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Network theory offers innovative tools to explore the complex ecological mechanisms regulating species associations and interactions. Although interest in ecological networks has grown steadily during the last two decades, the application of network approaches has been unequally distributed across different study systems: while some kinds of interactions (e.g. plant–pollinator and host–parasite) have been extensively investigated, others remain relatively unexplored. Among the latter, aquatic macrophyte–animal associations in coastal environments have been largely neglected, despite their major role in littoral ecosystems. The ubiquity of macrophyte systems, their accessibility and multi-faceted ecological, economical and societal importance make macrophyte–animal systems an ideal subject for ecological network science. In fact, macrophyte–animal networks offer an aquatic counterpart to terrestrial plant–animal networks. In this review, we show how the application of network analysis to aquatic macrophyte–animal associations has the potential to broaden our understanding of how coastal ecosystems function. Network analysis can also provide a key to understanding how such ecosystems will respond to on-going and future threats from anthropogenic disturbance and environmental change. For this, we: (i) identify key issues that have limited the application of network theory and modelling to aquatic animal– macrophyte associations; (ii) illustrate through examples based on empirical data how network analysis can offer new insights on the complexity and functioning of coastal ecosystems; and (iii) provide suggestions for how to design future studies and establish this new research line into network ecology.

Brown algae annually convert gigatons of carbon dioxide into carbohydrates, including the complex extracellular matrix polysaccharide fucoidan. Due to its persistence in the environment, fucoidan is potentially a pathway for marine carbon sequestration. Rates of fucoidan secretion by brown algae remain unknown due to the challenge of identifying and quantifying complex polysaccharides in seawater. We adapted the techniques of anion exchange chromatography, enzyme-linked immunosorbent assay, and biocatalytic enzyme-based assay for detection and quantification of fucoidan. We found the brown alga Fucus vesiculosus at the Baltic Sea coast of south-west Finland to secrete 0.3% of their biomass as fucoidan per day. Dissolved fucoidan concentrations in seawater adjacent to algae reached up to 0.48 mg L −1 . Fucoidan accumulated during incubations of F. vesiculosus , significantly more in light than in darkness. Maximum estimation by acid hydrolysis indicated fucoidan secretion at a rate of 28 to 40 mg C kg −1 h −1 , accounting for 44 to 50% of all exuded dissolved organic carbon. Composed only of carbon, oxygen, hydrogen, and sulfur, fucoidan secretion does not consume nutrients enabling carbon sequestration independent of algal growth. Extrapolated over a year, the algae sequester more carbon into secreted fucoidan than their biomass. The global utility of fucoidan secretion is an alternative pathway for carbon dioxide removal by brown algae without the need to harvest or bury algal biomass.

The bi-thiophene-vinylene-benzothiazole (bTVBT4) ligand developed for Alzheimers disease (AD)-specific detection of amyloid tau has been studied by a combination of several theoretical methods and experimental spectroscopies. With reference to the cryo-EM tau structure of the tau protofilament (Nature 2017, 547, 185), a periodic model system of the fibril was created, and the interactions between this fibril and bTVBT4 were studied with nonbiased molecular dynamics simulations. Several binding sites and binding modes were identified and analyzed, and the results for the most prevailing fibril site and ligand modes are presented. A key validation of the simulation work is provided by the favorable comparison of the theoretical and experimental absorption spectra of bTVBT4 in solution and bound to the protein. It is conclusively shown that the ligand-protein binding occurs at the hydrophobic pocket defined by the residues Ile360, Thr361, and His362. This binding site is not accessible in the Picks disease (PiD) fold, and fluorescence imaging of bTVBT4-stained brain tissue samples from patients diagnosed with AD and PiD provides strong support for the proposed tau binding site. Funding Agencies|European CommissionEuropean CommissionEuropean Commission Joint Research Centre [765739]; Swedish Research CouncilSwedish Research CouncilEuropean Commission [2018-4343, 2016-07213]; Swedish e-Science Research Centre (SeRC); German Research FoundationGerman Research Foundation (DFG) [KO 5423/1-1]; U.S. National Institutes of HealthUnited States Department of Health & Human ServicesNational Institutes of Health (NIH) - USA [UO1NS110437]

