The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
David A Demer - One of the best experts on this subject based on the ideXlab platform.
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variations in the biomass of antarctic Krill euphausia superba around the south shetland islands 1996 2006
Ices Journal of Marine Science, 2008Co-Authors: Christian S Reiss, Valerie J Loeb, Anthony M Cossio, David A DemerAbstract:The time-series of acoustically surveyed Antarctic Krill (Euphausia superba) biomass near the South Shetland Islands (SSI) between 1996 and 2006 is re-estimated using a validated physics-based model of target strength (TS), and a species-discrimination algorithm based on the length-range of Krill in plankton samples to identify Krill acoustically, derived from TS-model predictions. The SSI area is surveyed each austral summer by the US Antarctic Marine Living Resources Program, and the acoustic data are used to examine trends in Krill biomass and to assess the potential impact of fishing to the reproductive success of land-based predators (seals and penguins). The time-series of recomputed biomass densities varies greatly from that computed using an empirical log-linear TS-model and fixedranges of differences in volume –backscattering strengths (DSv), conventionally used to identify Krill acoustically. The new acoustic estimates of biomass are significantly correlated with both proportional recruitment and Krill abundance estimated from zooplankton samples. Two distinct peaks in biomass (1996 and 2003) are in accord with recruitment events shown by net-based Krill time-series. The foundation for the new TS-model and the associated Krill-discrimination algorithm, coupled with the agreement between acoustic- and net-survey results, provides strong support for the use of the new analytical technique. Variable biases in the re-estimated Krill biomass have been greatly reduced. However, survey variability increased as a result of the increased rejection of acoustic backscatter previously attributed to Krill. Management of Southern Ocean Krill stocks based on a precautionary approach may therefore result in decreased allocations of Krill, given its dependence on the variability of survey estimates.
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use of moored acoustic instruments to measure short term variability in abundance of antarctic Krill
Limnology and Oceanography-methods, 2006Co-Authors: Andrew S. Brierley, Ryan A Saunders, Douglas G Bone, Eugene J Murphy, Peter Enderlein, Stephane G Conti, David A DemerAbstract:Upward-looking acoustic Doppler current profilers (ADCPs) (300 kHz) and echosounders (125 kHz) were deployed on moorings at South Georgia to measure abundance of Antarctic Krill continuously over several months. Echoes from Krill were identified using the theoretical difference in echo intensity at 300 and 125 kHz and scaled to Krill density using target strengths appropriate for Krill in the region: Krill size was determined from diet samples from fur seals and penguins foraging near the moorings. A method using water flow past the moorings was developed to convert time-based acoustic observations of Krill to area-based abundance estimates. Flow past the stationary moorings was treated analogously to motion along-track of a research vessel through a nominally stationary body of water during a conventional survey. The moorings thus provide a Eulerian view of variation in Krill abundance. This is ecologically instructive for South Georgia, where Krill are generally passive drifters on currents and where temporal fluctuations in abundance have significant consequences for Krill-dependent predators. Moorings were positioned on routine research vessel survey transects, and validity of the mooring method was assessed by comparison of mooring and vessel observations. Krill density estimates from the moorings were not statistically different from vessel estimates in adjacent time periods. A time series of Krill density from a mooring revealed step-changes that were not seen during short-term vessel surveys. Moorings deliver data over time scales that cannot be achieved from research vessels and provide insight on environmental factors associated with variation in Krill abundance at South Georgia. Mooring data may aid ecosystem-based management.
