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Aim: Macroalgal habitats are believed to be the most extensive and productive of all coastal vegetated ecosystems. In stark contrast to the growing attention on their contribution to carbon export and sequestration, understanding of their global extent and production is limited and these have remained poorly assessed for decades. Here we report a first data‐driven assessment of the global extent and production of macroalgal habitats based on modelled and observed distributions and net primary production (NPP) across habitat types. Location: Global coastal ocean. Time period: Contemporary. Major taxa studied: Macroalgae. Methods: Here we apply a comprehensive niche model to generate an improved global map of potential macroalgal distribution, constrained by incident light on the seafloor and substrate type. We compiled areal net primary production (NPP) rates across macroalgal habitats from the literature and combined this with our estimates of the global extent of these habitats to calculate global macroalgal NPP. Results: We show that macroalgal forests are a major biome with a global area of 6.06–7.22 million km2, dominated by red algae, and NPP of 1.32 Pg C/year, dominated by brown algae. Main conclusions: The global macroalgal biome is comparable, in area and NPP, to the Amazon forest, but is globally distributed as a thin strip around shorelines. Macroalgae are expanding in polar, subpolar and tropical areas, where their potential extent is also largest, likely increasing the overall contribution of algal forests to global carbon sequestration. [ABSTRACT FROM AUTHOR]

The race between pathogens and their hosts is a major evolutionary driver, where both reshuffle their genomes to overcome and reorganize the defenses for infection, respectively. Evolutionary theory helps formulate predictions on the future evolutionary dynamics of SARS-CoV-2, which can be monitored through unprecedented real-time tracking of SARS-CoV-2 population genomics at the global scale. Here we quantify the accelerating evolution of SARS-CoV-2 by tracking the SARS-CoV-2 mutation globally, with a focus on the Receptor Binding Domain (RBD) of the spike protein determining infection success. We estimate that the > 820 million people that had been infected by October 5, 2021, produced up to 1021 copies of the virus, with 12 new effective RBD variants appearing, on average, daily. Doubling of the number of RBD variants every 89 days, followed by selection of the most infective variants challenges our defenses and calls for a shift to anticipatory, rather than reactive tactics involving collaborative global sequencing and vaccination. [ABSTRACT FROM AUTHOR]

• Eight nations have contributed 79% of all SARS-CoV-2 isolates that have been sequenced. • Two-thirds of SARS-CoV-2 variants that have been found were reported by five nations. • The number of detected variants increases at the square root of sequencing effort. • International cooperation for SARS-CoV-2 sequencing is urgently needed. • Effective monitoring and prevention require a global pathogen sequencing mechanism. To assess the efforts deployed by different nations and territories in sequencing SARS-CoV-2 isolates, thus enabling detection of variants, known and novel, of concern. The sources of over one million full genome sequences of SARS-CoV-2 virus available in the COVID-19 virus Mutation Tracker (CovMT) were analyzed to determine the number of variants in the RBD region of the genome determining infectivity detected in the various nations and territories. The number of detected variants increased as the square root of sequencing effort by nations. Eight nations have contributed 79% of all SARS-CoV-2 isolates that have been sequenced, with two-thirds of all unique variants, adding to 1118 RBD variants, reported by five nations. The median number of sequenced isolates required to detect, on average, one novel RBD variant is 24.05, which is a threshold achieved by 70 nations. Many developing nations have not contributed any sequences due to lack of capacity. This poses a risk of dangerous virus variants in these under-sampled regions spreading globally before being detected. A collaborative program to sequence SARS-CoV-2 isolates, and other pathogens of concern, is needed to monitor, track, and control the pandemic. [Display omitted] [ABSTRACT FROM AUTHOR]

The Red Sea depicts a north–south gradient of positively correlated temperature and nutrient concentration. Despite its overall oligotrophic characteristics, primary production rates in the Red Sea vary considerably. In this study, based on five cruises and a 2‐year time series (2016–2018) sampling in the Central Red Sea, we determined phytoplankton photosynthetic rates (PP) by using 13C as a tracer and derived phytoplankton net growth rates (μ) and chlorophyll a (Chl a)‐normalized photosynthesis (PB). Our results indicate a ninefold variation (14–125 mgC m−2 h−1) in depth‐integrated primary production and reveal a marked seasonality in PP, PB, and μ. Depth‐integrated PP remained <30 mg C m−2 h−1 during spring and summer, and peaked in autumn–winter, particularly in the southernmost stations (~17°N). In surface waters, phytoplankton grew at a slow rate (0.2 ± 0.02 d−1), with the population doubling every 3.5 days, on average. However, during the autumn–winter period, when Chl a concentrations peaked in the central and southern regions, μ increased to values between 0.60 and 0.84 d−1, while PB reached its maximum rate (7.8 mgC [mg Chl a]−1 h−1). We used path analysis to resolve direct vs. indirect components between correlations. Our results show that nutrient availability modulates the photosynthetic performance and growth of phytoplankton communities and that PB and μ fluctuations are not directly associated with temperature changes. Our study suggests that similarly to other oligotrophic warm seas, phosphorus concentration exerts a key role in defining photosynthetic rates and the biomass levels of phytoplankton communities in the region. [ABSTRACT FROM AUTHOR]

Global losses over the 20th century placed seagrass ecosystems among the most threatened ecosystems in the world, with eutrophication, and associated deterioration of the submarine light environment identified as the main driver. Growing appreciation of the ecological and societal benefits of healthy seagrass meadows has stimulated efforts to protect and restore them, largely focused on reducing nutrient input to coastal waters. Here we analyze a unique data set spanning 135 years on eelgrass (Zostera marina), the dominant seagrass of the northern hemisphere. We show that meadows in the Western Baltic Sea exhibited major declines relative to historic (1890–1910) reference due to the wasting disease in the 1930s followed by eutrophication peaking in the 1980s, but have only shown modest improvement despite major eutrophication mitigation, halving nitrogen input since the 1980s. Across the past century, we identified generally shallower colonization depths of eelgrass for a given submarine light penetration and, hence, increased apparent light requirements. This suggests that eelgrass recovery is limited by additional stressors. Our study indicates that bottom trawling and intense recent warming (0.5°C per decade, 1985–2018), which impact on deeper and shallower meadows, respectively, suppress eelgrass from fully recovering from eutrophication. Warming is most severe in shallow turbid waters, while clear‐water areas offer eelgrass refugia from warming in deeper, cooler waters; but trawling can prevent eelgrass from reaching these refugia. Efforts to reduce nutrient input and thereby improve water clarity have been instrumental in avoiding a catastrophic loss of eelgrass ecosystems. However, local‐scale future management must, in addition, reduce bottom trawling to facilitate eelgrass reaching deeper, cooler refugia, and increase resilience toward realized and further warming. Warming needs to be limited by meeting global climate change mitigation goals. [ABSTRACT FROM AUTHOR]

