Mechanisms and consequences of aquatic invasion in European Rivers
Final Report Abstract
The aim of the project was to describe the key mechanisms for a successful invasion as well as effects of a successful invader for the structure and the functions of the benthic community of large rivers using the example of Dikerogammarus villosus. It was assumed that high trait plasticity enables D. villosus to invade various ecosystems and the success of the invasion depends on the characteristics of a community. The consequences of the D. villosus invasion was assumed to be dramatic due to the extremely high benthic densities of the invader and its predatory life style. To address these questions several mesocosm experiments in the rivers Elbe, Rhine and Bure were performed and complemented by additional laboratory experiments and the analysis of long term-field data. For the experiments, we constructed three floating mesocosms with three experimental units each, consisting of a supporting frame, 8 floating bodies, and three stainless steel flumes (0.2 m wide, 0.6 m high and 4.10 m long) which were equipped with substratum baskets, containing river sediment already colonized with a near-natural benthic community. D. villosus density was manipulated to achieve three density treatments (natural, low and high density). The results of the mesocosm experiments and the analysis of the monitoring data indicate no ‘invasional meltdown’ in the studied ecosystems, because the number of positive density correlations as a proxy for positive species interactions was not higher between non-natives then between native taxa. However, the alternative hypothesis, the existence of a strong biotic resistance, seems also not very probable in the studied ecosystems because the establishment of D. villosus occurred much faster in the River Elbe (many native taxa) compared to the River Rhine (almost no native taxa) and no stronger community level effects were observed in the recently invaded River Bure. The effects of D. villosus on the benthic community are much weaker than previously assumed. They are river-specific and most likely determined by community traits and/or specific environmental factors. This might be caused by the fact that D. villosus seems not to act predominantly as predator in the studied river food webs. In contrary, it has a generally low trophic position and uses relatively large amounts of detritus, biofilm and leaves, indicating a likely function as primary consumer or at most as an omnivore. The most likely reasons for the large invasion success of D. villosus, seems to be its ability to withstand or compensate for intraspecific competition and to maintain its high consumption rates at high densities. In addition, although D. villosus does not exhibit a generally higher metabolic efficiency than other amphipods, it has a lower basic metabolic rate at medium temperatures and seems to be better able to compensate for low food quality, which also might represent a beneficial trait for invasive species. However, D. villosus shows strong physiological reactions to relatively low and environmental relevant concentrations of ammonia, which somewhat contradicts the idea that invasive taxa in general and D. villosus specifically show a high environmental tolerance.
Publications
- (2018) Food consumption of the invasive amphipod Dikerogammarus villosus in field mesocosms and its effects on leaf decomposition and periphyton. AI (Aquatic Invasions) 13 (2) 261–275
Worischka, Susanne; Richter, Luise; Hänig, Anne; Hellmann, Claudia; Becker, Jochen; Kratina, Pavel; Winkelmann, Carola
(See online at https://doi.org/10.3391/ai.2018.13.2.07) - The very hungry amphipod: the invasive Dikerogammarus villosus shows high consumption rates for two food sources and independent of predator cues. Biological Invasions
Richter L, Schwenkmetzger L, Becker J, Winkelmann C, Hellmann C, Worischka S
(See online at https://dx.doi.org/10.1007/s10530-017-1629-4) - (2015) Physiological and behavioral responses of the invasive amphipod, Dikerogammarus villosus to ammonia. Comparative Biochemistry and Physiology Part A 189:107-114
Normant-Saremba M, Becker J, Winkelmann C
(See online at https://doi.org/10.1016/j.cbpa.2015.08.003) - (2015) The trophic function of Dikerogammarus villosus (Sowinsky, 1894) in invaded rivers: a case study in the Elbe and Rhine. Aquatic Invasions 10: 385–397
Hellmann C, Worischka S, Mehler E, Becker J, Gergs R, Winkelmann C
(See online at https://doi.org/10.3391/ai.2015.10.4.03) - (2016) Metabolic activity and behavior of the invasive amphipod Dikerogammarus villosus and two common Central European gammarid species (Gammarus fossarum, Gammarus roeselii): Low metabolic rates may favor the invader. Comparative Biochemistry and Physiology, Part A 191: 119–126
Becker J, Ortmann C, Wetzel M A, Koop J H E
(See online at https://doi.org/10.1016/j.cbpa.2015.10.015) - (2017) River-specific effects of the invasive amphipod Dikerogammarus villosus (Crustacea: Amphipoda) on benthic communities. Biological Invasions 19: 381–398
Hellmann C, Schöll F, Worischka S, Becker J and Winkelmann C
(See online at https://doi.org/10.1007/s10530-016-1286-z)
