What are killer shrimps? How they pose a threat to European rivers

An image to illustrate the species of killer shrimps which are affecting European rivers
© Michal Grabowski, University of Lodz

The species known as killer shrimps pose a threat to European rivers, according to a new study from the University of Plymouth.

Due to the consumption of a vast range of species by the killer shrimps, the ecosystem of European rivers is changing and causing local extinctions.

What are killer shrimps?

The Dikerogammarus villosus is an invasive species which has been replacing the Gammarus species which is resident in European rivers over the past three decades.

The non-consumptive effect on prey

The new study shows that the mere presence of the killer shrimps has a non-consumptive effect (NCE) which can reduce the normal effectiveness of prey.

The non-consumptive effect means that the prey expends more energy through self-preservation by avoiding the predator, instead of on ecosystem tasks including shredding fallen leaf litter into smaller particles to be consumed by other species.

Understanding the threat to European rivers

Dr MacNeil has spent over twenty years studying the killer shrimps, and explained: “This study demonstrates an unappreciated and indirect impact of a biological invasion by a voracious predator. It shows that the mere presence of an invader can influence resident prey behaviour, in this case the feeding efficiency of naïve residents. The Gammarus in our experiment had no prior exposure to its predatory rival, and would not have known to respond to specific alarm cues. However, none of our samples showed any evidence of habituation during the course of the experiment – in fact quite the opposite.”

Professor Briffa added: “Our results indicate that the effect of NCEs on functionally important species may have ramifications, for example, impacting the recovery of stream communities following perturbation. A better understanding of the role of NCEs during biological invasions could enhance our ability to predict their progress and, in some cases, the wider ecosystem level ramifications.”

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