Biology subjects

Wurl, O.

Publications and source records attributed to Wurl, O..

4 recordsLinked to original sources

bioRxiv2025

Biogeochemical function of slicks in coastal surface waters of the Baltic Sea

The sea-surface microlayer (SML) is a crucial ocean-atmosphere interface involved in gas exchange and nutrient cycling. Slicks, i.e., viscous surface layers, common in coastal regions serve as microbial hotspots. We studied microbial abundance, surfactants, dissolved organic carbon (DOC), and net community production (NCP) of O2 in slick and non-slick SMLs and underlying water (ULW) in the coastal Baltic Sea. Slicks often showed higher surfactant levels compared to the ULW. Microbial respiration often exceeded production, resulting in net O2 consumption, although some ULW sites exhibited net O2 production. The SML was enriched with pico- and nanophytoplankton, with cyanobacteria being negatively correlated with total dissolved nitrogen. In contrast, microphytoplankton accumulated in the ULW, indicating niche separation with depth. Microscopy revealed ciliates and juvenile sporophytes dominating a slicks >100 {micro}m fraction. In eutrophic coastal systems, slicks influence plankton communities and O2 dynamics, supporting their role in surface biogeochemical cycling and climate-driven changes.

microbiology↗

bioRxiv2023

Ecogenomics reveals distinctive viral-bacterial communities in the surface microlayer of a natural surface slick

Visible surface films, termed slicks, can extensively cover the sea surface, particularly in coastal regions. The sea-surface microlayer (SML), the upper 1-mm at the air-water interface in slicks (slick SML) harbors a distinctive bacterial community, but little is known about SML viruses. Using flow cytometry, metagenomics, and cultivation, we investigated viruses and the bacterial community from a brackish slick SML in comparison to non-slick SML as well as the seawater below (SSW). We conducted size-fractionated filtration of all samples to distinguish viral attachment to hosts and particles. The slick SML contained higher abundances of virus-like particles, prokaryotic cells, and dissolved organic carbon compared to non-slick SML and SSW. The community of 428 viral operational taxonomic units (vOTUs), 426 predicted as lytic, distinctly differed across all size fractions in the slick SML compared to non-slick SML and SSW. The distinctness was underlined by specific metabolic profiles of bacterial metagenome assembled genomes and isolates, which revealed prevalence of motility genes and diversity of CAZymes in the slick SML. Despite overall lower diversity, several vOTUs were enriched in slick SML over slick SSW. Nine vOTUs were only found in slick SML and six of them were targeted by slick SML-specific CRISPR spacers likely originating from Gammaproteobacteria. Moreover, isolation of three previously unknown lytic phages for Alishewanella sp. and Pseudoalteromonas tunicata, representing abundant and actively replicating slick SML bacteria, suggests that viral activity in slicks can contribute to biogeochemical cycling in coastal ecosystems.

microbiology↗

bioRxiv2020

Short-term responses to ocean acidification: effects on relative abundance of eukaryotic plankton from the tropical Timor Sea

Anthropogenic carbon dioxide (CO2) emissions drive climate change and pose one of the major challenges of our century. The effects of increased CO2 in the form of ocean acidification (OA) on the communities of marine planktonic eukaryotes in tropical regions such as the Timor Sea are barely understood. Here, we show the effects of high CO2 (pCO2=1823{+/-}161 atm, pHT=7.46{+/-}0.05) versus in situ CO2 (pCO2=504{+/-}42 atm, pHT=7.95{+/-}0.04) seawater on the community composition of marine planktonic eukaryotes immediately and after 48 hours of treatment exposure in a shipboard microcosm experiment. Illumina sequencing of the V9 hypervariable region of 18S rRNA (gene) was used to study the eukaryotic community composition. Down-regulation of extracellular carbonic anhydrase occurred faster in the high CO2 treatment. Increased CO2 significantly suppressed the relative abundances of different eukaryotic operational taxonomic units (OTUs), including important primary producers. These effects were consistent between abundant (DNA-based) and active (cDNA-based) taxa after 48 hours, e.g., for the diatoms Trieres chinensis and Stephanopyxis turris. Effects were also very species-specific among different diatoms. Planktonic eukaryotes showed adaptation to the CO2 treatment over time, but many OTUs were adversely affected by decreasing pH. OA effects might fundamentally impact the base of marine biodiversity, suggesting profound outcomes for food web functioning in the future ocean.

ecology↗

bioRxiv2019

Marine foams represent compressed sea-surface microlayer with distinctive bacterial communities

The occurrence of foams at oceans surfaces is patchy and generally short-lived but a detailed understanding of bacterial communities inhabiting sea foams is lacking. Here we investigated how marine foams differ from the sea-surface microlayer (SML), a <1 mm thick layer at the air-sea interface and underlying water from 1 m depth. Samples of sea foams, SML and underlying water collected from the North Sea and Timor Sea indicated that foams were often characterized by a high abundance of small eukaryotic phototrophic and prokaryotic cells as well as a high concentration of surface-active substances (SAS). Amplicon sequencing of 16S rRNA (gene) revealed a distinctive foam bacterial community compared to SML and underlying water, with high abundance of Gammaproteobacteria. Especially Pseudoalteromonas and Vibrio, typical SML dwellers, were highly abundant, active foam inhabitants and thus might enhance foam formation and stability by producing SAS. Despite a clear difference in the overall bacterial community composition between foam and SML, the presence of SML bacteria in foams supports previous assumptions that foam is strongly influenced by the SML. We conclude that active and abundant bacteria from interfacial habitats potentially contribute to foam formation and stability, carbon cycling and air-sea exchange processes in the ocean. One-sentence summaryFloating foams at the oceans surface have a unique bacterial community signature in contrast to sea-surface microlayer and underlying water but receive and select for bacterial inhabitants from surface habitats.

microbiology↗