Environmental DNA-based taxon identification is transitioning from research to official biomonitoring. To assess whether combining amplicon sequencing with machine learning holds additional promise, we conducted a year-long, high-resolution sampling campaign in the War-now Estuary and along the Baltic Sea coast near Rostock. Our results highlight the use of large environmental amplicon datasets in combination with machine lear...

Eutrophication in the Baltic Sea has caused an imbalance in the inorganic nitrogen (N) to phosphorus (P) ratio, leaving excess phosphate (PO 4 ) after the phytoplankton spring bloom that terminates after N depletion. Using monitoring data, we demonstrated that the PO 4 concentration has continued to increase in the outermost Gulf of Finland during past decades. We further investigated the fate of such excess PO 4 in a two‐week...

Aim was to assess whether a comprehensive approach linking existing knowledge with monitoring and modeling can provide an improved insight into coastal and marine plastics pollution. We focused on large micro- and mesoplastic (1–25 mm) and selected macroplastic items. Emission calculations, samplings in the Warnow river and estuary (water body and bottom sediments) and a flood accumulation zone monitoring served as basis for m...

Microplastic particles have been found in all the world’s oceans. Since their surfaces are microbially colonised, research is currently determining whether microbes are able to degrade the synthetic polymers. We show that their contribution to the biodegradation of plastics seems to be extremely limited. Also, it is unlikely that microbes specialise in plastic degradation through evolutionary adaptation. This is not only due t...

Summary Microplastics in marine ecosystems are colonized by diverse prokaryotic and eukaryotic communities. How these communities and their functional profiles are shaped by the artificial surfaces remains broadly unknown. In order to close this knowledge gap, we set up an in situ experiment with pellets of the polyolefin polymer polyethylene (PE), the aromatic hydrocarbon polymer polystyrene (PS), and wooden beads along a coa...

Methane enrichments are frequently observed in the oxic upper water column of the central Baltic Sea during summer months. However, methane sources as well as the fate of methane produced in surface near waters still remain unclear. In the present study, we conducted ship-based grazing experiments to examine the presence of methanogenic archaea in copepod faecal pellets. We quantified bacterial and archaeal 16S rRNA and the mc...

We report on methane enrichments that were observed during summer in the upper water column of the Gotland Basin, central Baltic Sea. In the eastern part of the basin, methane concentrations just below the thermocline varied between 15 nM and 77 nM, in contrast to the western part where no methane enrichments could be detected. Stable carbon isotope ratios of methane ( δ 13 C‐CH 4 of −67.6‰) indicated its in situ biogenic orig...

Summary Despite increasing concerns about microplastic (MP) pollution in aquatic ecosystems, there is insufficient knowledge on how MP affect fungal communities. In this study, we explored the diversity and community composition of fungi attached to polyethylene (PE) and polystyrene (PS) particles incubated in different aquatic systems in north‐east Germany: the Baltic Sea, the River Warnow and a wastewater treatment plant. Ba...

Summary Chemolithoautotrophic sulfur‐oxidizing and denitrifying Gamma ‐ (particularly the SUP05 cluster) and Epsilonproteobacteria (predominantly Sulfurimonas subgroup GD17) are assumed to compete for substrates (electron donors and acceptors) in marine pelagic redox gradients. To elucidate their ecological niche separation we performed 34 S 0 , 15 and H 13 stable‐isotope incubations with water samples from Baltic Sea suboxic,...

Summary Knowledge on A ctinobacteria rhodopsin gene ( actR ) diversity and spatial distribution is scarce. The B altic S ea is characterized by strong salinity gradients leading to the coexistence of marine and freshwater bacteria and hence is an ideal study area to elucidate the dispersion and phylogenetic affiliation of actR in dependence on salinity . ActR DGGE fingerprints in summer 2008 revealed between 3 and 19 distinct...

Summary Barrier zones between oxic and anoxic water masses (redoxclines) host highly active prokaryotic communities with important roles in biogeochemical cycling. In B altic S ea pelagic redoxclines, Epsilonproteobacteria of the genus S ulfurimonas (subgroup GD 17) have been shown to dominate chemoautotrophic denitrification. However, little is known on the loss processes affecting this prokaryotic group. In the present study...

Summary Pelagic marine oxygen‐depleted zones often exhibit a redox gradient, caused by oxygen depletion due to biological demand exceeding ventilation, and the accumulation of reduced chemical species, such as hydrogen sulfide. These redox gradients harbour a distinct assemblage of epsilonproteobacteria capable of fixing carbon dioxide autotrophically in the dark and potentially of utilizing hydrogen sulfide chemolithotrophica...

Steep redoxclines form between oxic surface water and the stagnant, sulfidic hypolimnion in the eutrophied, brackish water Baltic Sea. Nitrification, denitrification, and anammox were measured at and below the redoxcline to quantify the role of water‐column nitrogen processes in the overall magnitude of nitrogen removal in the Baltic Sea. Rates of nitrification were very high (up to 85 nmol N L −1 d −1 ) at the oxic‐anoxic int...

Summary Molecular surveys of marine picoeukaryotes have revealed a large number of sequences unrelated to cultured organisms, such as those forming the marine stramenopile (MAST)‐4 clade. Recent FISH (fluorescent in situ hybridization) data have shown that MAST‐4 cells are uncultured heterotrophic flagellates of 2–3 μm in size that have a global distribution in non‐polar marine waters. However, FISH is time‐consuming and hard...

Summary Marine pelagic redoxclines are zones of high dark CO 2 fixation rates, which can correspond up to 30% of the surface primary production. However, despite this significant contribution to the pelagic carbon cycle, the identity of most chemolithoautotrophic organisms is still unknown. Therefore, the aim of this study was to directly link the dark CO 2 fixation capacity of a pelagic redoxcline in the central Baltic Sea (L...