Krill maintenance and experimentation at the australian antarctic division

Live Antarctic krill, Euphausia superba, have been maintained for experimental purposes at the Australian Antarctic Division since 1981. This population has been replenished on an annual basis with animals taken from the wild. Techniques used to capture and maintain live krill are discussed here, with particular reference given to the development of systems for their maintenance. Details are also provided for specific experimental systems that have been used to conduct research into the behaviour and physiology of krill both at-sea and in shore-based laboratories.     

Working with living krill – the people and the places

The fascination of Antarctic scientists with Antarctic krill and their capabilities has a long and varied history, and prompted many scientists to maintain and manipulate krill under laboratory conditions. Starting in the Discovery era with Mackintosh at the King Edward Point labs on South Georgia, 1930, scientists have collected krill from sailing vessels, small boats, inflatable zodiacs and large ice-breaking vessels. Krill have been maintained in small and large jars, deep rectangular tanks, large round tanks and in flow-through and recycling systems. They have been maintained both on board research vessels and in laboratories, in flowing seawater systems at ambient conditions and in temperature-controlled environmental rooms. A few researchers have transported living krill back to their home laboratories, for example tropical laboratories in Japan (Murano) and Australia (Ikeda), temperate laboratories (Nicol) in Australia, a northern European laboratory in Germany (Marschall) and a sunny maritime laboratory in California (Ross and Quetin). The goals have been varied: short-term experiments to understand in situ physiological rates, long-term experiments to test the effects of manipulations or controlled changes in environmental conditions, and behavioral responses. We take you on a brief historical tour as we trace the lineage of modern day research on living Antarctic krill.     

Working with living krill - the people and the places

The fascination of Antarctic scientists with Antarctic krill and their capabilities has a long and varied history, and prompted many scientists to maintain and manipulate krill under laboratory conditions. Starting in the Discovery era with Mackintosh at the King Edward Point labs on South Georgia, 1930, scientists have collected krill from sailing vessels, small boats, inflatable zodiacs and large ice-breaking vessels. Krill have been maintained in small and large jars, deep rectangular tanks, large round tanks and in flow-through and recycling systems. They have been maintained both on board research vessels and in laboratories, in flowing seawater systems at ambient conditions and in temperature-controlled environmental rooms. A few researchers have transported living krill back to their home laboratories, for example tropical laboratories in Japan (Murano) and Australia (Ikeda), temperate laboratories (Nicol) in Australia, a northern European laboratory in Germany (Marschall) and a sunny maritime laboratory in California (Ross and Quetin). The goals have been varied: short-term experiments to understand in situ physiological rates, long-term experiments to test the effects of manipulations or controlled changes in environmental conditions, and behavioral responses. We take you on a brief historical tour as we trace the lineage of modern day research on living Antarctic krill.     

Super-aggregations of krill and humpback whales in Wilhelmina Bay, Antarctic Peninsula

Ecological relationships of krill and whales have not been explored in the Western Antarctic Peninsula (WAP), and have only rarely been studied elsewhere in the Southern Ocean. In the austral autumn we observed an extremely high density (5.1 whales per km(2)) of humpback whales (Megaptera novaeangliae) feeding on a super-aggregation of Antarctic krill (Euphausia superba) in Wilhelmina Bay. The krill biomass was approximately 2 million tons, distributed over an area of 100 km(2) at densities of up to 2000 individuals m(-3); reports of such 'super-aggregations' of krill have been absent in the scientific literature for >20 years. Retentive circulation patterns in the Bay entrained phytoplankton and meso-zooplankton that were grazed by the krill. Tagged whales rested during daylight hours and fed intensively throughout the night as krill migrated toward the surface. We infer that the previously unstudied WAP embayments are important foraging areas for whales during autumn and, furthermore, that meso-scale variation in the distribution of whales and their prey are important features of this system. Recent decreases in the abundance of Antarctic krill around the WAP have been linked to reductions in sea ice, mediated by rapid climate change in this area. At the same time, baleen whale populations in the Southern Ocean, which feed primarily on krill, are recovering from past exploitation. Consideration of these features and the effects of climate change on krill dynamics are critical to managing both krill harvests and the recovery of baleen whales in the Southern Ocean.     

