Cryptic invasion of northeast Pacific estuaries by the Asian polychaete, Hediste diadroma (Nereididae)

Abstract

The estuarine polychaete, Hediste diadroma (Nereididae), of eastern Asia was found at all six sites sampled in October 2009 in northeast Pacific estuaries, including the Columbia River, along a 300-km stretch of coastline in Washington and Oregon, USA. The immature worms were returned to the laboratory in Japan where 13 of them were cultured to sexual maturity after 5–7 months. These worms had the diagnostic, epitoke-specific spinigers that distinguish H. diadroma from all other Hediste species. Their egg sizes (140–170 μm), paragnath numbers on the proboscis, and chromosome number (2n = 28) were also consistent with those previously reported for the Japanese population of H. diadroma. The widespread distribution of H.diadroma indicates that it is a successful invader of the North American Pacific and it may have long escaped detection because of its morphological similarity to the native species, H. limnicola. The long pelagic life of H.diadroma larvae could have facilitated its successful trans-ocean dispersal with ballast water of ships.