Global population structure of the Atlantic blue crab Callinectes sapidus reveals multiple introductions into North African waters

Abstract

20 The Atlantic blue crab, Callinectes sapidus, is globally recognized as one of the world's most 21 important invasive marine species. Its recent expansion beyond its native range has reshaped 22 estuarine and coastal ecosystems across multiple regions, particularly along the Mediterranean 23 and Eastern Atlantic coasts, with substantial ecological and economic impacts. This study 24 presents the first comprehensive genetic characterization of C. sapidus populations along the 25 Mediterranean and the eastern Atlantic, where the species has been introduced. It integrates 26 newly collected mitochondrial COI (cytochrome c oxidase subunit I) sequences with global 27 datasets to clarify its population structure and invasion pathways. To elucidate population 28 patterns, we performed genetic diversity analyses, constructed haplotype networks, and carried 29 out demographic assessments. Incorporating all COI sequences currently available enabled a 30 global assessment of the species' global population structure and invasive pathways. The 31 results revealed high genetic variation within Moroccan populations and suggest multiple 32 introduction events from the native range specifically from the eastern coast of North America. 33 Comparative analyses with native and other non-native populations highlight complex invasion 34 dynamics and suggest ongoing gene flow within invasive regions. The pronounced genetic 35 differentiation in its native range across the North and South American coasts is consistent with 36 patterns observed in other widely distributed marine crustaceans. In the introduced range, local 37 population dynamics, founder effects, and repeated introduction events appear to be key drivers 2 38 of genetic differentiation. Future work integrating genomic, ecological, and environmental data 39 will be essential for fully understanding the mechanisms driving the successful establishment 40 and spread of marine crustaceans in new environments, thereby contributing to a broader 41 understanding of how marine species expand and persist across coastal systems. 42 Keywords 43 coastal invasion, Morocco, multiple introductions, establishment, global population structure 44