Relative changes in krill abundance inferred from Antarctic fur seal

Antarctic krill Euphausia superba is a predominant species in the Southern Ocean, it is very sensitive to climate change, and it supports large stocks of fishes, seabirds, seals and whales in Antarctic marine ecosystems. Modern krill stocks have been estimated directly by net hauls and acoustic surveys; the historical krill density especially the long-term one in the Southern Ocean, however, is unknown. Here we inferred the relative krill population changes along the West Antarctic Peninsula (WAP) over the 20th century from the trophic level change of Antarctic fur seal Arctocephalus gazella using stable carbon (δ(13)C) and nitrogen (δ(15)N) isotopes of archival seal hairs. Since Antarctic fur seals feed preferentially on krill, the variation of δ(15)N in seal hair indicates a change in the proportion of krill in the seal's diets and thus the krill availability in local seawater. For the past century, enriching fur seal δ(15)N values indicated decreasing krill availability. This is agreement with direct observation for the past ～30 years and suggests that the recently documented decline in krill populations began in the early parts of the 20th century. This novel method makes it possible to infer past krill population changes from ancient tissues of krill predators.     

Spatial and temporal variability in reproductive timing of Antarctic krill (Euphausia superba Dana)

Spawning dates of Antarctic krill, Euphausia superba Dana, were calculated from larval stage compositions, and corrected using data on maturity stage composition of the adult krill. Both original and literature data obtained from the Antarctic Peninsula-Bellingshausen Sea area and around the Antarctic continent were used. A time series (1975/76–1986/87) for several subareas of the Antarctic Peninsula-Bellingshausen Sea area indicates considerable variation in the krill spawning start, maxima and completion. In particular years (1975/76, 1980/81), krill spawning in the western Atlantic sector began relatively early, was intensive, and completed early. Some years (1977/78, 1981/82) were characterised by long and non-synchronised krill spawning. Compiled data sets for the Atlantic sector (1980/81), the entire Antarctic (1983/84) and the east Indian-west Pacific Antarctic waters (1981–85) reveal some spatial patterns in krill reproductive timing. In relation to spawning timing variation, the habitats of the krill population fall into five categories: (1) areas with an early beginning (late Novemberearly December) and a variable, but normally long, duration (3–3.5 months) of krill spawning; this is generally the southern boundary of the Antarctic Circumpolar Current, (2) areas with an early beginning, but a short duration of krill spawning (Gerlache Strait), (3) areas with a highly variable (within 1–1.5 months) beginning and a relatively long duration (ca. 3 months) of krill spawning (Bransfield Strait, Palmer Archipelago), (4) areas with a late beginning (late December–January) and a long duration of krill spawning (Bellingshausen Sea, D'Urville Sea, and Balleny Islands area), and (5) areas with a delayed beginning, but a very short duration (ca. 1.5 months) of krill spawning (Ross Sea slope, probably the Coastal Current area off the Lasarev Sea shelf and in the south-eastern Weddell Sea. These patterns can be partly explained by peculiarities of the ice regime in particular areas and by routes of krill movement within water circulation systems.     

Environmental response of upper trophic-level predators reveals a system change in an Antarctic marine ecosystem

Long-term changes in the physical environment in the Antarctic Peninsula region have significant potential for affecting populations of Antarctic krill (Euphausia superba), a keystone food web species. In order to investigate this, we analysed data on krill-eating predators at South Georgia from 1980 to 2000. Indices of population size and reproductive performance showed declines in all species and an increase in the frequency of years of low reproductive output. Changes in the population structure of krill and its relationship with reproductive performance suggested that the biomass of krill within the largest size class was sufficient to support predator demand in the 1980s but not in the 1990s. We suggest that the effects of underlying changes in the system on the krill population structure have been amplified by predator-induced mortality, resulting in breeding predators now regularly operating close to the limit of krill availability. Understanding how krill demography is affected by changes in physical environmental factors and by predator consumption and how, in turn, this influences predator performance and survival, is one of the keys to predicting future change in Antarctic marine ecosystems.     

