Krill Behavior Research Articles

Climate change impacts on Antarctic krill behaviour and population dynamics

Climate change impacts on Antarctic krill behaviour and population dynamics

Plasticity and seasonality of the vertical migration behaviour of Antarctic krill using acoustic data from fishing vessels.

Understanding the vertical migration behaviour of Antarctic krill is important for understanding spatial distribution, ecophysiology, trophic interactions and carbon fluxes of this Southern Ocean key species. In this study, we analysed an eight-month continuous dataset recorded with an ES80 echosounder on board a commercial krill fishing vessel in the southwest Atlantic sector of the Southern Ocean. Our analysis supports the existing hypothesis that krill swarms migrate into deeper waters during winter but also reveals a high degree of variability in vertical migration behaviour within seasons, even at small spatial scales. During summer, we found that behaviour associated with prolonged surface presence primarily occurred at low surface chlorophyll a concentrations whereas multiple ascent-descent cycles per day occurred when surface chlorophyll a concentrations were elevated. The high plasticity, with some krill swarms behaving differently in the same location at the same time, suggests that krill behaviour is not a purely environmentally driven process. Differences in life stage, physiology and type of predator are likely other important drivers. Finally, our study demonstrates new ways of using data from krill fishing vessels, and with the routine collection of additional information in potential future projects, they have great potential to significantly advance our understanding of krill ecology.

Environmental and behavioural drivers of Antarctic krill distribution at the South Orkney Islands: A regional perspective

Antarctic krill (Euphausia superba) is a key species in the marine ecosystem of the Southern Ocean, but is also the target of a commercial fishery, with an important fishing ground in the South Orkney Islands region. The potential for competition for krill between predators and the fishery requires risk management strategies for the fishery, underpinned by an understanding of the key physical and behavioural drivers of krill movement and retention in target areas. Here, we present the results of a regional modelling study, combining a high-resolution ocean-sea ice model and an individual-based model parameterised for krill, to elucidate the roles of oceanographic variability and krill behaviour on patterns of transport and retention on and around the South Orkney Plateau. Simulations suggest that oceanic transport from sources around the Antarctic Peninsula is restricted by the northward flowing Antarctic Slope Current. Around the South Orkney Plateau, anticyclonic flows associated with the Weddell Front and the shelf edge transport krill rapidly towards the main fishing grounds to the northwest of the plateau. Transport onto the shelf and subsequent retention are influenced by the strength and direction of regional winds; weaker on-shelf transport and shorter retention times are associated with stronger westerly and northerly winds. The incorporation of sea-ice associated behaviour, whereby krill are moved with sea ice when sea ice is present, significantly modifies the patterns from purely oceanic transport; it reduces the influence of strong regional oceanic flows and increases transport of krill to the South Orkneys region from the Antarctic Peninsula. The inclusion of diel vertical migration also modifies predicted patterns from oceanic transport, but to a lesser extent, and moderates the impact of including sea-ice associated behaviour. We highlight the importance of understanding the behaviour of krill, including age-dependent behavioural changes in response to sea ice conditions, for modelling and management of Antarctic krill populations.

Self-organization and information transfer in Antarctic krill swarms.

Antarctic krill swarms are one of the largest known animal aggregations, and yet, despite being the keystone species of the Southern Ocean, little is known about how swarms are formed and maintained. Understanding the local interactions between individuals that provide the basis for these swarms is fundamental to knowing how swarms arise in nature, and what potential factors might lead to their breakdown. Here, we analysed the trajectories of captive, wild-caught krill in 3D to determine individual-level interaction rules and quantify patterns of information flow. Our results demonstrate that krill align with near neighbours and that they regulate both their direction and speed relative to the positions of groupmates. These results suggest that social factors are vital to the formation and maintenance of swarms. Furthermore, krill operate a novel form of collective organization, with measures of information flow and individual movement adjustments expressed most strongly in the vertical dimension, a finding not seen in other swarming species. This research represents a vital step in understanding the fundamentally important swarming behaviour of krill.

