1,721,048 research outputs found
Simulations and interpretations of cumulative trophic theory
Full text linkExamining marine ecosystems in a distinct way can produce new ecological, theoretical and applied insights. The common “S” and “hockey stick” -shaped curves, which result from examining the cumulative biomass and trophic level and the cumulative production and cumulative biomass curves of marine ecosystems, have strong potential to elucidate the mechanisms of marine food webs. These curves are based on the cumulative trophic theory, which can be summarized as the integration of biomass and production across trophic level that results from the relatively simple trophic transfer equation. Here we test the behavior of this theory via modeled simulations of the transfer equation under a variety of common mechanisms that can influence marine ecosystems. The simulated scenarios we present and evaluate here explore bottom-up driven changes (production, growth), internal dynamics (transfer efficiency) or top-down driven changes (mortality, selectivity), as well as multi-mechanism scenarios (overfishing and eutrophication) that are commonly experienced in marine ecosystems. We explore these scenarios at high, medium or low levels of change for each feature to ascertain how they can result in major changes to the realized trophodynamics of a marine ecosystem. Our results lend credence to the generality of the cumulative trophic theory by predicting the empirically observed “S” and “hockey stick” -shaped curves under a wide range of possible mechanisms. Given that common, repeatable and predictable dynamics is a key hallmark of increasingly robust theories, the application of cumulative trophic theory in managing marine ecosystems enables more repeatable and predictable responses across a wide range of conditions
Editorial: Fishing in the time of COVID-19: Effects on fishing activities, resources, and marine ecosystems
Full text linkBiomass accumulation across trophic level: analysis of landings for the Mediterranean Sea
Full text linkThe need to implement Ecosystem-Based-Management (EBM) in marine ecosystems and the recent adoption of European Union directives, such as the Marine Strategy Framework Directive (MSFD), make indicators that are able to describe ecosystem state particularly relevant. The trophodynamic context is promising in that it can define integrative ecosystem indicators from modelling and field data. Here we analyze energy accumulation across trophic levels (TLs), i.e. the accumulation of energy in various biomass components of an ecosystem. The analysis of biomass accumulation across TLs, previously applied to surveys and model output data, was applied to a time series (1970 to 2010) of landings in the Mediterranean Sea and its 8 sub-areas. The standardized cumulative biomass versus TL curves for each year were fit to a logistic function, revealing that the accumulation pattern was detectable using landings data and confirming prior patterns. Parameters describing the curve shape, i.e. basal biomass, inflection point and steepness, were considered as possible indicators for assessing changes of ecosystem state through time. These parameters were able to detect systems modification in terms of both space and time and exhibited differential sensitivity to external drivers. The inflection point was mainly fishery-driven, whereas steepness seems to respond to environmental features, indicating an ability to discriminate across major ecosystem drivers. The application of Monte Carlo un certainty analysis showed that all of the parameters are sufficiently robust to possible sampling errors in the TL assignment to the different taxa. Collectively, these results confirm the robustness of patterns for cumulative biomass across TL curves seen in a growing number of marine eco systems. These emergent features suggest that this approach could produce useful ecosystem indicators for the implementation of EBM and the MSFD
Exergy as ecosystem indicator: an application to the recovery process of marine benthic communities
No full textTrophodynamics in marine ecology: 70 years after Lindeman
Full text linkThe seminal work of Lindeman (1942), ‘The trophic-dynamic aspect of ecology’ (Ecology 23:399), has been an important starting point for the holistic view of ecosystem tropho - dynamics, but it was initially seldom applied to marine ecosystems. Over the past 70 years, research on marine trophodynamics has become more widespread, producing a variety of analytical methods, and increasing our understanding of marine ecosystem functioning. Yet difficulties remain in transforming this body of knowledge into operational management of marine ecosystems
and marine resources. This Theme Section on ‘Trophodynamics in marine ecology’ documents recent advances and lessons learned over the past 70 years, and provides an opportunity to reflect on future directions for marine researc
Who Is Where in Marine Food Webs? A Trait-Based Analysis of Network Positions