Protection of the antarctic ecosystem: A study in international environmental law

Abstract

The Antarctic region constitutes a fragile eco‐system closely related to the unique features of the physical environment of that continent. The Antarctic Ocean is central to the region's living systems, with krill as the ecological basis of life in the ocean and on land. So far, man's impact upon the Antarctic environment has been negligible, but there is concern that overharvesting of krill and possible marine pollution resulting from any future offshore oil exploration may undermine the krill basis of the Antarctic ecosystem. The legal status of Antarctica is largely determined by the 1959 Antarctic Treaty, and especially by the inner circle of the currently fourteen “consultative”; status signatories. These states have given high priority to ecological considerations by enacting a series of environmental and conservationist regulations, as well as two conventions, one protecting the Antarctic seals and the other marine living resources in general. Environmental regulations will form an important part of the legal regime for the exploration and exploitation of the Antarctic mineral resources, primarily oil and gas. The Antarctic Treaty framework does not legally bind nonsignatory states, but under general international law all states are bound to refrain from inflicting damage upon the planet's environment. Also, some marine pollution conventions apply to the Antarctic waters, and the 1982 U.N. Convention on the Law of the Sea comprehensively covers the protection and preservation of the marine environment of all oceans and seas. The preservation of the Antarctic environment will remain a high priority irrespective of what legal regime will govern Antarctica after 1991 when the Antarctic Treaty may, and most probably will, be subject to review.     

Decrease in stomach contents in the Antarctic minke whale (Balaenoptera bonaerensis) in the Southern Ocean

The Antarctic minke whale (Balaenoptera bonaerensis) is one of the major krill predators in Antarctic waters. A reported decline in energy storage over almost two decades indicates that food availability for the whales may also have declined recently. To test this hypothesis, catch data from 20 survey years in the Japanese Whale Research Program in the Antarctic (JARPA) and its second phase (JARPA II) (1990/91–2009/10), which covered the longitudinal sector between 35°E and 145°W south of 58°S, were used to investigate whether there was any annual trend in the stomach contents weight of Antarctic minke whales. A linear mixed-effects analysis showed a 31 % (95 % CI 12.6–45.3 %) decrease in the weight of stomach contents over the 20 years since 1990/1991. A similar pattern of decrease was found in both males and females, except in the case of females sampled at higher latitude in the Ross Sea. These results suggest a decrease in the availability of krill for Antarctic minke whales in the lower latitudinal range of the research area. The results are consistent with the decline in energy storage reported previously. The decrease in krill availability could be due to environmental changes or to an increase in the abundance of other krill-feeding predators. The latter appears somewhat more likely, given the recent rapid recovery of humpback whale. Furthermore, humpback whales are not found in the Ross Sea, where both Antarctic krill and ice krill (Euphausia crystallorophias) are available, and where no change in prey availability for Antarctic minke whales is indicated.     

Antarctic krill breeding facilities at port of nagoya public aquarium

Antarctic fishes and invertebrates, including Antarctic krill, are generally stenothermal, and it is necessary to maintain water temperature about 0°C to keep them in good condition. Because the effects of nitrifying bacteria are limited by the extremely low temperature of about 0°C, biological filtration does not keep up with the deterioration of water quality resulting from the excrement of animals and un-eaten food. It is therefore necessary to exchange seawater frequently in our present cold-water aquarium.

We developed a new system at Port of Nagoya Public Aquarium (PNPA) that keeps Antarctic marine animals in good condition. The improved system increases the temperature of sea water to 10°C prior to biological filtration and thereby increases the effectiveness of the biological filter. The krill-rearing container was constructed inside the main tank so that the water flow inside the rearing container could be stopped. This avoids a rapid reduction of phytoplankton feed due to turnover of the seawater in the system while krill were fed. As a result of these improvements, long-term rearing, mass culture and reproduction of Antarctic krill are possible. We have exhibited Antarctic marine animals since the opening of PNPA in 1992, and we have exhibited Antarctic krill continuously since 1997. In this article, we detail the Antarctic krill breeding facilities at PNPA.     

