Hjort Center for Marine Ecosystem Dynamics

Bergen, Norway

Hjort Center for Marine Ecosystem Dynamics

Bergen, Norway
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Certain G.,SLU Institute for Coastal Research | Certain G.,Norwegian Institute of Marine Research | Certain G.,Norwegian Institute for Nature Research | Planque B.,Norwegian Institute of Marine Research | Planque B.,Hjort Center for Marine Ecosystem Dynamics
ICES Journal of Marine Science | Year: 2015

Biodiversity is an increasingly important issue for the management of marine ecosystems. However, the proliferation of biodiversity indices and difficulties associated with their interpretation have resulted in a lack of clearly defined framework for quantifying biodiversity and biodiversity changes in marine ecosystems for assessment purpose. Recent theoretical and numerical developments in biodiversity statistics have established clear algebraic relationships between most of the diversity measures commonly used, and have highlighted those that most directly relates to the concept of biological diversity, terming them "true" diversity measures. In this study, we implement the calculation of these "true" diversity measures at the scale of a large-marine ecosystem, the Barents Sea. We applied hierarchical partitioning of biodiversity to an extensive dataset encompassing 10 years of trawl-surveys for both pelagic and demersal fish community. We quantify biodiversity and biodiversity changes for these two communities across the whole continental shelf of the Barents Sea at various spatial and temporal scales, explicitly identifying areas where fish communities are stable and variable. The method is used to disentangle areas where community composition is subject to random fluctuations from areas where the fish community is drifting over time. We discuss how our results can serve as a spatio-temporal biodiversity baseline against which new biodiversity estimates, derived from sea surveys, can be evaluated. © 2015 International Council for the Exploration of the Sea. All rights reserved.

Kolding J.,University of Bergen | Kolding J.,Hjort Center for Marine Ecosystem Dynamics | Bundy A.,Bedford Institute of Oceanography | Van Zwieten P.A.M.,Wageningen University | Plank M.J.,University of Canterbury
ICES Journal of Marine Science | Year: 2016

A global assessment of fishing patterns and fishing pressure from 110 different Ecopath models, representing marine ecosystems throughout the world and covering the period 1970-2007, show that human exploitation across trophic levels (TLs) is highly unbalanced and skewed towards low productive species at high TLs, which are around two TLs higher than the animal protein we get from terrestrial farming. Overall, exploitation levels from low trophic species were <15% of production, and only 18% of the total number of exploited groups and species were harvested >40% of their production. Generally, well-managed fisheries from temperate ecosystems were more selectively harvested at higher exploitation rates than tropical and upwelling (tropical and temperate) fisheries, resulting in potentially larger long-term changes to the ecosystem structure and functioning. The results indicate a very inefficient utilization of the food energy value of marine production. Rebuilding overfished components of the ecosystem and changing focus to balancing exploitation across a wider range of TLs, i.e. balanced harvesting, has the potential to significantly increase overall catches from global marine fisheries. © 2015 International Council for the Exploration of the Sea 2015.

Egge E.S.,University of Oslo | Johannessen T.V.,University of Bergen | Andersen T.,University of Oslo | Eikrem W.,University of Oslo | And 7 more authors.
Molecular Ecology | Year: 2015

