crab in the Moulouya River aligns with what has been described in the literature for its non-native range.