Exploration of iron-binding mode, digestion Kinetics, and iron absorption behavior of Antarctic Krill–derived heptapeptide–iron complex

A novel heptapeptide LVDDHFL derived from Antarctic krill was used to assemble an iron complex, of which the iron-binding mode, in vitro digestion kinetics, and iron absorption behavior were explored. Fe2+ bound to one carboxyl oxygen atom of Asp at position 4 and the imidazole group of His at position 5 on the LVDDHFL peptide at a stoichiometric ratio of 1:2, which induced the folding of LVDDHFL to form a more orderly structure. LVDDHFL–iron significantly enhanced the solubility of iron as compared to FeSO4 in the gastroduodenal tract (P < 0.05), making it up to 80.92 ± 3.02% at the end of gastroduodenal digestion. Moreover, iron complexation can enhance the digestive stability of LVDDHFL with the peptide retention rate as 62.26 ± 2.60% and approximately 27.54% of LVDDHFL were degraded to hexapeptide LVDDHF. Nevertheless, the enhancement of LVDDHF − iron on iron absorption was comparable to that of LVDDHFL − iron, but better than that of FeSO4.

The ecosystem approach to management of the Antarctic krill fishery - the ‘devils are in the detail’ at small spatial and temporal scales

Fishery demand for Antarctic krill is increasing, and projected to continue increasing into the future. Krill has the potential to contribute approximately 10% to all future marine landings, adding significantly to global food security. However, the fishery is effectively data-limited so is currently managed using precautionary assessments that relate to large spatial and temporal scales that preclude the need for fine-scale ecological data. To respond to recent changes in fishery operation and to mitigate possible ecological impacts, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) plans to revise its management strategy so that it takes into account ecosystem operation at smaller spatial and temporal scales, such as those relevant to krill-dependent predators. Here, we consider how catches in coastal areas potentially present challenges for these predators, where cumulative catches over the fishing season can sometimes be greater than local consumption by predators, and sometimes greater than the standing stock of krill within an area because of krill transport and replenishment by ocean currents. Protecting feeding areas used by land-based predators such as penguins and seals, whilst also offering a high level of protection for pelagic predators such as some species of fish and recovering populations of cetaceans, will require innovative solutions. We highlight critical ecological research needed to reduce management uncertainty. This is important as we demonstrate that krill consumption by predators in near-shore coastal habitats relies absolutely upon krill movement and oceanographic transport. We also highlight the need to improve understanding about krill behaviour, especially in relation to observed seasonal changes in krill biomass. Finally, we highlight that without up-to-date data about changes in krill, krill-dependent predator populations and their oceanographic environment, management will remain challenging in the context of increasing fishing pressure, recovering populations of marine mammals and a changing climate. • Antarctic krill fishing is increasing, and is likely to increase into the future. • Changes in fishing highlight the need for management at relevant ecological scales. • Krill demand by penguins and whales is a key management concern in coastal habitats. • Information about krill behaviour and movement in ocean currents is also important. • Precautionary management of krill requires more detailed ecological understanding.

Circadian regulation of diel vertical migration (DVM) and metabolism in Antarctic krill Euphausia superba

Antarctic krill (Euphausia superba) are high latitude pelagic organisms which play a key ecological role in the ecosystem of the Southern Ocean. To synchronize their daily and seasonal life-traits with their highly rhythmic environment, krill rely on the implementation of rhythmic strategies which might be regulated by a circadian clock. A recent analysis of krill circadian transcriptome revealed that their clock might be characterized by an endogenous free-running period of about 12–15 h. Using krill exposed to simulated light/dark cycles (LD) and constant darkness (DD), we investigated the circadian regulation of krill diel vertical migration (DVM) and oxygen consumption, together with daily patterns of clock gene expression in brain and eyestalk tissue. In LD, we found clear 24 h rhythms of DVM and oxygen consumption, suggesting a synchronization with photoperiod. In DD, the DVM rhythm shifted to a 12 h period, while the peak of oxygen consumption displayed a temporal advance during the subjective light phase. This suggested that in free-running conditions the periodicity of these clock-regulated output functions might reflect the shortening of the endogenous period observed at the transcriptional level. Moreover, differences in the expression patterns of clock gene in brain and eyestalk, in LD and DD, suggested the presence in krill of a multiple oscillator system. Evidence of short periodicities in krill behavior and physiology further supports the hypothesis that a short endogenous period might represent a circadian adaption to cope with extreme seasonal photoperiodic variability at high latitude.

