Asian Shore Crabs Hemigrapsus spp. (Crustacea: Brachyura: Grapsoidea) Continue Their Invasion around the Cotentin Peninsula, Normandy, France: Status of the Hemigrapsus Population in 2009

This paper reports on the state of the Asian shore crab Hemigrapsus sanguineus (de Haan, 1835) population around the Cotentin Peninsula (Normandy, France) for 2009. As in 2008, the year of the first survey, the northern and eastern Cotentin coasts remain the most densely colonised. On the western shore, H. sanguineus remains rare, except in two sites not surveyed in 2008. In the east most colonised sites, Gatteville-Phare and La Hougue, the populations for both years indicate a rapid increase of abundance: maximum density 50.ind.m-2 in 2009 compared to 10 ind.m-2 in 2008. This observation probably demonstrates that the species' current significant increase is comparable to that of an invasive species. A second species of Asian shore crab Hemigrapsus takanoi Asakura & Watanabe, 2005 was only present on one eastern site off Saint-Vaast-La-Houge, but remains isolated.