Search

In this paper, we propose non-negative intensity (NNI) as an alternative intensity-based technique for target strength identification in marine ecosystem research. NNI identifies local surface regions of a body with positive-only sound power contributions. NNI is employed for sound scattering by fluid-loaded, fluid-filled elastic structures with weak scattering boundary conditions. Three numerical case studies are presented for which fully coupled fluid-structure interaction models based on the finite element method (FEM) and the boundary element method (BEM) are developed. To validate the three-way coupling between the structural and fluid domains, an elastic shell submerged in water and filled with different internal fluids is initially considered. Results for the scattered acoustic intensity obtained numerically are compared with analytical results from the literature. Models representing Antarctic krill of simple and complex geometry are developed. A 3×3 cylinder array representing a simplified aggregation of krill is also presented. Target strength is calculated using both the scattered intensity and NNI for different incident excitation angles. Results for NNI identify the surface regions of an individual organism or group of organisms with the greatest contribution to the scattered sound at the target strength locations. [ABSTRACT FROM AUTHOR]

Antarctic krill mainly inhabit the Antarctic Ocean, not far from Antarctica, especially the Weddell Sea, where krill is dense. Marine fisheries have reached new levels, but the topic of sustainable use of marine fishery resources is far from reaching the required levels. In order to study the sustainable development of the Antarctic krill environment, this paper studies the living environment and applicability of Antarctic krill based on system dynamics, and provides some references for the sustainable development of marine resources. Mentioned the use of case analysis method, literature analysis method and other methods to collect data, build a Model, and read and analyse a large number of related literatures through the literature survey method. The experimental results proved that the salinity has a significant effect on the survival rate of Antarctic krill (p < 0.05). When the salinity is 34, the molting frequency reaches its maximum value, which is 70 %. It is concluded that the ability of Antarctic krill to adapt to gradual changes in salinity is stronger than that of sudden changes in salinity, and the suitable salinity for survival is 30-42. With 34 as the basic salinity, when the salinity rises within a certain range, the molting rate of krill will increase, and as the salinity decreases, the molting rate will gradually decrease. This shows that improving the environmental resources of Antarctic krill is an effective method for improving salinity. [ABSTRACT FROM AUTHOR]

In this paper, Antarctic krill was used as the raw material. Physicochemical indexes, flora changes and flavor substances of shrimp paste with different salt concentrations and fermentation days were investigated. The main dominant bacterial groups in the shrimp paste samples were detected by 16S rDNA high-throughput sequencing technology. At phylum level, the dominant bacteria groups were Proteobacteria , Firmicutes and Actinobacteria , while at genus level, the dominant bacteria groups were Staphylococcus , Psychrobacter and Herbaspirillum. Qualitative analysis of volatile compounds in shrimp paste samples by GC-IMS technique. A total of 29 volatiles were detected, and a total of 37 volatile flavor compounds including dimers and trimers were isolated and identified, including 16 aldehydes, 8 alcohols, 8 ketones, 2 ethers and 3 esters. Establishing correlations between important colonies and volatile compounds. • The flavor changes of shrimp paste under different salt concentrations and fermentation days. • Changes in the main microbial communities in shrimp paste under different salt concentrations and fermentation days. • 29 volatile substances were detected in shrimp paste samples. • There is a significant correlation between volatile compounds and bacterial colonies. [ABSTRACT FROM AUTHOR]

Antarctic krill (Euphausia superba, hereafter krill) is a pelagic living crustacean and a key species in the Southern Ocean ecosystem. Krill builds up a huge biomass and its synchronized behavioral patterns, such as diel vertical migration (DVM), substantially impact ecosystem structure and carbon sequestration. However, the mechanistic basis of krill DVM is unknown and previous studies of krill behavior in the laboratory were challenged by complex behavior and large variability. Using a new experimental set-up, we recorded the swimming activity of individual wild-caught krill under light–dark cycles. Krill individuals exhibited differential phototactic responses to the light regime provided. However, using a new activity metric, we showed for the first time a consistent nocturnal increase in krill swimming activity in a controlled environment. Krill swimming activity in the new set-up was strongly synchronized with the light–dark cycle, similar to the diel vertical migration pattern of krill in the field when the krill were sampled for the experiment, demonstrated by hydroacoustic recordings. The new set-up presents a promising tool for investigating the mechanisms underlying krill behavioral patterns, which will increase our understanding of ecological interactions, the spatial distribution of populations, and their effects on biogeochemical cycles in the future. [ABSTRACT FROM AUTHOR]

The northwestern Antarctic Peninsula is an important spawning, recruitment, and overwintering ground for Antarctic krill. The region is warming rapidly, and the current impacts of climate and environmental variability on the reproductive cycle of krill remain unclear. Here, we examine the reproductive stage of female krill in the austral winter from 2012 to 2016 in relation to climate and environmental data to assess what factors influence the timing of reproductive development. We observed significant interannual variability in the degree of maturation in female krill, ranging from 48% of female krill measured at a station in 2016 to a maximum of 94% of female krill measured at a station in 2014. On average, across all five years, three-quarters of the female krill sampled were in the stage known as previtellogenesis, the point at which the onset of sexual maturity begins. The preceding spring, summer, and autumn Southern Annular Mode and the Multivariate El Niño Index explained most of the variance in the data and indicated a strong, preconditioning storm-related effect on environmental conditions leading up to winter, affecting krill maturation status at the end of the winter season. Results from our study can be used to improve krill population models that are necessary for the management of the krill fishery and for conservation at the northwestern Antarctic Peninsula. [ABSTRACT FROM AUTHOR]