Caio Graco-Roza was funded by the Coordination for the Improvement of Higher Education Personnel (CAPES), the Carlos Chagas Filho Research Support Foundation (FAPERJ) and the Ella and Georg Erhnrooth Foundation; Jan Altman by research grants INTER-EXCELLENCE LTAUSA19137 provided by Czech Ministry of Education, Youth and Sports, 20-05840Y of the Czech Science Foundation, and long-term research development project no. RVO 67985939 of the Czech Academy of Sciences; Otso Ovaskainen was funded by Academy of Finland (grant no. 309581), Jane and Aatos Erkko Foundation, Research Council of Norway through its Centres of Excellence Funding Scheme (223257), and the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 856506; ERC-synergy project LIFEPLAN); and Jianjun Wang was funded by CAS Key Research Program of Frontier Sciences (QYZDB-SSW-DQC043) and National Natural Science Foundation of China (91851117). The "sPlot" project was initiated by sDiv, the Synthesis Centre of the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, funded by the German Research Foundation (DFG FZT 118), and is now a platform of iDiv. The study was supported by the TRY initiative on plant traits (). We are also grateful to Jens Kattge and TRY database. TRY is hosted, developed and maintained at the Max Planck Institute for Biogeochemistry (MPI-BGC) in Jena, Germany, in collaboration with the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig. The CESTES database of metacommunities is also an initiative of iDiv led by Alienor Jeliazkov. We thank sDiv for supporting the open science initiative., Aim: Understanding the variation in community composition and species abundances (i.e., β-diversity) is at the heart of community ecology. A common approach to examine β-diversity is to evaluate directional variation in community composition by measuring the decay in the similarity among pairs of communities along spatial or environmental distance. We provide the first global synthesis of taxonomic and functional distance decay along spatial and environmental distance by analysing 148 datasets comprising different types of organisms and environments. Location: Global. Time period: 1990 to present. Major taxa studied: From diatoms to mammals. Method: We measured the strength of the decay using ranked Mantel tests (Mantel r) and the rate of distance decay as the slope of an exponential fit using generalized linear models. We used null models to test whether functional similarity decays faster or slower than expected given the taxonomic decay along the spatial and environmental distance. We also unveiled the factors driving the rate of decay across the datasets, including latitude, spatial extent, realm and organismal features. Results: Taxonomic distance decay was stronger than functional distance decay along both spatial and environmental distance. Functional distance decay was random given the taxonomic distance decay. The rate of taxonomic and functional spatial distance decay was fastest in the datasets from mid-latitudes. Overall, datasets covering larger spatial extents showed a lower rate of decay along spatial distance but a higher rate of decay along environmental distance. Marine ecosystems had the slowest rate of decay along environmental distances. Main conclusions: In general, taxonomic distance decay is a useful tool for biogeographical research because it reflects dispersal-related factors in addition to species responses to climatic and environmental variables. Moreover, functional distance decay might be a cost-effective option for investigating community changes in heterogeneous environments., Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES) Fundacao Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio De Janeiro (FAPERJ), Ella and Georg Erhnrooth Foundation, Ministry of Education, Youth & Sports - Czech Republic LTAUSA19137 Grant Agency of the Czech Republic 20-05840Y Czech Academy of Sciences RVO 67985939, Academy of Finland 309581, Jane and Aatos Erkko Foundation, Research Council of Norway through its Centres of Excellence Funding Scheme 223257, European Research Council (ERC) 856506, CAS Key Research Program of Frontier Sciences QYZDB-SSW-DQC043, National Natural Science Foundation of China (NSFC) 91851117, German Research Foundation (DFG) DFG FZT 118, TRY initiative on plant traits