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new target strength model indicates more Krill in the southern ocean
Ices Journal of Marine Science, 2005Co-Authors: David A Demer, Stephane G ContiAbstract:Antarctic Krill, Euphausia superba, comprises the foundation of the foodweb in the Southern Ocean and is the target of a large fishery. Recently, the total abundance of Krill in the Scotia Sea was estimated from an international echosounder and net survey (CCAMLR 2000) to be 44.3 million metric tonnes (Mt; CV 11.4%) (Hewitt et al., 2002). The new biomass estimate prompted the Antarctic Treaty’s Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) to revise the precautionary catch level for Krill in the area from 1.5 to 4 Mt (SC-CAMLR, 2000). These survey results are based on the total echo energy attributed to Krill, scaled by the Greene et al. (1991) model of Krill acoustical reflectivity or target strength (TS). Presented here is a re-analysis of the CCAMLR 2000 data incorporating recent improvements in the characterization of Krill TS. The results indicate that the estimated Krill biomass in the Scotia Sea may be as high as 192.4 Mt (CVZ 11.7%), or as low as 109.4 Mt (CVZ 10.4%), depending solely on the expected distribution of Krill orientations. The new Stochastic, Distorted-Wave, BornApproximation (SDWBA) TS model solved with an empirically estimated distribution of in situ orientations leads to a Krill-biomass estimate that is nearly 2.5 times the previous estimate. In consequence, revisions may be warranted of the standard Krill TS model, the CCAMLR 2000 biomass estimate, and the associated precautionary catch level for Krill in the Scotia Sea. 2004 Published by Elsevier Ltd on behalf of International Council for the Exploration of the Sea.
Amir H Alavi - One of the best experts on this subject based on the ideXlab platform.
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a new hybrid method based on Krill herd and cuckoo search for global optimisation tasks
International Journal of Bio-inspired Computation, 2016Co-Authors: Gaige Wang, Amir H Gandomi, Xinshe Yang, Amir H AlaviAbstract:Recently, Gandomi and Alavi proposed a new heuristic search method, called Krill herd KH, for solving global optimisation problems. In order to make KH more effective, a hybrid meta-heuristic cuckoo search and Krill herd CSKH method is proposed for function optimisation. The CSKH introduces Krill updating KU and Krill abandoning KA operator originated from cuckoo search CS during the process when the Krill updating so as to greatly enhance its effectiveness and reliability dealing with numerical optimisation problems. The KU operator inspires the intensive exploitation and allows the Krill individuals implement a careful search in the later run phase of the search, while KA operator is used to further enhance the exploration of the CSKH in place of a fraction of the worse Krill at the end of each generation. The effectiveness of these improvements is tested by 14 standard benchmarking functions and experimental results show, in most cases, this hybrid meta-heuristic CSKH algorithm is more effective and efficient than the original KH and other approaches.
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an effective Krill herd algorithm with migration operator in biogeography based optimization
Applied Mathematical Modelling, 2014Co-Authors: Gaige Wang, Amir H Gandomi, Amir H AlaviAbstract:Abstract Krill herd (KH) is a novel search heuristic method. To improve its performance, a biogeography-based Krill herd (BBKH) algorithm is presented for solving complex optimization tasks. The improvement involves introducing a new Krill migration (KM) operator when the Krill updating to deal with optimization problems more efficiently. The KM operator emphasizes the exploitation and lets the Krill cluster around the best solutions at the later run phase of the search. The effects of these enhancements are tested by various well-defined benchmark functions. Based on the experimental results, this novel BBKH approach performs better than the basic KH and other optimization algorithms.
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Krill herd algorithm for optimum design of truss structures
International Journal of Bio-inspired Computation, 2013Co-Authors: Amir H Gandomi, S Talatahari, Faraz Tadbiri, Amir H AlaviAbstract:Krill herd KH algorithm, as a new metaheuristic optimisation, is developed to solve truss optimisation problems. The KH methodology draws its analogy from the herding behaviour of Krill individuals in nature. The objective function for the Krill movement is mostly influenced by the least distances of each Krill individual from food and from highest density of the herd. The new algorithm is examined by solving three truss design optimisation problems and its performance is further compared with various classical and advanced algorithms.
Valerie J Loeb - One of the best experts on this subject based on the ideXlab platform.