The present study is the attempt to combine oceanologic measurements and biochemical analysis, which is as possible to implement on board as in a laboratory with chosen certain statistics to reveal trophic conditions and the environment state in which Antarctic krill live in season in real time on site. The fatty acid constituents of total lipids in juvenile and mature Antarctic krill sampled from the Bransfield Strait (BS), the Antarctic Sound (AS), and waters at the eastern tip of the Antarctic Peninsula (AP) collected during the 87th cruise of the R/V Akademik Mstislav Keldysh in January–February 2022 were analyzed. The fatty acid (FA) profile in juvenile and mature Antarctic krill was studied by gas chromatography with a mass selective detector to identify the qualitative composition and a flame ionization detector to quantify the studied FAs. Using NMDS analysis (quantitative panel), great difference was found between krill from the BS compared to krill collected in the AS and the AP. The differences are reliable owing to the following 16 FAs, most of them trophic biomarkers of microphytoplankton, and suggest regional differences, mainly in abundance and ability of forage objects. CTD measurements discuss the abiotic factors (potential temperature, salinity, and chlorophyll "a"). Compensatory modifications of the composition of FA components in Antarctic krill inhabiting different water areas are a way of maintaining the species' viability under certain and variable habitat conditions. [ABSTRACT FROM AUTHOR]

The extent to which marine species avoid survey vessels is the subject of considerable debate, with stimuli such as noise and pressure waves receiving particular attention. By some estimates, avoidance behaviour is a major bias in the assessment of pelagic species distribution and density. Surveyors of the marine environment are increasingly using autonomous platforms; thus the question of avoidance of these novel platforms must be considered. A long-duration, underwater glider with an integrated echo-sounder was deployed to measure the density and distribution of Antarctic krill. We show that krill reacted to the glider, despite the low-noise profile of the platform. The weighted-mean depth of krill swarms was observed to deepen when a glider came within 30 m. In addition, we observed a near-range decrease in depth-integrated acoustic backscatter and we demonstrate that this effect is not explained by the instrument's acoustic footprint. The potential triggers for these behaviours are discussed. The list of sensors available for use on a glider is increasing, with some producing sound, light or other potential stimuli for behavioural response. Our paper demonstrates that caution should be used when designing mission payloads and in the interpretation of acoustic data for animal density from gliders. A key consideration for surveyors may be the factoring in of an exclusion zone from their analyses. • Antarctic krill swarms responded to the presence of the glider, interpreted as an avoidance response. • Near-range echo was less than expected without avoidance; simulation shows sampling does not account for the difference. • Slope of swarm centre of mass suggests and effect up to 40 m below the glider. • Often thought of as quiet vehicles, glider surveys of biomass will need to account for target disturbances. [ABSTRACT FROM AUTHOR]

The preliminary purification and antimicrobial mechanism of antimicrobial peptide from Antarctic Krill were studied in this paper. The results showed that the molecular weight range of antimicrobial polypeptide (CMCC-1) obtained by cation exchange chromatography was between 245-709D as detected by molecular sieve chromatography, and the minimum inhibition concentration (MIC) of CMCC-1 against Staphylococcus aureus was 5.0 mg mL. The antimicrobial mechanism of CMCC-1 was studied with S. aureus as indicator bacterium. Compared with control group, the results of the experimental group in which S. aureus was treated with CMCC-1 were as follows: 1) CMCC-1 could inhibit cell division at logarithmic phase. 2) The protein and reducing sugar content, and the conductivity of culture medium increased, and the activity of alkaline phosphatase and β-galactosidase could be detected in the culture medium. 3) Observation under scanning electron microscope revealed that somatic morphology became irregular, and then somatic surface became coarse. The cell became much smaller, and most somatic cells gathered. The boundary between cells became dim and finally fused as a whole. 4) Observation under transmission electron microscope showed that the surface of S. aureus became rough and the reproducing ability was restrained. The cell wall became thin and the cytoplasm shrunk. Substances inside cell leaked out, which caused cells death. 5) SDS-PAGE analysis showed that some bands disappeared, and the residual bands became vague. 6) The genomic DNA electrophoresis results showed that the genomic DNA bands of S. aureus were not degraded but the brightness significantly reduced. Thus, it is supposed that CMCC-1 could destroy the cell wall and membrane of S. aureu, increase the cell membrane permeability and the leaking-out of intracellular substances, and thus cause the death of S. aureu. [ABSTRACT FROM AUTHOR]

To reduce costs associated with the detection and population assessment of Antarctic krill and diversify the single detection approach, our team designed and deployed a drifting sonar buoy for krill detection in the waters surrounding Antarctica. The experimental results indicate that the drifting sonar buoy fulfills its primary functions and meets the requirements for krill detection in designated marine areas. The initial experiment lasted seven days, during which the buoy collected 157 records of speed and location data as well as 82 records of sea surface temperature and acoustic data, demonstrating its potential for krill detection. The experiment also revealed shortcomings in the initial design of the drifting sonar buoy, leading to proposed improvements. The paper further compares the advantages and disadvantages of the drifting sonar buoy and traditional fishing vessels in krill detection with the buoy offering unique benefits in low-cost deployment, labor savings, broad monitoring range, and continuous real-time data monitoring. The drifting sonar buoy serves as an excellent complement to fishing vessels in krill detection.