We conducted a short-term field sampling complemented with time integrating stable isotope analysis to holistically investigate status and ecological interactions in a remote NE Atlantic Zostera marina meadow. We found high nutrient water concentrations, large biomass of fast-growing, ephemeral macroalgae, low abundance, and biodiversity of epifauna and a food web with thornback ray (Raja clavata) as intermediate and cod (Gadus morhua) as top predator. We observed no variation with increasing depth (3.5–11 m) except for decreasing shoot density and biomass of Zostera and macroalgae. Our results indicate that the Finnøya Zostera ecosystem is eutrophicated. During the past three to four decades, nutrients from aquaculture have steadily increased to reach 75% of anthropogenic input while the coastal top predator cod has decreased by 50%. We conclude that bottom-up regulation is a predominant driver of change since top-down regulation is generally weak in low density and exposed Zostera ecosystems such as Finnøya. Effects of depth and overgrowth of ephemeral macroalgae on a remote subtidal NE Atlantic eelgrass (Zostera marina) community

The binding pocket proposed by Konig [ Chem. Commun. 2018, 54, 3030–3033] for the biomarker pentameric formyl thiophene acetic acid (p-FTAA) in the fibrillar structure of amyloid-β(1–42) has been p...

Coastal ecosystems act as filters of nutrients from land to the open sea. We investigated the role of eelgrass (Zostera marina) metabolism in the coastal filter transforming nitrogen, phosphorus, and organic carbon. Field campaigns following identical methodologies were carried out at two contrasting coastal locations: the mesohaline and nutrient-rich Roskilde Fjord, Denmark, and the mesotrophic brackish Tvärminne archipelago, Finland. Over the 24-h in situ benthic incubations, we measured oxygen concentrations continuously and assessed changes in DOM characteristics and net fluxes of carbon, nitrogen, and phosphorus. Ecosystem metabolism modeled on the basis of the O2 data showed that the systems were either net heterotrophic (Roskilde Fjord; − 1.6 and − 2.4 g O2 m−2 day−1 in eelgrass meadow and bare sand, respectively) or had balanced primary production and respiration (Tvärminne; 0.0 and 0.2 g O2 m−2 day−1). Overall, initial nutrient stoichiometry was a key factor determining benthic–pelagic fluxes of nutrients, which exacerbated the deviations from Redfield ratios of N and P, indicating an efficient use of the limiting nutrient. A net diel uptake of dissolved inorganic N was observed at both locations (− 2.3 μmol l−1 day−1 in Roskilde Fjord and − 0.1 μmol l−1 day−1 in Tvärminne). Despite minor changes in dissolved organic carbon concentrations during the incubations, a marked increase of fluorescent DOM was observed at both locations, suggesting rapid heterotrophic processing of the DOM pool. Our results underline that the biogeochemical role of eelgrass in the coastal filter is not inherent, but strongly dependent on the environmental conditions.

Understanding the ecological interactions that enhance the resilience of threatened ecosystems is essential in assuring their conservation and restoration. Top-down trophic interactions can increase resilience to bottom-up nutrient enrichment, however, as many seagrass ecosystems are threatened by both eutrophication and trophic modifications, understanding how these processes interact is important. Using a combination of approaches, we explored how bottom-up and top-down processes, acting individually or in conjunction, can affect eelgrass meadows and associated communities in the northern Baltic Sea. Field surveys along with fish diet and stable isotope analyses revealed that the eelgrass trophic network included two main top predatory fish species, each of which feeds on a separate group of invertebrate mesograzers (crustaceans or gastropods). Mesograzer abundance in the study area was high, and capable of mitigating the effects of increased algal biomass that resulted from experimental nutrient enrichment in the field. When crustacean mesograzers were experimentally excluded, gastropod mesograzers were able to compensate and limit the effects of nutrient enrichment on eelgrass biomass and growth. Our results suggest that top-down processes (i.e., suppression of algae by different mesograzer groups) may ensure eelgrass resilience to nutrient enrichment in the northern Baltic Sea, and the existence of multiple trophic pathways can provide additional resilience in the face of trophic modifications. However, the future resilience of these meadows is likely threatened by additional local stressors and global environmental change. Understanding the trophic links and interactions that ensure resilience is essential for managing and conserving these important ecosystems and the services they provide.