Microalgae in the division Haptophyta play key roles in the marine ecosystem and in global biogeochemical processes. Despite their ecological importance, knowledge on seasonal dynamics, community composition and abundance at the species level is limited due to their small cell size and few morphological features visible under the light microscope. Here, we present unique data on haptophyte seasonal diversity and dynamics from two annual cycles, with the taxonomic resolution and sampling depth obtained with high-throughput sequencing. From outer Oslofjorden, S Norway, nano- and picoplanktonic samples were collected monthly for 2 years, and the haptophytes targeted by amplification of RNA/cDNA with Haptophyta-specific 18S rDNA V4 primers. We obtained 156 operational taxonomic units (OTUs), from c. 400.000 454 pyrosequencing reads, after rigorous bioinformatic filtering and clustering at 99.5%. Most OTUs represented uncultured and/or not yet 18S rDNA-sequenced species. Haptophyte OTU richness and community composition exhibited high temporal variation and significant yearly periodicity. Richness was highest in September-October (autumn) and lowest in April-May (spring). Some taxa were detected all year, such as Chrysochromulina simplex, Emiliania huxleyi and Phaeocystis cordata, whereas most calcifying coccolithophores only appeared from summer to early winter. We also revealed the seasonal dynamics of OTUs representing putative novel classes (clades HAP-3-5) or orders (clades D, E, F). Season, light and temperature accounted for 29% of the variation in OTU composition. Residual variation may be related to biotic factors, such as competition and viral infection. This study provides new, in-depth knowledge on seasonal diversity and dynamics of haptophytes in North Atlantic coastal waters. See also the Perspective by Massana © 2015 The Authors. Molecular Ecology Published by John Wiley & Sons Ltd.

Libungan L.A.,University of Iceland | Slotte A.,Norwegian Institute of Marine Research | Slotte A.,Hjort Center for Marine Ecosystem Dynamics | Otis E.O.,Alaska Department of Fish and Game | Palsson S.,University of Iceland
Polar Biology | Year: 2016

Pacific herring (Clupea pallasii) is divided into three subspecies: two in northeast Europe and one in the north Pacific Ocean. Genetic studies have indicated that the populations in northeast Europe have derived from the northwest Pacific herring recently, or during the last 10–15 kyr, and that they are distinct from the population in the northeast Pacific. In addition, hybridization between the Pacific herring and the Atlantic herring has been documented. Otolith variation has been considered to be largely affected by environmental variation, but here we evaluate whether the genetic differentiation is reflected in otolith shape differences. A clear difference in otolith shape was observed between the genetically differentiated herring species Clupea harengus from the Atlantic and C. pallasii. The otolith shape of C. p. suworowi in the Barents Sea was different from the shape of C. pallasii in northern Norway and C. p. pallasii from the Pacific. Populations of C. p. pallasii, sampled east and west of the Alaska Peninsula, which belong to two genetically different clades of the C. p. pallasii in the Pacific Ocean, show a clear difference in otolith shape. C. p. suworowi and the local C. pallasii peripheral population in Balsfjord in northern Norway are more similar to the northwest Pacific herring (C. p. pallasii) than to the northeast Pacific herring (C. p. pallasii), both genetically and in otolith shape. The Balsfjord population, known to be influenced by introgression of mtDNA from the Atlantic herring, does not show any sign of admixture in otolith shape between the two species. A revised classification, considering the observed genetic and morphological evidence, should rather group the northwest Pacific herring in the Bering Sea together with the European populations of C. pallasii than with the northeast Pacific herring in the Gulf of Alaska. © 2016 Springer-Verlag Berlin Heidelberg

Siegelman-Charbit L.,Norwegian Institute of Marine Research | Siegelman-Charbit L.,University Pierre and Marie Curie | Planque B.,Norwegian Institute of Marine Research | Planque B.,Hjort Center for Marine Ecosystem Dynamics
Marine Ecology Progress Series | Year: 2016

The presence of a dense layer of organisms in the mesopelagic zone is a ubiquitous feature of the world oceans, and these organisms may constitute a major component of marine biomass worldwide. Many mesopelagic organisms perform light-dependent diel vertical migration. It has been hypothesised that extreme light regimes encountered at high latitudes may disturb these migration patterns and thereby limit the northern expansion of mesopelagic fauna into the Arctic. Using hydroacoustic data collected during 4 surveys conducted in the open Norwegian Sea during the summer season, we evaluated if the key features of mesopelagic fauna reported worldwide (high density and diel vertical migration) are also observed in the high latitudes of the Northeast Atlantic. The results confirm that the high-latitude Northeast Atlantic hosts a high density of mesopelagic fauna which performs daily migration patterns similar to those reported in other regions. They also support the limiting effect of photoperiod on its potential biomass. These results stress the need for thorough studies on the abundance, biodiversity and trophic ecology of the mesopelagic fauna in this region. © Institute of Marine Research, Norway 2016.