Cutter, G. R., Renfree, J. S., Cox, M. J., Brierley, A. S., and Demer, D. A. 2009. Modelling three-dimensional directivity of sound scattering by Antarctic krill: progress towards biomass estimation using multibeam sonar. – ICES Journal of Marine Science, 66: 1245–1251.Target strength (TS) estimation is a principal source of uncertainty in acoustic surveys of Antarctic krill (Euphausia superba). Although TS is strongly dependent on krill orientation, there is a paucity of information in this regard. This paper considers the potential for narrow-bandwidth, multibeam-echosounder (MBE) data to be used for estimating the orientations of krill beneath survey vessels. First, software was developed to predict MBE measurements of the directivity patterns of acoustic scattering from individual or aggregated krill in any orientation. Based on the distorted-wave, Born approximation model (DWBA), scattering intensities are predicted vs. MBE angles for specified distributions of krill orientations (pitch, roll, and yaw angles) and swarm densities. Results indicate that certain distributions of orientations, perhaps indicative of particular behaviour, should be apparent from the sonar data. The model results are compared with measurements on krill made using a 200-kHz MBE deployed from a small craft off Cape Shirreff, Livingston Island, Antarctica, in summer 2006. The stochastic DWBA model is then invoked to explain disparities between the model predictions and MBE measurements. [ABSTRACT FROM PUBLISHER]

At present, the primary fishing method of Antarctic krill is beam trawl, in which the fishing vessel drags the beam equipped with nets through the trawl warp for midwater trawling. Due to the behavioral characteristic of collective activities, the shoal of Antarctic krill often appears in some specific depths of the sea. The existing fishing method needs to adjust the trawling depth by modifying the length of the trawl warp and the navigation speed of the vessel, which cannot adjust the trawling depth independently. To solve this problem, we proposed a depth variable device installed on the beam to adjust the trawling depth independently, aiming to track the depth where the shoal of Antarctic krill is located for accurate fishing. Investigate the hydrodynamic feature of the proposed beam trawl device by numerical analysis and water channel experiment to design the wing's profile and determine the effective range of angle of attack. It was found that when the angle of attack of the wing is 0°–17.7°, the regulation effect of depth adjusting is better. The analysis results can be used as the parameter basis for compiling the control program for the depth variable beam. [ABSTRACT FROM AUTHOR]

There is an emerging consumption of the Antarctic krill (AK) muscle‐based food due to its excellent nutritional value and enormous biomass storage capacity. However, the coarse texture of the muscle and the weak gelling properties of AK protein impede its expansion in surimi‐based products. This investigation successfully prepared heat‐induced gels of AK surimi with desirable textural properties by including Litopenaeus vannamei in varying proportions. Higher concentrations of L. vannamei resulted in improved three‐dimensional printability, greater water‐holding capacity (WHC), larger viscoelastic modulus, and a well‐formed microstructural matrix of AK surimi, due to an increased level of myofibrillar protein. Compared with AK, L. vannamei muscle had double the salt‐soluble protein content, which was corroborated by increased intensity of bands of actin, paramyosin, tropomyosin, and myosin light chains on reducing SDS‐PAGE. DSC results indicated that a high ratio of L. vannamei elevated the denaturation temperature and enthalpy of myosin, sarcoplasmic protein, and actin, suggesting a high degree of cross‐linking. It was also found that when hydroxypropyl cassava starch was added at 0.5% (w/w), WHC and gel strength were further improved with a more compact gel matrix. The successful preparation of unwashed mixed surimi with AK meat fully exploited in this study provides an option for AK surimi‐based product industrialization. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the quality changes and shelf life of ready-to-eat roasted Antarctic krill, either untreated (CT) or treated with sodium diacetate (SD) or sodium diacetate and a deoxidizer (SDD), during storage at room temperature (25°C) by using sensory, physiochemical, and microbial assessment. Additionally, fluoride accumulation in this food product was used to evaluate its safety. Analysis showed that the addition of SD and SDD resulted in better sensory scores compared of that of CT samples (P <0.05). Accordingly, microorganism growth and total basic nitrogen (TVB-N) were maintained at a low level for the duration of storage with SD and SDD treatments. The total viable counts of SD and SDD reached (4.58 ± 0.08) log (CFU g−1) and (4.20 ± 0.11) log (CFU g−1), respectively. The mold was found after 6 and 18 days for SD and SDD treatment, and the numbers reached 5.2 × 106 and 8.5 × 104 respectively at the end of shelf life. The TVB-N values from CT continuously increased during the whole storage. While TVB-N values from SD and SDD remained significantly less change (P <0.05) during the early 20 days of the storage, and the values reached (12.11 ± 0.07) mg (100 g)−1 and (10.88 ± 0.15) mg (100 g)−1 on day 33 and day 70, respectively. Importantly, SDD treatment effectively minimized the oxidation values and retained the color of ready-to-eat roasted Antarctic krill. Our results showed that the shelf life of ready-to-eat roasted Antarctic krill treated with SDD was extended by up to 52 days. Additionally, rats fed ready-to-eat roasted Antarctic krill showed accumulation of fluoride exclusively in the thighbone. The accumulation of fluoride residues in the thighbone showed concentration-dependent. The concentrations of fluoride residues in rats were (1760.03 ± 38.21), (2371.52 ± 42.15) mg kg−1 and (3615.44 ± 30.53) mg kg−1, which were less than sodium fluoride feeding group (4621.01 ± 28.67) mg kg−1. The results suggested that the SD and SDD treatments led to better quality and shelf life extension of ready-to-eat roasted Antarctic krill during storage at room temperature (25°C). Therefore, the ready-to-eat roasted Antarctic krill can be of great interest to the seafood industry. [ABSTRACT FROM AUTHOR]

