1,721,033 research outputs found
Decadal patterns and trends in benthic-pelagic exchange processes
No full textIn marine environments, the exchange of particles and solutes between the seafloor and overlying water column, known as benthic-pelagic (B/P) coupling is an important component in many biological and biogeochemical cycles. Key processes and drivers involved in this exchange display strongly seasonal variability, especially in temperate coastal environments. The magnitude and timings of these seasonal patterns however are not identical year-on-year, and the influence of this inter-annual variability on the rate and direction of B/P exchange, as well as the influence of longer term, multi-year trends, are less well understood. In this current study, multi-year temporal patterns of benthic-pelagic solute and particle exchange were investigated on the examples of particulate organic carbon and dissolved inorganic nitrogen time series data, to assess connections between inter- and multi-annual processes and characterize their nature and what drives them. To this end, a decadal (2009-2018) time-series dataset that combines biological, physical, meteorological and chemical measurements from the Western Channel Observatory, Plymouth, UK was analyzed in combination with supplementary data from several environmental monitoring agencies. Time-series decomposition using seasonal decomposition with locally estimated scatterplot smoothing revealed that the main causes of inter-annual variability were extreme outlier events, some of which were influential enough to cause multi-annual trends. Stochastic meteorological and biological extremes, such as exceptional storms and phytoplankton blooms explained a large proportion of outlier events in the time series. Global-scale climatic fluctuations, such as North Atlantic Oscillation (NAO) and Southern Oscillation Index were reflected in benthic-pelagic exchange trends when they co-occurred in an additive manner (e.g. positive NAO and El Niño). The importance of multi-parameter long-term observatories, such as the Western Channel Observatory, is highlighted, and the use of transdisciplinary time-series datasets to identify individual events which have large ecosystem-level impacts is demonstrated. In order to identify and monitor long-term effects, such as climate trends or decadal global ocean cycles, multi-decadal sustained observations are of vital importance
Uncovering the environmental drivers of short-term temporal dynamics in an epibenthic community from the Western English Channel
No full textAdapting the dynamic energy budget (DEB) approach to include non-continuous growth (moulting) and provide better predictions of biological performance in crustaceans
No full textDynamic energy budget (DEB) theory offers a comprehensive framework for understanding the overall physiological performance (growth, development, respiration, reproduction, etc.) of an organism over the course of its life cycle. We present here a simplified DEB model for the swimming crab Liocarcinus depurator. To the best of our knowledge, this is the first to be presented for this species. Most applications of the standard DEB model assume continuous growth in all size metrics (length, wet mass, carbon content) of the modelled species. However, in crustaceans growth, measured as an increase of carapace length/width, occurs periodically via moult. To account for this, we have extended the model to track the continuous increase in carbon mass as well as the episodic increase in physical size. Model predictions were consistent with the patterns in the observed data, predicting both the moult increment and the intermoult period of an individual. In addition to presenting the model itself, we also make recommendations for further development, and evaluate the potential applications of such a model, both at the individual level (e.g. aquaculture) and as a potential tool for population level dynamics (e.g. fisheries stock assessment).</p
Intra-annual patterns in the benthic-pelagic fluxes of dissolved and particulate matter
No full textIn coastal temperate environments, many processes known to affect the exchange of particulate and dissolved matter between the seafloor and the water column follow cyclical patterns of intra-annual variation. This study assesses the extent to which these individual short term temporal variations affect specific direct drivers of seafloor-water exchanges, how they interact with one another throughout the year, and what the resulting seasonal variation in the direction and magnitude of benthic-pelagic exchange is. Existing data from a multidisciplinary long-term time-series from the Western Channel Observatory, United Kingdom, were combined with new experimental and in situ data collected throughout a full seasonal cycle. These data, in combination with and contextualized by time-series data, were used to define an average year, split into five ‘periods’ (winter, pre-bloom, bloom, post-bloom, and autumn) based around the known importance of pelagic primary production and hydrodynamically active phases of the year. Multivariate analyses were used to identify specific sub-sets of parameters that described the various direct drivers of seafloor-water exchanges. Both dissolved and particulate exchange showed three distinct periods of significant flux during the year, although the specific timings of these periods and the cause-effect relationships to the direct and indirect drivers differed between the two types of flux. Dissolved matter exchange was dominated by an upward flux in the pre-bloom period driven by diffusion, then a biologically induced upward flux during the bloom and an autumn downward flux. The latter was attributable to the interactions of hydrodynamic and biological activity on the seafloor. Particulate matter exchanges exhibited a strongly hydrologically influenced upward flux during the winter, followed by a biologically induced downward flux during the bloom and a second period of downward flux throughout post-bloom and autumn periods. This was driven primarily through interactions between biological activity, and physical and meteorological drivers. The integrated, holistic and quantitative data-based analysis of intra-annual variability in benthic/pelagic fluxes presented in this study in a representative temperate coastal environment, demonstrates not only the various process’ inter-connectivity, but also their relative importance to each other. Future investigations or modeling efforts of similar systems will benefit greatly from the relationships and baseline rules established in this study.</p
Effects of elevated CO2 and temperature on an intertidal meiobenthic community, supplement to: Meadows, AS et al. (2015): Effects of elevated CO2 and temperature on an intertidal meiobenthic community. Journal of Experimental Marine Biology and Ecology, 469, 44-56
