Distribution Of Antarctic Krill Research Articles

Predicted changes in the distribution of Antarctic krill in the Cosmonaut Sea under future climate change scenarios

Antarctic krill (Euphausia superba) are the key species of the ecological system in the Cosmonaut Sea. Long-term habitat alterations in krill due to climate change have been considered in recent decades. However, there is still a lack understanding about krill distribution. The MaxEnt model was used to forecast the suitable distribution area of krill for this study, which is based on data from the Coupled Model Intercomparison Project in its sixth phase (CMIP6) in the near future and far future. A total of 145 occurrence points and 15 environmental factors were selected to build the MaxEnt model. The current suitable habitat regions for krill were mostly detected in the western and central regions of the Cosmonaut Sea, which accounted for 10.07% of the total area. The most important environmental variables that influenced krill distribution were minimum surface solar radiation downward (ssrdmin), the mean temperature (tem) and the mean northward velocity (v). In the near future and far future, the suitable area of krill was seen to decline under all shared socioeconomic pathways (SSPs), with the smallest reduction under SSP1-2.6 and the greatest reduction under SSP5-8.5. The suitable area for krill dropped quicker from the near future to the far future than the present to the near future. Krill habitats were expected to shift to the poles. The tem continued to rise in the future under all SSP scenarios, particularly under the high radiative forcing scenario. The increase in water temperature is the main reason for the decrease in suitable areas for Antarctic krill. Our results show the future distribution of krill in the future and provide a reasonable reference for the ecological protection policy of the Cosmonaut Sea.

Antarctic krill likely avoid underwater gliders

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.

Winter distribution of juvenile and sub-adult male Antarctic fur seals (Arctocephalus gazella) along the western Antarctic Peninsula

Detailed knowledge of habitat use by marine megafauna is critical to understand their ecological roles and for the adequate management of marine resources. Antarctic fur seals (Arctocephalus gazella) inhabiting the Atlantic sector of the Southern Ocean prey largely on Antarctic krill (Euphausia superba) and play a central role in managing the krill fishery. Here, we assessed the demographic structure of three post-mating, early moult male haul-outs in the South Shetland Islands in early March and calculated the relative contribution of juveniles (1–4 years old) and sub-adult males (5–6 years) to the population remaining in maritime Antarctica after the breeding season. We also satellite tagged 11 juvenile males and four sub-adult males to analyze their movements and develop a species distribution model including both age classes. Our results highlighted the dominance of young individuals in the male population, revealed that they do not behave as central place foragers and identified key environmental drivers that affected their distribution at-sea throughout winter. Predicted potential foraging habitat overlapped highly with the known distribution of Antarctic krill, and identified the waters off the western Antarctic Peninsula and the Scotia Sea as the core of the distribution area of juvenile and sub-adult male Antarctic fur seals in winter. This pattern is similar to that of adult males but totally different from that of adult females, as the latter overwinter in areas at latitude 45–55° S. This segregation has implications for the ecology and management of the krill fishery.

Progress in Southern Ocean Biologyfrom the Indian Sector: Half-Decadal (2009-13) overview

This manuscript reviews the scientific insight gained from biological studies performed during Indian Southern Ocean Expeditions (ISOE) in the last 5 years. India’s research activities in the Southern Ocean (SO) region emphasize the importance of enhanced understanding of the SO processes, biogeochemical cycles, marine productivity and global climate change scenario. Under the aegis of Ministry of Earth Sciences, Government of India, concerted efforts are put in place by NCAOR to carryout research in Indian sector of the SO since 2004, with a primary focus to comprehend the role (response) of the SO in regional and global climate variability. The findings discussed here are based on of a wide array of biological data collected during different expeditions (4th to 7th expedition conducted during 2009-13) which highlights: causal mechanisms of variability in phytoplankton community structure and productivity among frontal regions (i.e.,Subtropical Front (STF), Subantarctic Front (SAF) and Polar Front (PF)), patterns of phytoplankton biomass distribution within and among the fronts, role of diatoms in deciphering environmental change, food-web dynamics, bio-optical characterisation of water column, response of bacteria and phytoplankton to micronutrient amendments, biochemical profiling of squids, distribution of Antarctic krill, and occurrence of different marine mammals/birds in the above frontal regions. Here, we attempt to succinctly capture the findings of published literature engendered from ISOE to put forward our present perception of this lesser-understood region in the SO. This document is expected to contribute to an increased understanding of the Indian sector of SO, besides providing the much needed visibility to our ongoing scientific endeavours among the international community.