Summary: Massive metagenomic sequencing combined with gene prediction methods were previously used to compile the gene catalogue of the ocean and host‐associated microbes. Global expeditions conducted over the past 15 years have sampled the ocean to build a catalogue of genes from pelagic microbes. Here we undertook a large sequencing effort of a perturbed Red Sea plankton community to uncover that the rate of gene discovery increases continuously with sequencing effort, with no indication that the retrieved 2.83 million non‐redundant (complete) genes predicted from the experiment represented a nearly complete inventory of the genes present in the sampled community (i.e., no evidence of saturation). The underlying reason is the Pareto‐like distribution of the abundance of genes in the plankton community, resulting in a very long tail of millions of genes present at remarkably low abundances, which can only be retrieved through massive sequencing. Microbial metagenomic projects retrieve a variable number of unique genes per Tera base‐pair (Tbp), with a median value of 14.7 million unique genes per Tbp sequenced across projects. The increase in the rate of gene discovery in microbial metagenomes with sequencing effort implies that there is ample room for new gene discovery in further ocean and holobiont sequencing studies. [ABSTRACT FROM AUTHOR]

Seagrass meadows store globally significant organic carbon (Corg) stocks which, if disturbed, can lead to CO2 emissions, contributing to climate change. Eutrophication and thermal stress continue to be a major cause of seagrass decline worldwide, but the associated CO2 emissions remain poorly understood. This study presents comprehensive estimates of seagrass soil Corg erosion following eutrophication‐driven seagrass loss in Cockburn Sound (23 km2 between 1960s and 1990s) and identifies the main drivers. We estimate that shallow seagrass meadows (<5 m depth) had significantly higher Corg stocks in 50 cm thick soils (4.5 ± 0.7 kg Corg/m2) than previously vegetated counterparts (0.5 ± 0.1 kg Corg/m2). In deeper areas (>5 m), however, soil Corg stocks in seagrass and bare but previously vegetated areas were not significantly different (2.6 ± 0.3 and 3.0 ± 0.6 kg Corg/m2, respectively). The soil Corg sequestration capacity prevailed in shallow and deep vegetated areas (55 ± 11 and 21 ± 7 g Corg m−2 year−1, respectively), but was lost in bare areas. We identified that seagrass canopy loss alone does not necessarily drive changes in soil Corg but, when combined with high hydrodynamic energy, significant erosion occurred. Our estimates point at ~0.20 m/s as the critical shear velocity threshold causing soil Corg erosion. We estimate, from field studies and satellite imagery, that soil Corg erosion (within the top 50 cm) following seagrass loss likely resulted in cumulative emissions of 0.06–0.14 Tg CO2‐eq over the last 40 years in Cockburn Sound. We estimated that indirect impacts (i.e. eutrophication, thermal stress and light stress) causing the loss of ~161,150 ha of seagrasses in Australia, likely resulted in the release of 11–21 Tg CO2‐eq since the 1950s, increasing cumulative CO2 emissions from land‐use change in Australia by 1.1%–2.3% per annum. The patterns described serve as a baseline to estimate potential CO2 emissions following disturbance of seagrass meadows. [ABSTRACT FROM AUTHOR]

Concerns over overexploitation have fueled an ongoing debate on the current state and future prospects of global capture fisheries, associated threats to marine biodiversity, and declining yields available for human consumption. Management reforms have aimed to reduce fishing pressure and recover depleted stocks to biomass and exploitation rates that allow for maximum sustainable yield. Recent analyses suggest that scientifically assessed stocks, contributing over half of global marine fish catch, have, on average, reached or even exceeded these targets, suggesting a fundamental shift in the effectiveness of fisheries governance. However, such conclusions are based on calculations requiring specific choices to average over high interstock variability to derive a global trend. Here we evaluate the robustness of these conclusions by examining the distribution of recovery rates across individual stocks and by applying a diversity of plausible averaging techniques. We show that different methods produce markedly divergent trajectories of global fisheries status, with 4 of 10 methods suggesting that recovery has not yet been achieved, with up to 48% of individual stocks remaining below biomass targets and 40% exploited above sustainable rates. Furthermore, recent rates of recovery are only marginally different from zero, with up to 46% of individual stocks trending downward in biomass and 29% of stocks trending upward in exploitation rate. These results caution against overoptimistic assessments of fisheries writ large and support a precautionary management approach to ensure full rebuilding of depleted fisheries worldwide. [ABSTRACT FROM AUTHOR]

Remote sensing is the main approach to map aquatic vegetation, and classification tree (CT) is superior to various classification methods. Based on previous studies, modified CT can be developed from traditional CT by adjusting the thresholds based on the statistical relationship between spectral features to classify different images without ground-truth data. However, no studies have yet employed this method to resolve marine vegetation. In this study, three Gao-Fen 1 satellite images obtained on 30 January 2014, 5 November 2014 and 21 January 2015 were selected, and two features were then employed to extract macroalgae farms. Results show that the overall accuracies of traditional CTs for three images are 92.0, 94.2 and 93.9%, respectively, whereas those of the two corresponding modified CTs for images obtained on 21 January 2015 and 5 November 2014 are 93.1 and 89.5%, respectively. This indicates modified CTs can map macroalgae with multi-date imagery and monitor their spatiotemporal distribution in coastal environments. [ABSTRACT FROM AUTHOR]

Accurately forecasting the response of global biota to warming is a fundamental challenge for ecology in the Anthropocene. Within-species variation in thermal sensitivity, caused by phenotypic plasticity and local adaptation of thermal limits, is often overlooked in assessments of species responses to warming. Despite this, implicit assumptions of thermal niche conservatism or adaptation and plasticity at the species level permeate the literature with potentially important implications for predictions of warming impacts at the population level. Here we review how these attributes interact with the spatial and temporal context of ocean warming to influence the vulnerability of marine organisms. We identify a broad spectrum of thermal sensitivities among marine organisms, particularly in central and cool-edge populations of species distributions. These are characterized by generally low sensitivity in organisms with conserved thermal niches, to high sensitivity for organisms with locally adapted thermal niches. Important differences in thermal sensitivity among marine taxa suggest that warming could adversely affect benthic primary producers sooner than less vulnerable higher trophic groups. Embracing the spatial, temporal and biological context of within-species variation in thermal physiology helps explain observed impacts of ocean warming and can improve forecasts of climate change vulnerability in marine systems. This article is part of the theme issue 'Physiological diversity, biodiversity patterns and global climate change: testing key hypotheses involving temperature and oxygen'. [ABSTRACT FROM AUTHOR]

Abstract: Although climate warming is affecting most marine ecosystems, the Mediterranean is showing earlier impacts. Foundation seagrasses are already experiencing a well‐documented regression in the Mediterranean which could be aggravated by climate change. Here, we forecast distributions of two seagrasses and contrast predicted loss with discrete regions identified on the basis of extant genetic diversity. Under the worst‐case scenario, Posidonia oceanica might lose 75% of suitable habitat by 2050 and is at risk of functional extinction by 2100, whereas Cymodocea nodosa would lose only 46.5% in that scenario as losses are compensated with gained and stable areas in the Atlantic. Besides, we predict that erosion of present genetic diversity and vicariant processes can happen, as all Mediterranean genetic regions could decrease considerably in extension in future warming scenarios. The functional extinction of Posidonia oceanica would have important ecological impacts and may also lead to the release of the massive carbon stocks these ecosystems stored over millennia. [ABSTRACT FROM AUTHOR]

