A global invader or a complex of regionally distributed species? Clarifying the status of an invasive calcareous tubeworm Hydroides dianthus (Verrill, 1873) (Polychaeta: Serpulidae) using DNA barcoding

Clarifying taxonomic status is essential to understanding invasion source and the spread of invasive species. Here we used barcoding gene cytochrome c oxidase subunit I to explore the issue in a common fouling invasive species Hydroides dianthus . The species was originally described from off New England, USA, reported along the east coast of North America down to Florida and the Caribbean region, introduced to China, Europe, Japan and West Africa via anthropogenic transport and is now collected in Brazil for the first time. Unlike most congeners, H. dianthus has tolerance for a wide temperature range, being distributed from temperate to subtropical waters. Our results based on 112 specimens collected from 17 localities worldwide confirmed that H. dianthus sensu stricto is indeed a global invader. Observed higher haplotypes diversity in the Mediterranean seems to contradict the currently accepted native range of H . dianthus sensu stricto in the USA. The study also revealed the existence of a potential cryptic species H . cf. dianthus with a genetic distance of 5.6%. The cryptic lineage found in Texas was evidently introduced to the Black Sea only recently. Given that both lineages within H. dianthus are invasive, a greater emphasis on adequate monitoring and management of the routes responsible for introductions of this species is needed.