Riverine vertebrate metacommunities using eDNA

In traditional ecology, the composition and biodiversity of communities is explained mainly by determining environmental factors such as light, water availability or competition. Metacommunity ecology complements exchanges between different local communities as another important factor influencing biodiversity and community composition. In this project, we add another important component: time. We investigate how the interplay between changes in environmental conditions and inter-community exchanges affects composition and biodiversity over time. For this purpose, we investigate floodplains with their strong dynamics as model systems. Depending on the water level, from dry periods to floods, both the environmental factors in the water bodies and the exchange between communities in the water bodies change over time. Due to this dynamics, floodplains are also among the most diverse and species-rich habitats worldwide and are, therefore, particularly suitable for the research of these complex interrelationships. An important innovation in the project is the use of environmental DNA to study the biotic communities. DNA, the carrier of genetic information, is released into the environment by organisms and can subsequently be used to identify species in communities. This method is particularly efficient because it is possible to record the entire community, in this case vertebrates, with water samples. The project is being implemented on the River Danube in order to investigate the dynamics in floodplain systems in Hungary and Austria. At the end of the project, we will have a better understanding of the spatial and temporal organisation of fish and amphibian communities. As the investigated communities are including a high number of endangered species, the results also provide an important basis for the protection and conservation of these species and directly support the management of the protected areas along the River Danube.

In the four-year research project "eDNA Analysis of Vertebrate Metacommunities in River Floodplains," a team of scientists from the HUN-REN Balaton Limnological Research Institute and the University of Natural Resources and Life Sciences, Vienna (BOKU) investigated the dynamics of fish and amphibian communities in the floodplain ecosystems of the Danube River. In the first phase of the project, the environmental DNA (eDNA) method was specifically tested for its applicability in floodplains. The results showed that eDNA provides high detection accuracy under both flowing and standing water conditions. This made it possible to collect a comprehensive dataset over a three-year period from two major floodplain areas - the Donau-Auen National Park (Austria) and Gemenc (Hungary). The study covered a wide range of aquatic habitats, from periodically drying ponds and temporarily connected side channels to the main channel of the Danube, encompassing all hydrological conditions typical of floodplains - from flood events to extended dry phases. The central research question addressed how fish and amphibian communities are influenced by spatial differences among waterbody types, temporal changes in water levels, species exchange, species interactions, and the interplay among these factors. The results reveal the complex functioning of aquatic communities. During low-water conditions, floodplain waterbodies are largely isolated, and local habitat characteristics primarily determine community composition. As water levels rise, hydrological connectivity between sites increases, facilitating species exchange and leading to a homogenization of communities. This effect depends strongly on the location and type of waterbody: in sites that remain largely disconnected even during floods, community composition remains stable and shaped by local conditions. In contrast, in regularly connected floodplain waters, connectivity and exchange processes play a dominant role in determining biodiversity. In addition, the data demonstrate that species interactions, such as predator-prey relationships, significantly contribute to the spatial distribution of species. The studied species differ markedly in their dependence on water level fluctuations, dispersal capacity, and sensitivity to local conditions. These insights provide valuable guidance for the targeted conservation of endangered species and for the management of dynamic floodplain ecosystems.