Recently, Gallagher et al. (2022) suggested that seaweed ecosystems are net heterotrophic carbon sources due to CO2 released from the consumption of external subsidies. Here we outline several flaws in their argument, which we believe confuse research on the blue carbon potential of seaweed ecosystems, and unjustifiably generate doubt around initiatives to protect and restore seaweed forests. Gallagher et al.'s evidence relies on 18 studies with highly variable measures of net ecosystem production, which do not statistically support their conclusion that most seaweed ecosystems are heterotrophic. This dataset is also inappropriate as it is incomplete and misrepresents seaweed ecosystems globally, particularly seaweed forests, which contribute disproportionately to global seaweed productivity. We maintain that the climate change mitigation value of an ecosystem depends on the net difference in CO2 uptake between the original ecosystem and its replacement ecosystem. We provide evidence that most seaweed ecosystems, which drawdown the largest carbon flux of any vegetated coastal habitat, are indeed net autotrophic ecosystems. We recognize that substantial uncertainties remain concerning the magnitude of CO2 drawdown by seaweed ecosystems and recommend that carbon fluxes around seaweed ecosystems should be considered more broadly and taken into account in estimates of their CO2 mitigation potential. [ABSTRACT FROM AUTHOR]

Rising temperatures in the Arctic Ocean are causing sea ice and glaciers to melt at record breaking rates, which has consequences for carbon cycling in the Arctic Ocean that are yet to be fully understood. Microbial carbon cycling is driven by internal processing of in situ produced organic carbon (OC), however recent research suggests that melt water from sea ice and glaciers could introduce an allochthonous source of OC to the microbial food web with ramifications for the metabolic balance of plankton communities. In this study, we characterized autochthonous and allochthonous sources of OC to the Western Svalbard fjord system using stable isotopes of carbon. We quantified δ13C of eukaryotic and prokaryotic planktonic groups using polar lipid-derived fatty acids as biomarkers in addition to measuring δ13C of marine particulate OC and dissolved OC from glacial runoff. δ13C of bacteria (−22.5‰) was higher than that of glacial runoff OC (−28.5‰) and other phytoplankton groups (−24.7 to −29.1‰), which suggests that marine bacteria preferentially use a third source of OC. We present a Bayesian three-source δ13C mixing model whereby ∼ 60% of bacteria carbon is derived from OC in sea ice, and the remaining carbon is derived from autochthonous production and glacial-derived OC. These results suggest that subsidies of OC from melting glaciers will not likely influence microbial carbon cycling in Svalbard fjords in the future and that further research is needed to determine the effects of melting sea ice on microbial carbon cycling in fjord systems and elsewhere in the Arctic Ocean. [ABSTRACT FROM AUTHOR]

Mobile phones and other geolocated devices have produced unprecedented volumes of data on human movement. Analysis of pooled individual human trajectories using big data approaches has revealed a wealth of emergent features that have ecological parallels in animals across a diverse array of phenomena including commuting, epidemics, the spread of innovations and culture, and collective behaviour. Movement ecology, which explores how animals cope with and optimize variability in resources, has the potential to provide a theoretical framework to aid an understanding of human mobility and its impacts on ecosystems. In turn, big data on human movement can be explored in the context of animal movement ecology to provide solutions for urgent conservation problems and management challenges. [ABSTRACT FROM AUTHOR]

The proliferation of a number of pressures affecting the ocean is leading to a growing concern that the state of the ocean is compromised, which is driving society into pessimism. Ocean calamities are disruptive changes to ocean ecosystems that have profound impacts and that are widespread or global in scope. However, scrutiny of ocean calamities to ensure that they can be confidently attributed to human drivers, operate at widespread or global scales, and cause severe disruptions of marine social-ecosystems shows that some of the problems fail to meet these requirements or that the evidence is equivocal. A number of biases internal and external to the scientific community contribute to perpetuating the perception of ocean calamities in the absence of robust evidence. An organized auditing of ocean calamities may deliver a more precise diagnosis of the status of the oceans, which may help to identify the most pressing problems that need be addressed to conserve a healthy ocean. [ABSTRACT FROM AUTHOR]

Antarctic krill are known to release large amounts of inorganic and organic nutrients to the water column. Here we test the role of krill excretion of dissolved products in stimulating heterotrophic bacteria on the basis of three experiments where ammonium and organic excretory products released by krill were added to bacterial assemblages, free of grazers. Our results demonstrate that the addition of krill excretion products (but not of ammonium alone), at levels expected in krill swarms, greatly stimulates bacteria resulting in an order-of-magnitude increase in growth and production. Furthermore, they suggest that bacterial growth rate in the Southern Ocean is suppressed well below their potential by resource limitation. Enhanced bacterial activity in the presence of krill, which are major sources of DOC in the Southern Ocean, would further increase recycling processes associated with krill activity, resulting in highly efficient krill-bacterial recycling that should be conducive to stimulating periods of high primary productivity in the Southern Ocean. [ABSTRACT FROM AUTHOR]

Seagrass meadows are important carbon sinks, and they are experiencing a global decline. Restoration of seagrass meadows provides a strategy to mitigate climate change while conserving these important ecosystems., We examined the long-term carbon sequestration expected for seagrass restoration programmes by developing a model that combined models of patch growth, patch survival in seagrass planting projects and estimates of seagrass CO2 sequestration per unit area for the five seagrass species commonly used in restoration programmes., The model results indicated that the cumulative C sequestered increased rapidly over time and with planting density to reach an asymptote at a planting density of 100 units ha−1 (or 6 m spacing between units). At this planting density, the modelled cumulative C sequestered ranges from 177 to over 1337 tons CO2 ha−1 after 50 years., The value corresponding to this carbon sequestration suggests that the costs of seagrass restoration programmes may be fully recovered by the total CO2 captured in societies with a carbon tax in place, providing additional ecosystem services derived from the role of seagrasses in providing ecosystem services, such as enhanced biodiversity., Synthesis and applications. Seagrass restoration programmes are economically viable strategies to mitigate climate change through carbon sequestration, particularly in subtropical and tropical island states where land-based options have a limited scope. [ABSTRACT FROM AUTHOR]

A perceived recent increase in global jellyfish abundance has been portrayed as a symptom of degraded oceans. This perception is based primarily on a few case studies and anecdotal evidence, but a formal analysis of global temporal trends in jellyfish populations has been missing. Here, we analyze all available long-term datasets on changes in jellyfish abundance across multiple coastal stations, using linear and logistic mixed models and effect-size analysis to show that there is no robust evidence for a global increase in jellyfish. Although there has been a small linear increase in jellyfish since the 1970s, this trend was unsubstantiated by effect-size analysis that showed no difference in the proportion of increasing vs. decreasing jellyfish populations over all time periods examined. Rather, the strongest nonrandom trend indicated jellyfish populations undergo larger, worldwide oscillations with an approximate 20-y periodicity, including a rising phase during the 1990s that contributed to the perception of a global increase in jellyfish abundance. Sustained monitoring is required over the next decade to elucidate with statistical confidence whether the weak increasing linear trend in jellyfish after 1970 is an actual shift in the baseline or part of an oscillation. Irrespective of the nature of increase, given the potential damage posed by jellyfish blooms to fisheries, tourism, and other human industries, our findings foretell recurrent phases of rise and fall in jellyfish populations that society should be prepared to face. [ABSTRACT FROM AUTHOR]