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Krill euphausia superba distribution contracts southward during rapid regional warming
Nature Climate Change, 2019Co-Authors: A. Atkinson, Geraint A Tarling, Simeon L Hill, Evgeny A Pakhomov, Volker Siegel, Christian S Reiss, Valerie J Loeb, Deborah K Steinberg, Katrin Schmidt, Laura GerrishAbstract:High-latitude ecosystems are among the fastest warming on the planet1. Polar species may be sensitive to warming and ice loss, but data are scarce and evidence is conflicting2–4. Here, we show that, within their main population centre in the southwest Atlantic sector, the distribution of Euphausia superba (hereafter, ‘Krill’) has contracted southward over the past 90 years. Near their northern limit, numerical densities have declined sharply and the population has become more concentrated towards the Antarctic shelves. A concomitant increase in mean body length reflects reduced recruitment of juvenile Krill. We found evidence for environmental controls on recruitment, including a reduced density of juveniles following positive anomalies of the Southern Annular Mode. Such anomalies are associated with warm, windy and cloudy weather and reduced sea ice, all of which may hinder egg production and the survival of larval Krill5. However, the total post-larval density has declined less steeply than the density of recruits, suggesting that survival rates of older Krill have increased. The changing distribution is already perturbing the Krill-centred food web6 and may affect biogeochemical cycling7,8. Rapid climate change, with associated nonlinear adjustments in the roles of keystone species, poses challenges for the management of valuable polar ecosystems3. As the southwest Atlantic sector of the Southern Ocean has warmed, the distribution of a key species, Antarctic Krill, has contracted southwards. This has occurred in tandem with a decline in recruitment of juveniles, linked to increasingly positive anomalies of the Southern Annular Mode.
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variations in the biomass of antarctic Krill euphausia superba around the south shetland islands 1996 2006
Ices Journal of Marine Science, 2008Co-Authors: Christian S Reiss, Valerie J Loeb, Anthony M Cossio, David A DemerAbstract:The time-series of acoustically surveyed Antarctic Krill (Euphausia superba) biomass near the South Shetland Islands (SSI) between 1996 and 2006 is re-estimated using a validated physics-based model of target strength (TS), and a species-discrimination algorithm based on the length-range of Krill in plankton samples to identify Krill acoustically, derived from TS-model predictions. The SSI area is surveyed each austral summer by the US Antarctic Marine Living Resources Program, and the acoustic data are used to examine trends in Krill biomass and to assess the potential impact of fishing to the reproductive success of land-based predators (seals and penguins). The time-series of recomputed biomass densities varies greatly from that computed using an empirical log-linear TS-model and fixedranges of differences in volume –backscattering strengths (DSv), conventionally used to identify Krill acoustically. The new acoustic estimates of biomass are significantly correlated with both proportional recruitment and Krill abundance estimated from zooplankton samples. Two distinct peaks in biomass (1996 and 2003) are in accord with recruitment events shown by net-based Krill time-series. The foundation for the new TS-model and the associated Krill-discrimination algorithm, coupled with the agreement between acoustic- and net-survey results, provides strong support for the use of the new analytical technique. Variable biases in the re-estimated Krill biomass have been greatly reduced. However, survey variability increased as a result of the increased rejection of acoustic backscatter previously attributed to Krill. Management of Southern Ocean Krill stocks based on a precautionary approach may therefore result in decreased allocations of Krill, given its dependence on the variability of survey estimates.
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effects of sea ice extent and Krill or salp dominance on the antarctic food web
Nature, 1997Co-Authors: Valerie J Loeb, Volker Siegel, O Holmhansen, Roger P Hewitt, William R Fraser, W Trivelpiece, S TrivelpieceAbstract:Krill (Euphausia superba) provide a direct link between primary producers and higher trophic levels in the Antarctic marine food web1,2,3,4,5,6. The pelagic tunicate Salpa thompsoni can also be important during spring and summer through the formation of extensive and dense blooms6,7,8,9. Although salps are not a major dietary item for Antarctic vertebrate predators7,10, their blooms can affect adult Krill reproduction and survival of Krill larvae. Here we provide data from 1995 and 1996 that support hypothesized relationships between Krill, salps and region-wide sea-ice conditions11,12. We have assessed salp consumption as a proportion of net primary production, and found correlations between herbivore densities and integrated chlorophyll-a that indicate that there is a degree of competition between Krill and salps. Our analysis of the relationship between annual sea-ice cover and a longer time series of air temperature measurements12,13 indicates a decreased frequency of winters with extensive sea-ice development over the last five decades. Our data suggest that decreased Krill availability may affect the levels of their vertebrate predators. Regional warming and reduced Krill abundance therefore affect the marine food web and Krill resource management.
