Search

Current research revealed distinct changes in ecosystem functions, and thus in ecosystem stability and resilience, caused by changes in community structure and diversity loss. Benthic species play an important role in benthic-pelagic coupling, such as through the remineralization of deposited organic material, and changes to benthic community structure and diversity have associated with changes in ecosystem functioning, ecosystem stability and resilience. However, the long-term variability of traits and functions in benthic communities is largely unknown. By using abundance and bioturbation potential of macrofauna samples, taken along a transect from the German Bight towards the Dogger Bank in May 1990 and annually from 1995 to 2017, we analysed the taxonomic and trait-based macrofauna long-term community variability and diversity. Taxonomic and trait-based diversity remained stable over time, while three different regimes were found, characterised by changes in taxonomic and trait-based community structure. Min/max autocorrelation factor analysis revealed the climatic variables sea surface temperature (SST) and North Atlantic Oscillation Index (NAOI), nitrite, and epibenthic abundance as most important environmental drivers for taxonomic and trait-based community changes.

Transparent exopolymer particles (TEPs) are a major source for both organic matter (OM) and carbon transfer in the ocean and into the atmosphere. Consequently, understanding the vertical distribution of TEPs and the processes which impact their movement is important in understanding the OM and carbon pools on a larger scale. Additionally, most studies looking at the vertical profile of TEPs have focused on large depth scales from 5 to 1000 m and have omitted the near-surface environment. Results from a study of TEP enrichment in the sea surface microlayer (SML) in different regions (tropical, temperate) has shown that, while there is a correlation between TEP concentration and primary production (PP) on larger or seasonal scales, such relationships break down on shorter timescales and spatial scales. Using a novel small-scale vertical sampler, the vertical distribution of TEPs within the uppermost 2 m was investigated. For two regions with a total of 20 depth profiles, a maximum variance of TEP concentration of 1.39×106 µg XG eq2 L−2 between depths and a minimum variance of 6×102 µg XG eq2 L−2 was found. This shows that the vertical distribution of TEPs was both heterogeneous and homogeneous at times. Results from the enrichment of TEPs and Chl a between different regions have shown TEP enrichment in the SML to be greater in oligotrophic waters, when both Chl a and TEP concentrations were low, suggesting the importance of abiotic sources for the enrichment of TEPs in the SML. However, considering multiple additional parameters that were sampled, it is clear that no single parameter could be used as a proxy for TEP heterogeneity. Other probable biochemical drivers of TEP transport are discussed.

Spin wave logic circuits using quantum oscillations of spins (magnons) as carriers of information have been proposed for next generation computing with reduced energy demands and the benefit of easy parallelization. Current realizations of magnonic devices have micrometer sized patterns. Here we demonstrate the feasibility of biogenic nanoparticle chains as the first step to truly nanoscale magnonics at room temperature. Our measurements on magnetosome chains (ca 12 magnetite crystals with 35 nm particle size each), combined with micromagnetic simulations, show that the topology of the magnon bands, namely anisotropy, band deformation, and band gaps are determined by local arrangement and orientation of particles, which in turn depends on the genotype of the bacteria. Our biomagnonic approach offers the exciting prospect of genetically engineering magnonic quantum states in nanoconfined geometries. By connecting mutants of magnetotactic bacteria with different arrangements of magnetite crystals, novel architectures for magnonic computing may be (self-) assembled., The capability to engineer magnon states in confined geometries is vital to future nano-magnonics. Here the authors demonstrate that the topology of the magnon bands is determined by the local arrangement and orientation of nanoparticles and can be controlled by the genotype of magnetotactic bacteria.