Abstract: Major advances in analytical chemistry and instrumentation have prompted major advances in our understanding of trace metal biogeochemistry. However, the deep-water concentration of most trace elements has not been yet assessed across broad regions of the oceans. A synthesis of data on trace metals (i.e. Cd, Co, Cu, Mo, Ni, Pb and Zn) measured and reported for depths 1000m or deeper, between 1976 and 2009 revealed major gaps in our coverage of this key property. Cadmium and Cu have been the elements more extensively measured with 264 and 210 deep profiles reported in 64 and 57 articles, respectively, while Mo and Co have been reported only at 17 and 60 ocean sites, respectively. Globally 68.1% (216.1 106 km2) of deep oceans (1000m or deeper) have not been sampled. The bulk of depth profiles published in peer reviewed scientific literature are from the Northern hemisphere (69.7% of the total reported profiles) rendering the Southern hemisphere as a poorly explored region for these important properties (mainly in the South and Eastern Pacific Ocean and in the Tropical Indian Ocean). Vertical profiles of dissolved elements plotted with data compiled during the last 34years indicate that, in addition to the variation of concentrations, vertical distributions differs per ocean basin. [Copyright &y& Elsevier]

Abstract: Shoot meristematic activity of Mediterranean seagrass Posidonia oceanica has been assessed in eleven different meadows located around Balearic Islands (Spanish Mediterranean). Moreover, in six of them, the meristematic activity has been determined hourly (or every 2 or 3h, depending on the meadow) for at least 24h, with the aim of detecting a possible circadian rhythm in the % of dividing nuclei. Meristematic activity was inferred by applying flow cytometry techniques combined with DNA labeling to determine the percentage of nuclei in each phase of the cell cycle (i.e. G0+G1, S, G2). The percentage of nuclei in G2 phase of the cell cycle reflects the percentage of nuclei that are dividing in a specific moment. In the meristems of vertical shoots of P. oceanica the percentage of nuclei in G2 phase was on average 7±0.11%, and it ranged from 2% to 12% across the meadows studied. The average percentage of nuclei in the G2 phase in P. oceanica meristems is lower than reported for other plants. No circadian rhythms were detected in meristems of P. oceanica. The variability observed for meristematic activity across meadows suggests that it could be used as indicator of seagrass stress and, thus, to assess impacts to meristems before population declines could be observed. [Copyright &y& Elsevier]

In this paper we describe for the first time the use of astable multivibrator circuits for computer-less control of solenoid micropumps and application for analytical flow techniques. Triggering and powering were accomplished using the NE555 integrated circuit. The activation and deactivation time intervals were adjusted using 10-turn trimmer potentiometers. The potential and characteristics of the instrumentation were studied on a two-channel flow system injecting an indigo carmine indicator solution. Subsequently, a three-channel flow system was assembled and successfully applied to the determination of nitrite in well waters. One circuit was used to control the activation time intervals of three further circuits used for the control of the flow rates or pulsation of solenoid micropumps. These were used for driving carrier, reagent, and sample in an analytical flow system. In the present work, the utility of the circuits for the construction of simple multipumping flow systems was demonstrated. A main feature to be highlighted was the simplicity and very low costs of the controlling circuits, favouring economic and miniaturised flow analysers. Second, no expenses or knowledge are required for the usual software control of the solenoid micropumps. This allows working with every existing detector without considering any problems of software and control compatibility. Third, owing to these features, the proposed assembly is especially suited for simple monitoring analysers, sample provision from an environmental or industrial process, or chemical education. [ABSTRACT FROM PUBLISHER]

The maximum size and age that clonal organisms can reach remains poorly known, although we do know that the largest natural clones can extend over hundreds or thousands of metres and potentially live for centuries. We made a review of findings to date, which reveal that the maximum clone age and size estimates reported in the literature are typically limited by the scale of sampling, and may grossly underestimate the maximum age and size of clonal organisms. A case study presented here shows the occurrence of clones of slow-growing marine angiosperm Posidonia oceanica at spatial scales ranging from metres to hundreds of kilometres, using microsatellites on 1544 sampling units from a total of 40 locations across the Mediterranean Sea. This analysis revealed the presence, with a prevalence of 3.5 to 8.9%, of very large clones spreading over one to several (up to 15) kilometres at the different locations. Using estimates from field studies and models of the clonal growth of P. oceanica, we estimated these large clones to be hundreds to thousands of years old, suggesting the evolution of general purpose genotypes with large phenotypic plasticity in this species. These results, obtained combining genetics, demography and model-based calculations, question present knowledge and understanding of the spreading capacity and life span of plant clones. These findings call for further research on these life history traits associated with clonality, considering their possible ecological and evolutionary implications. [ABSTRACT FROM AUTHOR]

Abstract: In this article, a simple, economic, and miniature flow analyzer for ammonium in seawater based on the solenoid micropumps is presented. A single reagent of sodium tetraborate, ortho-phthaldialdehyde (OPA), and sodium sulfite was used and optimized applying the modified SIMPLEX method. A special-made detection cell for fluorescence detection of the reaction product isoindol-1-sulfonat was made and combined with a commercial photomultiplier tube, a long-pass optical filter, and an UV-LED as excitation light source. A LOD down to 13nmol/L was achieved. The fabrication and application of a miniature reaction coil heating device for reaction rate enhancement is further described. The system featured an injection frequency of 32h−1 at average standard deviation of 3%. [Copyright &y& Elsevier]

The effect of warming on the oxygen requirements and the survival of benthic organisms under hypoxia was tested using a meta-analysis of published results of experiments evaluating the effects of temperature on the median lethal time and median lethal concentration of benthic macrofauna under hypoxia. The meta-analysis confirmed that survival times under hypoxia were reduced by on average 74% and that median lethal concentration increased by on average 16% when marine benthic organisms were exposed to warmer temperatures. Warming reduced survival times of marine benthic macrofauna under hypoxia by a median of 3.95±1.67 h °C and increased the oxygen thresholds for hypoxia-driven mortality by a median of 1.02±0.15% saturation °C or 0.07±0.01 mg O L °C. The corresponding Q values averaged 3.01±0.29 for the median survival time and 2.09±0.20 for the median lethal oxygen concentration. Use of these Q values predicts that the 4 °C warming expected during the 21st century will lead to survival times 35.6% lower under hypoxia and that the threshold oxygen concentrations for high mortality to occur will increase by, on average, 25.5% if bottom water temperature increased by 4 °C. Hence, ocean warming is expected to increase the vulnerability of benthic macrofauna to reduced oxygen concentrations and expand the area of coastal ecosystems affected by hypoxia. [ABSTRACT FROM AUTHOR]

