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Help stem the Asian shore crab invasion

The first sightings of a highly invasive crab from the northwest Pacific have been reported on mainland Britain.

The Asian shore crab, Hemigrapsus sanguineus, is native to the coasts of Japan, China, Taiwan, Korea and Russia and probably arrived here clinging to the hull of a ship from France.

The crab is already an invasive species on the eastern coast of America and the northern coasts of France, Belgium and Holland, where it is displacing native shore crabs and destroying shellfish.

Now, with two confirmed sightings during May in Glamorgan, South Wales and Herne Bay, Kent, it looks set to establish itself on mainland Britain.

H. sanguineus is an aggressive and highly opportunistic omnivore, known to feed on commercially important species such as mussels,’ said Museum crab specialist Dr Paul Clark. The Asian shore crab would also compete with our native shore crab, Carcinus maenas, causing its population to decline.

Illegal alien

Last April, scientists including Dr Paul Clark, ranked H. sanguineus third on a list of alien species most likely to invade Britain and threaten native biodiversity in the next ten years.

Non-native species are a growing problem throughout Europe due to increased world trade and tourism and a warmer climate. The GB Non-Native Species Secretariat estimates the cost to the UK of controlling invasive species at £1.7bn annually.

The Marine Biological Association (MBA) have asked the public to help identify Asian shore crabs. The crab is small (up to 4.5 cm across), has a distinctive square shaped shell (carapace) with three teeth on each side, and distinctively banded legs.

If you find an Asian shore crab, please report it to the MBA. Dr Clark is also interested in a live specimen. If you find one, please email him, stating whether you can provide a photo for identification.

Our native shore crab, Carcinus maenas, is plainer. The juveniles are green © Hans Hillewaert, Wikimedia Creative Commons.


Aggressive invader

The Asian shore crab was first reported outside of its natural range in New Jersey, on the eastern coast of the USA, and in only two years it had established a breeding population. It spread rapidly, extending its range over 650 kilometres of coastline in just seven years.

The crab has more recently been established along the Opal Coast of northern France. Dr Clark thinks that as well as arriving by ship, they may also be able to drift across the short English Channel while in a larval stage, where they would have no problem making a home in Britain.

Stubborn newcomer

‘No special conditions are required by this species in temperate regions as it can tolerate a wide range of salinities and temperatures,’ he said. ‘Ecological conditions here are similar to those found in its native habitat and other coastlines from where this crab has been recorded as an invasive species.’

Dr Clark said stopping them early is the only way to prevent an invasion. Once they have established a breeding colony, they will be difficult, if not impossible, to eradicate.

‘This species has an extremely effective breeding strategy. The breeding season is from May to September, and females can bear two to four broods of eggs, producing around 50,000 eggs per spawning,’ he said.