Antarctic krill (Euphausia superba) of the Euphausiidae family comprise one of the largest biomasses in the world and play a key role in the Antarctic marine ecosystem. However, the study of E. superba-derived microbes and their secondary metabolites has been limited. Chemical investigation of the secondary metabolites of the actinomycetes Nocardiopsis sp. LX-1 (in the family of Nocardiopsaceae), isolated from E. superba, combined with molecular networking, led to the identification of 16 compounds a–p (purple nodes in the molecular network) and the isolation of one new pyrroline, nocarpyrroline A (1), along with 11 known compounds 2–12. The structure of the new compound 1 was elucidated by extensive spectroscopic investigation. Compound 2 exhibited broad-spectrum antibacterial activities against A. hydrophila, D. chrysanthemi, C. terrigena, X. citri pv. malvacearum and antifungal activity against C. albicans in a conventional broth dilution assay. The positive control was ciprofloxacin with the MIC values of <0.024 µM, 0.39 µM, 0.39 µM, 0.39 µM, and 0.20 µM, respectively. Compound 1 and compounds 7, 10, and 11 displayed antifungal activities against F. fujikuroi and D. citri, respectively, in modified agar diffusion test. Prochloraz was used as positive control and showed the inhibition zone radius of 17 mm and 15 mm against F. fujikuroi and D. citri, respectively. All the annotated compounds a–p by molecular networking were first discovered from the genus Nocardiopsis. Nocarpyrroline A (1) features an unprecedented 4,5-dihydro-pyrrole-2-carbonitrile substructure, and it is the first pyrroline isolated from the genus Nocardiopsis. This study further demonstrated the guiding significance of molecular networking in the research of microbial secondary metabolites. [ABSTRACT FROM AUTHOR]

We used 22 years of seasonally and spatially consistent monitoring data to explore marine predator–prey numerical response relationships. Specifically, we tested whether indices of offspring performance (e.g. offspring mass near the time of their independence and/or growth rate) from three Antarctic krill-dependent predators, showed positive relationships with estimates of krill density, determined using fishery-independent acoustic surveys undertaken towards the middle of the predator breeding season. Results showed that indices of predator reproductive performance had little relationship with krill density. In most years, average krill densities were higher on-shelf than off-shelf, potentially providing ecological buffering for predators provisioning offspring. Interestingly, positive response relationships were evident between predator offspring mass and the spatial distribution of krill, measured using indices that represent levels of inequality (patchiness) in krill distribution. These relationships were strongest using indices that reflected the off-shelf krill spatial distribution. We found that krill density and predator offspring mass were also both negatively influenced by sea surface temperature and the Southern Annular Mode, indicating that the environment exerts strong control over ecosystem processes. Finally, we consider the relevance of our results to the ecological framework used by managers responsible for setting catch limits for the regional fishery for krill. [ABSTRACT FROM AUTHOR]

The objective of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) is conservation (CCAMLR, 1980), and the management provision that distributes krill catches throughout the Scotia Sea expires in November. Conservation does not require undetectable ecosystem effects of fishing, but CCAMLR intended to manage the krill fishery so that any such effect would be minor. Conservation Measure 51-01 specifies two annual catch limits: an aspirational limit (5.61 Mt, the "precautionary catch limit") and an interim "trigger limit" (620 kt) (CCAMLR, 1991). Keywords: Antarctica; Antarctic krill; CCAMLR; fishery management; krill predators; precaution; risk assessment EN Antarctica Antarctic krill CCAMLR fishery management krill predators precaution risk assessment 1 4 4 10/04/22 20221001 NES 221001 INTRODUCTION If, by 1 December 2022, the total allowable catch of Antarctic krill ( I Euphausia superba i ) taken from the Scotia Sea (here, waters between 50-70°S and 20-70°W) (Figure 1) is not partitioned in space and time, the objective of an international conservation regime will be jeopardized. [Extracted from the article]