In this article, we review evidence of how climate change has already resulted in clearly discernable changes in marine Arctic ecosystems. After defining the term 'footprint' and evaluating the availability of reliable baseline information we review the published literature to synthesize the footprints of climate change impacts in marine Arctic ecosystems reported as of mid-2009. We found a total of 51 reports of documented changes in Arctic marine biota in response to climate change. Among the responses evaluated were range shifts and changes in abundance, growth/condition, behaviour/phenology and community/regime shifts. Most reports concerned marine mammals, particularly polar bears, and fish. The number of well-documented changes in planktonic and benthic systems was surprisingly low. Evident losses of endemic species in the Arctic Ocean, and in ice algae production and associated community remained difficult to evaluate due to the lack of quantitative reports of its abundance and distribution. Very few footprints of climate change were reported in the literature from regions such as the wide Siberian shelf and the central Arctic Ocean due to the limited research effort made in these ecosystems. Despite the alarming nature of warming and its strong potential effects in the Arctic Ocean the research effort evaluating the impacts of climate change in this region is rather limited. [ABSTRACT FROM AUTHOR]

ic areas of deep-water convection have a large potential for export of organic carbon from surface waters into the deep sea and, therefore, are an important part of the global carbon cycle. As the Arctic is reportedly heating up faster than any other part of the planet, temperature-driven changes in the biogeochemical cycling in these areas can be very significant. Here, we study the regulation of bacterial carbon metabolism, which process vast amounts of organic carbon, by temperature and the availability of resources. The response of bacterial production and respiration of natural bacterial assemblages from the Fram Strait was studied by experimental manipulations of temperature and resources in combination. Both bacterial production and respiration were enhanced by temperature so that the total bacterial carbon demand increased sixfold following a temperature increase of 6°C. Respiration responded more strongly than production so that bacterial growth efficiency decreased with increasing temperature. Although neither production nor respiration was limited by resource availability under in situ conditions, the response to temperature was higher in resource-amended treatments, indicative of a substrate-temperature interaction regulating both components of bacterial metabolism. In conclusion, the results show that warming can result in a substantial increase of the carbon flow through bacteria and that most of the carbon consumed would be released as CO. Moreover, the results suggest that both temperature and availability of resources need to be considered to accurately be able to predict changes in bacterial carbon metabolism in response to climate change. [ABSTRACT FROM AUTHOR]

Abstract: Computational optimization strategies using algorithms (e.g., modified SIMPLEX method) present a fast, efficient alternative to univariant studies of chemical and physical experimental parameters of analytical flow systems. In this review, we give an overview of the applications of the SIMPLEX algorithm for optimizing analytical systems based on unsegmented flow techniques. We compare the different response functions used for evaluating the experimental data for optimization. We also discuss their advantages and shortcomings, and, with special focus on real-time applications, the problems involved in using SIMPLEX. We summarize in tabular form the analytical applications and the parameters optimized by the SIMPLEX method. [ABSTRACT FROM AUTHOR]

Rapid warming of the Mediterranean Sea threatens marine biodiversity, particularly key ecosystems already stressed by other impacts such as Posidonia oceanica meadows. A 6-year monitoring of seawater temperature and annual P. oceanica shoot demography at Cabrera Archipelago National Park (Balearic Islands, Western Mediterranean) allowed us to determine if warming influenced shoot mortality and recruitment rates of seagrasses growing in relative pristine environments. The average annual maximum temperature for 2002–2006 was 1 °C above temperatures recorded in 1988–1999 (26.6 °C), two heat waves impacted the region (with seawater warming up to 28.83 °C in 2003 and to 28.54 °C in 2006) and the cumulative temperature anomaly, above the 1988–1999 mean annual maximum temperature, during the growing season (i.e. degree-days) ranged between 0 °C in 2002 and 70 °C in 2003. Median annual P. oceanica shoot mortality rates varied from 0.067 year−1 in 2002 to 0.123 year−1 in 2003, and exceeded recruitment rates in all stations and years except in shallow stations for year 2004. Interannual fluctuations in shoot recruitment were independent of seawater warming ( P>0.05). P. oceanica meadows experienced a decline throughout the study period at an average rate of −0.050±0.020 year−1. Interannual variability in P. oceanica shoot mortality was coupled ( R2>0.40) to seawater warming variability and increasing water depth: shoot mortality rates increased by 0.022 year−1 (i.e. an additional 2% year−1) for each additional degree of annual maximum temperature and by 0.001 year−1 (i.e. 0.1% year−1) for each accumulated degree water temperature remained above 26.6 °C during the growing season. These results demonstrate that P. oceanica meadows are highly vulnerable to warming, which can induce steep declines in shoot abundance as well indicating that climate change poses a significant threat to this important habitat. [ABSTRACT FROM AUTHOR]

The study of transparent exopolymer particles (TEP) in the Mediterranean Sea is particularly relevant as they can be promoters of mucilage events, a frequent phenomenon there. We assessed the influence of bacterioplankton on TEP distribution and dynamics across the west–east axis of the Mediterranean Sea. We performed an extensive study of TEP, dissolved carbohydrates, and their relationships with bacterial abundance and bacterial production (BP). A significant and positive relationship was observed between BP and TEP in the study region ( r2 = 0.51, p < 0.001). The direct release of TEP by bacteria was experimentally corroborated using regrowth cultures where increases in TEP tracked bacterial growth in abundance and production. These TEP increases were positively related to the increases in BP ( r2 = 0.78, p < 0.05). The consistency (similar slopes) of the regression lines between BP and TEP in natural conditions and between the increases of BP and TEP in the experiments underlines the relevant role of bacteria in the formation of TEP in this area. [ABSTRACT FROM AUTHOR]

The effect of the presence of sulfide on the survival of benthic organisms under hypoxia was tested using a meta-analysis of published experimental results evaluating the effects of the presence of hydrogen sulfide on the median survival time of benthic macrofauna under hypoxia. The meta-analysis confirmed that survival times under hypoxia are reduced by an average of 30% in marine benthic communities exposed to hydrogen sulfide. The effect of sulfide on survival was higher for egg forms than for juvenile or adult stages. The aggravation of the negative effects of spreading hypoxia in the presence of sulfide suggests that the threats derived from hypoxia to marine biodiversity are greater than anticipated on the basis of the direct effects of low oxygen concentration alone. [ABSTRACT FROM AUTHOR]

An analysis of the contents and conclusions of the papers contained in this issue ( Hydrobiologia Volume xxx) suggests that a new vision is taking shape that may correspond to an emerging new paradigm in the way we understand and manage coastal eutrophication. This new paradigm emphasizes its global dimension and the connections with other global environmental pressures, and re-evaluates the targets of remedial actions and policies. Eutrophication research must evolve toward a more integrative, ecosystem perspective which requires that it be extended to include impacts beyond primary producers and to examine possible cascading effects and feedbacks involving other components of the ecosystem. A quantitative framework that incorporates the interacting top-down and bottom-up effects in eutrophication models must be urgently developed to guide diagnostics and establish targets to mitigate coastal eutrophication. The required macroscopic view must also be extended to the managerial and policy frameworks addressing eutrophication, through the development of policies that examine activities in the environment in an integrative, rather than sectorial, manner. Recent evidence of complex responses of coastal ecosystems to nutrient reduction requires that management targets, and the policies that support them, be reconsidered to recognize the complexities of the responses of coastal ecosystems to reduced nutrient inputs, including non-linear responses and associated thresholds. While a predictive framework for the complex trajectories of coastal ecosystems subject to changes in nutrient inputs is being developed, the assessment of managerial actions should be reconsidered to focus on the consideration of the status achieved as the outcome of nutrient reduction plans against that possibly derived from a ‘do nothing’ scenario. A proper assessment of eutrophication and the efforts to mitigate it also requires that eutrophication be considered as a component of global change, in addressing both its causes and its consequences, and that the feedbacks between other components of global change (e.g., climate change, overfishing, altered biogeochemical cycles, etc.) be explicitly considered in designing eutrophication research and in managing the problem. [ABSTRACT FROM AUTHOR]