Lindstrom U.,Norwegian Institute of Marine Research | Planque B.,Norwegian Institute of Marine Research | Planque B.,Hjort Center for Marine Ecosystem Dynamics | Subbey S.,Hjort Center for Marine Ecosystem Dynamics | Subbey S.,Norwegian Institute of Marine Research
Ecosystems | Year: 2016

Understanding and predicting patterns arising from the dynamics of marine food webs is central to trophic and community ecology and numerical models of food webs constitute a primary tool to simulate these dynamics. Food web simulation models are often highly complex while at the same time often too constrained to reproduce the level of variability observed in real systems. The recently developed non-deterministic network dynamics (NDND) modelling framework has been suggested as a simulation alternative, which can generate multiple patterns of food web variability despite great structural simplicity. Two important aspects of the NDND modelling framework remain unexplored: first the derivation of model input parameters from empirical or theoretical studies and second the evaluation of the model simulations against observations. We provide a methodology for the derivation of model parameters based on empirical observations, the metabolic theory of ecology and life-history theory and apply it to the specific case of the Barents Sea food web. We then evaluate the ability of the NDND simulations to reproduce a wide range of patterns of food web dynamics against observations collected in the Barents Sea during 28 years. Patterns emerging from the simulations include trends and cycles in biomass, trophic levels and transfer efficiency, density-dependent growth, top-down vs bottom-up oscillations, ecosystem level stability and synchrony and trophic functional responses. The ability of the NDND to generate so many patterns observed empirically in the Barents Sea is remarkable given that it is based only on random trophic interactions operating within few constraints set by ecological rules. Our results show that investigations of food web dynamics in marine ecosystems, including the definition of reference states and responses to climate and exploitation pressures, may be achieved with models that are structurally simple and based on few well-established assumptions. © 2016 Springer Science+Business Media New York

Howell D.,Norwegian Institute of Marine Research | Howell D.,Hjort Center for Marine Ecosystem Dynamics | Hansen C.,Norwegian Institute of Marine Research | Hansen C.,Hjort Center for Marine Ecosystem Dynamics | And 3 more authors.
ICES Journal of Marine Science | Year: 2016

Balanced fishing proposes a considerable change to current fisheries management to increase overall biomass harvested while reducing the ecosystem impacts of large-scale fisheries. However, to date, the work to a large degree has focused on simplified models, which exclude much of the variability in real ecosystems, as well as basing harvesting rates on a perfect, but unrealistic, knowledge on stock productivity. Furthermore, the published studies have avoided examining the practicalities of implementing balanced fishing in a real world. This has resulted in a gap that remains to be overcome before balanced fishing can be considered a viable management strategy for large marine ecosystems. We discuss variability in recruitment, in biology and life history characteristics, in data quality, and in fishing practice and management, and their implications for implementation of balanced fishing, using examples from the Barents Sea. We try to outline the complexities that need to be investigated as a precursor to moving balanced fishing from an academic exercise to a practical management scheme. Given the difficulties in moving to "full" balanced fishing, we highlight the importance of investigating to what extent benefits can be gained by implementing only the most achievable parts of a balanced fishing regime. © 2016 International Council for the Exploration of the Sea. Published by Oxford University Press.

Kolding J.,University of Bergen | Kolding J.,Hjort Center for Marine Ecosystem Dynamics | Jacobsen N.S.,Technical University of Denmark | Andersen K.H.,Technical University of Denmark | van Zwieten P.A.M.,Wageningen University
Canadian Journal of Fisheries and Aquatic Sciences | Year: 2016

Under the ecosystem approach to fisheries, an optimal fishing pattern is one that gives the highest possible yield while having the least structural impact on the community. Unregulated, open-access African inland fisheries have been observed to sustain high catches by harvesting a broad spectrum of species and sizes, often in conflict with current management regulations in terms of mesh and gear regulations. Using a size- and trait-based model, we explore whether such exploitation patterns are commensurable with the ecosystem approach to fisheries by comparing the impacts on size spectrum slope and yield with the different size limit regimes employed in the Zambian and Zimbabwean sides of man-made Lake Kariba. Long-term multispecies data under fished and unfished conditions are used to compare and validate the model results. Both model and observations show that the highest yields and low structural impact on the ecosystem are obtained by targeting small individuals in the community. These results call for a re-evaluation of the size-based management regulations that are ubiquitous in most fisheries. © 2016 Published by NRC Research Press. All Rights Resreved.