Verification of the Backscattering Strength Based on the Swimming Behavior of Antarctic Krill

This study provides an estimate of the SDWBA-modelled mean target strength for given sets of krill length and swimming orientation. The range of the dB identification window for krill length was between 28 mm and 67 mm and the distribution of swimming orientation N[11.0°, 4.0°] was estimated to be between 0.06–10.97 dB, while the range estimated using N[53.1°, 21.4°], i.e., the distribution of orientation obtained under the brightest illuminance level, was 5.21–9.82 dB. The range of the dB window calculated using N[45.2°, 23.0°], obtained under the second brightest illuminance level, was 3.83–11.76 dB, and the range calculated with N[48.1°, 23.0°], obtained under the third illuminance level, was 3.83–11.76 dB. The range of the dB window calculated by N[45.9°, 23.0°] was 3.41–11.75 dB, and the range of the dB window for krill length ranging from 28 mm to 67 mm was 4.05–11.34 dB. In all the swimming orientations, the smaller the krill size was the lower the averaged target strength value was; likewise, the larger the krill size was the higher the averaged target strength value was. The result indicated that swimming orientation impacted greatly on the range of frequency differences of Antarctic krill.

Seasonal gene expression profiling of Antarctic krill in three different latitudinal regions.

The Antarctic krill, Euphausia superba, has evolved seasonal rhythms of physiology and behaviour to survive under the extreme photoperiodic conditions in the Southern Ocean. However, the molecular mechanisms generating these rhythms remain far from understood. The aim of this study was to investigate seasonal differences in gene expression in three different latitudinal regions (South Georgia, South Orkneys/Bransfield Strait, Lazarev Sea) and to identify genes with potential regulatory roles in the seasonal life cycle of Antarctic krill. The RNA-seq data were analysed (a) for seasonal differences between summer and winter krill sampled from each region, and (b) for regional differences within each season. A large majority of genes showed an up-regulation in summer krill in all regions with respect to winter krill. However, seasonal differences in gene expression were less pronounced in Antarctic krill from South Georgia, most likely due to the milder seasonal conditions of the lower latitudes of this region, with a less extreme light regime and food availability between summer and winter. Our results suggest that in the South Orkneys/Bransfield Strait and Lazarev Sea region, Antarctic krill entered a state of metabolic depression and regressed development (winter quiescence) in winter. Moreover, seasonal gene expression signatures seem to be driven by a photoperiodic timing system that may adapt the flexible behaviour and physiology of Antarctic krill to the highly seasonal environment according to the latitudinal region. However, at the lower latitude South Georgia region, food availability might represent the main environmental cue influencing seasonal physiology.

Phytoplankton odor modifies the response of Euphausia superba to flow

Antarctic krill, Euphausia superba, are critical components of the Antarctic food web as well as important targets for conservation and management. Krill behavior has important effects on demographic properties and aggregation characteristics, but remains incompletely known. Krill clearly respond to different environmental stimuli such as light, flow and chemicals, but few studies have quantified these behaviors. We examined the behavior of krill in well-quantified current speeds in a laboratory flume and examined interactions of phytoplankton odor and flow. Krill are sensitive to flow speeds as low as 1 mm s−1, and flow polarizes krill swimming and orientation in the up-current direction. Phytoplankton odor increases the sensitivity of krill to flow, and induces area-restricted search behaviors that presumably allow krill to exploit food patches efficiently. The ability to quantify krill behavior could have important consequences for understanding demographic processes and the properties of krill aggregations.

Krill-Herd-Based Investigation for Energy Saving Opportunities in Offshore Liquefied Natural Gas Processes

For offshore natural gas liquefaction operation, the single mixed refrigerant process is considered as one of the best and most suitable processes. However, multivariable nonlinear thermodynamic interactions among operating conditions and flow rates of mixed refrigerant ingredients lead to energy losses, which ultimately contributes to high energy consumption for liquefied natural gas production. The present work investigates the energy saving opportunities in the single mixed refrigerant liquefaction process through “krill-herd” strategy which is based on the biological flocking (herding) behavior of individual krill. To find the energy saving opportunities, the krill-herd approach effectively reduced the exergy losses of the compression units and cryogenic heat exchanger up to 18.6 and 41.1%, respectively, as compared to the published liquefaction process. The figure of merit was found as 27.0% in the krill-herd-optimized single mixed refrigerant process, whereas it was 22.2% in the base case.