Coastal ecosystems and the services they provide are adversely affected by a wide variety of human activities. In particular, seagrass meadows are negatively affected by impacts accruing from the billion or more people who live within 50 km of them. Seagrass meadows provide important ecosystem services, including an estimated $1.9 trillion per year in the form of nutrient cycling; an order of magnitude enhancement of coral reef fish productivity; a habitat for thousands of fish, bird, and invertebrate species; and a major food source for endangered dugong, manatee, and green turtle. Although individual impacts from coastal development, degraded water quality, and climate change have been documented, there has been no quantitative global assessment of seagrass loss until now. Our comprehensive global assessment of 215 studies found that seagrasses have been disappearing at a rate of 110 km² yr-1 since 1980 and that 29% of the known areal extent has disappeared since seagrass areas were initially recorded in 1879. Furthermore, rates of decline have accelerated from a median of 0.9% yr-1 before 1940 to 7% yr-1 since 1990. Seagrass loss rates are comparable to those reported for mangroves, coral reefs, and tropical rainforests and place seagrass meadows among the most threatened ecosystems on earth. [ABSTRACT FROM AUTHOR]

The notion that less productive marine planktonic communities tend to be heterotrophic was tested by synthesizing reported estimates of the relationships between the net community production or community respiration and gross primary production (GPP), allowing calculation of the threshold GPP separating less productive, heterotrophic communities from more productive, autotrophic ones. A total of 35 estimates of the threshold GPP were assembled, derived from reports of comparative analyses of individual regions (Mediterranean Sea, Atlantic Ocean, Southern Ocean, Pacific Ocean, and Indian Ocean) and global comparative analyses for open-ocean and coastal environments, time-series analyses of changes in planktonic metabolism at individual locations, experimental manipulations in mesocosms, and a semi-empirical modeling exercise. Planktonic communities of the open ocean and continental shelf showed threshold GPP values ranging 30-fold, from 0.34 mmol O2 m-3 d-1 to 9.45 mmol O2 m-3 d-1, with those for estuarine and coastal locations reaching 50.60 mmol O2 m-3 d-1. Antarctic and ultra-oligotrophic ecosystems showed the lowest threshold GPP values (<2.2 mmol O2 m-3 d-1), with a general consistency across approaches for a given ecosystem. Plankton community respiration in the absence of or under low primary production is not negligible and is supported by semi-labile dissolved organic carbon. The analysis of GPP thresholds suggests that allochthonous organic inputs to the less productive regions of the ocean must be in the order of 5-6 mmol C m-2 d-1, consistent with recent estimates of allochthonous inputs of organic carbon to the ocean. [ABSTRACT FROM AUTHOR]

Hypoxia is a mounting problem affecting the world's coastal waters, with severe consequences for marine life, including death and catastrophic changes. Hypoxia is forecast to increase owing to the combined effects of the continued spread of coastal eutrophication and global warming. A broad comparative analysis across a range of contrasting marine benthic organisms showed that hypoxia thresholds vary greatly across marine benthic organisms and that the conventional definition of 2 mg O2/liter to designate waters as hypoxic is below the empirical sublethal and lethal O2 thresholds for half of the species tested. These results imply that the number and area of coastal ecosystems affected by hypoxia and the future extent of hypoxia impacts on marine life have been generally underestimated. [ABSTRACT FROM AUTHOR]

Abstract: The role of microorganisms in the transfer of carbon of marine systems is very important in open oligotrophic oceans. Here, we analyze the picoplankton structure, the heterotrophic bacterioplankton activity, and the predator–prey relationships between heterotrophic bacteria and nanoflagellates during two large scale cruises in the Central Atlantic Ocean (∼29°N to ∼40°S). Latitud cruises were performed in 1995 between March–April and October–November. During both cruises we crossed the regions of different trophic statuses; where we measured different biological variables both at the surface and at the deep chlorophyll maximum (DCM). The concentration of chlorophyll a varied between 0.1 and 0.8mgm−3, the abundance of heterotrophic bacteria varied between <1.0×105 and >1.0×106 cellsml−1, and that of heterotrophic nanoflagellates between <100 and >1.0×104 cellsml−1. The production of heterotrophic bacteria varied more than three orders of magnitude between <0.01 and 24μgCL−1 d−1; and the growth rates were in the range <0.01–2.1d−1. In the Latitud-II cruise, Prochlorococcus ranged between <103 and >3×105 cellsml−1, Synechococcus between <100 and >1.0×104 cellsml−1, and picoeukaryotes between <100 and >104 cellsml−1. Two empirical models were used to learn more about the relationship between heterotrophic bacteria and nanoflagellates. Most bacterial production was ingested when this production was low, the heterotrophic nanoflagellates could be controlled by preys during Latitud-I cruise at the DCM, and by predators in the surface and in the Latitud-II cruise. Our results were placed in context with others about the structure and function of auto- and heterotrophic picoplankton and heterotrophic nanoplankton in the Central Atlantic Ocean. [Copyright &y& Elsevier]

Abstract: Ecosystem transformation and depletion of natural resources by human activity with associated increase in species extinctions renders research to understand the consequences of these transformations and design strategies to conserve biological diversity a fundamental priority. Since the introduction of the term biodiversity, accumulated research in this field has expanded exponentially. An analysis of existing literature was conducted to examine patterns in the resulting research effort. The analysis, conducted using the Web of Science (WoS), identified 13336 published articles between 1987 and 2005 concerning biodiversity research. Research efforts are increasing, with 72% of the research effort addressing terrestrial ecosystems. Most of the research is experimental in nature, with few models developed, and focuses on species. Despite constant technical improvements, research on genetic diversity still represents a minor component. Research on different systems is disseminated through different publication outlets, fragmenting the community and derived knowledge. Reported results, here measured as strength of the correlation between biodiversity and ecosystem function, do not differ across ecosystems but are stronger when the study focused on functional groups instead of species level. Collaborative efforts remain limited, as the average number of authors per paper is not increasing with time, unlike patterns in other disciplines. The international distribution of research efforts is highly skewed, with the USA and the EU conducting nearly 90% of the research. [Copyright &y& Elsevier]

Abstract: The relationship between sedimentary Fe inputs and net seagrass population growth across a range of Posidonia oceanica meadows growing in carbonate Mediterranean sediments (Balearic Islands, Spain; SE Iberian Peninsula, Spain; Limassol, Cyprus; Sounion, Greece) was examined using comparative analysis. Sedimentary Fe inputs were measured using benthic sediment traps and the net population growth of P. oceanica meadows was assessed using direct census of tagged plants. The meadows examined ranged from meadows undergoing a severe decline to expanding meadows (specific net population growth, from −0.14yr−1 to 0.05yr−1). Similarly, Fe inputs to the meadows ranged almost an order of magnitude across meadows (8.6–69.1mgFem−2 d−1). There was a significant, positive relationship between sedimentary iron inputs and seagrass net population growth, accounting for 36% of the variability in population growth across meadows. The relationship obtained suggested that seagrass meadows receiving Fe inputs below 43mgFem−2 d−1 are vulnerable and in risk of decline, confirming the pivotal role of Fe in the control of growth and the stability of seagrass meadows in carbonate sediments. [Copyright &y& Elsevier]