No full textIn the near future, the marine environment is likely to be subjected to simultaneous increases in temperature and decreased pH. The potential effects of these changes on intertidal, meiofaunal assemblages were investigated using a mesocosm experiment. Artificial Substrate Units containing meiofauna from the extreme low intertidal zone were exposed for 60 days to eight experimental treatments (four replicates for each treatment) comprising four pH levels: 8.0 (ambient control), 7.7 & 7.3 (predicted changes associated with ocean acidification), and 6.7 (CO2 point-source leakage from geological storage), crossed with two temperatures: 12 °C (ambient control) and 16 °C (predicted). Community structure, measured using major meiofauna taxa was significantly affected by pH and temperature. Copepods and copepodites showed the greatest decline in abundance in response to low pH and elevated temperature. Nematodes increased in abundance in response to low pH and temperature rise, possibly caused by decreased predation and competition for food owing to the declining macrofauna density. Nematode species composition changed significantly between the different treatments, and was affected by both seawater acidification and warming. Estimated nematode species diversity, species evenness, and the maturity index, were substantially lower at 16 °C, whereas trophic diversity was slightly higher at 16 °C except at pH 6.7. This study has demonstrated that the combination of elevated levels of CO2 and ocean warming may have substantial effects on structural and functional characteristics of meiofaunal and nematode communities, and that single stressor experiments are unlikely to encompass the complexity of abiotic and biotic interactions. At the same time, ecological interactions may lead to complex community responses to pH and temperature changes in the interstitial environment.</span
Effects of elevated CO2 and temperature on an intertidal harpacticoid copepod community
No full textWarming and ocean acidification have been shown to have significant impacts on marine organisms. However, none studies have addressed the impact of these two stressors on harpacticoid copepod community structure. A mesocosm experiment was conducted to assess the potential interactive impact of different levels of elevated CO2 and temperature on an intertidal harpacticoid copepod ommunity. Artificial substrate units (ASUs) colonized by meiofauna from the extreme low intertidal zone were exposed to eight experimental treatments (four pH levels: 8.0, 7.7, 7.3 and 6.7, crossed with two temperature levels: 12 and 16C). After 60 days exposure communities were significantly affected by both stressors. The dominant harpacticoid species were mainly affected at treatments held at pH 6.7, but with divergent biological response patterns. At pH 6.7 Tisbe sp and Ectinosoma sp2 exhibited important density reductions, while considerable density increases were observed for Amphiascus longarticulatus and Amphiascoides golikovi. This study has demonstrated that elevated levels of CO2 and ocean warming may have substantial effects on the structure of harpacticoid communities. Importantly, the increase in malformations observed at pH 6.7 indicated that we need to consider sub-lethal effects that could have consequences for populations after long periods of exposure
Observations of nitrogen chemistry and fluxes under high CO2 conditions: implications for the Mediterranean Sea
No full textFollowing a review of published reports and small-scale experiments performed on coastal waters and sediments of the English Channel, the currently known impacts of ocean acidification on the microbial nitrogen cycle are presented to enable discussion of direct and indirect effects which are relevant to the biogeochemistry of the Mediterranean Sea. There is great potential for changes in the balance of the nitrogen nutrients NO3- and NH4+ and between nitrogen and other nutrients including phosphorus, which ultimately infer changes in community composition and ecological status. Data from the English Channel support theoretical predictions that the balance of theNH4+:NH3 equilibrium in seawater favours NH4+ under acidic conditions, which when coupled with stable PO43- concentrations may act to increase the ratio of dissolved N:P. In surface waters, nitrifying bacteria were found to be sensitive to conditions of elevated CO2, so that nitrification rates were reduced by approximately 30% as a result of a reduction in pH of 0.18. In coastal sediments, the removal of NO3- from overlying water, increased under high CO2, as did the activity of denitrifying and/or annamox bacteria which coupled with changes in nitrification may lead todepletion of pelagic NO3- in absolute terms and relative to NH4+.Yet robust information on many of these processes under the influence of enhanced pCO2 is scarce. Recent research related to the fixation of carbon into organic and inorganic material, which is relevant to this study, has intensified, but has produced information that is at times contradictory. A condition which fuels ourcall for focussed experimental and model studies of decreasing pH in the Mediterranean basin. We tentatively propose that ocean acidification will act to increase the oligotrophic nature of the Mediterranean Sea and increase the degree of phosphorus limitation currently found, which will almost by definition, contribute to reduced productivity and carbon export
Will the declining sea ice extent in the Arctic cause a reversal of net benthic-pelagic exchange directions?
Full text linkIn the Arctic, loss of sea ice due to climate change and the northward shift of the Polar Front are predicted to affect many ecosystem processes such as the ecologically important process of particulate and dissolved matter exchange between the seafloor and the water column. In this study, we show for the first time that a change from an ice-covered, Arctic water-dominated system to an Atlantic -dominated ice-free one is likely to reverse seafloor-water exchange directions. A north – south transect across the Barents Sea was studied over two years with differing sea ice cover conditions, recording biological, biogeochemical, hydrographic, geophysical, and oceanographic data. There was a clear difference between the direction and magnitude of key benthic-pelagic fluxes present at Atlantic-dominated environments, and those in Arctic water – dominated ones. Currently, the southern Barents Sea exhibits a net downward flux of dissolved matter and a net upward flux of particulates, while in the northern region solutes fluctuate upwards and particulates downward, making the North a more depositional region that promotes near-surface primary productivity. Broad scale assessments of net fluxes in rapidly changing ecosystems should be employed to monitor impacts of climate change and anthropogenic activities
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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