Inge Bruheim - One of the best experts on this subject based on the ideXlab platform.
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bioavailability of fatty acids from Krill oil Krill meal and fish oil in healthy subjects a randomized single dose cross over trial
Lipids in Health and Disease, 2015Co-Authors: Anton Kohler, Essi Sarkkinen, Niina Tapola, Tarja Niskanen, Inge BruheimAbstract:Background Krill contains two marine omega-3 polyunsaturated fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), mainly bound in phospholipids. Typical products from Krill are Krill oil and Krill meal. Fish oils contain EPA and DHA predominantly bound in triglycerides. The difference in the chemical binding of EPA and DHA has been suggested to affect their bioavailability, but little is known on bioavailability of EPA and DHA in Krill meal. This study was undertaken to compare the acute bioavailability of two Krill products, Krill oil and Krill meal, with fish oil in healthy subjects.
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Bioavailability of fatty acids from Krill oil, Krill meal and fish oil in healthy subjects–a randomized, single-dose, cross-over trial
Lipids in Health and Disease, 2015Co-Authors: Anton Kohler, Essi Sarkkinen, Niina Tapola, Tarja Niskanen, Inge BruheimAbstract:Background Krill contains two marine omega-3 polyunsaturated fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), mainly bound in phospholipids. Typical products from Krill are Krill oil and Krill meal. Fish oils contain EPA and DHA predominantly bound in triglycerides. The difference in the chemical binding of EPA and DHA has been suggested to affect their bioavailability, but little is known on bioavailability of EPA and DHA in Krill meal. This study was undertaken to compare the acute bioavailability of two Krill products, Krill oil and Krill meal, with fish oil in healthy subjects.
S Kawaguchi - One of the best experts on this subject based on the ideXlab platform.
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The importance of Antarctic Krill in biogeochemical cycles.
Nature Communications, 2019Co-Authors: E. L. Cavan, S Kawaguchi, A. Atkinson, Simeon L Hill, Stephen Nicol, Anna Belcher, S. Mccormack, Bettina Meyer, L. Ratnarajah, Katrin SchmidtAbstract:Antarctic Krill (Euphausia superba) are swarming, oceanic crustaceans, up to two inches long, and best known as prey for whales and penguins – but they have another important role. With their large size, high biomass and daily vertical migrations they transport and transform essential nutrients, stimulate primary productivity and influence the carbon sink. Antarctic Krill are also fished by the Southern Ocean’s largest fishery. Yet how Krill fishing impacts nutrient fertilisation and the carbon sink in the Southern Ocean is poorly understood. Our synthesis shows fishery management should consider the influential biogeochemical role of both adult and larval Antarctic Krill. Swarms of crustaceans called Krill dominate Antarctic ecosystems, yet their influence on biogeochemical cycles remains a mystery. Here Cavan and colleagues review the role of Krill in the Southern Ocean, and the impact of the Krill fishery on ocean fertilisation and the carbon sink.
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Understanding the variability in the iron concentration of Antarctic Krill
Limnology and Oceanography, 2016Co-Authors: L. Ratnarajah, S Kawaguchi, Stephen Nicol, Ashley T. Townsend, Delphine Lannuzel, Klaus M Meiners, Andrew R. BowieAbstract:Antarctic Krill may play a significant role in the Southern Ocean iron cycle. However, understanding the control on iron budgets by Antarctic Krill is hampered by the large range in the reported iron concentration of Krill. The aim of this study was to investigate the causes of the large range of iron concentrations in Krill reported in the literature (6–190 mg kg−1). Antarctic Krill samples were collected from three research voyages to Pyrdz Bay, Antarctica, and analysed individually. Iron concentrations were measured using sector field inductively coupled plasma mass spectrometry in whole Krill specimens and in the isolated stomach, digestive gland, muscle, body (whole Krill excluding stomach and digestive gland), exoskeleton and faecal pellets. Iron concentrations in stomach (6–98 mg/kg), digestive gland (14–82 mg kg−1), and faecal pellet (683–1039 mg kg−1) were higher compared to muscle (4–7 mg kg−1), exoskeleton (6–15 mg kg−1), and body (4–18 mg kg−1) indicating that Krill may ingest more iron than they require for physiological processes. Iron concentrations in whole Krill from March 2012 (10 ± 3 mg kg−1) were significantly lower compared to February 2003 (19 ± 7 mg kg−1) and February 2015 (18 ± 12 mg kg−1). Overall, the iron concentrations in Krill from this study were consistently at the lower end of the published range. We propose that the large range in reported whole iron concentrations of Krill can be accounted for by a combination of seasonal and regional differences in sampling, reflecting differences in the quantity and quality of their diet.