Latitudinal diversity gradients are well-known for plants and animals, but only recently similar patterns have been described for some specific microbial communities in distinct habitats. Although microbial diversity is well-investigated worldwide, most of the studies are spatially too restricted to allow general statements about global diversity patterns. Additionally, methodological differences make it hard and often impossible to compare several studies. This study investigated the cyanobacterial diversity in tidal flats along geographical and ecological gradients based on high-throughput sequencing of 16S rRNA gene fragments (Illumina MiSeq) and environmental data on a large spatial scale from the subtropics to the Arctic. Latitude and strongly correlated environmental parameters (e.g. temperature) were identified as important drivers of cyanobacterial diversity on global scale resulting in a latitudinal diversity gradient similar to that known from plants and animals. Other non-correlated parameters (e.g. grain size) were shown to be more important on local scales, although no consistent pattern occurred across different locations. Among a total number of 989 operational taxonomic units (OTUs) only one cosmopolitan (classified as Coleofasciculus chthonoplastes), but many location-specific and putative endemic ones (78%) were detected. High proportions of rare members of the community (up to 86%) were found in all samples. Phylogenetic beta diversity was shown to be influenced by the developmental stage of the mat community becoming increasingly similar with increasing stabilization.

In the central nervous system, neuronal processing relies on the precisely orchestrated formation of synapses during development. The first synapse of the visual system is a triad synapse, comprising photoreceptors, horizontal cells and bipolar cells. During the second postnatal week, the axon terminal processes of horizontal cells invaginate rod spherules, followed by rod bipolar cell dendrites. Both elements finally oppose the synaptic ribbon (the release site of glutamate). However, it has not been fully elucidated whether horizontal cells are essential for rod bipolar cell dendrites to find their way into the rod terminal. In the present study, we investigated this question by specifically ablating horizontal cells from the early postnatal mouse retina. We monitored the formation of the rod-to-rod bipolar cell synapse during retinal maturation until postnatal day 21. Based on quantitative electron microscopy, we found that without horizontal cells, the dendrites of rod bipolar cells never entered rod terminals. Furthermore, rods displayed significantly fewer and shorter presynaptic ribbons, suggesting that glutamate release is decreased, which coincided with significantly reduced expression of postsynaptic proteins (mGluR6, GPR179) in rod bipolar cells. Collectively, our findings uncover that horizontal cells are indeed necessary guideposts for rod bipolar cells. Whether horizontal cells release diffusible guidance cues or provide structural guidance by expressing specific cell adhesion molecules remains to be seen.

Neuronal gap junctions formed by connexin36 (Cx36) and chemical synapses share striking similarities in terms of plasticity. Ca2+/calmodulin-dependent protein kinase II (CaMKII), an enzyme known to induce memory formation at chemical synapses, has recently been described to potentiate electrical coupling in the retina and several other brain areas via phosphorylation of Cx36. The contribution of individual CaMKII isoforms to this process, however, remains unknown. We recently identified CaMKII-β at electrical synapses in the mouse retina. Now, we set out to identify cell types containing Cx36 gap junctions that also express CaMKII-β. To ensure precise description, we first tested the specificity of two commercially available antibodies on CaMKII-β-deficient retinas. We found that a polyclonal antibody was highly specific for CaMKII-β. However, a monoclonal antibody (CB-β-1) recognized CaMKII-β but also cross-reacted with the C-terminal tail of Cx36, making localization analyses with this antibody inaccurate. Using the polyclonal antibody, we identified strong CaMKII-β expression in bipolar cell terminals that were secretagogin- and HCN1-positive and thus represent terminals of type 5 bipolar cells. In these terminals, a small fraction of CaMKII-β also colocalized with Cx36. A similar pattern was observed in putative type 6 bipolar cells although there, CaMKII expression seemed less pronounced. Next, we tested whether CaMKII-β influenced the Cx36 expression in bipolar cell terminals by quantifying the number and size of Cx36-immunoreactive puncta in CaMKII-β-deficient retinas. However, we found no significant differences between the genotypes, indicating that CaMKII-β is not necessary for the formation and maintenance of Cx36-containing gap junctions in the retina. In addition, in wild-type retinas, we observed frequent association of Cx36 and CaMKII-β with synaptic ribbons, i.e., chemical synapses, in bipolar cell terminals. This arrangement resembled the composition of mixed synapses found for example in Mauthner cells, in which electrical coupling is regulated by glutamatergic activity. Taken together, our data imply that CaMKII-β may fulfill several functions in bipolar cell terminals, regulating both Cx36-containing gap junctions and ribbon synapses and potentially also mediating cross-talk between these two types of bipolar cell outputs.