Understanding the variation in community composition and species abundances, i.e., β-diversity, is at the heart of community ecology. A common approach to examine β-diversity is to evaluate directional turnover in community composition by measuring the decay in the similarity among pairs of communities along spatial or environmental distances. We provide the first global synthesis of taxonomic and functional distance decay along spatial and environmental distance by analysing 149 datasets comprising different types of organisms and environments. We modelled an exponential distance decay for each dataset using generalized linear models and extracted r2 and slope to analyse the strength and the rate of the decay. We studied whether taxonomic or functional similarity has stronger decay across the spatial and environmental distances. We also unveiled the factors driving the rate of decay across the datasets, including latitude, spatial extent, realm, and organismal features. Taxonomic distance decay was stronger along spatial and environmental distances compared with functional distance decay. The rate of taxonomic spatial distance decay was the fastest in the datasets from mid-latitudes while the rate of functional decay increased with latitude. Overall, datasets covering larger spatial extents showed a lower rate of decay along spatial distances but a higher rate of decay along environmental distances. Marine ecosystems had the slowest rate of decay. This synthesis is an important step towards a more holistic understanding of patterns and drivers of taxonomic and functional β-diversity.

Aquatic plant meadows are valuable components to the ‘coastal filter’ and it is important to understand the processes that drive their ability to cycle nutrients. However, at present, the field-based evidence for understanding the drivers of nutrient uptake by plants is lacking. This study aimed to investigate how well individual shoots of aquatic plants could meet their nitrogen demands using the sediment nutrient pool (porewater ammonium) and to explore which traits helped to facilitate such uptake. Several species were investigated in shallow, submerged (2–4 m) mixed-species communities in the northern Baltic Sea using incubation experiments with enriched ammonium. After a 3.5 h incubation time, individuals were collected and analysed for nitrogen (% DW) and 15N (at-%) concentrations. Uptake by plants was calculated per unit nitrogen in response to the 15 N-labelled source and to overall nitrogen availability. Background porewater ammonium availability was highly variable between individual plants. Species identity did not significantly affect uptake metrics and the effect of ambient porewater availability was weak. As biomass increased there were significant logarithmic declines in the 95th quantiles of nutrient uptake rates, ambient porewater nutrient availability and aboveground nitrogen tissue concentrations (% DW). Such findings suggested that uptake rates of plants were significantly demand-driven and the nutrient conditions of the porewater were significantly driven by the demands of the plant. Findings parameterised the unfulfilled potential for some aquatic plants to cycle nutrients more efficiently and highlighted the potential importance of access to new nutrient sources as a way of enhancing nutrient cycling by aquatic plants. Plant traits and community properties such as the activity of infauna could facilitate such an access and are likely important for nutrient uptake.

1. Aquatic plant meadows are important coastal habitats that sustain many ecosystem functions such as primary production and carbon sequestration. Currently, there is a knowledge gap in understanding which plant functional traits, for example, leaf size or plant height underlie primary production in aquatic plant communities. 2. To study how plant traits are related to primary production, we conducted a field survey in the Baltic Sea, Finland, which is characterized by high plant species and functional diversity. Thirty sites along an exposure gradient were sampled (150 plots), and nine plant morphological and chemical traits measured. The aim was to discern how community-weighted mean traits affect community production and whether this relationship changes along an environmental gradient using structural equation modelling (SEM). 3. Plant height had a direct positive effect on production along an exposure gradient (r = 0.33) and indirect effects through two leaf chemical traits, leaf δ15N and leaf δ13C (r = 0.24 and 0.18, respectively) resulting in a total effect of 0.28. In plant communities experiencing varying exposure, traits such as root N concentration and leaf δ15N had positive and negative effects on production, respectively. 4. Synthesis. Our results demonstrate that the relationship between aquatic plant functional traits and community production is variable and changes over environmental gradients. Plant height generally has a positive effect on community production along an exposure gradient, while the link between other traits and production changes in plant communities experiencing varying degrees of exposure. Thus, the underlying biological mechanisms influencing production differ in plant communities, emphasizing the need to resolve variability and its drivers in real-world communities. Importantly, functionally diverse plant communities sustain ecosystem functioning differently and

