Invader crabs muscle their way onto Purbeck beaches

A new species of crab to the Purbeck Coast is beginning to make itself at home among the rockpools – and may soon start to edge out the sitting tenants.

The furrowed crab, a common resident of Devon and Cornwall, was recorded as far east as Kimmeridge in Dorset for the first time in 2019, but has since been spotted more frequently as sea temperatures warm up year on year.

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DORSET WILDLIFE TRUST

Volunteers on the monthly furrowed crab survey at Kimmeridge check for inhabitants of the seashore

Climate change indicator

Volunteers are now carrying out monthly surveys on the Kimmeridge shoreline to see exactly how many are making their way here, whether it is the start of an invasion and what consequences it might have for an established Dorset resident, the edible crab.

The furrowed crab is a climate change indicator, a warning that climate change is beginning to change the abundance and species of marine creatures on the seashore.

The average sea temperature over the last 10 years in Kimmeridge on 28th August – typically the highest it will reach – is 16.94 degrees centigrade, but over the last three years the figure has been 17.5 degrees in 2021, 19.1 degrees in 2022 and 17.6 degrees in 2023.

In 2022, 16 furrowed crabs were found during surveys at Kimmeridge, as opposed to 471 edible crabs, and although their numbers appear low, there are concerns that the new nippers on the block may adapt to warming conditions better than the established species.

DORSET WILDLIFE TRUST

Marine awareness officer Julie Hatcher is concerned about a possible explosion in the furrowed crab population

Population explosion in recent years

Julie Hatcher, marine awareness officer for Dorset Wildlife Trust said:

“The wildlife rich shallows and seashore of Kimmeridge Bay were designated as a protected area under UK law in 2019 and form part of the Purbeck Coast Marine Conservation Zone.

“An important part of our work at the Wild Seas Centre is to record and monitor the marine life along this coastline.

“One such survey focuses on the furrowed crab, a native to the south west coast but a recent arrival in Dorset. Further west, this crab has undergone a population explosion in recent decades, raising concerns about its impact on other long-term residents.

“The problem comes when the new arrivals compete with the resident creatures as they may impact on their numbers and have unforeseen consequences.”

DORSET WILDLIFE TRUST

Volunteer Val Fogarty is leading the furrowed crab survey at Kimmeridge

DORSET WILDLIFE TRUST

The survey also measures and sexes the crabs it finds to build up an information database

Furrowed crabs may have an advantage

Edible crabs move to progressively deeper water as they grow, so the ones found in the Kimmeridge intertidal zone are the small, immature youngsters.

Furrowed crabs may have an advantage over juvenile edible crabs – once they are established in an area they can outcompete a same sized edible crab for shelter.

They can live all their lives on the shore and breed without the female needing to moult her shell, and their diet is also different which may give them an advantage.

DORSET WILDLIFE TRUST

A furrowed crab making itself at home in Kimmeridge Bay

DORSET WILDLIFE TRUST

The resident edible crabs may find themselves competing for shelter and food in the near future

Just starting to increase in number

Sarah Hodgson, of the Fine Foundation Wild Seas Centre at Kimmeridge, said:

“We have noticed their numbers increasing here. It is an interesting place to monitor and study them because we are on the edge of their boundary – further west in Devon and Cornwall they are much more abundant than they are here currently.

“They are just starting to increase in number, so it is the perfect place and time to see how quickly their numbers rise and if it has any effect on any other local wildlife.

“There is not necessarily a direct competition between species yet, but in other places where furrowed crabs are more abundant there has been a decline in some other species, perhaps due to competition for food, space or habitat.

“It is too early to draw any conclusions and certainly we are still recording much higher percentages of edible crabs than we are of furrowed crabs.

“Hopefully it will be something we can continue to collect data on over a longer period of time to see what, if any, impact they might have.”

DORSET WILDLIFE TRUST

A small cushion star, once native to Portugal and the Mediterranean, is now a regular find in Purbeck

Anemone shrimp
JULIE HATCHER

The anemone shrimp, first found in the UK in 2007, and now a permanent resident of Swanage pier

Other seashore species arrive in Purbeck

Other seashore species have also been spreading eastwards from Devon and Cornwall to Kimmeridge, Swanage and beyond in recent years.

A species of sea snail called a toothed topshell was unknown in Dorset in 2000 but is now a regular find along the Jurassic Coast, while the small cushion starfish – once only found in Portugal and the Mediterranean – has also become common at Kimmeridge after first being found in 2014.

The anemone shrimp, an exotic looking relative of common prawns that was first recorded in mainland Britain as recently as 2007, is now also a common sight under Swanage pier and in rockpools at Kimmeridge. 

It lives within the stinging tentacles of the snakelocks anemone, a very common rock pool creature, and with an almost transparent body can be quite difficult to spot, but divers have been finding growing numbers of these tiny shrimps in the last three years at Swanage.  

The Fine Foundations Wild Seas Centre sits right on the seafront at Kimmeridge

Kisses 4 Fishes litter pick event

The Wild Seas Centre at Kimmeridge, with interactive displays and aquaria, is on a mission to encourage people of all ages to explore the bay, its ledges and rockpools.

It has been running eco crabbing events for families through the summer, teaching children how to catch, keep and then return crabs in a responsible way so that the crustaceans are not injured in the process.

Late summer and early autumn continues to be a busy time at the Wild Seas Centre, especially when the weather is good, including a self guided snorkel trail in Kimmeridge Bay to see the rich variety of underwater life.

A litter and craft event, Kisses 4 Fishes, has been organised for Tuesday 19th September 2023. Fishermen’s kisses are small pieces of discarded fishing net which litter beaches, and the aim will be to collect them from the shore at Kimmeridge before making something crafty out of them.

And from Saturday 30th September 2023 for four weeks, there is a ceramics and art exhibition at the Fine Foundation Wild Seas Centre, where all the work has drawn inspiration from the nature of Kimmeridge.

Further information

  • Discover more about the Dorset Wildlife Trust’s work at Kimmeridge on its website

Watch video of Kimmeridge volunteers searching for crabs

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