The impact of killer shrimp on crayfish.

Freshwater ecosystems worldwide are facing the establishment of non-native species, which, in certain cases, exhibit invasive characteristics. The impacts of invaders on native communities are often detrimental, while the number and spread of non-native invasive species are increasing. This is resulting in novel and often unexpected combinations of non-native and native species in natural communities. While the impact of invaders on native species is well-documented, the interactions of more non-native invaders are less studied.

We assessed the potential of an invasive amphipod, the killer shrimp Dikerogammarus villosus, to cope with other established invaders in European waters, the North American crayfish represented by signal crayfish Pacifastacus leniusculus, and marbled crayfish Procambarus virginalis. The main goal of this study was to investigate if killer shrimp, besides their role as prey of crayfish (also confirmed here), can significantly influence their stocks by predating upon their eggs, hatchlings, and free-moving early juveniles. Our results confirmed that killer shrimp can predate not only on free-living juveniles and lost eggs but even directly on eggs and hatchlings attached to a female’s abdomen where they are incubated and actively guarded by a mother. Our findings illustrate the high voracity and competitiveness of killer shrimp as well as unexpected boldness (or even impudence) of this small creature which can affect even much bigger taxa by its pressure on their different developmental stages. Due to this aggressiveness, boldness, and voracity killer shrimp is not only possible prey for fish and crayfish but also their strong competitor. Species with smaller eggs and first developmental stages are more prone to killer shrimp predation as presented by higher predation on marbled crayfish marbled eggs and juveniles than those of signal crayfish.

Further detailed information can be found in the original article: Roje, S., Veselý, L., Švagrová, K., Kozák, P., Kouba, A., Buřič, M., 2021. Pilferer, a murderer of innocents or prey? The impact of killer shrimp (Dikerogammarus villosus) on crayfish. Aquatic Sciences 83: 5. (IF 2019 = 2.402; Q2).

Boldness, impudence, or deviousness? Killer shrimp can use signal crayfish as a shelter despite of its direct predation pressure on its stock.