Becky Hitchin presents a tale of two crabs , both unwelcome guests on either side of the planet
BECKYHITCHIN
Claws for concern
Becky Hitchin presents a tale of two crabs , both unwelcome guests on either side of the planet
This month , I want to tell tales of two invasive species , both crustaceans . One of these is native in UK waters and has become invasive worldwide , and one has invaded the UK .
So firstly , the shore crab , aka the green crab , Carcinus maenas , beloved of small children due to its attraction to pieces of bacon hung on the end of long strings over jetties . This seemingly inoffensive little crab has also been listed as one of the ‘ 100 worst invasive species ’. It is native to European coasts , but has sequentially invaded the world . It was first seen on the east coast of North America in 1817 , and now occurs from South Carolina to Newfoundland . In the 1850s , it was also introduced into Australia . These periods of dispersal occurred through transport by ships ( in hull fouling or in solid ballast ).
The shore crab reached New South Wales in 1971 , South Australia in 1976 and Tasmania in 1993 . It reached South Africa in 1983 and South America by 2003 . In 1989 , it was also found in California and in Canada in 1999 . Making its way up the Pacific coast of America , the shore crab extended its range by 750km in 10 years . These introductions are more likely to have occurred through a greater variety of dispersal mechanisms , including the more traditional hull fouling and ballast water releases but also more technological mechanisms such as fouling on semisubmersible drilling platforms , transport with fisheries products intended for food or bait , scientific research or releases from aquaria .
This inoffensive little crab has caused major economic impacts on shellfisheries in New England , and may have similar effects on fisheries on the West Coast of North America and Australia . Ecologically , it has impacted many shore communities by preying on , and competing with , other crabs , bivalves and gastropods . Not so inoffensive really !
The second crab is an invader of our waters – the Chinese Mitten Crab , Erocheir sinensis , also known as the Shanghai
“ This seemingly inoffensive little crab has also been listed as one of the ‘ 100 worst invasive species "
Shore crab
Hairy Crab and the Big Sluice Crab . It ’ s a burrowing crab native to rivers , estuaries and other coastal habitats of East Asia named for its furry , brown , mitten-like claws . It is also listed as one of the world ’ s 100 worst invasive species due to the damage it can wreak
on the environment by burrowing into riverbeds and embankments , blocking drainage systems and damaging fishing gear with its sharp claws . They eat fish eggs and outcompete native species for resources . Over the past century , the crabs have spread around the world , including Europe and North America , migrating through ballast water in commercial ships .
The species was first spotted in the UK in 1935 in the Thames and has since
The Ecology Center at Yangcheng Lake in Jiangsu Province , China has been modelled on a vast mitten crab
Mitten crab
become established around the country . There are a few dive lakes in Kent where you can see the crabs marching between the waterbodies at dusk . In 1995 residents of Greenwich saw them crawling out of the River Thames , and in 2014 one was found in the Clyde , in Scotland . The crabs have even been known to take up residence in swimming pools .
What to do about these invaders ? There have been fisheries set up to try and decrease their numbers . In Massachusetts , more than 10 tonnes of shore crabs were caught in one year in an experimental fishery . In China , there have been ideas of reimporting crabs from the West to replenish Chinese fisheries , where the mitten crab is seen as a delicacy .
There ’ s no moral to this story . No easy way to reverse invasions . Our underwater world is changing , forever , and it ’ s up to us as divers , snorkellers and shore surveyors to at least document , photograph these changes and help understand our changing seas . �
27