Presence of a second Eriocheir species in Europe as confirmed by molecular and morphological data

New Chinese mitten crab sequence data were obtained from eight European localities spanning France, The Netherlands, England and Wales. The Netherlands and Wales samples were taken from two areas where mitten crab populations had never before been sequenced. DNA results uncovered the presence of a second Eriocheir species coexisting sympatrically with E. sinensis H. Milne Edwards, 1853 in the Dee Estuary, Wales and at two sites sampled in The Netherlands. Molecular results and comparative morphology analyses suggest that the second species in European waters is likely to be an undescribed cryptic species. Additional evidence for the presence of a second European invasive mitten crab species is provided by confocal laser scanning microscopy of the male first gonopod. The origins of the Welsh introduction may date back to the early 2000s, when several Dutch dredging operators were active in the Dee Estuary. Despite several localities being sampled, the Eriocheir cryptic species was not found in England, which suggests that English and Welsh mitten crab populations originate from independent introductions. These results radically challenge current assessments of Eriocheir invasion in Europe and should be considered by stakeholders as a new baseline to implement efficient management strategies against invasive mitten crabs