A targeted search in 2011 for A. grayana on the tidal River Severn and its estuary down to Aust, using the same techniques which found it in over 30 one km squares on the Anglo-Welsh Dee, failed to find any.
In 2023 the above specimen was found in the same search area and another further west in Somerset (see fig. 10) so it seems to have arrived widely on the Severn Estuary.
Saul Warth, upper Severn Estuary, England, December 2023. © D. Cormack