Recent expansion of the non-indigenous amphipod Chelicorophium curvispinum (G.O. Sars, 1895) in the Seine estuary

Recent sampling of the upper part of the Seine estuary (oligohaline, freshwater reaches) has led to the observation of the non-indigenous amphipod Chelicorophium curvispinum for the first time in the downstream part of the Seine Basin (between the Tancarville Bridge and Paris). Specimens were collected using a suprabenthic sledge along a salinity gradient ranging from freshwater to mesohaline, with observations of C. curvispinum all along this gradient. Samples collected were characterized by a relatively small number of individuals, reaching a maximum abundance of 15 individuals / 100 m 3 when temperatures were the highest, during the summer. The sex ratio was dominated by females, with approximately twice as many females than males. Interestingly, adults reach a size which allowed the reproduction of the species, but no ovigerous females were observed. Despite the rapid expansion of C. curvispinum in the Seine estuary, this study cannot assess whether this species should be considered as invasive in the Seine Basin. Nevertheless, as the sampling was carried out within the navigation channel, further observations will be necessary to determine the abundance of this species on soft and hard bottoms of the riverbanks.