What has the ‘killer shrimp’ taught us? By Trevor Renals, Environment Agency
Last year, the presence of the ‘killer shrimp’ Dikerogammarus villosus, was recorded for the first time in Great Britain. It was first recorded from Grafham Water, Cambridgeshire in September and subsequently found at Cardiff Bay and Eglwys Nunydd reservoir near Port Talbot. This shrimp is one of approximately seventeen species of freshwater invertebrate that originate from the Ponto-Caspian Region of Eastern Europe and is spreading into the West.
Dikerogammarus villosus has earned the rather sensational title of ‘killer shrimp’ from its voracious appetite, particularly in the early stages of colonising new habitats. Unusually for an animal, it appears to kill other freshwater organisms, such as invertebrates and small fish, without actually eating them. This appears to be a mechanism to reduce competition. Other shrimps have a particularly hard time and are often totally replaced by the invading species.
We don’t know how the invasive shrimp got here. It is one of a range of species that can move across the globe within ballast water. Ships take on large volumes of ballast water after they have discharged their cargo. The ballast water is then discharged at another port, prior to loading another cargo. The Ballast Water Management Convention was adopted in
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2004 under the auspices of the International Maritime Organization (IMO). The Convention will enter into force after ratification by 30 nations, representing 35% of the world merchant shipping tonnage. To date, 26 States have ratified the Convention, comprising 24.66% of the world total merchant shipping tonnage. Annually, 3-5 billion tonnes of ballast water are transferred, vectoring 7,000- 10,000 different invasive non-native species.
We had expected Dikerogammarus to arrive in this manner, from a freshwater port such as Rotterdam. Dikerogammarus shrimp can tolerate brackish conditions and would be able to migrate up many of our busy river systems. It is possible that it did enter the UK by this route and we have yet to locate the original point of entry. We have limited control over this pathway of spread, but technology is increasingly providing solutions for ballast water treatment that will reduce the risk of vectoring invasive species. There are other pathways, however, over which we do have more control.
D. villosus has mostly spread throughout Western Europe through the various canal systems that link catchments. Research has shown that the shrimp can survive up to six days in damp conditions, out of water. Any activity based on inland waters, such as sailing, kayaking, diving
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