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Aim: Waterbirds are important dispersal vectors of multicellular organisms; however, no study to date has focused on their potential role in dispersing aquatic microbial communities. We explicitly studied endozoochory of prokaryotes and unicellular microeukaryotes by waterbirds using DNA metabarcoding. By directly comparing the dispersed set of organisms to the source pool of a natural metacommunity, we aimed at a realistic estimate of the importance of waterbird zoochory for natural microbial communities. Location: Temporary saline soda pans in Austria and Hungary. Taxon: Prokaryotes and unicellular microeukaryotes. Methods: In 2017 and 2018, water samples were collected from a network of 25 temporary ponds along with fresh droppings of five waterbird species including the dominant greylag goose (Anser anser). Prokaryotic and microeukaryotic communities were identified via 16S and 18S rRNA gene amplicon sequencing. After quality filtering of sequence reads, pro‐ and microeukaryotic amplicon sequence variant (ASV) compositions were compared between the aquatic and dropping samples, across years and waterbird species. Results: 28% of the dominant aquatic prokaryotic and 19% of the microeukaryotic ASVs were transported by A. anser. ASV richness was lower, but compositional variation was higher in A. anser droppings than in aquatic communities, probably resulting from stochastic pick‐up from multiple aquatic habitats. The composition of prokaryotic ASVs in bird droppings differed among the 2 years and reflected the actual aquatic communities. The dispersed set of microbes were largely similar among the waterbird species except for the planktivore filter‐feeder northern shoveler (Spatula clypeata), which dispersed more microeukaryotes than the other waterbirds. Main conclusions: Using an amplicon sequencing approach to characterize aquatic microorganisms in waterbird droppings and in the associated environment, our study provides strong evidence for endozoochory of natural communities. These results imply that waterbirds may be crucial in maintaining ecological connectivity between aquatic habitats at the level of microbial communities. [ABSTRACT FROM AUTHOR]

Omnivory is widespread in food webs, with an important stabilising effect. The strength of omnivorous trophic interactions may change considerably with changes in the local environment.Shallow temporary waters are often characterised by high levels of inorganic turbidity that may directly limit the food uptake of filter‐feeding organisms, but there is little evidence on how it might affect omnivorous species. Anostracans are key species of temporary waters and recent evidence suggests that these organisms are omnivorous consumers of both phyto‐ and zooplankton.Using Branchinecta orientalis as a model species, our aim was to test how turbidity affects the feeding of an omnivorous anostracan. To do this, we used short‐term feeding experiments and stable isotope analyses, with animals collected from soda pans in eastern Austria. In the feeding experiments, algae and zooplankton were offered as food either separately or in combination. The prey type treatments were crossed with turbidity levels in a factorial design.There was a pronounced decrease in the ingested algal biomass with increasing turbidity. Conversely, ingestion rates on zooplankton were less affected by turbidity. Stable isotope analyses from field material supported our experimental results by showing a positive relationship of the trophic position of anostracans and the trophic niche of the communities with turbidity.Our results show that turbidity modulates the intraguild trophic relationship between anostracans and their prey by shifting the diet of anostracans from more herbivorous in transparent to more carnivorous in turbid waters. Thus, inorganic turbidity might also have a community‐shaping role in plankton communities of temporary waters through altering trophic relationships. [ABSTRACT FROM AUTHOR]