Adult antarctic krill feeding at abyssal depths

Antarctic krill (Euphausia superba) is a large euphausiid, widely distributed within the Southern Ocean [1], and a key species in the Antarctic food web [2]. The Discovery Investigations in the early 20(th) century, coupled with subsequent work with both nets and echosounders, indicated that the bulk of the population of postlarval krill is typically confined to the top 150 m of the water column [1, 3, 4]. Here, we report for the first time the existence of significant numbers of Antarctic krill feeding actively at abyssal depths in the Southern Ocean. Biological observations from the deep-water remotely operated vehicle Isis in the austral summer of 2006/07 have revealed the presence of adult krill (Euphausia superba Dana), including gravid females, at unprecedented depths in Marguerite Bay, western Antarctic Peninsula. Adult krill were found close to the seabed at all depths but were absent from fjords close inshore. At all locations where krill were detected they were seen to be actively feeding, and at many locations there were exuviae (cast molts). These observations revise significantly our understanding of the depth distribution and ecology of Antarctic krill, a central organism in the Southern Ocean ecosystem.     

Discovery of ciliates reproducing in the gut of Antarctic krill

During a recent Antarctic research cruise (December 1994/February 1995), dissection of fresh Antarctic krill (Euphausia superba) on board ship revealed live motile ciliates in the gut of krill. Further observation of gut samples by scanning electron microscopy indicated that the ciliates were symbionts located within the gut. We inferred that the ciliates may have enabled the krill to digest a wider range of food items, and as a consequence, this had became an important strategy for Antarctic krill's survival in the Antarctic ecosystem. Received: 1 August 1996 / Accepted: 1 December 1996     

The effects of prey demography on humpback whale (Megaptera novaeangliae) abundance around Anvers Island, Antarctica

Baleen whales and Adelie penguins in the near-shore waters around the Antarctic Peninsula forage principally on Antarctic krill. Given the spatial overlap in the distribution of these krill predators (particularly humpback whales) and their dependence on krill, the goals of this paper are to determine if the inter-annual community structure and relative abundance of baleen whales around Anvers Island is related to krill demography and abundance, and if the potential exists for inter-specific interactions between Adelie penguins and baleen. We use whale sightings and prey data from both net tows and Adelie penguin stomach samples to correlate the abundance of humpback whales with krill demography and abundance from 1993 to 2001. We find significant relationships between whale abundance and the size–frequency distribution of krill targeted by Adelie penguins, as well as the foraging success of Adelie penguins. These findings suggest both krill predators share common prey preferences in the upper portions of the water column around Anvers Island. These findings highlight the need for better knowledge of baleen whale foraging ecology and inter-specific interactions with penguins, as sea ice and krill populations around the Antarctic Peninsula are affected by rapid changes in climate.     

The association of Antarctic krill Euphausia superba with the under-ice habitat

The association of Antarctic krill Euphausia superba with the under-ice habitat was investigated in the Lazarev Sea (Southern Ocean) during austral summer, autumn and winter. Data were obtained using novel Surface and Under Ice Trawls (SUIT), which sampled the 0-2 m surface layer both under sea ice and in open water. Average surface layer densities ranged between 0.8 individuals m(-2) in summer and autumn, and 2.7 individuals m(-2) in winter. In summer, under-ice densities of Antarctic krill were significantly higher than in open waters. In autumn, the opposite pattern was observed. Under winter sea ice, densities were often low, but repeatedly far exceeded summer and autumn maxima. Statistical models showed that during summer high densities of Antarctic krill in the 0-2 m layer were associated with high ice coverage and shallow mixed layer depths, among other factors. In autumn and winter, density was related to hydrographical parameters. Average under-ice densities from the 0-2 m layer were higher than corresponding values from the 0-200 m layer collected with Rectangular Midwater Trawls (RMT) in summer. In winter, under-ice densities far surpassed maximum 0-200 m densities on several occasions. This indicates that the importance of the ice-water interface layer may be under-estimated by the pelagic nets and sonars commonly used to estimate the population size of Antarctic krill for management purposes, due to their limited ability to sample this habitat. Our results provide evidence for an almost year-round association of Antarctic krill with the under-ice habitat, hundreds of kilometres into the ice-covered area of the Lazarev Sea. Local concentrations of postlarval Antarctic krill under winter sea ice suggest that sea ice biota are important for their winter survival. These findings emphasise the susceptibility of an ecological key species to changing sea ice habitats, suggesting potential ramifications on Antarctic ecosystems induced by climate change.     

