First evidence of establishment of the rayed pearl oyster, Pinctada imbricata radiata (Leach, 1814), in the eastern Adriatic Sea.

The Mediterranean Sea is increasingly under threat from invasive species that may negatively affect biodiversity and/or modify ecosystem structure and function. The bivalve mollusc Pinctada imbricata radiata is listed among the 100 most invasive species in the Mediterranean. A first finding of an established population of P. imbricata radiata in the coastal waters of the eastern Adriatic Sea, is presented in this paper. Six and then 30 live specimens were collected in 2015 and in 2017, respectively, at depths of 5 to 15 m from the island of Mljet, Croatia. DNA sequencing of the mitochondrial cytochrome c oxidase I gene (COI) revealed three different haplotypes. All samples showed greatest similarity (98 to > 99%) to P. radiata COI sequence records in GenBank (= P. imbricata radiata as used in this paper). A Neighbour Joining tree placed all Croatian samples within the 100% bootstrap supported clade for P. imbricata radiata . [ABSTRACT FROM AUTHOR]