Parasites of the invasive Atlantic Blue Crab Callinectes sapidus and native crabs Carcinus maenas and Afruca tangeri in Merja Zerga Lagoon, Moroccan Atlantic coast

Crustaceans play a fundamental role in the structure and functioning of coastal ecosystems. Their health is closely linked to that of local biodiversity and human activities. In Morocco, the native species Carcinus maenas and Afruca tangeri are crucial to the marine environment and fisheries. C. maenas plays a key role in regulating benthic communities by preying on various invertebrates, thereby maintaining ecological balance. Meanwhile, A. tangeri contributes to sediment stabilization and bioturbation, which enhances nutrient cycling and supports the productivity of local fisheries. Since 2017, the non-native Atlantic blue crab Callinectes sapidus has been introduced to Moroccan coastal waters, raising concerns about its ecological effects, particularly with respect to parasite-associated diseases, alongside its impact on fisheries and native crustacean populations. This study analyzes the presence of the parasites of C. sapidus and native crab species, namely C. maenas and A. tangeri in Merja zerga Lagoon, Moroccan Atlantic coast. The objective is to test the enemy release hypothesis and to check for parasite spillover or spillback events. A total of 120 specimens of C. sapidus, 15 of C. maenas, and 30 of A. tangeri were collected and dissected. The hemolymph of each specimen was examined for the presence of Hematodinium sp., a parasitic dinoflagellate known to cause diseases in crustaceans. Additionally, the organs (hepatopancreas, gills, heart, stomach, and thoracic ganglion) were crushed and examined under a compound microscope to identify other parasites. Preliminary results revealed the presence of Hematodinium in the hemolymph of all three crab species. Additionally, C. sapidus was found to harbor digenean trematodes and microsporidians, while C. maenas and A. tangeri contained haplosporidians, and amoebae and ciliates were observed in C. maenas. Ongoing molecular analysis will help understanding whether the blue crab carries new parasites into Moroccan ecosystems, potentially leading to increased disease transmission or ecological disruption. The results of this study will provide critical insights into the potential risks posed by the bioinvasion of C. sapidus.