Background The use of ultrasound (US) outside the radiology department has increased the last decades, but large studies assessing the quality of bedside US are still lacking. This study evaluates surgeon-performed US (SPUS) and radiologist-performed US (RPUS) with respect to biliary disease and appendicitis. Methods Between October 2011 and November 2012, 300 adult patients, with a referral for an abdominal US, were prospectively enrolled in the study and examined by a radiologist as well as a surgeon. The surgeons had undergone a 4-week-long US education. US findings of the surgeon and of the radiologist were compared to final diagnosis, set by an independent external observer going through each patient’s chart. Results Among 183 patients with suspected biliary disease, 74 had gallstones and 21 had acute cholecystitis. SPUS and RPUS diagnosed gallstones with a sensitivity of 87.1 versus 97.3%. Specificity was 96.0 versus 98.9%, and the accuracy 92.3 versus 98.2%. The sensitivity, specificity and accuracy for acute cholecystitis by SPUS and RPUS were: 60.0 versus 80.0%, 98.6 versus 97.8% and 93.9 versus 95.6%, respectively. Among 58 patients with suspected appendicitis, 15 had the disease. The sensitivity, specificity and accuracy for appendicitis by SPUS and RPUS were: 53.3 versus 73.3%, 89.7 versus 93.3% and 77.3 versus 86.7%, respectively. Conclusion SPUS is reliable in diagnosing gallstones. Diagnosing cholecystitis and appendicitis with US is more challenging for both surgeons and radiologists. Trial registration number The study was registered at clinicaltrials.gov. Registration number: NCT02469935.

Existing data on the safety of out-of-hours cholecystectomy are conflicting. The aim of this study was to investigate whether out-of-hours cholecystectomy for acute cholecystitis is associated with a higher risk for complications compared with surgery during office hours.This was a population-based cohort study. The Swedish Gallstone Surgery and Endoscopic Retrograde Cholangiopancreatography Register (GallRiks) was used to investigate the association between out-of-hours cholecystectomy for acute cholecystitis and complications developing within 30 days. Data from patients who underwent cholecystectomy between 2006 and 2017 were collected. Out-of-hours surgery was defined as surgery commencing between 19.00 and 07.00 hours on weekdays, or any time at weekends (Friday 19.00 hours to Monday 07.00 hours). Multivariable logistic regression analysis was used to assess the risk of complications, with time of procedure as independent variable. The proportion of open procedures and proportion of procedures exceeding 120 min were also analysed. Adjustments were made for sex, age, ASA grade, time between admission and surgery, and hospital-specific features.Of 11 153 procedures included, complications occurred within 30 days in 1573 patients (14·1 per cent). The adjusted odds ratio (OR) for complications for out-of-hours versus office-hours surgery was 1·12 (95 per cent c.i. 0·99 to 1·28). The adjusted OR for procedures completed as open surgery was 1·39 (1·25 to 1·54), and that for operating time exceeding 120 min was 0·63 (0·58 to 0·69).Out-of-hours complications may relate to patient factors and the higher proportion of open procedures.Los datos existentes sobre la seguridad de la colecistectomía fuera del horario laboral son discordantes. El objetivo de este estudio fue investigar si la colecistectomía para el tratamiento de la colecistitis aguda realizada fuera del horario laboral se asocia con un mayor riesgo de complicaciones en comparación con la cirugía efectuada durante el horario laboral. MÉTODOS: Se trata de un estudio de cohortes de base poblacional. Se utilizó el registro Swedish Gallstone Surgery and Endoscopic Retrograde Cholangiopancreatography Register (GallRiks) para examinar la asociación entre la colecistectomía por colecistitis aguda realizada fuera del horario laboral y las complicaciones a los 30 días. Se recogieron los datos de los pacientes en los que se realizó una colecistectomía entre 2006 y 2017. Se definió como cirugía fuera del horario laboral aquella realizada entre las 19:00 y las 07:00 de lunes a viernes y en cualquier momento durante los fines de semana (de viernes 19:00 a lunes 07:00) Se realizó un análisis de regresión logística multivariable para evaluar el riesgo de complicaciones, considerando la hora de la cirugía como variable independiente. También se analizó el porcentaje de intervenciones por vía abierta y el de aquellas cuya duración excedió de los 120 minutos. Se realizaron ajustes por sexo, edad, puntuación ASA, días desde el ingreso hasta la cirugía y características específicas del hospital.Se produjeron 1.573 (14,1%) complicaciones en las 11.153 intervenciones incluidas. La razón de oportunidades, odds ratio (OR) ajustada para las complicaciones comparando la cirugía fuera del horario laboral con la cirugía dentro del horario laboral, fue de 1,12 (i.c. del 95% 0,99-1,28). La OR ajustada para los procedimientos realizado por vía abierta fue de 1,39 (1,25-1,54). La OR ajustada para el tiempo operatorio120 minutos fue de 0,63 (0,58-0,69). CONCLUSIÓN: Las complicaciones que suceden en la cirugía efectuada fuera del horario laboral es más probable que se deban a factores relacionados con el paciente que con la hora del día en que se practica la cirugía. Debe tenerse en cuenta que las intervenciones realizadas por vía abierta fuera del horario laboral tienen una mayor morbilidad.