Plant mortality and birth rates are critical components of plant life history affecting the stability of plant populations and the ecosystems they form. Although allometric theory predicts that both plant birth and mortality rates should be size-dependent, this prediction has not yet been tested across plants ranging the full size spectrum. Here we show that both population mortality and population birth rates scale as the -¼ power and plant lifespan as the ¼ power of plant mass across plant species spanning from the tiniest phototrophs to the largest trees. Whereas the controls on plant lifespans are as yet poorly understood, our findings suggest that plant mortality rates have evolved to match population birth rates, thereby helping to maintain plant communities in equilibrium and optimizing plant life histories. [ABSTRACT FROM AUTHOR]

We describe shoot density, aboveground and belowground biomass, form and leaf production per shoot over a one-year cycle for Cymodocea nodosa meadows in the Ria Formosa lagoon (South Portugal). Habitat conditions in Ria Formosa allow the development of lush meadows (up to 1752 shoots m-2), supporting high shoot biomass (up to 945 g DW m-2), high leaf productivity (up to 14 g DW m-2 d-1) and large shoots (up to 113 cm leaf length) despite being located at the northern limit of the distributional range in the Atlantic Ocean. Biomass in the meadows examined is higher than other Atlantic sites with C. nodosa, and comparable to the most productive seagrass meadows yet reported. Shoot morphometry and biomass distribution were variable within Ria Formosa, with the stands growing in muddy sediments having a lower ratio of belowground/aboveground biomass than those in sandy sites. C. nodosa had a clear unimodal growth cycle, reaching maximum leaf development in summer. Mean leaf length and number of leaves per shoot, the rate of appearance of new leaves and the rate of leaf fall, average leaf growth and leaf turnover rates (P/B) were minimal in February and March, and maximal in July and September. The high production of the meadows examined may be related to the high nutrient availability in Ria Formosa, evidenced by the high leaf nutrient content (3.4% of DW and 0.38% of DW for nitrogen and phosphorus, respectively). [ABSTRACT FROM AUTHOR]

Recent, parallel developments in the study of freshwater and marine ecosystems have provided evidence that net heterotrophic systems (those in which respiratory organic matter destruction exeeds photosynthetic production) are more prevalent than hitherto believed, including most rivers, oligo- to mesotrophic lakes and some oligotrophic regions of the ocean. In parallel, these aquatic ecosystems have been shown to act as CO2 sources to the atmosphere, as expected from the heterotrophic nature of the communities they contain. The prevalence of net heterotrophic aquatic ecosystems indicates that they must receive significant inputs of organic carbon from adjacent ecosystems, assigning an important role to the lateral exchanges of carbon between land and aquatic ecosystems, between coastal and open ocean ecosystems, as well as internal redistribution within large or complex aquatic ecosystems in determining their metabolic status and the gaseous exchange with the atmosphere. The examination of the carbon budget of ecosystems requires, therefore, an integrative approach that accounts for exchanges between compartments often studied in isolation. These recent findings conform a new paradigm of the functioning of aquatic ecosystems, and the metabolic connectivity between ecosystems in the biosphere. [ABSTRACT FROM AUTHOR]

A set of eight large (20 m³) mesocosms were moored in Johnson's Dock (62°39.576'S, 60°22.408'W, Livingston Island, Antarctica) to experimentally generate a gradient of phytoplankton biomass and production in order to test the extent of coupling between bacteria (heterotrophic Bacteria and Archaea) and phytoplankton, as well as the role of bacterial losses to protist grazers. This was achieved by imposing four light levels (100%, 50%, 25%, and 10%) in the presence or absence of nutrient additions (0.1 mol NH4Cl, 0.1 mol F6Na2Si, and 0.01 mol KH2PO4 per day per mesocosm). The experimental treatments resulted in a broad range of chlorophyll a (Chl a) (0.31-93.5 µg Chl a L-1) and average primary production rates, while bacteria responded in a much narrower range of biomass (3-447 µg C L-1) and production (0.21-15.71 µg C L-1d-1). Results confirm that bacteria--chlorophyll and bacterial production--primary production relationships in the Southern Ocean differ from the typical relationships applicable to aquatic ecosystems elsewhere. Bacteria respond to phytoplankton blooms, but they respond so weakly that bacterial production represents a small percentage of primary production (1-10%). Although other mechanisms might also contribute to the weak bacterial response to phytoplankton blooms, we demonstrate that the reason for it is likely the tight control of bacterial populations by their predators. Protist grazers are able to sustain faster growth rates in the cold waters of the Southern Ocean than are bacteria, thereby preventing bacteria from responding to phytoplankton blooms more forcibly. [ABSTRACT FROM AUTHOR]

Here we demonstrate, through experimental iron additions to a Mediterranean seagrass meadow, that iron plays a pivotal role in seagrass systems on carbonate sediments, directly through its role as a limiting nutrient, and indirectly by stimulating phosphorus recycling through the activity of the enzyme alkaline phosphatase and by buffering the development of reduced conditions in sediments. Iron additions were performed throughout the active root zone (30 cm depth) to two Posidonia oceanica meadows, one on organic-enriched sediments and one on organic poor sediments (Reference). Seagrass growth, nutrient incorporation and sediment biogeochemical conditions were followed for four months. Iron additions had positive effects on seagrass growth (leaf production increased with 55%) and nutrient incorporation (increased 46–91%) in the organic-enriched site, increasing to levels found at the Reference site. There was no effect of iron additions in the Reference seagrass meadow suggesting that iron was not the most important controlling factor at this site. The iron pools were about two times higher compared to the organic-enriched site. The main effect on the sediment biogeochemical conditions at the organic-enriched site was a suppression of sulfate reduction activity to the levels encountered at the Reference site (6.7 mmol m−2d−1 vs. 4.7–5.9 mmol m−2d−1). This suggests that the sulfide stress on the seagrasses was removed and that the iron availability increased due to reduced precipitation of iron-sulfides and thus improving seagrass growth conditions in these organic-enriched sediments. [ABSTRACT FROM AUTHOR]

The proposed threshold planktonic gross primary production (GPP) value for O2 of 2.05 mmol m-3 d-1 separating net heterotrophic from net autotrophic communities in the Southern Ocean was tested experimentally using large mesocosms (20 m³). A set of eight mesocosms was moored in Johnson's Dock (62°39.576′S, 60°22.408′W, Livingston Island, Antarctica) and a gradient of GPP was experimentally generated by imposing four light levels (100%, 50%, 25%, and 10%) in the presence or absence of nutrient additions (0.1 mol NH4Cl, 0.1 mol of F6Na2Si, and 0.01 mol KH2PO4 per mesocosm per day). The experimental treatments resulted in a broad range of chlorophyll a (Chl a) (0.31-93.5 mg m-3) and GPP (O2, 0.17-16.7 mmol m-3 d-1). Community respiration (R) increased with increasing GPP, but not proportionately, resulting in a range of P:R ratios ranging from 0.12 in intensely shaded communities to 1.3 in those receiving high irradiance and nutrient additions, with the compensation irradiance for community metabolism (i.e., percentage irradiance at P : R = 1) being reached at 83% of the ambient irradiance. The experimental estimate of the threshold GPP for metabolic balance of the community investigated (i.e., P:R = 1) was 2.2 (SE ± 0.016) mmol O2 m-3 d-1, thereby validating the estimate of 2.05 mmol O2 m-3 d-1 derived in the past from comparative analyses of planktonic metabolism across the Southern Ocean. The validation of this threshold suggests that net heterotrophic planktonic communities may be more prevalent in the Southern Ocean than hitherto believed. [ABSTRACT FROM AUTHOR]

