Killer shrimp INVASION: Why Europe’s rivers are at risk from tiny 'voracious PREDATOR’

Killer shrimp INVASION: Why Europe’s rivers are at risk from tiny 'voracious PREDATOR’

An invasive killer shrimp species has recently arrived in European rivers and they are not only eating the existing shrimp populations. The visiting crustaceans are also effectively changing their native prey’s behaviour as they attempt to avoid being devoured, a new study has shown. Native shrimps have been discovered to be expending more energy hiding from the interlopers than they are on their usual behaviour.

And this consequently means they are incapable of performing their vital role in river systems.

Dikerogammarus villosus, dubbed killer shrimp, is a species native to the Black Sea and Caspian Sea drainage basins in eastern Europe.

But from the late 20th century the shrimp has also become commonplace across the western Europe.

The thriving of killer shrimp in its new home comes at the expense of various resident species of the Gammarus genus.

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The University of Plymouth scientific team has described the shrimp as a “voracious predator”.

This is because it consumes a vast range of species, with its behaviour subsequently being linked to ecosystem change and even entire extinctions.

The new study, conducted by independent consultant Dr Calum MacNeil and Professor Mark Briffa, has for the first time documented that the predator mere presence of the can reduce the normal effectiveness of its prey.

This non-consumptive effect (NCE) is due to the native species expending more energy to avoid the predator in a bid for self-preservation.

This behaviour means its focus is distracted from its usual tasks such as shredding fallen leaf litter into smaller particles to be consumed by other species.

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The study saw one of three different Gammarus species, commonly found in European rivers, placed inside a tank.

In half of the tanks, a sample of the invasive “killer shrimp” was also present in small cages.

The Gammarus’ behaviour were then assessed, with researchers measuring whether the shrimp shredded leaves to the normal extent.

The results showed after four days each Gammarus species showed lower shredding efficiency in the presence of the killer shrimp, compared to the treatments where it was absent.

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Dr MacNeil, who has spent more than 20 years studying the species said: “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 naive 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.”

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