Under the Trust's Research and Monitoring programme, a team of 6 students from Royal Holloway University and University of Surrey set out in search of the demon shrimp on the River Wey, to find out if it had spread since it was first found in Surrey in 2015. Josie Lawrence, from the University of Surrey, wrote about the project in this blog. If you're interested in the Trust's research and monitoring work, please take a look at our page here 

"Demon shrimp, scientifically known as Dikerogammarus haemobaphes, are a species of shrimp which have spread from their home in the Ponto-Caspian region of eastern Europe across the continent. In 2015 this invader was found by the Environment Agency at multiple sites in the River Wey, which was a cause of concern for the Trust and the Wey Catchment Partnership.

Non-native species are any species found in a location outside of their normal range but when these organisms threaten the native wildlife, they are termed invasive species. Invasive species can threaten local wildlife in many ways: they may outcompete native species for food, space, and other resources, they may predate directly on native species, or they may have the ability to change the environmental conditions of the surrounding habitats. Since freshwater shrimp are an important part of river food webs and decomposition cycles this was thought to be a very real threat.

As part of a Surrey Wildlife Trust Project, my teammate Ash Wood and I from the University of Surrey and another team from Royal Holloway University, went down to the river to survey for these Demon shrimp. Over 2 months in the winter of 2021 we surveyed 29 different sites along the river system (see following map). We collected a range of abiotic data like flow speed, channel depth, and phosphate levels, at each site to see how changes in conditions affected biotic samples. Biotic (or living) samples were collected using a common technique called ‘Kick-stool sampling’, where a net is submerged in the water and the riverbed is agitated by kicking around to dislodge any hidden critters. The contents of the net can then be emptied into a tray where animals can be identified using a careful eye and ID guys. Many native shrimp, Gammarus sp., were found during the study, alongside other invertebrate larvae including caddisflies and mayflies. And thankfully, I’m happy to report that we found no Demon shrimp at any site! This means that Demon shrimp failed to establish a breeding population in the river Wey and therefore are not currently a threat to the ecosystem here."

"While the numbers of native shrimp didn’t change significantly between 2015 and 2021, Demon shrimp clearly suffered a detrimental decline over the years, becoming locally extinct. There are many reasons why this may have happened. Demon shrimp may have been maladapted to the local environment, being less successful predators, easier prey or with poor resistance to changing abiotic conditions. They may have faced inbreeding depression due to small and isolated populations. Or, there is even an argument to be made that exposure to novel diseases carried by natives could have killed them.

The spread of invasive species is often driven by human action, and this means that we’re not safe from the threat of invasive species in our rivers. The movement of boats and equipment through waterways and the changing conditions of rivers due to pollution and climate change increase the chances of invasive species movement. Remembering to Check, Clean, and Dry wet boots and equipment between different areas can dramatically reduce species spread. Studies like this one are vital in uncovering the establishment of species in local areas, as they provide up-to-date species records and allow a comparison between past and current states to be made."

Thanks to the work of the students on this project, Surrey Wildlife Trust and the Wey Catchment Partnership have now realised that the demon shrimp are certainly not as widespread as was feared. We are hoping to continue studying the Wey to confirm that the shrimp are truly absent, and delve deeper into the question of how their invasion failed. Watch this space!