Anionic pentameric thiophene acetates can be used for fluorescence detection and diagnosis of protein amyloid aggregates. Replacing the central thiophene unit by benzothiadiazole (BTD) or quinoxaline (QX) leads to large emission shifts and basic spectral features have been reported [Chem. Eur. J. 2015, 21, 15133‐13137]. Here we present new detailed experimental results of solvent effects, time‐resolved fluorescence and examples employing multi‐photon microscopy and lifetime imaging. Quantum chemical response calculations elucidate how the introduction of the BTD/QX groups changes the electronic states and emissions. The dramatic red‐shift follows an increased conjugation and quinoid character of the π‐electrons of the thiophene backbone. An efficient charge transfer in the excited states S1 and S2 compared to the all‐thiophene analogue makes these more sensitive to the polarity and quenching by the solvent. Taken together, the results guide in the interpretation of images of stained Alzheimer disease brain sections employing advanced fluorescence microscopy and lifetime imaging, and can aid in optimizing future fluorescent ligand development., Fluorescent biomarkers: The introduction of donor‐acceptor‐donor moieties in luminescent conjugated oligothiophenes gives a drastic shift in spectroscopic profile. This opens up for designing novel fluorescent biomarkers that can classify different types of amyloid folds and differentiate different morphological protein topologies.

In species-poor communities, genetic diversity potentially plays an important role for ecosystem functioning, though this is still largely unexplored in marine and estuarine ecosystems. We studied how genetic diversity (sensu genotypic diversity and/or allelic richness) affects ecosystem functioning in marine habitat-forming plant communities. First, we conducted a 15-month field experiment in the highly seasonal Baltic Sea and established mono- and polycultures of different genotypes and genotype combinations of Zostera marina. Second, we reviewed existing literature and performed a meta-analysis of 12 studies including this study. We found no evidence of positive genetic diversity effects on shoot production in the field experiment, but diversity enhanced community stability over time. The literature review revealed that a majority of the included studies observed positive effects of genetic diversity on ecosystem functions such as primary production and nutrient uptake. The results from the meta-analysis support the hypothesis that genetic diversity effects on productivity are stronger during or after periods of stress. These diversity effects were also more positive in the field compared to mesocosm studies. Our results indicate that genetic diversity has positive effects on ecosystem functioning, particularly during increased environmental stress. Thus, local genetic diversity should be preserved especially in species-poor ecosystems, where it potentially provides insurance against environmental change.

Symptomatic gallstone disease is a common diagnosis in patients with abdominal pain. Ultrasound is considered the gold standard method to identify gallstones. Today the examination may be performed bedside by the treating clinician. Bedside ultrasound could provide a safe and time-saving diagnostic resource for surgeons evaluating patients with suspected symptomatic gallstones; however, large validation studies of the accuracy and reliability are lacking. The aim of this study was to prospectively investigate the accuracy of surgeon-performed ultrasound for the detection of gallstones. Between October 2011 and November 2012, 179 adult patients, with an acute or elective referral for an abdominal ultrasound examination, were examined with a right upper quadrant ultrasound scan by a radiologist as well as a surgeon. The surgeons had undergone a four-week-long ultrasound education before participating in the study. Ultrasound findings of the surgeon were compared to those of the radiologist, using radiologist-performed ultrasound as reference standard. Surgeon-performed ultrasound agreed with radiologist findings in 169 of 179 patients regarding the detection of gallstones, providing an accuracy of 94 %. The sensitivity was 88 % (67/76), specificity 99 % (102/103), positive predictive value 99 % (67/68), and negative predictive value 92 % (102/111). Agreement between the diagnosis set by the radiologists and the surgeons was high: Cohen’s Kappa coefficient = 0.88. Ultrasound-trained surgeons may accurately diagnose gallstones using ultrasound and reach a high level of agreement with radiologists.

