Distribution and conservation status of fairy shrimps (Crustacea: Anostraca) in the astatic soda pans of the Carpathian basin: the role of local and spatial factors

The distribution of Branchinecta orientalis, B. ferox and Chirocephalus carnuntanus was assessed in the natural and semi-natural astatic soda pans of the Carpathian basin. In Europe, these habitats are exclusively restricted to Hungary (Great Hungarian Plain), Austria (Seewinkel) and Serbia (Vojvodina). The present research is the first comprehensive large-scale study – covering an area of approximately 125,000 km2 – on these three fairy shrimp species in the region, and it is important especially in the case of Branchinecta spp., due to former taxonomical uncertainties. The local, land use and spatial effects on the species distribution were also analysed. The three anostracans were found to adopt different strategies, mainly according to the salinity of the pans. The apparently halophilous B. orientalis tolerated higher salinities than the other species, which can be regarded as habitat-generalist halotolerants, showing a high preference for soda waters in Central Europe. The density of the species was significantly affected only by local factors, while their occurrence was influenced also by pan isolation. Land use did not explain a significant amount of variation in either case. In conclusion, soda pans with a wide range of different salinities constitute a suitable habitat for all the three species. Also, protected areas with high number of pans – as Seewinkel (in Austria) or Kiskunság (in Hungary) – can play an essential role in the long-term conservation of these anostracans. Finally, we suggest that these species should be legally protected, primarily because the number of their habitats in the basin is seriously declining

Environmental changes associated with drying climate are expected to affect functional groups of pro- and microeukaryotes differently in temporary saline waters

Temporary ponds are among the most sensitive aquatic habitats to climate change. Their microbial communities have crucial roles in food webs and biogeochemical cycling, yet how their communities are assembled along environmental gradients is still understudied. This study aimed to reveal the environmental drivers of diversity (OTU-based richness, evenness, and phylogenetic diversity) and community composition from a network of saline temporary ponds, soda pans, in two consecutive spring seasons characterized by contrasting weather conditions. We used DNA-based molecular methods to investigate microbial community composition. We tested the effect of environmental variables on the diversity of prokaryotic (Bacteria, Cyanobacteria) and microeukaryotic functional groups (ciliates, heterotrophic flagellates and nanoflagellates, fungi, phytoplankton) within and across the years. Conductivity and the concentration of total suspended solids and phosphorus were the most important environmental variables affecting diversity patterns in all functional groups. Environmental conditions were harsher and they also had a stronger impact on community composition in the dry spring. Our results imply that these conditions, which are becoming more frequent with climate change, have a negative effect on microbial diversity in temporary saline ponds. This eventually might translate into community-level shifts across trophic groups with changing local conditions with implications for ecosystem functioning

Life-history omnivory in the fairy shrimp Branchinecta orientalis (Branchiopoda: Anostraca)

Very little is known about the feeding of naupliar and juvenile life stages of omnivorous fairy shrimps (Crustacea: Anostraca). Here, we aim to reveal whether the fairy shrimp Branchinecta orientalis is an ontogenetic omnivore and at which age and ontogenetic stage they gain the ability to feed on zooplankton. We assess how food uptake rates change with age until reaching maturity by providing algae (pico- and nanoplanktonic unicellular algae) and zooplankton (rotifers and copepod nauplii) as food in individual experiments. We found that the fairy shrimp B. orientalis started to feed on both types of algal prey immediately after hatching. Nanoplanktonic algae likely represented the most important food source until reaching maturity. Moreover, fairy shrimps started to feed on zooplankton already when they were 7 days old. Slow-moving rotifers gradually gained importance in the fairy shrimp diet with time. Our results reveal an ontogenetic change in the prey spectrum of fairy shrimp. The systematic shift towards omnivory likely affects both phyto- and zooplankton community composition, possibly contributing to temporal changes in food web dynamics in fairy shrimp habitats, and temporary ponds, which may warrant more detailed investigations in future studies

Interesting diatoms from a special habitat

The epiphytic diatoms of the soda ponds of bomb craters were sampled in 2014. The small ponds (area: 7.1-86.5 m2, depth: 4 to 60 cm) are located in the northern part of the Kiskunság National Park (47°7.403 'N, 19°8.187'E), near the village of Apaj in Hungary. Their salinity ranges from fresh water to moderately saline levels (conductivity of 1.3 to 7.1 mS cm-1). This area has patchy surface salinization, because the flow pattern of groundwater results extensive surface salinization in those discharge areas where the infiltrating freshwater does not superimpose the upwelling saline water. The salts origin from the overpressured NaCl-type water of the Pre-Neogene basement and the NaHCO3-type water of the Neogene sediments. The ponds can be characterized by different areal extent, depth and salinity, various conductivity, hydroperiod (1–9 months, the deepest ones do not dry out in years with high amount of precipitation due to probably more or less continuous supply by groundwater), plant coverage and width of macrophyte belt. All of the ponds were sampled except for the ones with very short (shorter than one month) hydroperiod. A total of 80 diatom taxa, representing 33 genera, were identified in these ponds. The genus Nitzschia was represented by the largest number of species (16), followed by the genus Gomphonema with 9 taxa. IndVal analysis identified 15 species with significant indicator values for ponds. Some interesting, rare or new diatoms for Hungarian flora have also been recorded, including Gomphonema jadwigiae, Halamphora dominici, Navicula wiesneri, Nitzschia austriaca, N. vitrea, Surirella peisonis

Pleistocene allopatric differentiation followed by recent range expansion explains the distribution and molecular diversity of two congeneric crustacean species in the Palaearctic

Pleistocene glaciations had a tremendous impact on the biota across the Palaearctic, resulting in strong phylogeographic signals of range contraction and rapid postglacial recolonization of the deglaciated areas. Here, we explore the diversity patterns and history of two sibling species of passively dispersing taxa typical of temporary ponds, fairy shrimps (Anostraca). We combine mitochondrial (COI) and nuclear (ITS2 and 18S) markers to conduct a range-wide phylogeographic study including 56 populations of Branchinecta ferox and Branchinecta orientalis in the Palaearctic. Specifically, we investigate whether their largely overlapping ranges in Europe resulted from allopatric differentiation in separate glacial refugia followed by a secondary contact and reconstruct their postglacial recolonization from the inhabited refugia. Our results suggest the existence of distinct refugia for the two species, with genetic divergence among intraspecific lineages consistent with late Pleistocene glacial cycles. While B. ferox lineages originated from Mediterranean refugia, the origin of B. orientalis lineages was possibly located on the Pannonian Plain. We showed that most dispersal events predominantly happened within 100 km, coupled with several recent long-distance events (> 1000 km). Hence the regional habitat density of suitable habitats in Central Europe is possibly a key to the co-existence of the two species. Overall, our study illustrates how isolation in combination with stochastic effects linked to glacial periods are important drivers of the allopatric differentiation of Palaearctic taxa

Microbial stowaways: Waterbirds as dispersal vectors of aquatic pro‐ and microeukaryotic communities

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 mi- croeukaryotes 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 tem- porary ponds along with fresh droppings of five waterbird species including the domi- nant 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) composi- tions 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 varia- tion was higher in A. anser droppings than in aquatic communities, probably resulting from stochastic pick-up from multiple aquatic habitats. The composition of prokary- otic 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