Full text linkNetworks of trophic interactions provide a lot of information on the functioning of marine ecosystems. Beyond feeding habits, three additional traits (mobility, size, and habitat) of various organisms can complement this trophic view. The combination of traits and food web positions are studied here on a large food web database. The aim is a better description and understanding of ecological roles of organisms and the identification of the most important keystone species. This may contribute to develop better ecological indicators (e.g., keystoneness) and help in the interpretation of food web models. We use food web data from the Ecopath with Ecosim (EwE) database for 92 aquatic ecosystems. We quantify the network position of organisms by 18 topological indices (measuring centrality, hierarchy, and redundancy) and consider their three, categorical traits (e.g., for mobility: sessile, drifter, limited mobility, and mobile). Relationships are revealed by multivariate analysis. We found that topological indices belong to six different categories and some of them nicely separate various trait categories. For example, benthic organisms are richly connected and mobile organisms occupy higher food web positions
Mixed Trophic Impact e Transfer Efficiency come indicatori del ruolo di una specie e dello stato dell’ecosistema
No full textComparative production of fisheries yields and ecosystem overfishing in African Large Marine Ecosystems
No full textMarine capture fisheries in African Large Marine Ecosystems (LMEs) are important from economic, cultural, social, and food provision perspectives. These African fisheries have a long history of high exploitation in the context of data-limited situations. There is a growing, global movement (both in terms of management requirements and scientific efforts) to develop measures of ecosystem overfishing (EOF) that detect overfishing of an entire ecosystem using readily available data and based on widely repeatable patterns. These EOF indicators extend the thinking beyond single stock overfishing to an entire ecosystem and are largely based on well-established trophic theory. Moreover, they need to be germane for data limited situations, easily interpretable, and simple to calculate. Here we introduce and present the results of several of these indicators—the Ryther index, Fogarty index, and Friedland index—as well as indices based on cumulative biomass-Trophic Level curve parameters for eight African LMEs. Significantly, all these EOF indicators also have thresholds beyond which EOF is indicated, particularly when coupled with other evidence. These thresholds were applied to the African LME EOF indicators to determine the degree to which EOF may be occurring. Five out of eight African LMEs exhibited symptoms of EOF, one with significant EOF, with at least one LME still currently experiencing EOF, and three more that may be close to EOF thresholds. One LME exhibited evidence of recovering trends. Additionally, EOF indicators detected changes in the LMEs five-ten years prior to major impacts that would be identified by piecing together fishing impacts on a stock-by-stock basis. We conclude that if EOF is detected, at the very least these relative simple measures should be monitored and means to mitigate total fishing pressure in an ecosystem should be explored
EUROPEAN HAKE DIET IN THE ADRIATIC SEA: A METABARCODING APPROACH
No full textEuropean hake (Merluccius merluccius), is a demersal fish distributed from the North Sea and Atlantic to the Levantine Sea in the Mediterranean. It is an important predator of deep Mediterranean upper shelf slope communities currently characterised by growth overexploitation. M. merluccius adults feed mainly on fish and squids whereas the juveniles (<16 cm) feed on crustaceans. All current European hake diet studies relied on the morphological identification of prey remains in stomach content, however this method is labour intensive and it precludes the identification of strongly digested food. In this study we applied High-Throughput Sequencing (HTS) approaches that allow the simultaneous detection of many consumed species (DNA metabarcoding). Our approach is based on COI (cytochrome oxydase I) PCR amplification of stomach content remains and sequencing by using the Miseq Illumina paired-end technology. We sequenced 95 stomach remains of M. merluccius (representing all the size classes) and one pooled DNA sample of European hake preys used to assess the efficiency of the technique. Classic microscopic morphological analyses on stomach content remains have been carried out contextually to compare the results of the two methods. The molecular approach clearly outperformed the morphological prey analysis both in sensitivity and specificity. Statistical analysis of diet composition revealed a lack of differentiation among the size classes, suggesting an opportunistic feeding behaviour also supported by the homogenous bathymetry and, therefore, relatively homogeneous biocenosis of the sampling sites. Moreover the results of the artificially pooled sample allowed to confirm the semi-quantitative nature of this analysis
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