This paper describes the use of immobilized phospholipase A1 (PLA1) for the production of phosphatidylcholine (PC) rich in docosahexaenoic acid (DHA) using PC from Antarctic krill and fish fatty acids (FA) as the substrates, and supercritical carbon dioxide (SCCO 2 ) as the solvent medium. Detailed studies of immobilization were performed, and PLA1 was immobilized by physical adsorption onto DA-201. The best conditions for adsorption were as follows: protein loading = 85 mg PLA1/g support at a pH of 5 with 10 h of contact. For synthesis of PC with high levels of DHA, the effects of several parameters, including pressure, reaction time, temperature, enzyme loading and substrate molar ratio, were investigated to determine optimal conditions. The optimal substrate molar ratio of the FA to PC was 10. Under 12 MPa and 50 °C SCCO 2 , 59.0 mol% DHA was incorporated into PC after only 7 h at an immobilized enzyme loading rate of 15 wt% of the total substrates. The PC yield was 27.5 mol% under the optimal conditions. [ABSTRACT FROM AUTHOR]

Large marine animals may play a crucial role in storing and recycling bioavailable iron in surface waters by consuming iron-rich prey and subsequent defecation of iron that is excess to their requirements. This biological recycling of iron could enhance primary productivity in iron-limited waters. However, quantifying the effects of marine animals on ocean primary productivity remains challenging because of a limited understanding of the key biogeochemical processes involved. In this paper, we develop a preliminary model that explores these uncertainties and examines the potential effects of historical populations of blue, fin and humpback whales, and the biomass of Antarctic krill required to support the whale populations, on primary productivity in the Southern Ocean. Our results suggest that, despite conservative estimates for key processes in our model, pre-exploitation populations of blue whales and, to a lesser extent fin and humpback whales, could have contributed to iron recycling, resulting in enhanced phytoplankton production in iron-limited Southern Ocean waters. Iron-rich defecation by un-exploited whale populations in the Southern Ocean, and the biomass Antarctic krill required to support them, could have resulted in a contribution to primary productivity of between 1.5 × 10 −4 to 23.4 g C m −2 yr −1 (blue whales), 1.4 × 10 −4 to 13.9 g C m −2 yr −1 (fin whales), and 2.4 × 10 −5 to 1.7 g C m −2 yr −1 (humpback whales). However, only when all parameter estimates are at their upper limits does there appear to be this significant role for whales in enhancing primary productivity, and thus we need to assess the likelihood of these values arising. The high degree of uncertainty around the magnitude of these increases in primary productivity is mainly due to our limited quantitative understanding of key biogeochemical processes. To reduce uncertainty regarding the effect of whales on Southern Ocean primary productivity, future research will need to refine our understanding of five influential model parameters: iron content in krill; krill consumption rates by whales; persistence of whale faecal iron in the photic zone; bioavailability of this retained iron; and the carbon-to-iron ratio of phytoplankton. [ABSTRACT FROM AUTHOR]

Poleward range shifts are a global‐scale response to warming, but these vary greatly among taxa and are hard to predict for individual species, localized regions or over shorter (years to decadal) timescales. Moving poleward might be easier in the Arctic than in the Southern Ocean, where evidence for range shifts is sparse and contradictory. Here, we compiled a database of larval Antarctic krill, Euphausia superba and, together with an adult database, it showed how their range shift is out of step with the pace of warming. During a 70‐year period of rapid warming (1920s–1990s), distribution centres of both larvae and adults in the SW Atlantic sector remained fixed, despite warming by 0.5–1.0°C and losing sea ice. This was followed by a hiatus in surface warming and ice loss, yet during this period the distributions of krill life stages shifted greatly, by ~1000 km, to the south‐west. Understanding the mechanism of such step changes is essential, since they herald system reorganizations that are hard to predict with current modelling approaches. We propose that the abrupt shift was driven by climatic controls acting on localized recruitment hotspots, superimposed on thermal niche conservatism. During the warming hiatus, the Southern Annular Mode index continued to become increasingly positive and, likely through reduced feeding success for larvae, this led to a precipitous decline in recruitment from the main reproduction hotspot along the southern Scotia Arc. This cut replenishment to the northern portion of the krill stock, as evidenced by declining density and swarm frequency. Concomitantly, a new, southern reproduction area developed after the 1990s, reinforcing the range shift despite the lack of surface warming. New spawning hotspots may provide the stepping stones needed for range shifts into polar regions, so planning of climate‐ready marine protected areas should include these key areas of future habitat. [ABSTRACT FROM AUTHOR]

Abstract: We simulate the formation of social aggregations in a turbulent fluid environment. The theoretical framework is employed to investigate the ecological consequences of spatial patchiness in the density distribution of krill, which often assemble in swarms or schools. We first describe the formation of aggregations resulting from the interplay of social forces and population dynamics, and then consider an idealized ecosystem model of zooplankton with social behavior who feed on phytoplankton; this is solved analytically for the initial growth of patches and numerically for the steady-state distributions of predator and prey biomass. Environmental variability changes the linear instability criterion for spontaneous aggregation. The second part of the paper addresses the evolution of social behavior in a population with density-dependent mating success. The model simulates the transmission of a gene controlling social behavior; natural selection determines whether the grouping or non-grouping type becomes dominant. It is found that the behavior can evolve when mixing occurs rapidly enough for resources to remain available to the clustered organisms. Turbulent advection prevents the grouping type from becoming dominant if the shear of the flow is strong enough to disrupt the patches; otherwise the aggregated zooplankton benefit from enhanced diffusion of resources by the turbulent flow. [Copyright &y& Elsevier]

