Until recently, there were very few records of either species from within the UK.
But a recent survey conducted by APEM found 64 brush-clawed crabs. In fact, when our scientists analysed the first sample from the survey they immediately identified more of the crabs than had previously been found in total anywhere in the UK.
A follow-up survey then found a further 310 brush-clawed crabs.
Chris Ashelby said: “I had long expected that this crab would turn up in Britain so when we found them in our samples I decided to head to a nearby shore and have a scout around. The crabs were so abundant that I managed to collect more than 70 of them in about half an hour.
“Not only were the crabs very abundant, but it was also clear that they were breeding. Among the ones I found were many juveniles and many females carrying eggs.”
Chris submitted records of the findings to the website of the Great Britain Non-Native Species Secretariat.
Previously, a horizon-scanning study published in 2014 by a team that included Dr Michael Dobson, also a scientist at APEM, had predicted that both Hemigrapsus species were highly likely to invade the UK. At that point, however, there were no records of them in the country.
As Chris began to make contact with other researchers, including at the Natural History Museum and the Marine Biological Association of the United Kingdom, further records emerged from south-east England.
These included photos that had been posted on the NaturePlus discussion forum. Dating from 2011, the photos established that Japanese brush-clawed crabs had in fact been present in the UK for far longer than anyone had previously known.
At the time that the 2014 horizon-scanning study was predicting the imminent arrival of the crabs, they had already been present – but undiscovered – for at least three years.
Chris Ashelby’s full research has been published in the journal Crustaceana.
A crab recording scheme, Crab Watch, has just been launched by the Marine Biological Association and records of Hemigrapsus, or any other species of crab, can be posted on it.
If you have any queries, please contact Dr Chris Ashelby, crustacean specialist.
Alternatively you can email them here. Or call 0161 442 8938.