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risk maps for antarctic Krill under projected southern ocean acidification
Nature Climate Change, 2013Co-Authors: S Kawaguchi, Akio Ishida, Robert King, Ben Raymond, N Waller, Andrew Constable, Stephen NicolAbstract:Little is known about the sensitivity of Antarctic Krill, a key part of the food chain, to ocean acidification. A circumpolar risk map of Krill hatching success is presented for projected ocean acidification levels. Important Krill recruitment habitats are likely to become high-risk this century, with the possibility of collapse of the Krill population by 2300 without mitigation of CO2 emissions.
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Impact of climate change on Antarctic Krill
Marine Ecology Progress Series, 2012Co-Authors: H Flores, C. Reiss, S. Nicol, Gennadi Milinevsky, Bjorn A Krafft, R. Werner, S Kawaguchi, Geraint A Tarling, A. Atkinson, E. Bravo RebolledoAbstract:Antarctic Krill Euphausia superba (hereafter `Krill') occur in regions undergoing rapid environmental change, particularly loss of winter sea ice. During recent years, harvesting of Krill has in creased, possibly enhancing stress on Krill and Antarctic ecosystems. Here we review the overall impact of climate change on Krill and Antarctic ecosystems, discuss implications for an ecosystem-based fisheries management approach and identify critical knowledge gaps. Sea ice decline, ocean warming and other environmental stressors act in concert to modify the abundance, distribution and life cycle of Krill. Although some of these changes can have positive effects on Krill, their cumulative impact is most likely negative. Recruitment, driven largely by the winter survival of larval Krill, is probably the population parameter most susceptible to climate change. Predicting changes to Krill populations is urgent, because they will seriously impact Antarctic ecosystems. Such predictions, however, are complicated by an intense inter-annual variability in recruitment success and Krill abundance. To improve the responsiveness of the ecosystem-based management approach adopted by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), critical knowledge gaps need to be filled. In addition to a better understanding of the factors influencing recruitment, management will require a better understanding of the resilience and the genetic plasticity of Krill life stages, and a quantitative understanding of under-ice and benthic habitat use. Current precautionary management measures of CCAMLR should be maintained until a better understanding of these processes has been achieved. [GRAPHICS] .
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Male Krill grow fast and die young
Marine Ecology Progress Series, 2007Co-Authors: S Kawaguchi, Volker Siegel, Mikio Naganobu, Luke A. Finley, Simon N. Jarman, Steven G. Candy, Robin M. Ross, Langdon B. Quetin, Wayne Z. Trivelpiece, Stephen NicolAbstract:The size-differentiated sex ratio (proportion of males, PM) of Antarctic Krill Euphausia superba was examined with an extensive dataset derived from scientific surveys in the Indian Ocean sector and the southwest Atlantic sector, and from the Krill fishery in the Southern Ocean. The percentage of males in size classes of adult Krill was generally high in Krill of 30 to 35 mm total length, always low in 38 to 42 mm Krill, sometimes showed higher values in 45 to 50 mm Krill, but always decreased in the largest Krill (>50 mm). This pattern was reproduced by a model simulation that assumed faster growth and a shorter lifespan for males when compared to females. These results suggest that the numbers of males should decline with time unless new recruits enter the population. Indeed, interannual variations in PM from the field (net collected data and penguin diet data) showed a decline in the proportion of males when several years of low recruitment followed a recruitment pulse. These results lead us to conclude that male Krill grow faster and have a shorter lifespan than females in the natural environment.