Estuaries play a key role in controlling the land-ocean fluxes of dissolved organic matter (DOM), nutrients and trace metals. Here, we study how mangrove-fringed areas affect the molecular DOM and trace metal composition in a subtropical estuary. We combined molecular analysis of solid-phase extractable (SPE) DOM using ultrahigh-resolution mass spectrometry with organic and inorganic bulk parameter analyses in surface and porewater along the estuarine gradient of a mangrove-fringed estuary in Australia (Coffs Creek). Statistical analysis and mixing models demonstrate that the fluvial and mangrove-porewater derived DOM and inorganic chemical species were altered and/or removed by the estuarine filter before reaching the coastal ocean. The mangrove-fringed central estuary was a net source for dissolved Mn and Ba as well as total dissolved nitrogen (TDN) and dissolved organic carbon (DOC) to the tidal creek, likely due to the exchange of mangrove-porewater strongly enriched in these constituents. Dissolved Fe was removed from the water column, probably during the tidally driven circulation of creek water through the sulfidic mangrove sediments. In the mangrove-porewater dominated tidal creek, sulfur- and nitrogen-containing as well as aromatic DOM compounds were relatively enriched, whereas phosphorous-containing DOM was relatively depleted compared to non-mangrove fringed areas. In areas with intense mixing of estuarine and marine water masses we observed a strong decrease of these DOM compounds relative to values expected from conservative mixing, suggesting their removal by photodegradation and co-precipitation with particles such as Mn(hydr)oxides and/or as organometallic complexes, leading to more aliphatic DOM signatures at the creek-mouth. Tidally driven porewater exchange and surface water runoff from the mangroves had a stronger effect on the biogeochemical cycling in the estuary than the fluvial input during a dry compared to a wet season. Our study confirms that mangroves can significantly contribute to biogeochemical budgets of (sub)tropical estuaries.

Transparent exopolymer particles (TEP) act as a major transport mechanism for organic matter (OM) to the sea surface microlayer (SML) via bubble scavenging, and into the atmosphere via bubble bursting. However, little is known about the effects of bubble scavenging on TEP enrichment in the SML. This study examined the effects of several bubbling conditions and algae species on the enrichment of TEP in the SML. TEP enrichment in the SML was enhanced by bubbling, with a larger impact from bubbling rate than bubble size and increasing enrichment over time. Depth profiles showed that any TEP aggregates formed in the underlying water (ULW) were rapidly (&lt, 2 min) transported to the SML, and that TEP was entrained in the SML by bubbling. Species experiments determined that the presence of different phytoplankton species and their subsequent release of precursor material further enhance the effectiveness of TEP enrichment via bubble scavenging.

We present here an assessment of in situ hyperspectral bio-optical variability in the Vaigat-Disko Bay and Godthabsfjord along the southwest coast of Greenland. The dataset consists of state-of-the-art profiler measurements of hyperspectral apparent and inherent optical properties of water complemented by traditional observations of Secchi disk and Forel Ule scale in the context of ocean color. Water samples were collected and analyzed for concentration of optically active constituents (OACs). Near-surface observations of hydrographic parameters revealed three different water masses in the Bay: meltwater plume, frontal zone, and Atlantic water mass. Underwater spectral light availability reveals three different spectral types. Low salinity, increased temperature, deep euphotic depths, and case-1 water type remote sensing reflectance spectra with tabletop peaks in the 400–500 nm wavelength range characterize the glacial meltwater plume in the Vaigat-Disko Bay. The conservative relationship between salinity and chromophoric dissolved organic matter (CDOM) commonly observed in estuarine and shelf seas is weaker in the Godthabsfjord and reverses in the Vaigat-Disko Bay. Efficiency of machine learning techniques such as cluster analysis is tested in delineating water masses in the bay w.r.t. hydrographic and bio-optical parameters. Tests of optical closure yield low root mean square error at longer wavelengths. The study provides strong evidence that despite similar geographic setting, fjord ecosystems exhibit contrasting bio-optical properties which necessitate fjord-specific investigations.

