Genetic structure and parasite diversity of the invasive Atlantic blue crab Callinectes sapidus in Moroccan coastal ecosystems

Abstract

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 components of the marine environment and fisheries. Carcinus 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 effects on the native fauna and ecosystem balance, particularly with respect to parasite-associated diseases, alongside its impact on fisheries and native crustacean populations. The main objectives of this study are to determine the origin and structure of Moroccan populations of C. sapidus, track their introduction pathways, and investigate the diversity of parasites. Knowledge about the symbionts associated with these populations will enable us to assess their effects on native biodiversity and associated marine diseases. Overall, 110 specimens of C. sapidus from Morocco were analyzed, including 30 from the Marchica Lagoon (Mediterranean coast), and 80 specimens from the Atlantic coast (30 from Merja Zerga Lagoon, 30 from Sidi Moussa Lagoon, and 20 from Oualidia Lagoon). Molecular analyses were performed on a 572 bp fragment of the Cytochrome c oxidase subunit 1 (COI) marker. Comparison with previously published sequences from both native and non-native areas revealed a high genetic variation within Moroccan C. sapidus populations, suggesting multiple introduction events from the native range in the eastern coast of North America, rather than a single colonization. Comparative analyses further suggested ongoing gene flow between regions. These results provide key insights into introduction pathways and potential sources of parasite co-introduction.

To assess parasite diversity, 165 crab specimens (C. sapidus, C. maenas, A. tangeri) from Merja Zerga were examined through screening of hemolymph and various internal organs. Hematodinium sp., a parasitic dinoflagellate of major concern in crustacean health, was detected in all three species. Haplotype network analysis revealed a central haplotype shared by Hematodinium among multiple crab hosts and locations in Moroccan coastal lagoons. However, parasite community composition and infection levels differed markedly between hosts. Callinectes sapidus showed the highest overall parasite diversity and the lowest Hematodinium prevalence, additionally harboring digenean trematodes and microsporidians that were absent in A. tangeri. In contrast, C. maenas exhibited the highest prevalence of Hematodinium, with only occasional haplosporidian infection. A. tangeri ranked intermediate, presenting moderate haplosporidian and Hematodinium infections, but lacking trematodes and microsporidians. Preliminary results suggest potential parasite exchange between native and invasive hosts, spillback risk, and possible implications for marine disease transmission affecting native biodiversity and fisheries. Results of the project emphasize the need for ongoing genetic surveillance and coordinated management efforts to mitigate the ecological and socio-economic impacts of C. sapidus invasion in the studied region. Future research should focus on expanding sampling to additional sites following the non-native distribution range of C. sapidus and integrating nuclear markers for a more comprehensive understanding of invasion dynamics.