Related antipodes: a comparative study on digestive endopeptidases from Northern krill and Antarctic krill (Euphausiacea)

The Antarctic krill, Euphausia superba, and the Northern krill, Meganyctiphanes norvegica, are closely related species but occupy significantly different trophic and climatic environments. E. superba holds a key position as a phytoplankton grazer in the Southern Ocean. The omnivorous M. norvegica is an important member of plankton communities in the Northeast Atlantic. Both species expressed high proteolytic activities which were dominated by serine proteinases. In the stomachs of Antarctic krill, activities of total proteinase, trypsin, and chymotrypsin were significantly higher than in Northern krill. In the midgut glands, however, total proteinase and trypsin activities were similar in both species, but chymotrypsin activity was significantly higher in Antarctic krill. Moreover, Antarctic krill expressed four trypsin isoforms while only one isoform appeared in Northern krill. Chymotrypsin was present in either species as one single isoform. Antarctic krill adapted to the low and patchy distribution of food by elevated enzyme activities and the expression of trypsin isoforms with slightly different catalytic properties. Presumably, these enzymes facilitate in concerted action the efficient utilization of proteins from phytoplankton, the major food. Northern krill, in contrast, seems not to be equipped to face food limitation. It expresses a “simple” or “basic” set of digestive enzymes for utilizing abundant and easily digestible prey.     

南极磷虾粉替代鱼粉对雌性黄鳝生长及生殖性能的影响

试验旨在研究南极磷虾粉替代鱼粉对雌性黄鳝(Monopterus albus)生长性能、体组成、抗氧化能力、非特异性免疫能力及生殖力的影响。选取二冬龄雌性黄鳝[初始体重(36.41±3.62) g]900尾,随机分为6组(每组3个重复,每个重复50尾),分别饲喂以南极磷虾粉替代饲料中0(对照)、20%、40%、60%、80%和100%的鱼粉制成的6种等氮等能配合饲料,试验周期12周。结果表明:20%磷虾粉替代鱼粉时,雌性黄鳝的增重率(WGR)、特定生长率(SGR)与对照组无显著性差异(P>0.05),但随着替代水平的进一步提高其生长性能显著下降(P<0.05)。20%替代组黄鳝肌肉的粗蛋白质含量显著高于其他组(P<0.05),而粗脂肪、粗灰分各组间无显著差异(P>0.05)。对黄鳝卵巢营养成分进行分析表明,当磷虾粉替代鱼粉比例超过60%时,其粗蛋白、粗脂肪含量均显著下降,水分含量逐渐升高(P<0.05)。进一步对黄鳝肝脏的抗氧化能力进行分析显示,当磷虾粉替代鱼粉比例大于40%时,其超氧化物歧化酶(SOD)活性逐渐下降,而丙二醛(MDA)含量逐渐升高; 100...     

