| 1. |
- Rahlff, Janina, et al.
(författare)
-
Ecogenomics and cultivation reveal distinctive viral-bacterial communities in the surface microlayer of a Baltic Sea slick
- 2023
-
Ingår i: ISME Communications. - : Springer Nature. - 2730-6151. ; 3:1
-
Tidskriftsartikel (refereegranskat)abstract
- Visible surface films, termed slicks, can extensively cover freshwater and marine ecosystems, with coastal regions being particularly susceptible to their presence. The sea-surface microlayer (SML), the upper 1-mm at the air-water interface in slicks (herein slick SML) harbors a distinctive bacterial community, but generally little is known about SML viruses. Using flow cytometry, metagenomics, and cultivation, we characterized viruses and bacteria in a brackish slick SML in comparison to non-slick SML as well as seawater below slick and non-slick areas (subsurface water = SSW). Size-fractionated filtration of all samples distinguished 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. Specific metabolic profiles of bacterial metagenome-assembled genomes and isolates in the slick SML included a prevalence of genes encoding motility and carbohydrate-active enzymes (CAZymes). Several vOTUs were enriched in slick SML, and many virus variants were associated with particles. Nine vOTUs were only found in slick SML, six of them being targeted by slick SML-specific clustered-regularly interspaced short palindromic repeats (CRISPR) spacers likely originating from Gammaproteobacteria. Moreover, isolation of three previously unknown lytic phages for Alishewanella sp. and Pseudoalteromonas tunicata, abundant and actively replicating slick SML bacteria, suggests that viral activity in slicks contributes to biogeochemical cycling in coastal ecosystems.
|
|
| 2. |
- Rahlff, Janina, et al.
(författare)
-
Ecogenomics reveals distinctive viral-bacterial communities in the surface microlayer of a natural surface slick
- 2024
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- 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.
|
|
| 3. |
- Cunliffe, Michael, et al.
(författare)
-
Sea surface microlayers : A unified physicochemical and biological perspective of the air-ocean interface
- 2013
-
Ingår i: Progress in Oceanography. - : Elsevier BV. - 0079-6611 .- 1873-4472. ; 109, s. 104-116
-
Forskningsöversikt (refereegranskat)abstract
- The sea surface microlayer (SML) covers more than 70% of the Earth's surface and is the boundary layer interface between the ocean and the atmosphere. This important biogeochemical and ecological system is critical to a diverse range of Earth system processes, including the synthesis, transformation and cycling of organic material, and the air-sea exchange of gases, particles and aerosols. In this review we discuss the SML paradigm, taking into account physicochemical and biological characteristics that define SML structure and function. These include enrichments in biogenic molecules such as carbohydrates, lipids and proteinaceous material that contribute to organic carbon cycling, distinct microbial assemblages that participate in air-sea gas exchange, the generation of climate-active aerosols and the accumulation of anthropogenic pollutants with potentially serious implications for the health of the ocean. Characteristically large physical, chemical and biological gradients thus separate the SML from the underlying water and the available evidence implies that the SML retains its integrity over wide ranging environmental conditions. In support of this we present previously unpublished time series data on bacterioneuston composition and SML surfactant activity immediately following physical SML disruption; these imply timescales of the order of minutes for the reestablishment of the SML following disruption. A progressive approach to understanding the SML and hence its role in global biogeochemistry can only be achieved by considering as an integrated whole, all the key components of this complex environment.
|
|
| 4. |
- Gassen, Lisa, et al.
(författare)
-
The impact of rainfall on the sea surface salinity : a mesocosm study
- 2024
-
Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 14
-
Tidskriftsartikel (refereegranskat)abstract
- Sea surface salinity may serve as a tracer for freshwater fluxes because it is linked to evaporation and precipitation that force the freshwater balance of the ocean's surface. The relationship between freshwater fluxes and salinity anomalies in the upper few centimeters remains widely unknown. In a mechanistic approach, we investigated how these anomalies develop by conducting experiments with artificial rain over a large basin. We measured conductivity and temperature at different depths and rain characteristics (intensity, rain temperature, droplet sizes, and velocities). In the absence of turbulence, the rain causes a strong salinity change of up to 6.02 g kg-1 in 0-4 cm depth. At the highest rain intensity of 56 mm h-1 salinity changed thrice as fast as at an intensity of 18 mm h-1. At the sea surface microlayer (first millimeter of the surface) the anomalies are always highest and reached a maximum of 14.18 g kg-1. With mechanical mixing, salinity changes were less pronounced (maximum SML salinity anomaly: 6.17 g kg-1, and freshwater was mixed fast with the existing seawater body. In general, our study shows that freshwater remains in the upper few centimeters, and even with induced turbulence, are not mixed below 16 cm.
|
|
| 5. |
- Rahlff, Janina, et al.