Squalene–hopene cyclase catalyzes the cyclization of squalene to hopanoids. A previous study has identified a network of tunnels in the protein, where water molecules have been indicated to move. Blocking these tunnels by site-directed mutagenesis was found to change the activation entropy of the catalytic reaction from positive to negative with a concomitant lowering of the activation enthalpy. As a consequence, some variants are faster and others are slower than the wild type (wt) in vitro under optimal reaction conditions for the wt. In this study, molecular dynamics (MD) simulations have been performed for the wt and the variants to investigate how the mutations affect the protein structure and the water flow in the enzyme, hypothetically influencing the activation parameters. Interestingly, the tunnel-obstructing variants are associated with an increased flow of water in the active site, particularly close to the catalytic residue Asp376. MD simulations with the substrate present in the active site indicate that the distance for the rate-determining proton transfer between Asp376 and the substrate is longer in the tunnel-obstructing protein variants than in the wt. On the basis of the previous experimental results and the current MD results, we propose that the tunnel-obstructing variants, at least partly, could operate by a different catalytic mechanism, where the proton transfer may have contributions from a Grotthuss-like mechanism. QC 20180914

Harmful algal blooms are considered to be one of the biggest threats to benthic vegetation. The amount of annual algal mats has increased due to eutrophication but their effects on perennial vegetation have rarely been tested in field experiments. In regions where eelgrass ( Zostera marina ) grows in mixed meadows, plant species richness may ameliorate algal-induced stress through facilitative mechanisms and improve eelgrass growth and survival. To test this, we conducted a 3 mo. field experiment at 3.5 m depth in the Baltic Sea, where we applied filamentous brown algae (300 g ww) to eelgrass monocultures and polycultures ( Z. marina , Ruppia cirrhosa , Stuckenia pectinata and Potamogeton perfoliatus ). The algal stress period lasted for 13 d and plots were sampled after a 5 wk recovery period. In both algal-stressed mono- and polycultures, the presence of algal mats significantly reduced eelgrass shoot and root biomass production and affected the leaf growth negatively. Plant richness did not have strong effects on eelgrass growth and eelgrass in both algal-stressed mono- and polycultures showed significantly reduced productivity. Our results clearly demonstrate that loose-lying algal mats pose a serious threat to seagrass meadows and that plant diversity cannot alone ameliorate negative effects by macroalgal mats.

The macrofaunal colonization of isolated habitats is affected by many factors, ranging from distance to the nearest source population to the dispersal mechanism of the species. We investigated the initial epifaunal colonization at two sites, one situated in the Northern Gulf of Mexico and the other in the Northern Baltic Sea. At each site, artificial seagrass units were placed at 10- and 20-m distances from a continuous seagrass meadow, as well as inside the meadow over a 5-day colonization time. With the exception of amphipods in Gulf of Mexico, patch isolation had a negative effect on colonization for the other faunal species, irrespective of the sites. This inverse colonization pattern of amphipods suggests that they are not equally sensitive to patch isolation in different regions. Our results indicate that increasing habitat isolation can have serious consequences for the community composition of seagrass epifauna. Furthermore, we emphasize the need for larger-scale latitudinal comparative studies.

Knowledge of the connection between aquatic plant diversity and ecosystem processes is still limited. To examine how plant species diversity affects primary productivity, plant nutrient use, functional diversity of secondary producers and population/community stability, we manipulated submerged angiosperm species diversity in a field experiment lasting 15 weeks. Plant richness increased the shoot density for three of four species. Polyculture biomass production was enhanced by increasing richness, with positive complementarity and selection effects causing positive biodiversity effects. Species richness enhanced the community stability for biomass production and shoot density. Sediment ammonium availability decreased with plant diversity, suggesting improved nutrient usage with increasing plant richness. Interestingly, positive multitrophic effects of plant species richness on structural and functional diversity of macrobenthic secondary producers were recorded. The results suggest that mixed seagrass meadows play an important role for ecosystem functioning and thus contribute to the provision of goods and services in coastal areas.

