How to coexist with the ‘killer shrimp’ Dikerogammarus villosus? Lessons from other invasive Ponto‐Caspian peracarids

Abstract

Studying interactions among co‐evolved invaders might help us in understanding, predicting, and perhaps mitigating the impact of the invading species on the native biota. The factors of spatial niche differentiation were investigated among invasive Ponto‐Caspian peracarids with the aim of revealing how co‐evolved species can coexist with the ‘killer shrimp’ Dikerogammarus villosus, an invasive gammarid replacing non‐Ponto‐Caspian species throughout Europe. Multi‐habitat samples from the third Joint Danube Survey were analysed by partitioning the variation in species density data between environmental and spatial explanatory variable sets. Relevant predictors were identified by forward selection and their role was interpreted based on the redundancy analysis (RDA) triplot. The effect of substrate types was further analysed in certain species using generalized linear models. The analysis revealed characteristic differences in habitat preference (i.e. spatial niche differentiation) among the species, allowing coexistence with D. villosus at different spatial scales. The relatively small and lean body of Chaetogammarus ischnus and Jaera sarsi might allow the avoidance of interference with large Dikerogammarus specimens by using narrow interstices among pebbles and stones (microhabitat‐scale differentiation). The remaining Ponto‐Caspian species included in the analysis showed an affinity for substrate types (Obesogammarus obesus) or current velocity intervals (Dikerogammarus bispinosus) that differed from those preferred by D. villosus (mesohabitat‐scale differentiation), presumably in connection with feeding preferences in some cases (Dikerogammarus haemobaphes and Trichogammarus trichiatus). These results provide a framework for a preliminary risk assessment concerning the continuing high potential for range expansion of D. villosus: i.e. the identification of the most vulnerable species in those regions of the world not invaded at present but potentially colonizable, based on their habitat preference and morphology. The lessons learned from Ponto‐Caspian peracarids can be applied to the whole macroinvertebrate fauna, as the same principles (i.e. the avoidance of interference) can be expected to determine their coexistence with D. villosus.

Cryptic diversity and mtDNA phylogeography of the invasive demon shrimp, Dikerogammarus haemobaphes (Eichwald, 1841), in Europe

“…Already in the 1950s, the demon shrimp was reported from the middle Danube above Györ in Hungary, and in 1994, it was found as high as the Danube-Main canal in Germany (Straškraba 1962;Schleuter et al 1994;Borza et al 2015). In the early 1990s it was abundant in the German part of the Danube, but soon after the appearance of the killer shrimp, the population of demon shrimp in that area declined (Weinzierl et al 1996;Kley and Maier 2006;Borza et al 2018). Similar observations were made in other rivers: Rhine, Lahn, Drava, Oder, and Vistula (Weinzierl et al 1996;Bernauer and Jansen 2006;Kley and Maier 2006;Grabowski et al 2007b;Chen et al 2012;Ćuk et al 2019; own unpublished data), suggesting effective replacement of this species by D. villosus, even if in some conditions co-existence of D. haemobaphes and D. villosus was observed (Borza et al 2017;Hellmann et al 2017).…”

What doesn’t kill you doesn’t make you stronger: Parasites modify interference competition between two invasive amphipods

“…In the wild, D. haemobaphes can retreat to habitats avoided by its stronger competitor, e.g. with stronger water flow (Borza et al 2018). Anyway, our study shows that, when migration is not possible, D. haemobaphes is capable of withstanding the direct co-existence with D. villosus without any visible negative consequences in shelter use, at least over a short term tested in our study.…”

Global distribution and diversity of alien Ponto-Caspian amphipods

“…An affinity for hard substrata has been proposed as an important factor favoring the dispersal of Ponto-Caspian peracarid crustaceans into heavily anthropized habitats (Borza et al 2017). Indeed, numerous studies reported a preference of alien Ponto-Caspian amphipods for hard substrates, although relatively few species were studied thus far (Dermott et al 1998; Hesselschwerdt et al 2008; Jermacz et al 2015; Borza et al 2018; Poznańska-Kakareko et al 2021). Clingers and symbionts seem to be associated with more specific substrates, which may limit dispersal potential.…”