Dispatches

Dispatches

Abundance and distribution of Antarctic krill (Euphausia superba) nearshore of Cape Shirreff, Livingston Island, Antarctica, during six austral summers between 2000 and 2007

Abundance and distribution of Antarctic krill ( Euphausia superba ) in the nearshore waters north of Livingston Island, Antarctica, were characterized from six small-boat surveys conducted in late January or early February from 2000 to 2007. The first three surveys (2000, 2002, 2004) were conducted using a 120 kHz split-beam echosounder to measure water column acoustic backscatter. The last three surveys (2005–2007) were conducted using 38 kHz and 200 kHz single-beam echosounders. A portion of the acoustic backscatter was attributed to Antarctic krill based on the results of net tows, underwater video observations, and a multiple-frequency acoustic classification algorithm. The annual mean krill biomass density in the survey area ranged from 11 to 84 g·m–2. Results are compared with the western Scotia Sea area of the US Antarctic Marine Living Resources (AMLR) program’s acoustic surveys of krill biomass density for the same years. Nearshore krill biomass densities were significantly larger (t test, p < 0.05), more stable, and the coefficients of variation were smaller than the much larger AMLR surveys. Increased competition between seals, penguins, and humans for the nearshore krill resource, especially during the austral summer months, could impact the recruitment success of these land-based krill predators. Implications of nearshore krill biomass on small-scale management units are discussed.

Modeling the krill transport pathways in the Scotia Sea: spatial and environmental connections generating the seasonal distribution of krill

Abstract A coupled physical–biological model analysis was undertaken to examine the seasonal development of the distribution of antarctic krill (Euphausia superba Dana) in the Scotia Sea. The origin and fate of krill observed during the CCAMLR 2000 survey were studied using output from the OCCAM model. Lagrangian particle tracking for the period prior to the survey showed the expected dominance of the west to east flow of material associated with the main direction of the current flow, but there was no simple association of particle transport with any of the fronts of the Antarctic Circumpolar Current. Most of the krill were associated with areas to the south of the Antarctic Circumpolar Current in the Weddell–Scotia Confluence (WSC) and farther east in Weddell Sea-influenced waters. Examining the pathways of krill transport in relation to satellite-derived sea-ice distributions suggests that particles present in the high krill biomass regions in January would have come from areas that were covered by sea-ice during late winter/early spring (September–October). The results of Eulerian grid-based simulations of the development of the biomass distribution after the survey period showed transport of particles around South Georgia, probably in association with the Southern Antarctic Circumpolar Current Front. However, many of the krill encountered in the eastern Scotia Sea would have exited toward the east, passing north of the South Sandwich Islands, probably in association with the Southern Boundary of the Antarctic Circumpolar Current and Weddell Sea waters that penetrate to the north in this area. These krill may return to more southern regions where further spawning is possible in later years. Simulations of particle tracks that included diurnal vertical migration showed that krill behavior could modify the pathways of transport, although the current flows probably dominate the movement of krill in open ocean regions. This study suggests that the summer distribution of krill in the Scotia Sea is connected to the winter sea-ice distribution and probably to the pattern and rate of the spring sea-ice retreat. Many of the krill in the survey region in the summer of 1999/2000 came from under the sea-ice in the eastern Scotia Sea, the southern Scotia Arc, and the northern Weddell Sea. This highlights that the spatial association of the sea-ice with the Weddell–Scotia Confluence and frontal regions of the Antarctic Circumpolar Current during winter and spring will be crucial in determining the summer krill distribution. Variation in the extent and timing of sea-ice retreat, and fluctuations in Weddell–Scotia Confluence and Scotia Sea flows, will change the pathways of transport resulting in large changes in the distribution of the krill during summer.