The dynamics of the nutrient pools and their stoichiometry as well as their control by ecosystem metabolism (benthic and planktonic) and benthic-pelagic exchanges (sedimentation rates and sediment waterfluxes) were examined in the Mediterranean littoral (Blanes Bay, NE Spain). Dissolved organic nitrogen comprised about half of the nitrogen present in the water column and the carbon pool was dominated by the inorganic pool (95% of the carbon present in the water column). The dissolved and particulate organic pools were deficient in P relative to C and N, indicating a rapid recycling of P from organic matter. The pelagic compartment was heterotrophic, supported by significant allochthonous inputs of land material, which also contributed greatly to the sedimentary inputs (37% of total sedimenting carbon). In contrast, the benthic compartment was autotrophic, with the excess net benthic community production balancing the deficit in pelagic community production, leading to metabolic equilibrium at the station studied. Sedimentary inputs of nitrogen, phosphorus and silicon exceeded the benthic release, indicating that the benthic compartment acted as a sink for nutrients, consistent with its autotrophic nature. Carbon inputs to the benthic compartment also exceeded requirements, due to the allochthonous subsidies to the system, so that the benthic compartment stored or exported organic carbon. [ABSTRACT FROM AUTHOR]

Protein–DNA interactions are crucial for many biological processes. Attempts to model these interactions have generally taken the form of amino acid–base recognition codes or purely sequence-based profile methods, which depend on the availability of extensive sequence and structural information for specific structural families, neglect side-chain conformational variability, and lack generality beyond the structural family used to train the model. Here, we take advantage of recent advances in rotamer-based protein design and the large number of structurally characterized protein–DNA complexes to develop and parameterize a simple physical model for protein–DNA interactions. The model shows considerable promise for redesigning amino acids at protein–DNA interfaces, as design calculations recover the amino acid residue identities and conformations at these interfaces with accuracies comparable to sequence recovery in globular proteins. The model shows promise also for predicting DNA-binding specificity for fixed protein sequences: native DNA sequences are selected correctly from pools of competing DNA substrates; however, incorporation of backbone movement will likely be required to improve performance in homology modeling applications. Interestingly, optimization of zinc finger protein amino acid sequences for high-affinity binding to specific DNA sequences results in proteins with little or no predicted specificity, suggesting that naturally occurring DNA-binding proteins are optimized for specificity rather than affinity. When combined with algorithms that optimize specificity directly, the simple computational model developed here should be useful for the engineering of proteins with novel DNA-binding specificities. [Copyright &y& Elsevier]

Long-term and experimental approaches were used to examine the metabolic balance of the planktonic community in the Bay of Blanes (Spanish Mediterranean). Incubation measurements at weekly intervals for 6 yr revealed that community respiration, R, was consistently larger than gross primary production (GPP) by a factor of 2. The plankton community was net heterotrophic for 2/3 of the study period, with a median P/R ratio of 0.65. The biomass of autotrophs comprised, on average, 41% ± 3% of the planktonic biomass, and the total microplankton biomass was about 2.5-fold greater than that of the primary producers. The monthly average GPP and R were positively correlated with day length, and the planktonic respiration and gross production per unit microplankton biomass increased with increasing water temperature. Experimental nutrient additions had a greater effect on GPP than respiration rates; the increase in R along the nutrient gradient was 7.8% (± 0.4%) of the increase in GPP. As a result, net community production increased in parallel with GPP, shifting from net heterotrophic at low GPP to net autotrophic when GPP increased because of nutrient additions. Our results show that Be R that would be supported by allocthonous inputs was 3.83 ± 0.67 µmol O2 L-1 d-1, and the average GPP required to shift the community from net heterotrophic to net autotrophic was about 4 µmol O2 L-1 d-1. This is well above the average GPP recorded in the Bay of Blanes along this study (2.56 ± 0.13 µmol O2 L-1 d-1), explaining the net heterotrophic nature of the community. [ABSTRACT FROM AUTHOR]

The hypothesis that the importance of dissolved organic matter (DOM) as a reservoir of C, N, and P declines, relative to that of the particulate pool, with increasing nutrient inputs was tested using mesocosms exposed to a gradient of nutrient inputs in the Spanish Mediterranean. The nutrient additions included a treatment equivalent to the loading in the coastal ecosystem studied (5 mmol N m-2 d-1), and mesocosms receiving half , 2-, 4-, 8-, and 16-fold this value, as well as a mesocosm to which no nutrients were added. Nutrients were added at ratios of 20 N (as ammonium) : 7 Si : 1 P. The initial concentration of dissolved inorganic nutrients was very low (dissolved inorganic nitrogen < 0.05 μM, phosphate < 0.01) and comprised, together with the particulate pool < 25% of the total N and P in the system, with the bulk N and P in the system present as DOM (> 75%). Particulate and dissolved organic matter was depleted in N (C/N ratio > 15) and, particularly, P (C/P ratio > 1000), indicative of a strongly nutrient, particularly phosphorus, deficient ecosystem. Experimental nutrient additions lead to a parabolic change in C/N and C/P ratios in the dissolved organic matter with increasing nutrient inputs, which approached the Redfield stoichiometry at nutrient inputs > 8 fold above the ambient loading. The relative size of the dissolved inorganic nutrient pools (about 20% of the N and P) did not vary, but there was a tendency towards an increase in the relative size of the particulate pool at the expense of a decrease in the relative importance of DOM as a reservoir of N, P and C, with increasing nutrient inputs. The production of nutrient-depleted organic matter at low nutrient inputs likely prevents efficient recycling, leading to the dominance of nutrients in DOM in the system. [ABSTRACT FROM AUTHOR]

Microbial activity was assayed in sediments under five nutrient-limited Posidonia oceanica meadows on the north-east coast of Spain by measuring potential DMSO reduction to dimethylsulfide (DMS) throughout an annual cycle. Nutrient enrichment of the sediments was used to examine the importance of nutrient availability for potential DMSO reduction. DMSO reduction was observed in all the sediments analysed. Values were higher under anaerobic conditions, and low in spring when seagrass uptake removed most of the interstitial sediment phosphorus. DMSO reduction was correlated with α-glucosidase activity suggesting a link with other microbial activities. Nutrient additions significantly increased DMSO reduction in the meadows studied. The extent of the response varied substantially over the year and was highest during November–December. Microbial DMSO reduction was coupled with nutrient cycles like other bacterial activities. This suggests a possibly important role of nutrient additions in bacterial activity in Mediterranean seagrass sediments. [Copyright &y& Elsevier]