Fear of "killer shrimps" could pose a major threat to European rivers

A new study suggests that the fear of invasive "dead prawns" can intimidate indigenous organisms to such an extent that they are unable to play their vital role in river systems.

Write in the newspaper Acta oecologicaScientists are focusing on the invasive species Dikerogammarus villosus, which regularly replaces resident Gammarus species in Europe's rivers over the last three decades.

This has major localized effects since the voracious predator consumes a wide range of species, its behavior being subsequently linked to changes in the ecosystem and even to local extinctions.

The new study shows for the first time that the mere presence of the predator – a non-consumable effect (NCE) – can reduce the normal efficiency of its prey.

This causes them to spend more energy to simply avoid the predator in order to preserve themselves, rather than focusing on the basic tasks of the ecosystem, such as shredding dead leaf litter into the water. smaller particles that can be consumed by other species.

The research was conducted by the independent consultant, Dr. Calum MacNeil and Mark Briffa, professor of animal behavior at the University of Plymouth.

For the study, one of three species of Gammarus (all present in European rivers) was placed in a reservoir. In half of the tanks, a sample of Dikerogammarus villosus was also placed in a cage.

The behavior of Gammarus was then evaluated over several days. The researchers measured how well they shredded the leaves in the way they were supposed to do in their natural environment.

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

Dr. MacNeil, who has been studying this species for more than 20 years, said, "This study demonstrates an unappreciated and indirect impact of the biological invasion of a voracious predator. of an invader can prey behavior, in this case the food efficiency of naïve residents.In our experience, Gammarus had not been exposed before to his predator rival and would not have However, none of our samples showed any signs of habituation during the experiment, quite the contrary. "

Professor Briffa, whose research previously included evaluations of species fighting such as hermit crabs and sea anemones, added: "Our results indicate that the effects of NCEs on species of functional importance can have consequences, particularly on the recovery of A better understanding of the role of NCEs during biological invasions could enhance our ability to predict their progress and, in some cases, more ramifications. at the level of the ecosystem. "