Organism groups

Organism groups

RESIST addresses components of the entire riverine food web:

Viruses

Aquatic prokaryotes and eukaryotes are infected by a large diversity of viruses. We assume that viral diversity within fluvial systems is directly correlated with that of their bacterial hosts, which in turn is influenced by different environmental factors.

Bacteria

Bacteria are the main players for important ecosystem functions such as nutrient cycling and DOC degradation in aquatic ecosystems. The ExStream experiment in phase I revealed flow velocity as a key driver for stream microbiomes, outcompeting the effects of other stressors. After recovery, however, some stressed river microbiomes did not return to their unexposed composition highlighting the legacy of stressor effects.

Fungal heterotrophs

Fungal heterotrophs, together with bacteria, dominate microbial decomposer communities, which degrade coarse particulate organic matter (CPOM). A leaf-litter decomposition experiment within the Boye catchment tested the hypothesis that litter decomposition would be least efficient at recently restored sites.  However, decomposition dynamics was independent of the time elapsed since restoration and mainly explained by land use, pH, and chloride concentrations, suggesting extremely rapid recovery of ecosystem functioning or persisting functional impairment across the stream network.

Protists

The response of heterotrophic nanoflagellates to salinity and temperature differs between taxa and this difference is more pronounced for temperature. The taxon-specific responses result in a shift of community composition. The turn-over of differently adapted cryptic species with similar feeding preferences and predator-prey interactions may stabilise microbial food webs facing environmental change. Diatom species responded with a bell-shaped growth curve to temperature changes, while their growth tended to decrease with increasing electrical conductivity.

Invertebrates

Benthic invertebrates are a large and diverse organism group colonising all riverine bottom habitats and feeding on a great variety of food sources. In our field studies, we observed an increasing similarity of benthic invertebrate communities with time since restoration in the Boye catchment, indicating a random starting community that is increasingly streamlined with the development of environmental conditions.

Fish

Freshwater fish, as large organisms and top predators of riverine food webs, integrate larger spatial and temporal scales. We could show in an ExStream experiment involving fish affect macroinvertebrate dispersal by release of chemical cues. Exposure to anthropogenic stressors suppressed this reaction.

Parasites

Parasites are a diverse and widespread group occurring in many aquatic hosts. We showed that diversity and abundance of microsporidians in amphipods are not related to the state of degradation of the Boye and Kinzig sites, and that parasite diversity is not related to the diversity of macroinvertebrates. This may indicate that there are still other factors preventing the further development of parasite communities. In controlled feeding experiments, carbon-based isotope analysis of amino acids revealed parasite (cestode) nutrient assimilation closely linked to the liver metabolism of the fish host (three-spined stickleback). Additionally, increased amino acid fractionation in infected sticklebacks suggested increased (immune-) metabolic activities due to parasitic infection.