The Demon shrimp and the importance of benchmarking…
Nick Measham is alarmed by the rapid spread of this foreign invader
Dr Nick Everall from Aquascience Consultancy and a fellow ecologist, Nick Mott from Staffordshire Wildlife Trust, have reported some worrying evidence about the demon shrimp, Dikerogammarus haemobaphes, from a site in the River Churnet, a tributary of the Dove in Staffordshire. On the evidence from this site, the threat to native invertebrates could be significant.
This demon shrimp, like its cousin, the killer shrimp, is an eastern European invader about which we know only a little. It is an omnivorous beast and its diet is thought to include other aquatic invertebrates. It was also originally thought to only inhabit the slower reaches of rivers and canals. Yet, it has now successfully colonised a fast flowing riffle on the Churnet with disturbing ease and appears to be wreaking havoc by feasting on the indigenous aquatic invertebrate community.
The results from these three-minute kick-sweep samples taken at one Churnet site on five occasions from January 2014 to October 2016 are stark.
The demon shrimp population has boomed rising from zero in 2014 to 442 in the October 2016 sample after it invaded in 2015. The native freshwater shrimp, Gammarus pulex, has disappeared along with many of the other mayflies (Heptagenia sulpherea, Ecdyonurus sp., Rithrogena semicolorata and Baetis rhodani). Other Mayfly, Stonefly and Caddis species have suffered severe declines. Conversely, the silt-burrowing Ephemera danica, the armoured cased caddis Silo pallipes and the tunnel living caseless caddis Hydropsyche pellucidula have thrived.
Other factors may be a to work but it is hard to avoid the unpalatable truth that the demon shrimp has eaten many of the native aquatic invertebrates. The potential threat from the spread of this invader is clear. These are early indications but it is clear further monitoring and studies are urgently required.
These results also emphasise the importance of species benchmarking of our aquatic invertebrate populations. This fundamental component of the S&TC Riverfly Census needs to be taken up by all who care for their rivers and is now available widely through the new River Invertebrate Identification and Monitoring (RIIM) courses run through S&TC UK. Without species level data on what was and what is now in our rivers, we cannot force the guardians of our environment to act.