Biomass and energy transfer to baleen whales in the South Atlantic sector of the Southern Ocean

Baleen whales are an important group of predators on Antarctic krill in the Southern Ocean. During the CCAMLR 2000 Survey to estimate the biomass and distribution of Antarctic krill, International Whaling Commission observers carried out a visual line transect survey to estimate the number of baleen whales occurring in the survey area. This paper reviews techniques used to estimate krill consumption by baleen whales and in combination with estimates of whale abundance estimates of krill consumption are generated for the South Atlantic sector of the Southern Ocean. This survey estimates that the present populations of whales feeding in this region are likely to consume approximately 1.6 million tonnes, but possibly up to as much as 2.7 million tonnes of krill within the summer season. Although this only represents 4–6% of the estimated krill biomass in the region (and probably less than this percentage of the total annual krill production), the depleted numbers of baleen whales resulting from past or current whaling activities should be taken into account when setting quotas for the commercial exploitation of krill if there is to be a recovery to pre-exploitation biomass levels of baleen whales.

Factors influencing the distribution, biomass, and productivity of phytoplankton in the Scotia Sea and adjoining waters

During January and February 2000 four research vessels,f rom Russia,t he UK, Japan, and the United States, conducted an oceanographic survey with 137 hydrographic stations within the Scotia Sea and adjoining waters as part of a survey sponsored by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) to estimate the biomass and distribution of Antarctic krill in the Scotia Sea. Chlorophyll-a (Chl-a) measurements showed great variability in phytoplankton biomass within the Scotia Sea,wi th some areas having among the lowest Chl-a concentrations found in Antarctic waters (o0.1mgm_3 in surface waters) while other areas were among the richest with 410mgm_3. This paper describes the distribution and concentration of Chl-a in the upper 100m of the water column and relates the Chl-a profiles at individual stations to profiles of upper water-column stability,t o the depth of the upper mixed layer, and to the mixing of different water masses. The 58 stations with the lowest Chl-a values in surface waters also had low values for integrated Chl-a (33.9+-9.5mgm_2) and a Chl-a maximum at depths of between 70 and 90m,in contrast to all other stations where deep Chl-a maxima did not occur. The T/S diagrams at many of these stations were indicative of Antarctic Circumpolar Current (ACC) waters. The central Scotia Sea and areas to the west and north of South Georgia had significantly higher integrated Chl-a values (98.1+-46.0mgm_2, n ¼ 57),i n addition to five stations with very high Chl-a values (mean of 359+-270mgm_2). The mean rate of integrated primary production,wh ich was estimated using the Chl-a data and the mean incident solar radiation measured from previous cruises as well as from satellite data,w as estimated to be 994mg carbon m_2 day_1. The temperature profiles at these stations suggested that considerable interleaving and mixing of water types had occurred,w hich was also evident in the T/S diagrams,w hich indicated mixing of ACC waters with coastal waters originating from Bransfield Strait or theWeddell Sea. There was no significant correlation between integrated Chl-a values and the profiles of upper water column stability or the depth of the upper mixed layer. The spatial variability in phytoplankton biomass within the Scotia Sea is discussed in relation to the hypothesis that low iron concentrations are the major factor controlling phytoplankton biomass in these pelagic Antarctic waters and that concentrations of iron available for phytoplankton uptake are strongly influenced by fronts and the mixing of different water masses.

An overview of the biological/oceanographic survey by the RTV Umitaka-Maru III off Adelie Land, Antarctica in January–February 1996

A biological/oceanographic survey was conducted around the Antarctic Divergence (AD) off Adelie Land, Antarctica by the RTV Umitaka-Maru III of Tokyo University of Fisheries in the 1995/1996 Austral summer. Investigations were included (1) characteristics of oceanic structure, (2) primary production and related upper water mass structure, (3) phytoplankton community structure, (4) zooplankton community structure, (5) distribution of Antarctic krill, and (6) optical properties and development of biooptical algorithms for future use of ocean color remote sensing in monitoring phytoplankton biomass. The existence of dense water on the continental slope suggests that the survey area is one of major sources of the Antarctic Bottom Water. We observed a southward meandering of ACC, which allowed the warmer, saline offshore water to intrude south in the eastern part of the area. This east–west gradient in water mass seems to influence the formation of the local trophic structure in the research area. In the western area, primary productivity was high, and diatoms and copepods dominated, particularly around the AD. The eastern part, however, showed low primary productivity, with a relative dominance of pico- and nanophytoplankton and high abundance of salps. Antarctic krill was distributed mostly in the south of the AD, and its biomass was low compared to previous records, both from adjacent areas and from other Antarctic regions. A biooptical algorithm obtained from this study did not agree with the conventional global algorithm, suggesting the need for constructing local algorithms appropriate for Antarctic Waters.

