The Asian shore crab, native to the Western Pacific, was found in a rockpool near Niton.
Islander Mike Wilson made the discovery on Monday (September 14).
He said he had never seen a crab like it in all his years going to the beach, so contacted marine biologist Theo Vickers to find out what it was.
Theo said it is a Hemigrapsus sanguineus – or Asian shore crab – and while there had been reports of them on the mainland, this is a first for the Island.
The crabs are considered a high-risk invasive species due to their rapid reproduction, aggressive feeding habits, and ability to displace native marine life.
How to report sightings of the Asian shore crab
Only a handful of sightings have been recorded in the UK.
Theo said the crabs first reached British waters in the Channel Islands in 2000 and the coast of mainland Britain in 2014, in Wales and Kent.
“They are invasive and do have a potential to negatively impact native intertidal communities if they reach high enough densities”, he said.
Asian shore crab (Image: Mike Wilson)
“This single record isn’t enough evidence to say anything like that is happening here at the moment though, so I don’t think a major concern until or IF we see quite a few more records of them.
“Best thing to do is just keep an eye out and report any more observations!”
He said he reported the find to Roger Herbert, the Island’s county marine recorder.