Seabird and fur seal responses to vertically migrating winter krill swarms in Antarctica

Summary The foraging behaviour of fur seals and two species of surface feeding seabirds was observed over swarms of vertically migrating krill along the Antarctic Peninsula in July 1987. Fur Seal haul out patterns were correlated with krill in the upper 30 m of the water column. Krill moved to the surface at night; seals subsequently foraged from 1400-0700 hours before returning to floes. Foraging was continuous through the night. Dive duration decreased as krill moved up to the surface; shorter dives may have been more successful than longer ones. It is possible that very deep dives, which occur early in a foraging bout, represent more of an attempt to assess krill depth and distribution rather than being a genuine foraging effort. Seabirds responded to the presence of a surface krill swarm by circling over it and foraging; krill at depths greater than 30 m elicited directional flight and low frequencies of prey capture attempts. Both Snow Petrels and Antarctic Terns preyed on krill, but each species approached the swarms from different habitats. Snow Petrels primarily overflew areas covered by ice; terns preferred open water. This suggested that prey encounters are essentially opportunistic, although the search for prey is limited to rather specific marine habitats. This feature may be important to our understanding of the factors that determine the pelagic distribution of seabirds.     

The krill maturity cycle: a conceptual model of the seasonal cycle in Antarctic krill

A long-term study on the maturity cycle of Antarctic krill was conducted in a research aquarium. Antarctic krill were either kept individually or in groups for 8 months under different temperature and food conditions, and the succession of female maturity stages and intermoult periods were observed. In all cases regression and re-maturation of external sexual characteristics were observed, but there were differences in length of the cycle and intermoult periods between the experimental conditions. Based on these results, and information available from previous studies, we suggest a conceptual model describing seasonal cycle of krill physiology which provides a framework for future studies and highlight the importance of its link to the timings of the environmental conditions.     

Hierarchical patch dynamics and animal movement pattern

In hierarchical patch systems, small-scale patches of high density are nested within large-scale patches of low density. The organization of multiple-scale hierarchical systems makes non-random strategies for dispersal and movement particularly important. Here, we apply a new method based on first-passage time on the pathway of a foraging seabird, the Antarctic petrel (Thalassoica antarctica), to quantify its foraging pattern and the spatial dynamics of its foraging areas. Our results suggest that Antarctic petrels used a nested search strategy to track a highly dynamic hierarchical patch system where small-scale patches were congregated within patches at larger scales. The birds searched for large-scale patches by traveling fast and over long distances. Once within a large-scale patch, the birds concentrated their search to find smaller scale patches. By comparing the pathway of different birds we were able to quantify the spatial scale and turnover of their foraging areas. On the largest scale we found foraging areas with a characteristic scale of about 400 km. Nested within these areas we found foraging areas with a characteristic scale of about 100 km. The large-scale areas disappeared or moved within a time frame of weeks while the nested small-scale areas disappeared or moved within days. Antarctic krill (Euphausia superba) is the dominant food item of Antarctic petrels and we suggest that our findings reflect the spatial dynamics of krill in the area.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Ecological drivers of change at South Georgia: the krill surplus,or climate variability

Macaroni penguins Eudyptes chrysolophus are thought to be one of the most important mesopredators in the Southern Ocean having a greater impact on prey availability and abundance than any other seabird species. Their population centre has long been held to be South Georgia where populations were thought to comprise many million animals. Here we report the results of a recent census of the macaroni population at South Georgia undertaken using aerial survey methods. We report dramatic declines in numbers (～1.0 million breeding pairs) compared to numbers observed in the late 1970s (～5.4 million pairs), but show that these reductions have occurred principally at sites where numbers had previously been very large. During the breeding season, the main foraging grounds of birds from these sites overlap with the foraging grounds of Antarctic fur seals Arctocephalus gazella, a major competitor for their principal prey, Antarctic krill Euphausia superba. We suggest that the redistribution of the macaroni penguin population at South Georgia reflects the recent recovery of fur seal populations and thus the ongoing consequences of human intervention at South Georgia, a process which started more than 2 centuries previously. The implied resource competition and the observed population changes may also be exacerbated by recent reductions in Antarctic krill abundance which have been linked with reductions in seasonal sea ice following recent, rapid, regional warming in the Antarctic; however, the recovery of fur seal populations, and the ongoing recovery of krill‐eating whale populations argues that tropho‐dynamic interactions may be sufficient to explain the observed changes.