The nutraceutical market for EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) is promoting fishing for Euphasia superba (Antarctic krill) in the Southern Ocean and Calanus finmarchicus in Norwegian waters. This industry argues that these species are underexploited, but they are essential in their ecosystems, and climate change is altering their geographical distribution. In this perspective, we advocate the cessation of fishing for these species to produce nutraceuticals with EPA and DHA. We argue that this is possible because, contrary to what this industry promotes, the benefits of these fatty acids only seem significant to specific population groups, and not for the general population. Next, we explain that this is desirable because there is evidence that these fisheries may interact with the impact of climate change. Greener sources of EPA and DHA are already available on the market, and their reasonable use would ease pressure on the Arctic and Antarctic ecosystems. [ABSTRACT FROM AUTHOR]

Antarctic krill is a high-quality animal protein resource, but the presence of fluorine limits its development. Antarctic krill defluoridated hydrolysate products (DHPs) generally have a bitter taste that is unacceptable to consumers. Therefore, it is necessary to improve the flavor of defluoridated hydrolysate. In this work, flavor improvement of DHPs by the Maillard reaction was evaluated by sensory analysis, electronic nose (E-nose), and gas chromatography-mass spectrometry (GC-MS). The potential correlations among the signals of sensory attributes, E-nose, and volatile components were analyzed using the analysis of partial least squares regression (PLSR). A total of 63 volatile compounds were identified and quantified via GC-MS. The flavors in Maillard reaction products were mainly attributed to pyrazines, aldehydes, ketones, and furans. After the Maillard reaction, the two main aromatic compounds generated were 3-ethyl-2,5-dimethylpyrazin (roast odor, OAV = 32.7) and 3-(methylthio) propionaldehyde (shrimp meat odor, OAV = 16.43), which contributed to flavor improvement in DHPs. PLSR results showed a good correlation between most variables of sensory attributes, E-nose, and volatile compounds, which indicates that the overall flavor of DHPs was improved by the Maillard reaction. Abbreviations: DHPs: defluoridated hydrolysate products; MRPs: Maillard reaction products; GC-MS: gas chromatography-mass spectrometry; E-nose: electronic nose; OAV: odor activity value; SPME: solid-phase microextraction; GC-O: gas chromatography-olfactometry; PCA: principal component analysis; PLSR: partial least squares regression [ABSTRACT FROM AUTHOR]

Productivity in the oceans is heightened around oceanographic and bathymetric features such as fronts and islands. This can have a flow‐on effect, providing increased food availability for higher trophic level species. Using data from a 5‐day combined visual and acoustic survey, we examined the hypothesis that higher Antarctic krill (Euphausia superba) density provides a lucrative resource for humpback whales (Megaptera novaeangliae) at a remote Antarctic feeding area, the Balleny Islands (67oS, 164°E). We assessed whale presence at the feeding area in relation to prey (krill), productivity and environmental variables using density surface modeling. We found stark differences between krill swarms near the islands and those in adjacent open water. Swarms were twice as dense and three times more numerous near the Balleny Islands compared to an open water pelagic environment, suggesting that the islands offered a profitable feeding opportunity. At the feeding area, whales were found in deeper and more productive waters with medium krill densities. These relationships, along with the high krill availability around the islands, may be the result of the Island Mass Effect. [ABSTRACT FROM AUTHOR]

This study was designed to evaluate the effect of dietary replacement fish meal supplemented with freeze‐dried powder of the Antarctic krill Euphausia superba (FDPE) on the growth performance, molting, and fatty acid composition of the Pacific white shrimp Litopenaeus vannamei (initial weight 1.27 ± 0.09 g). Four diets containing 0% (S0 group), 10% (S10 group), 20% (S20 group), and 30% (S20 group) FDPE were used in the present study. At the end of growth trial, the final body weight, weight gain rate, and specific growth rate in the S10, S20, and S30 groups were higher than those in the S0 group. The shrimp in the S10 and S20 groups exhibited better molting synchronism than those in the S0 group. The astaxanthin content in the hepatopancreas from the shrimp in the groups supplemented with FDPE was significantly higher than that in the S0 group (p < 0.05) and increased as the FDPE content in the feed increased. The shrimp in the S10, S20, and S30 groups had a higher monounsaturated fatty acid (MUFA) content in the hepatopancreas than those in the S0 group. The sum of EPA and DHA in the muscles from the shrimp in the S0 group was lower than that in the other groups. These results indicate that the dietary inclusion of 10%–20% FDPE can be used as practical diets in L. vannamei farmed under a clear water system. [ABSTRACT FROM AUTHOR]

A few studies conducted over the past few decades have demonstrated the health benefits of a diet rich in marine products, but limited studies have investigated the effects of different krill products on the nitrogen balance and their potential health benefits. In our study, after a 14‐day acclimation period, 50 female Sprague–Dawley rats were randomly assigned to five groups, each of which was fed a different diet, for 28 days. We then evaluated the effect of krill protein complex (KPC), krill powder, and defatted krill powder on the nitrogen balance, growth, and antioxidant activity through analyses of MDA, CAT, GSH‐Px, and T‐SOD. An in vivo analysis suggested that the nitrogen retention rate, protein digestibility, and bioutilization of krill products were equal to those of casein. Moreover, the KPC diet resulted in the highest nitrogen intake and retention among the groups, and the biological value and net protein utilization obtained with KPC were higher than those obtained with defatted krill powder, which was consistent with the weight gains observed for these two groups. The hematological test also showed that KPC contributed to the production of functional proteins in the body. The antioxidant activity analysis indicated that higher GSH‐Px and T‐SOD activities were obtained with krill products and KPC, respectively, compared with casein. The results from this study suggested that krill proteins could promote growth and improve the antioxidant status of an organism. Although further studies on the safety of krill products for human consumption are needed, this work provides insights into the use of krill proteins as a potential substitute for other proteins and restructured foods. [ABSTRACT FROM AUTHOR]