(författare)
-
High wind speeds prevent formation of a distinct bacterioneuston community in the sea-surface microlayer
- 2017
-
Ingår i: FEMS Microbiology Ecology. - : Oxford University Press. - 0168-6496 .- 1574-6941. ; 93:5
-
Tidskriftsartikel (refereegranskat)abstract
- The sea-surface microlayer (SML) at the boundary between atmosphere and hydrosphere represents a demanding habitat for bacteria. Wind speed is a crucial but poorly studied factor for its physical integrity. Increasing atmospheric burden of CO2, as suggested for future climate scenarios, may particularly act on this habitat at the air–sea interface. We investigated the effect of increasing wind speeds and different pCO2 levels on SML microbial communities in a wind-wave tunnel, which offered the advantage of low spatial and temporal variability. We found that enrichment of bacteria in the SML occurred solely at a U10 wind speed of ≤5.6 m s−1 in the tunnel and ≤4.1 m s−1 in the Baltic Sea. High pCO2 levels further intensified the bacterial enrichment in the SML during low wind speed. In addition, low wind speed and pCO2 induced the formation of a distinctive bacterial community as revealed by 16S rRNA gene fingerprints and influenced the presence or absence of individual taxonomic units within the SML. We conclude that physical stability of the SML below a system-specific wind speed threshold induces specific bacterial communities in the SML entailing strong implications for ecosystem functioning by wind-driven impacts on habitat properties, gas exchange and matter cycling processes.
|
|
| 6. |
- Rahlff, Janina, et al.
(författare)
-
Overlooked Diversity of Ultramicrobacterial Minorities at the Air-Sea Interface
- 2020
-
Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 11:11
-
Tidskriftsartikel (refereegranskat)abstract
- Members of the Candidate phylum Patescibacteria, also called Candidate Phyla Radiation (CPR), are described as ultramicrobacteria with limited metabolic capacities. Wide diversity and relative abundances up to 80% in anaerobic habitats, e.g., in groundwater or sediments are characteristic for Candidatus Patescibacteria. However, only few studies exist for marine surface water. Here, we report the presence of 40 patescibacterial candidate clades at air-sea interfaces, including the upper water layer, floating foams and the sea-surface microlayer (SML), a < 1 mm layer at the boundary between ocean and atmosphere. Particle-associated (>3 mu m) and free-living (3-0.2 mu m) samples were obtained from the Jade Bay, North Sea, and 16S rRNA (gene) amplicons were analyzed. Although the abundance of Cand. Patescibacteria representatives were relatively low (<1.3%), members of Cand. Kaiserbacteria and Cand. Gracilibacteria were found in all samples. This suggests profound aerotolerant capacities of these phylogenetic lineages at the air-sea interface. The presence of ultramicrobacteria in the >3 mu m fraction implies adhesion to bigger aggregates, potentially in anoxic niches, and a symbiotic lifestyle. Due to their small sizes, Cand. Patescibacteria likely become aerosolized to the atmosphere and dispersed to land with possible implications for affecting microbial communities and associated processes in these ecosystems.
|
|
| 7. |
- Rahlff, Janina, et al.
(författare)
-
Oxygen profiles across the sea-surface microlayer - effects of diffusion and biological activity
- 2019
-
Ingår i: Frontiers in Marine Science. - : Frontiers Media S.A.. - 2296-7745. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- Gas exchange across the air-water interface is strongly influenced by the uppermost water layer (< 1 mm), the sea-surface microlayer (SML). However, a clear understanding about how the distinct physicochemical and biological properties of the SML affect gas exchange is lacking. We used an automatic microprofiler with Clark-type microsensors to measure small-scale profiles of dissolved oxygen in the upper 5 cm of the water column in a laboratory tank filled with natural seawater. We aimed to link changing oxygen concentrations and profiles with the metabolic activity of plankton and neuston, i.e., SML-dwelling organisms, in our artificial, low-turbulence set-up during diel cycles. We observed that temporal changes of the oxygen concentration in near surface water (5 cm depth) could not be explained by diffusive loss of oxygen, but by planktonic activity. Interestingly, no influence of strong neuston activity on oxygen gradients at the air-water interface was detectable. This could be confirmed by a modeling approach, which revealed that neuston metabolic activity was insufficient to create distinct curvatures into these oxygen gradients. Moreover, the high neuston activity in our study contributed only ≤ 7.1% (see Supplementary Table 4) to changes in oxygen concentration in the tank. Overall, this work shows that temporal and vertical variation of oxygen profiles across the air-water interface in controlled laboratory set-ups is driven by biological processes in the underlying bulk water, with negligible effects of neuston activity.