In the mammalian retina, amacrine cells represent the most diverse cell class and are involved in the spatio-temporal processing of visual signals in the inner plexiform layer. They are connected to bipolar, other amacrine and ganglion cells, forming complex networks via electrical and chemical synapses. The small-field A8 amacrine cell was shown to receive non-selective glutamatergic input from OFF and ON cone bipolar cells at its bistratified dendrites in sublamina 1 and 4 of the inner plexiform layer. Interestingly, it was also shown to form electrical synapses with ON cone bipolar cells, thus resembling the rod pathway-specific AII amacrine cell. In contrast to the AII cell, however, the electrical synapses of A8 cells are poorly understood. Therefore, we made use of the Ier5-GFP mouse line, in which A8 cells are labeled by GFP, to study the gap junction composition and frequency in A8 cells. We found that A8 cells form

Marine sponges (Phylum Porifera) are globally distributed within marine and freshwater ecosystems. In addition, sponges host dense and diverse prokaryotic communities, which are potential sources of novel bioactive metabolites and other complex compounds. Those sponge-derived natural products can span a broad spectrum of bioactivities, from antibacterial and antifungal to antitumor and antiviral compounds. However, most analyses concerning sponge-associated prokaryotes have mainly focused on conveniently accessible relatively shallow sampling locations for sponges. Hence, knowledge of community composition, host-relatedness and biotechnological potential of prokaryotic associations in temperate and cold-water sponges from greater depths (mesophotic to mesopelagic zones) is still scarce. Therefore, we analyzed the prokaryotic community diversity of four phylogenetically divergent sponge taxa from mesophotic to mesopelagic depths of Antarctic shelf at different depths and locations in the region of the South Shetland Islands using 16S rRNA gene amplicon-based sequencing. In addition, we predicted functional profiles applying Tax4Fun from metagenomic 16S rRNA gene data to estimate their biotechnological capability and possible roles as sources of novel bioactive compounds. We found indications that cold and deep-water sponges exhibit host-specific prokaryotic communities, despite different sampling sites and depths. Functional prediction analysis suggests that the associated prokaryotes may enhance the roles of sponges in biodegradation processes of xenobiotics and their involvement in the biosynthesis of secondary metabolites.

The Peruvian upwelling system (PUS) is among the most productive regions in the ocean, with high rates of primary production and an intense oxygen minimum zone (OMZ). The main perturbation of this system is associated to “El Niño” (EN), which affects water mass distribution and reduces primary production. Previous studies in the PUS provided first insights into the dynamics of dissolved organic matter (DOM), but high-resolution studies involving the molecular characterization of the DOM pool to reveal the processes that affect the carbon cycle in this highly productive system are lacking. We characterized the molecular composition of solid-phase extractable DOM (SPE-DOM) in the coastal upwelling system off Central Peru and linked it to specific processes that affect DOM cycling. Seasonal sampling (April, August, and December) was carried out off Central Peru (12°S) during 2015, a low productivity year marked by EN conditions. The DOM molecular composition was obtained via Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Solid-phase extractable dissolved organic carbon (SPE-DOC) concentrations showed significant differences (p < 0.05) between the water masses present off central Peru. In order to explore if changes in SPE-DOC concentrations were the result of water mass mixing, we applied a conservative mixing (CM) model. The model revealed a non-conservative behavior of SPE-DOC and allowed us to identify two distinct groups of samples with increased and decreased SPE-DOC concentrations, respectively, and one group of samples inside the CM range. Differences in environmental parameters characterizing these groups were in accordance with respective processes associated to production and degradation of SPE-DOC. The trends observed for molecular parameters revealed the imprint of processes related to DOM production and DOM degradation, both biotic (microbial degradation) and abiotic (photodegradation). Our study suggests that even under low productivity conditions like EN, there is an active cycling of the DOM pool off central Peru.