In this study, the dB difference and characteristics of krill swarms inhabiting Subarea 48.1, which includes the west and south of the South Shetland Island and the Elephant Island peripheries, were estimated to distinguish Antarctic krill, using acoustics. From April 13 to 24, 2016, acoustic data were collected along 24 survey lines using the frequencies 38 and 120 kHz, and middle trawling was performed at 7 stations. Using the difference between the dB values of two volume backscattering strength (Sv) frequencies (38 and 120 kHz), a clear acoustic distinction could be made between Antarctic krill (4.9 to 12.0 dB) and fish (−4.0 to −0.2 dB). The distributions and mean Sv of krill swarms in the Elephant Island peripheries and south of South Shetland Island were higher than those in the west of South Shetland Island. The mean length/ height ratio of krill swarms in the west of the South Shetland Island (64.5) was higher than that in the south (35.9) and the Elephant Island peripheries (33.8), with the length of the aggregations exceeding their height. Most krill swarms were distributed between the surface layer (less than 10 m below sea level) and within 200 m of water depth. These results are expected to serve as baseline data for evaluating krill density and biomass by distinguishing them from fish, using acoustics. [ABSTRACT FROM AUTHOR]

The fatty acid content and composition of the Antarctic krill Euphausia superba Dana, 1850 were investigated using samples collected by a commercial fishing vessel. This dataset allowed comparison between seasons, years (2013–2016), and different fishing locations. Quantities of omega 3 fatty acids 20:5n-3 and 22:6n-3 (mg/g dry mass; DM) were highest in autumn and decreased through winter to reach a spring low. Quantities of the flagellate marker 18:4n-3 and diatom marker 16:1n-7c were variable and did not display the same seasonal fluctuations. In summer, krill had high percentages (% total fatty acids) of 20:5n-3 and 22:6n-3, total PUFA, and low 18:1n-9c/18:1n-7c ratios, indicating a more herbivorous diet. Krill became more omnivorous from autumn to spring, indicated by increasing ratios of 18:1n-9c/18:1n-7c and percentages of Σ 20:1 + 22:1 isomers. Bacterial fatty acids (Σ C15+ C17+ C19isomers) were minor components year-round (0.9–1.8 %). Seasonal levels of herbivory and omnivory differed between years, and levels of specific fatty acid ratios differed between fishing locations. The fatty acid 18:4n-3 was a major driver of variability in krill fatty acid composition, with no obvious seasonal driver. This is the first study to report krill fatty acid data during all four seasons over consecutive years. This large-scale study highlights the value of using fisheries samples to examine seasonal and annual fluctuations in krill diet and condition. [ABSTRACT FROM AUTHOR]

Abstract: Penguins are a monophyletic group in which many species are found breeding sympatrically, raising questions regarding how these species coexist successfully. Here, the isotopic niche of three sympatric pygoscelid penguin species was investigated at Powell Island, South Orkney Islands, during two breeding seasons (austral summers 2013–2014 and 2015–2016). Measurements of carbon (δ13C) and nitrogen (δ15N) stable isotope ratios were obtained from blood (adults) or feather (chicks) samples collected from Adélie Pygoscelis adeliae, chinstrap P. antarctica, and gentoo P. papua penguins. Isotopic niche regions (a proxy for the realized trophic niches) were computed to provide estimates of the trophic niche width of the studied species during the breeding season. The isotopic niche regions of adults of all three species were similar, but gentoo chicks had noticeably wider isotopic niches than the chicks of the other two species. Moderate to strong overlap in isotopic niche among species was found during each breeding season and for both age groups, suggesting that the potential for competition for shared food sources was similar during the two study years, although the actual level of competition could not be determined owing to the lack of data on resource abundance. Clear interannual shifts in isotopic niche were seen in all three species, though of lower amplitude for adult chinstrap penguins. These shifts were due to variation in carbon, but not nitrogen, isotopic ratios, which could indicate either a change in isotopic signature of their prey or a switch to an alternative food web. The main conclusions of this study are that (1) there is a partial overlap in the isotopic niches of these three congeneric species and that (2) they responded similarly to changes that likely occurred at the base of their food chain between the 2 years of the study. [ABSTRACT FROM AUTHOR]

