Extension of the geographical distribution of the crab Asthenognathus atlanticus Monod, 1932, in the eastern English Channel through its commensal relationship with the polychaete Chaetopterus variopedatus (Renier, 1804)

Abstract

Asthenognathus atlanticus Monod, 1932, is reported here for the first time in the area around Dieppe-Le Treport (Normandy coast in the eastern part of the English Channel). A total of 26 specimens were collected in 2015–2016 from fine and coarse sands at water depths between 12 and 25 m. Two specimens were found in the stomach of two thornback rays Raja clavata. The eastward progression of A. atlanticus is consistent with tidal residual currents in the English Channel. The period of global warming is likely favorable for this easterly progression, and the species could reach the southern part of the North Sea in a few years. Our observations in the eastern part of the English Channel also illustrate a new commensal association between the tubicolous polychaete C. variopedatus and the crab A. atlanticus, the latter being found in a variety of soft-bottom sediments ranging from muddy to coarse sands, in agreement with reports of its presence in the Rade de Cherbourg and the Bay of Seine.