Size selection of Antarctic krill (Euphausia superba) in a commercial codend and trawl body

During fishing, many fish species are able to avoid the net walls of the trawl body and so the majority of size selection occurs in the codend of the net. Antarctic krill (Euphausia superba) are regarded as true planktonic organisms passively drifting with currents, but they also display self-locomotion by active swimming. There is a lack of knowledge regarding the behavior of krill during the fishing process, and extrapolating results obtained for other species to krill is of limited value. In the case of krill, it is largely unknown to what extent the codend versus the trawl body contributes to the size selection process. The current study aims to quantify the size selection of krill in a commercially applied codend during experimental fishing. Combining these results with a model for full trawl size selectivity it was possible to provide an insight to the size selection process in the trawl body. Specifically, the study applied a two-step approach by first estimating the size selectivity of a commercial codend and second used the codend size selectivity obtained in this study to estimate the trawl body size selectivity of a commercial trawl based on entire trawl-selectivity obtained in a previous study. The results of this two-step analysis revealed that the trawl body contributes significantly to the total size selection process, demonstrating that size selectivity of Antarctic krill in commercial trawls is affected by both the trawl body and the codend.

A Novel Optimization Technique to Improve Gas Recognition by Electronic Noses Based on the Enhanced Krill Herd Algorithm.

An electronic nose (E-nose) is an intelligent system that we will use in this paper to distinguish three indoor pollutant gases (benzene (C6H6), toluene (C7H8), formaldehyde (CH2O)) and carbon monoxide (CO). The algorithm is a key part of an E-nose system mainly composed of data processing and pattern recognition. In this paper, we employ support vector machine (SVM) to distinguish indoor pollutant gases and two of its parameters need to be optimized, so in order to improve the performance of SVM, in other words, to get a higher gas recognition rate, an effective enhanced krill herd algorithm (EKH) based on a novel decision weighting factor computing method is proposed to optimize the two SVM parameters. Krill herd (KH) is an effective method in practice, however, on occasion, it cannot avoid the influence of some local best solutions so it cannot always find the global optimization value. In addition its search ability relies fully on randomness, so it cannot always converge rapidly. To address these issues we propose an enhanced KH (EKH) to improve the global searching and convergence speed performance of KH. To obtain a more accurate model of the krill behavior, an updated crossover operator is added to the approach. We can guarantee the krill group are diversiform at the early stage of iterations, and have a good performance in local searching ability at the later stage of iterations. The recognition results of EKH are compared with those of other optimization algorithms (including KH, chaotic KH (CKH), quantum-behaved particle swarm optimization (QPSO), particle swarm optimization (PSO) and genetic algorithm (GA)), and we can find that EKH is better than the other considered methods. The research results verify that EKH not only significantly improves the performance of our E-nose system, but also provides a good beginning and theoretical basis for further study about other improved krill algorithms’ applications in all E-nose application areas.

A Robust and Economical Underwater Stereo Video System to Observe Antarctic Krill (Euphausia superba)

In situ characterization of krill morphometry, behaviour and orientation is not yet routinely feasible, yet is critical to understanding swarm characteristics. A first step is to measure individual and aggregation behaviour. We report on successful use of a robust, low-cost underwater stereo video camera system to observe live Antarctic krill (Euphausia superba) in aquaria. The application of photogrammetry techniques allows animal length, orientation and three-dimensional position to be calculated from stereo video camera observations. Initially, we tested the efficacy of the stereo system by observing synthetic targets of known length and orientation to obtain estimates of measurement error. We found that on average the stereo camera system underestimated length by 0.6 mm and vertical tilt angle by +0.34°(head up), but that photogrammetric measurements of 100 randomly selected krill lengths were not significantly different from measurements of 100 randomly caught krill measured physically. During our investigation, we analysed three krill behavioural metrics: swimming speed, tortuosity, and vertical orientation under three behavioural states (undisturbed, feeding, and escape). We found that swim speed and tortuosity significantly increased when animals were feeding or exhibiting an escape response, but vertical orientation was not significantly different across states. Our investigation demonstrates that low-cost stereo video cameras can produce precise measurements that can be used for monitoring krill behaviour and population structure.

Simulated Annealing-Based Krill Herd Algorithm for Global Optimization

Recently, Gandomi and Alavi proposed a novel swarm intelligent method, called krill herd (KH), for global optimization. To enhance the performance of the KH method, in this paper, a new improved meta-heuristic simulated annealing-based krill herd (SKH) method is proposed for optimization tasks. A new krill selecting (KS) operator is used to refine krill behavior when updating krill’s position so as to enhance its reliability and robustness dealing with optimization problems. The introduced KS operator involves greedy strategy and accepting few not-so-good solutions with a low probability originally used in simulated annealing (SA). In addition, a kind of elitism scheme is used to save the best individuals in the population in the process of the krill updating. The merits of these improvements are verified by fourteen standard benchmarking functions and experimental results show that, in most cases, the performance of this improved meta-heuristic SKH method is superior to, or at least highly competitive with, the standard KH and other optimization methods.

