Der Einfluss von invasiven Amphipoden auf trophische Interaktionen und Lebensgemeinschaften in aquatischen Systemen
Final Report Abstract
The results of this project show that the presumed high predatory potential of the invasive Dikerogammarus villosus is not as relevant under field conditions at least in the River Rhine system. Furthermore, the trophic annidation of this invasive species is comparable to native and other invasive amphipod species. This suggests a stronger importance of competition for food or space between these species. However, it needs to be mentioned that most samplings were done in autumn and seasonal difference in predatory cannot be excluded based on the results of this project. To explore trophic interactions a combination of stable isotope and genetic gut content analyses was used. For the latter approach 22 group-specific primers were developed covering a broad range of aquatic invertebrate taxa. These methods were applied on macroinvertebrates collected from different site from the River Rhine system. At an invasion front of D. villosus in the Untere Lorze it was investigated if the predatory potential of the species would be one key factor for displacing native amphipod species. However, there was no evidence for intraguild predation, because for one thing the invasive amphipod species showed a strong overlap of the isotopic niche to the native ones, for the other thing DNA of native gammarid species was not detected in any gut of D. villosus. Comparable results were found for sites where D. villosus is well established; overlap of the isotopic niche to coexisting native or other invasive amphipod species was at least 40% and only single individuals of D. villosus had recently ingested at least parts of gammarids. Genetic gut content analyses from specimen of D. villosus from ten different microhabitats sampled in the River Rhine revealed only a low degree of consumed macroinvertebrates in general based on 16 group-specific primers for potential relevant prey taxa of D. villosus. Stable isotope analyses showed a comparable trophic level of the invasive amphipod species to those of primary consumers. Hence, D. villosus is rather an omnivore than a predator under natural conditions. Analyses of the diversity and density of taxa determined by quantitative benthic samples from the ten sites identified D. villosus as one of the nine taxa determining the pattern of the community, but only explaining 4.35% variation in the benthic community. However, following the invasion of D. villosus density of indigenous amphipods declined in many cases. Therefore, such a case with Gammarus roeselii was investigated in Lake Constance in order to evaluate a potential reduction in genetic diversity. Based on microsatellite analyses, no evidence for a genetic depletion of G. roeselii was found, neither on the temporal nor on the spatial scale, but an impact on the genetic structure cannot be excluded completely as effects on the genetic scale might also occur with a temporal delay. This project was one of the first assessing trophic interactions between native and the invasive amphipod D. villosus in the field, and thus its effect on the benthic community structure on the population level. It can be concluded from the results that the strong predatory effect of D. villosus, which is known from the several laboratory experiments is not the main factor explaining the success of this invasive species in European waterways. Furthermore, the contribution to structuring the benthic community might be smaller than supposed from earlier studies.
Publications
- (2013). Characterization of the first twelve microsatellite loci for the amphipod Gammarus roeselii (Crustacea: Amphipoda). Conservation Genetics Resources 5: 955-957
Gemmer, I. and R. Gergs
(See online at https://doi.org/10.1007/s12686-013-9941-5) - (2013). Establishment of group-specific PCR primers for the identification of freshwater macroinvertebrates. Conservation Genetics Resources 5: 1091-1093
Koester, M., S. Claßen and R. Gergs
(See online at https://doi.org/10.1007/s12686-013-9998-1) - (2014). No evidence for intraguild predation of Dikerogammarus villosus (Sowinsky 1894) at an invasion front in the Untere Lorze, Switzerland. Aquatic Invasions, 9, 489–497
Koester, M. and R. Gergs
(See online at https://doi.org/10.3391/ai.2014.9.4.07) - (2015). First detection of prey DNA in Hygrobates fluviatilis (Hydrachnidia, Acari) - a new approach for determining predator-prey relationships in water mites. Experimental and Applied Acarology
Martin, P., M. Koester, L. Schynawa and R. Gergs
(See online at https://doi.org/10.1007/s10493-015-9956-6)
