Analysis of potential distribution and impacts for two species of alien crabs in Northern Europe

The Asian shore crab (Hemigrapsus sanguineus) and the brush-clawed shore crab (H. takanoi) both originate from east Asia but have in recent years established viable populations throughout coastal European waters. The two species are highly competitive and can occur in very high densities. Both species have been linked to the decrease of otherwise abundant native species such as the European shore crab (Carcinus maenas) and the common periwinkle (Littorina littorea). As both crabs are relatively new in European coastal waters, little is known about the full distribution range that may be achieved by these crabs and the ecological impact that may follow with an invasion of coastal habitats. In this study we investigated the potential distribution of Hemigrapsus in coastal waters of Northern Europe and the potential impact on the native competitor C. maenas. To this end we collected crabs on the Swedish west coast and on Helgoland and used these for behavioural experiments. We also collected new observation records of both species in Sweden and used these occurrences for building ecological niche models. We report that the potential distribution range of both H. sanguineus and H. takanoi extends from western Sweden to eastern Ireland (east–west) and southern Norway to western France (north–south). We also found evidence that H. takanoi can establish viable populations in nutrient-rich inshore areas of the western and southern Baltic Sea and that competition by H. sanguineus is likely to affect abundances of C. maenas in the areas where these species co-occur.