As one of the most common and dominant species in the Southern Ocean, Antarctic krill ( Euphausia superba) play a significant role in food web structure and the process of energy flow. The diet of Antarctic krill in the Prydz Bay during austral summer of 2012/2013 was investigated and the ontogenetic shift in krill diet was evaluated using the stable isotope method. The nitrogen stable isotope values (δN) of adults ((2.78±0.58)‰) were much higher than those of juveniles ((1.69±0.70)‰), whereas the carbon stable isotope values (δC) of adults (-(28.26±1.08)‰) were slightly lower than those of juveniles (-(27.48±1.35)‰). Particulate organic matter (POM) from 0, 25, and 50 m depth combined (0/25/50 m) represented phytoplankton food items. The results showed that phytoplankton food items in surface water and mesozooplankton were two essential food items for Antarctic krill in the Prydz Bay during summer. POM (0/25/50 m) contributes 56%-69% and 26%-34% to the diet of juvenile and adult krill, respectively, whereas mesozooplankton composes 13%-34% and 58%-71% of the diet of juvenile and adult krill, respectively. Thus, an ontogenetic diet shift from POM (0/25/50 m), which consists mainly of phytoplankton, to a higher trophic level diet containing mesozooplankton, was detected. The capacity for adults to consume more zooplankton food items may minimize their food competition with juveniles, which rely mostly on phytoplankton food items. This suggests 'diet shift with ontogeny' which may somehow help krill keep their dietary energy budget balanced and well adapted to the Antarctic marine ecosystem as a dominant species. [ABSTRACT FROM AUTHOR]

Water-washing removes fluoride from Antarctic krill but produces large volumes of wash water containing water- soluble proteins and fluoride. The freeze concentration method was tested to determine if it could be used to recover water-soluble proteins while leaving the fluoride in solution. After freezing and thawing the wash water, protein and fluoride contents of the thawed fractions were determined to explore the melting regularity of components in the wash water. The highest concentration factors of protein and fluoride were obtained after 80 min of thawing, such as 1.48 ± 0.06 and 1.35 ± 0.04 times, respectively. The free amino-nitrogen (FAN) content and sodium dodecyl sulfate-polyacrylamide gel electrophoresis pattern results revealed that the highest concentrations of all ingredients were obtained after 80 min of the process. The degree of hydrolysis of all fractions from the thawing process fluctuated in a narrow range around 12% during the entire process, indicating that the thawing order did not change with various proteins or time during the entire thawing course. These results demonstrate that the freeze concentration method can be used to concentrate protein solutions, even those with fluoride. It was concluded that condensation was achieved and no ingredient could be separated, regardless of fluoride, amino acids, or different proteins in the water. [ABSTRACT FROM AUTHOR]

The dielectric properties of ten solid amino acids, namely, glycine, proline, cysteine, glutamine, lysine, methionine, histidine, arginine, tyrosine, and tryptophan, and the effects of amino acid concentrations (0, 1, 3, and 5%) on the dielectric properties of minced Antarctic krill ( Euphausia superba) were studied within a frequency range of 300-3000 MHz at 20.0 ± 0.5 °C. The dielectric constants and dielectric loss factor of amino acids were 2.0 ± 0.4 and 0.2 ± 0.3, respectively (moisture contents, 0.05-0.33%), except those of lysine (5.5 ± 0.5 and 1.5 ± 1.0, respectively) (moisture content, 4.5%). The dielectric properties of non-polar, neutral-polar, alkaline amino acids added to Antarctic krill were affected by the frequency and moisture contents, molecular weight, and isoelectric points (p I) of amino acids. As the molecular weight and p I values increased, the critical frequencies of aliphatic amino acid added to minced Antarctic krill decreased, whereas heterocyclic amino acid added to minced Antarctic krill increased. Quantitative relationships between parameters that define both the real and the imaginary parts of the Debye relations and the weight fraction of amino acid contents in Antarctic krill were determined. Moreover, glycine (at 5%) or lysine (at 5%) significantly influenced the dielectric constants and dielectric loss factor of minced Antarctic krill ( p < 0.05) but did not have significant effects on temperature history and distribution ( p < 0.05) during microwave heating at 2450 MHz. [ABSTRACT FROM AUTHOR]

Antarctic krill, Euphausia superba , is a highly abundant and ecologically important zooplankton species in the Southern Ocean. Regions of elevated Antarctic krill biomass exist around Antarctica, often as a result of the concentrating effect of bathymetry and ocean currents. Such areas are considered biological hotspots and are key foraging grounds for numerous top predators in the region. A hotspot of Antarctic krill biomass exists off the southern extent of Anvers Island, Western Antarctic Peninsula, and supports a population of Adélie penguins that feed almost exclusively on it, as well as numerous other top predators. We investigated the spatio-temporal variability in Antarctic krill biomass and aggregation structure over four consecutive summer seasons, identifying environmental factors that were responsible. We identified three distinct krill aggregation types (Large-dense, Small-close and Small-sparse), and found that the relative proportion of each type to total aggregation numbers varied significantly between survey days. Large-dense aggregations occurred more frequently when westerly winds predominated and when the local mixed tide was in the diurnal regime. Small-close aggregations were also more frequent during diurnal tides and were negatively correlated with phytoplankton biomass. Small-sparse aggregations, on the other hand, were more prevalent when the mixed tide was in the semi-diurnal phase. We suggest that, under certain conditions (i.e. diurnal tides and westerly winds), the biological hotspot in the nearshore waters off Palmer Station, Anvers Island, functions as a zone of accumulation, concentrating krill biomass. Our findings provide important information on the dynamics of Antarctic krill at the local scale. [ABSTRACT FROM AUTHOR]