Krill herd: A new bio-inspired optimization algorithm

In this paper, a novel biologically-inspired algorithm, namely krill herd (KH) is proposed for solving optimization tasks. The KH algorithm is based on the simulation of the herding behavior of krill individuals. The minimum distances of each individual krill from food and from highest density of the herd are considered as the objective function for the krill movement. The time-dependent position of the krill individuals is formulated by three main factors: (i) movement induced by the presence of other individuals (ii) foraging activity, and (iii) random diffusion. For more precise modeling of the krill behavior, two adaptive genetic operators are added to the algorithm. The proposed method is verified using several benchmark problems commonly used in the area of optimization. Further, the KH algorithm is compared with eight well-known methods in the literature. The KH algorithm is capable of efficiently solving a wide range of benchmark optimization problems and outperforms the exciting algorithms.

The functional biology and trophic role of krill (Thysanoessa raschii) in a Greenlandic fjord

Despite being a key zooplankton group, knowledge on krill biology from the Arctic is inadequate. The present study examine the functional biology and evaluate the trophic role of krill in the Godthabsfjord (64°N, 51°W) SW Greenland, through a combination of fieldwork and laboratory experiments. Krill biomass was highest in the middle fjord and inner fjord, whereas no krill was found offshore. The dominating species Thysanoessa raschii revealed a type III functional response when fed with the diatom Thalassiosira weissflogii. At food saturation, T. raschii exhibited a daily ration of 1% body C d−1. Furthermore, T. raschii was capable of exploiting plankton cells from 5 to 400 μm, covering several trophic levels of the pelagic food web. The calculated grazing impact by T. raschii on the fjord plankton community was negligible. However, the schooling and migratory behaviour of krill will concentrate and elevate the grazing in specific areas of the euphotic zone.

Ocean-bottom krill sex

For the first time the entire sequence of the mating behaviour of Antarctic krill (Euphausia superba) in the wild is captured on underwater video. This footage also provides evidence that mating can take place near the seafloor at depths of 400–700 m. This observation challenges the generally accepted concept of the pelagic lifestyle of krill. The mating behaviour observed most closely resembles the mating behaviour reported for a decapod shrimp (Penaeus). The implications of the new observation are also discussed.

Swarm characteristics of Antarctic krill Euphausia superba relative to the proximity of land during summer in the Scotia Sea

We studied the relationship between the proximity of land and the distribution and swarming characteristics of Antarctic krill across the Scotia Sea in January and February 2003. Krill swarms identified with a Simrad EK60 (38 kHz, 120 kHz) echosounder were grouped into 4 categories according to distance from shoreline: 0 to 50 km, 50 to 100 km, 100 to 200 km and >200 km. Cross-sectional areas of swarms were significantly larger inshore, with a mean value of 120 m(2) in the 0 to 50 km zone compared to < 80 m(2) further offshore. The packing concentration of krill within inshore swarms was also significantly greater, with an average density of 95 ind. m(-3) compared to between 24 and 31 ind. m(-3) elsewhere. A large proportion of the biomass was concentrated into a small number of large, dense swarms throughout the survey area, and this trend increased with decreasing distance from shore. The highest median number of swarms per km and krill acoustic biomass per km was found in the 50 to 100 km zone. However, a significantly greater number of large, biomass-rich swarms occurred in the 0 to 50 km zone compared to all other zones. Swarms in the 0 to 50 km zone were also significantly further apart. The majority of swarms were located in the upper 50 m during the daytime although they were marginally deeper in the night in offshore regions. Krill are likely to move between inshore and offshore environments continuously over their lifetimes. The change in krill behaviour between environments could be a response to local predatory threats over short spatial and temporal scales.

An experimental aquarium for observing the schooling behaviour of Antarctic krill (Euphausia superba)

Schooling behaviour of Antarctic krill was induced repeatedly over a period of one year in the Australian Antarctic Division research aquarium. The details of the laboratory setup suitable for krill to school are described. Light intensity and food condition were found to affect krill swimming patterns and schooling behaviour. Krill swam in polarised groups and responded as a group to objects that produced sharp contrasts but not to less distinct objects. Schools broke up when they encountered dense phytoplankton patches, and aggregated more tightly when kept with a white featureless background. The diel nature of school formation was observed under simulated natural light conditions with stronger and tighter schools during daytime and no obvious schooling behaviour during night. These behavioural patterns are further discussed in terms of their costs and benefits of feeding and predation risk, in conjunction with the diel vertical migration behaviour of krill.