|
|
| 8. |
- Rahlff, Janina, et al.
(författare)
-
Sea foams are ephemeral hotspots for distinctive bacterial communities contrasting sea-surface microlayer and underlying surface water.
- 2021
-
Ingår i: FEMS Microbiology Ecology. - : Oxford Academic. - 0168-6496 .- 1574-6941. ; 97:4
-
Tidskriftsartikel (refereegranskat)abstract
- 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 distinctive foam bacterial communities compared with SML and underlying water, with high abundance of Gammaproteobacteria. Typical SML dwellers such as Pseudoalteromonas and Vibrio 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 the previous assumption 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.
|
|
| 9. |
- Rahlff, Janina, et al.
(författare)
-
Short-term responses to ocean acidification : effects on relative abundance of eukaryotic plankton from the tropical Timor Sea
- 2021
-
Ingår i: Marine Ecology Progress Series. - : Inter-Reserch Science Publisher. - 0171-8630 .- 1616-1599. ; 658, s. 59-74
-
Tidskriftsartikel (refereegranskat)abstract
- 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 (mean ± SD pCO2 = 1823 ± 161 μatm and pHT = 7.46 ± 0.05) versus in situ CO2 (504 ± 42 µatm, 7.95 ± 0.04) seawater on the community composition of marine planktonic eukaryotes after 3 and 48 h 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. Increased CO2 significantly suppressed the relative abundances of different eukaryotic operational taxonomic units (OTUs), including important primary producers, although the chlorophyll a concentration remained constant. OA effects on eukaryotes were consistent between total (DNA-based) and active (cDNA-based) taxa after 48 h, e.g. for the diatoms Trieres chinensis and Stephanopyxis turris. Effects of OA on the relative abundances of OTUs were often species- or even ecotype-specific, and the incubation selectively allowed for detection of the OA-sensitive OTUs that benefitted the most from incubation in a closed bottle, as containment effects on the community structure were evident after 48 h. Many OTUs were adversely affected by sudden decreases of seawater pH, suggesting high sensitivity to OA at the base of the tropical marine biodiversity and difficult-to-predict outcomes for food-web functioning in the future ocean.
|
|
| 10. |
- Rahlff, Janina, et al.
(författare)
-
SISI: A new device for in situ incubations at the ocean surface
- 2017
-
Ingår i: Journal of Marine Science and Engineering. - : MDPI. - 2077-1312. ; 5:4
-
Tidskriftsartikel (refereegranskat)abstract
- The sea-surface microlayer (SML) forms the uppermost boundary layer between atmosphere and ocean, and has distinctive physico-chemical and biological features compared to the underlying water. First findings on metabolic contributions of microorganisms to gas exchange processes across the SML raised the need for new in situ technologies to explore plankton-oxygen turnover in this special habitat. Here, we describe an inexpensive research tool, the Surface In Situ Incubator (SISI), which allows simultaneous incubations of the SML, and water samples from 1 m and 5 m, at the respective depths of origin. The SISI is deployed from a small boat, seaworthy up to 5 bft (Beaufort scale), and due to global positioning system (GPS) tracking, capable of drifting freely for hours or days. We tested the SISI by applying light/dark bottle incubations in the Baltic Sea and the tropical Pacific Ocean under various conditions to present first data on planktonic oxygen turnover rates within the SML, and two subsurface depths. The SISI offers the potential to study plankton-oxygen turnover within the SML under the natural influence of abiotic parameters, and hence, is a valuable tool to routinely monitor their physiological role in biogeochemical cycling and gas exchange processes at, and near, the sea surface.
|
|