Studies conducted in terrestrial ecosystems have shown that increasing plant diversity enhances ecosystem processes such as primary production. In marine systems, knowledge of how plant diversity influences ecosystem processes and higher trophic levels is still limited. To examine how plant richness and composition influence recruitment and colonization processes, defaunated eelgrass ( Zostera marina ), sago pondweed ( Potamogeton pectinatus ) and perfoliate pondweed ( Potamogeton perfoliatus ) were planted on an unvegetated, sandy bottom in all possible combinations in July and August. Both field experiments lasted 1 week. Our results showed that in these plant assemblages plant richness had a negative effect on faunal diversity ( H′ ) and evenness ( J′ ), while total abundance showed strong temporal variation with weak, positive relationships with plant species richness in both August and July. Plant species composition had strong effects on amphipods ( Gammarus spp.), thus both the abundance and biomass were higher in treatments containing P. perfoliatus . The colonization process was significantly influenced by the numerical dominance of a few faunal species, e.g. the settlement of lagoon cockles ( Cerastoderma glaucum ), and by the timing of the experiments. The results indicate that faunal colonization in these communities is rapid and significantly influenced by the traits of particular plant species.

Submerged aquatic vegetation (SAV) usually hosts higher numbers of both inverte- brates and fish than do unvegetated substrates. In addition, based on prior laboratory experiments predation risk is thought to decrease with increasing SAV biomass or stem/shoot density, resulting in higher abundance and diversity of potential prey species in dense vegetation. However, all previous tests of the effects of vegetation on prey capture have been similar: constant numbers of predators and prey have been tested at different vegetation densities. Because sampling has repeatedly shown that the abundance of both predators and prey increases with increasing SAV density, an experiment that tests the effects of increasing SAV density on prey capture would mirror reality more closely than would the design of prior experiments and would also allow predator and prey numbers to increase. Thus, in laboratory trials we increased the number of predators (pinfish Lagodon rhomboides (Linnaeus)) and prey (grass shrimp Palaemonetes pugio Hulthuis) in proportion to increases in SAV shoot density to re-evaluate whether increasing SAV density altered prey survival rates under these more realistic conditions. Treatments included an unvegetated substrate and 3 different densities (400, 2000 and 4000 leaves m -2 of artificial SAV (mimicking turtlegrass Thalassia testudinum Banks and Sol). Our results conflicted with those of prior experiments and showed no significant differences in grass shrimp survival among the different SAV densities (although there was greater grass shrimp survival in SAV than on unvegetated substrate), and indicated that increasing vegetation density will not consistently lead to proportionally greater prey survival rates.

Nutrient pollution and reduced grazing each can stimulate algal blooms as shown by numerous experiments. But because experiments rarely incorporate natural variation in environmental factors and biodiversity, conditions determining the relative strength of bottom-up and top-down forcing remain unresolved. We factorially added nutrients and reduced grazing at 15 sites across the range of the marine foundation species eelgrass (Zostera marina) to quantify how top-down and bottom-up control interact with natural gradients in biodiversity and environmental forcing. Experiments confirmed modest top-down control of algae, whereas fertilisation had no general effect. Unexpectedly, grazer and algal biomass were better predicted by cross-site variation in grazer and eelgrass diversity than by global environmental gradients. Moreover, these large-scale patterns corresponded strikingly with prior small-scale experiments. Our results link global and local evidence that biodiversity and top-down control strongly influence functioning of threatened seagrass ecosystems, and suggest that biodiversity is comparably important to global change stressors. National Science Foundation [OCE-1031061] info:eu-repo/semantics/publishedVersion

This paper focuses on the marine foundation eelgrass species, Zostera marina, along a gradient from the northern Baltic Sea to the north-east Atlantic. This vast region supports a minimum of 1480 km2 eelgrass (maximum >2100 km2), which corresponds to more than four times the previously quantified area of eelgrass in Western Europe.Eelgrass meadows in the low salinity Baltic Sea support the highest diversity (4–6 spp.) of angiosperms overall, but eelgrass productivity is low (