Law R.,University of York | Plank M.J.,University of Canterbury | Kolding J.,University of Bergen | Kolding J.,Hjort Center for Marine Ecosystem Dynamics
Fish and Fisheries | Year: 2016

This paper examines some effects of exploitation on a simple ecosystem containing two interacting fish species, with life histories similar to mackerel (Scomber scombrus) and cod (Gadus morhua), using a dynamic, size-spectrum model. Such models internalize body growth and mortality from predation, allowing bookkeeping of biomass at a detailed level of individual predation and growth and enabling scaling up to the mass balance of the ecosystem. Exploitation set independently for each species with knife-edge, size-at-entry fishing can lead to collapse of cod. Exploitation to achieve a fixed ratio of yield to productivity across species can also lead to collapse of cod. However, harvesting balanced to the overall productivity of species in the exploited ecosystem exerts a strong force countering such collapse. If balancing across species is applied to a fishery with knife-edge selection, size distributions are truncated, changing the structure of the system and reducing its resilience to perturbations. If balancing is applied on the basis of productivity at each body size as well as across species, there is less disruption to size-structure, resilience is increased, and substantially greater biomass yields are possible. We note an identity between the body size at which productivity is maximized and the age at which cohort biomass is maximized. In our numerical results based on detailed bookkeeping of biomass, cohort biomass reaches its maximum at body masses <1 g, unlike standard yield-per-recruit models, where body growth and mortality are independent externalities, and cohort biomass is maximized at larger body sizes. © 2016 John Wiley & Sons Ltd.

Simon E.,National Polytechnic Institute of Toulouse | Samuelsen A.,Nansen Environmental and Remote Sensing Center | Samuelsen A.,Hjort Center for Marine Ecosystem Dynamics | Bertino L.,Nansen Environmental and Remote Sensing Center | Mouysset S.,National Polytechnic Institute of Toulouse
Journal of Marine Systems | Year: 2015

A sequence of one-year combined state-parameter estimation experiments has been conducted in a North Atlantic and Arctic Ocean configuration of the coupled physical-biogeochemical model HYCOM-NORWECOM over the period 2007-2010. The aim is to evaluate the ability of an ensemble-based data assimilation method to calibrate ecosystem model parameters in a pre-operational setting, namely the production of the MyOcean pilot reanalysis of the Arctic biology. For that purpose, four biological parameters (two phyto- and two zooplankton mortality rates) are estimated by assimilating weekly data such as, satellite-derived Sea Surface Temperature, along-track Sea Level Anomalies, ice concentrations and chlorophyll-a concentrations with an Ensemble Kalman Filter. The set of optimized parameters locally exhibits seasonal variations suggesting that time-dependent parameters should be used in ocean ecosystem models. A clustering analysis of the optimized parameters is performed in order to identify consistent ecosystem regions. In the north part of the domain, where the ecosystem model is the most reliable, most of them can be associated with Longhurst provinces and new provinces emerge in the Arctic Ocean. However, the clusters do not coincide anymore with the Longhurst provinces in the Tropics due to large model errors. Regarding the ecosystem state variables, the assimilation of satellite-derived chlorophyll concentration leads to significant reduction of the RMS errors in the observed variables during the first year, i.e. 2008, compared to a free run simulation. However, local filter divergences of the parameter component occur in 2009 and result in an increase in the RMS error at the time of the spring bloom. © 2015 Elsevier B.V.

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