Disentangling invasions in the sea: molecular analysis of a global polychaete species complex (Annelida: Spionidae: Pseudopolydora paucibranchiata)

The spionid polychaete Pseudopolydora paucibranchiata (Okuda, 1937) was originally described from Japan and has since been reported as a non-indigenous species in soft bottom communities in the Northeast Pacific, the Mediterranean Sea, around Europe, Australia, Brazil, and Florida. The diagnostic features of the adults are palps with ramified yellow chromatophores, prostomium rounded anteriorly, short occipital antenna on the caruncle, and a small disc-like pygidium. We collected Pseudopolydora with these features from locations worldwide and compared them by a molecular analysis. The Bayesian analysis of the combined dataset of three genetic markers (mitochondrial 16S rDNA, nuclear 28S rDNA and Histone 3 ; 811 bp in total) showed that the worms form a monophyletic group comprising four genetically different clades. We name this group the P. paucibranchiata complex and consider the clades as four pseudocryptic species. The largest examined clade comprises individuals from the Pacific Canada (British Columbia), Russia (Sea of Japan), South Korea (East Sea), Italy (Tyrrhenian and Ionian Seas), Australia (Victoria), Netherlands, and Japan, which we identify as P. paucibranchiata . The morphology, reproductive biology and ecology of P. paucibranchiata are briefly reviewed. The other three clades are referred to as Pseudopolydora vexillosa Radashevsky and Hsieh, 2000 (Vietnam, Nha Trang Bay), Pseudopolydora sp. A (Australia, Northern Territory), and Pseudopolydora sp. B (Kuwait, Arabian Gulf). We explain the occurrence of P. paucibranchiata outside of the Northwest Pacific by unintentional human-mediated transportation in ballast water and/or with commercial oyster movements in aquaculture operations, followed by successful invasions.