Hotspot of Exotic Benthic Marine Invertebrates Discovered in the Tropical East Atlantic: DNA Barcoding Insights from the Bijagós Archipelago, Guinea-Bissau

Aim: This study aimed to explore and document putative exotic marine benthic invertebrate species in the Bijagós Archipelago, Guinea-Bissau, to enhance understanding of marine biodiversity and address the extent of marine species introductions. Location: The research was conducted in the Bijagós Archipelago, a UNESCO Biosphere Reserve located in Guinea-Bissau. Methods: The study involved the region's first scuba-diving survey of marine biodiversity. DNA barcoding was employed to assist in the identification of benthic invertebrate species. Molecular phylogenetic analyses were conducted with the available DNA barcodes to ensure accurate taxonomic assignments, detect cryptic species, and investigate the phylogeography of the taxa. Results: The survey resulted in the discovery of 28 new species records for the Bijagós Archipelago, including octocorals, scleractinians, hydroids, bryozoans, barnacles, and ascidians. Among these, seven species were documented for the first time in the East Atlantic: Stragulum bicolor, Tubastraea tagusensis, Nemalecium lighti, Diphasia sp., Amathia alternata, A. distans, and Symplegma rubra. Molecular analyses revealed pervasive cryptic diversity within species previously listed as exotic, suggesting that some, such as the hydroids Plumularia setacea, Obelia geniculata, and Dynamena disticha, are not exotic due to their restricted biogeographic distributions. Many other species reported as introduced present only a few genetic lineages capable of long-distance dispersal due to human activities. Main Conclusions: The study highlights considerable gaps in the knowledge of West African marine biodiversity and suggests a substantial underestimation of the anthropogenic trade in exotic marine species between the Tropical East Atlantic and the Americas, and between the Indo-Pacific and West Africa. Detailed taxonomic and genomic analyses are necessary for understanding marine exotic species' biogeography and adaptive traits. Our findings challenge current classifications of exotic species and underscore the need for improved monitoring and management to prevent the spread of non-native marine species.