How many marine aliens come to UK shores?
ANo one knows for certain. Many will perish on arrival, particularly those that hail from warmer waters. Just 10 per cent are likely to survive and only 10 per cent of those will become invasive.
Many aliens arrive by natural means, driven by wind or ocean currents. But with the huge increase in global trade and human movement over the past century, opportunities to hitch a lift – usually via hulls and ballast tanks – have risen.
Many invasive species in the UK come from other temperate habitats in Japan, Australia and the US. They include the carpet sea squirt Didemnum
vexillum, which can smother the seabed for kilometres, and the slipper limpet
Crepidula fornicata, which alters habitats over huge scales. Such newcomers are estimated to cost the economy £1.7 billion per year, but we export species, too. Our common shore crab is now prolific in Australia, South Africa and North America, and counts among the world’s 100 worst invasive species.