Submarine groundwater discharge (SGD) is a ubiquitous source of meteoric fresh groundwater and recirculating seawater to the coastal ocean. Due to the hidden distribution of SGD, as well as the hydraulic- and stratigraphy-driven spatial and temporal heterogeneities, one of the biggest challenges to date is the correct assessment of SGD-driven constituent fluxes. Here, we present results from a 3-dimensional seasonal sampling campaign of a shallow subterranean estuary in a high-energy, meso-tidal beach, Spiekeroog Island, Northern Germany. We determined beach topography and analyzed physico-chemical and biogeochemical parameters such as salinity, temperature, dissolved oxygen, Fe(II) and dissolved organic matter fluorescence (FDOM). Overall, the highest gradients in pore water chemistry were found in the cross-shore direction. In particular, a strong physico-chemical differentiation between the tidal high water and low water line was found and reflected relatively stable in- and exfiltrating conditions in these areas. Contrastingly, in between, the pore water compositions in the existing foreshore ridge and runnel system were very heterogeneous on a spatial and temporal scale. The reasons for this observation may be the strong morphological changes that occur throughout the entire year, which affect the exact locations and heights of the ridge and runnel structures and associated flow paths. Further, seasonal changes in temperature and inland hydraulic head, and the associated effect on microbial mediated redox reactions likely overprint these patterns. In the long-shore direction the pore water chemistry varied less than the along the cross-shore direction. Variation in long-shore direction was probably occurring due to topography changes of the ridge-runnel structure and a physical heterogeneity of the sediment, which produced non-uniform groundwater flow conditions. We conclude that on meso-tidal high energy beaches, the rapidly changing beach morphology produces zones with different approximations to steady-state conditions. Therefore, we suggest that zone-specific endmember sampling is the optimal strategy to reduce uncertainties of SGD-driven constituent fluxes.

General studies on benthic microbial communities focus on fundamental biogeochemical processes or the most abundant constituents. Thereby, minor fractions such as the Rhodobacteraceae are frequently neglected. Even though this family belongs to the most widely distributed bacteria in the marine environment, their proportion on benthic microbial communities is usually within or below the single digit range. Thus, knowledge on these community members is limited, even though their absolute numbers might exceed those from the pelagic zone by orders of magnitudes. To unravel the distribution and diversity of benthic, metabolically active Rhodobacteraceae, we have now analyzed an already existing library of bacterial 16S rRNA transcripts. The dataset originated from 154 individual sediment samples comprising seven oceanic regions and a broad variety of environmental conditions. Across all samples, a total of 0.7% of all 16S rRNA transcripts was annotated as Rhodobacteraceae. Among those, Sulfitobacter, Paracoccus, and Phaeomarinomonas were the most abundant cultured representatives, but the majority (78%) was affiliated to uncultured family members. To define them, the 45 most abundant Rhodobacteraceae-OTUs assigned as “uncultured” were phylogenetically assembled in new clusters. Their next relatives particularly belonged to different subgroups other than the Roseobacter group, reflecting a large part of the hidden diversity within the benthic Rhodobacteraceae with unknown functions. The general composition of active Rhodobacteraceae communities was found to be specific for the geographical location, exhibiting a decreasing richness with sediment depth. One-third of the Rhodobacteraceae-OTUs significantly responded to the prevailing redox regime, suggesting an adaption to anoxic conditions. A possible approach to predict their physiological properties is to identify the metabolic capabilities of their nearest relatives. Those need to be proven by physiological experiments, as soon an isolate is available. Because many uncultured members of these subgroups likely thrive under anoxic conditions, in future research, a molecular-guided cultivation strategy can be pursued to isolate novel Rhodobacteraceae from sediments.

In order to increase the monitoring capabilities of inland and coastal waters, there is a needfor new, affordable, sensitive and mobile instruments that could be operated semi-automatically inthe field. This paper presents a prototype device to measure chlorophyll a fluorescence: the SmartFluo.The device is a combination of a smartphone offering an intuitive operation interface and an adapterimplying a cuvette holder, as well as a suitable illumination source. SmartFluo is based on stimulatedfluorescence of water constituents such as chlorophyll a. The red band of the digital smartphonecamera is sensitive enough to detect quantitatively the characteristic red fluorescence emission.The adapter contains a light source, a strong light emitting diode and additional filters to enhancethe signal-to-noise ratio and to suppress the impact of scattering. A novel algorithm utilizingthe red band of the camera is provided. Laboratory experiments of the SmartFluo show a linearcorrelation (R2 = 0.98) to the chlorophyll a concentrations measured by reference instruments, suchas a high-performance benchtop laboratory fluorometer (LS 55, PerkinElmer).