Seasonal variability in the distribution of Antarctic krill, Euphausia superba, west of the Antarctic Peninsula

A unique Antarctic data set from four multidisciplinary cruises (spring, Nov 1991; summer, Jan–Feb 1993; fall, Mar–May 1993; winter, Aug–Sept 1993) was analyzed to provide a description of seasonal variability in the distribution and abundance of Antarctic krill, Euphausia superba, west of the Antarctic Peninsula. Analyses of acoustic observations revealed distinct seasonal variations in estimates of krill abundance, the dimensional parameters used to characterize individual krill aggregations, the geographic area over which krill were acoustically detected, and the depth distribution of krill biomass. Spatially averaged estimates of krill biomass were an order of magnitude higher in spring (32 g m -2) and summer (95 g m -2) compared to fall (12 g m -2) and winter (8 g m -2). In summer, krill were detected throughout the region and most of the krill biomass was associated with aggregations of small cross-sectional area (<2000 m 2) and high mean biomass (>150 g m -3), which were positioned in the upper 50 m of the water column. Winter observations, in contrast, were characterized by the absence of krill throughout most of the region and aggregations occuring deeper than 100 m with large cross-sectional area (>10000 m 2) and low mean biomass (<10 g m -3). Two features common to all seasons were the presence of higher krill biomass (>50 g m -2) at selected locations on the inner shelf and the disproportionate contribution, in terms of total krill biomass (>80%), by a small number of aggregations (<20%). The length frequency distributions of krill collected by nets showed an across-shelf pattern of larger (>40 mm) krill positioned offshore of smaller krill (32–38 mm) in all seasons except winter. Synthesis of these data and historical observations suggest that there is a seasonal shift in the primary habitat of krill and that changes in krill behavior are an important factor affecting variations in krill distributions.

Sampling biological characteristics of krill: Effect of heterogeneous nature of swarms

An effect of the very patchy distribution of Antarctic krill (Euphausia superba Dana) in various forms of aggregation is that a single swarm may not provide an unbiased estimate of population parameters such as mean length of krill in the local area. Here, we analyse the number of samples required to estimate the characteristics of a local population as precisely as if there were no differences between krill swarms in terms of their biological composition. Krill were intensively sampled over different spatial and temporal scales around South Georgia in 1981 and 1982, and in the Bransfield Strait in 1985. These varied from replicate hauls at a single station over 24 h and repeat sampling in restricted areas over periods of 6 to 14 d to regional surveys around South Georgia and in the Bransfield Strait. Various biological characteristics were measured such as length, maturity, moult stage and feeding state. Depending upon the biological characteristic examined and the area covered by the sampling programme, the number of samples needed to obtain the same degree of precision as would be found in the absence of heterogeneity varied from 3 to > 80 samples. This has important implications for the design of net-sampling programme for monitoring krill populations.

Abundance and distribution of krill in the ice edge zone of the Weddell Sea, austral spring 1983

The effect of the ice edge zone on the abundance and distribution of Antarctic krill was investigated by acoustic and net sampling methods in the northwestern Weddell Sea during austral spring, 1983. The dominant acoustic target was Euphausia superba which occurred over the entire study area in the upper 100 m of the water column, either in aggregations or loosely defined layers. The vertical depth distribution under the pack ice was similar to that of open water. Average krill biomass under the ice ranged from 1 to 68 g m −2 and in open water range from 10 to 100 g m −2. Another euphausiid, Thysanoessa macrura, appeared to be ubiquitous but was much less abundant than E. superba. T. macrura also formed aggregations. All stages were found in open water, but only adults and juveniles under the ice. A few adults and larvae of a third euphausiid, E. frigida, were found only in open water. Salps, which were abundant in open water, were not present under the pack ice. The pack ice directly influenced the abundance and distribution of young krill. Juvenile E. superba were much more abundant under the ice than in open water north of the ice edge. Numerous observations were made of juvenile krill feeding on the undersurface of ice floes where chlorophyll concentrations were much greater than in the water column below. These observations appear to indicate that the pack ice serves as a giant nursery area for young krill, providing a refugium from predators as well as a vast food resource that may be critical to the survival of overwintering juvenile E. superba.