The absence of krill from the South Georgia zone, winter 1983

Heywood, R. B.; Everson, Inigo; Priddle, J.

doi:10.1016/0198-0149(85)90085-8

Cited by 84 publications

(53 citation statements)

References 8 publications

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“…Concentrations of chl a within the sea ice and water column in the pack-ice zone found during our study were consistent with previous data from the Weddell Sea and other regions of the Southern Ocean in winter (western Antarctic Peninsula region, northwestern Weddell Sea, Lazarev Sea, East Antarctica) 8,[13][14][15][23][24][25][26] . Previous larval krill winter studies in the western Antarctic Peninsula region demonstrate significantly different growth rates between years, at the same time and location, due to variable chl a concentration in the water column.…”

Section: Nature Ecology and Evolutionsupporting

confidence: 92%

The winter pack-ice zone provides a sheltered but food-poor habitat for larval Antarctic krill

et al. 2017

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A ntarctic krill Euphausia superba, a key species in Southern Ocean food webs 1 , plays a central role in ecosystem processes and community dynamics of apex predators, and is the target of a commercial fishery 2 . Krill spawn in late spring and their larvae develop during summer, autumn and under the ice in winter to emerge as juveniles in the following spring. The newly spawned eggs sink from the surface to up to 1,000 m depth where they hatch and the developing larvae actively swim upwards to feed in the upper water column 1 . Larval Antarctic krill have low lipid reserves, which are insufficient to support long periods of starvation. Therefore, winter, when primary production is minimal, is assumed to be a critical bottleneck for larval krill development and hence recruitment to the adult population 3,4 . Present hypotheses suggest that high algal biomass in winter sea ice enhances larval krill winter-feeding conditions and growth [5][6][7][8] . This implies that larvae have access to this high algal biomass within the sea ice. However, recent observations 9,10 indicate that the linkage between sea ice and krill recruitment success is not as direct as has been suggested. The timing of ice-edge advance and annual ice-season duration is highly variable, and does not necessarily show a clear link to krill recruitment in the following year ( Supplementary Figs. 1 and 2). Along the Antarctic Peninsula, adult krill have a five to six year population cycle with oscillations in biomass exceeding an order of magnitude 9 . According to bioenergetics models, part of the variability is due to interannual variation in reproductive output 11 as well as autumn blooms that may govern the possible overwinter survival rate of larvae 11,12 . In the Bransfield Strait, three krill winter surveys have shown that krill abundance is an order of magnitude higher than in summer, regardless of concurrent sea-ice conditions 10 A dominant Antarctic ecological paradigm suggests that winter sea ice is generally the main feeding ground for krill larvae. Observations from our winter cruise to the southwest Atlantic sector of the Southern Ocean contradict this view and present the first evidence that the pack-ice zone is a food-poor habitat for larval development. In contrast, the more open marginal ice zone provides a more favourable food environment for high larval krill growth rates. We found that complex under-ice habitats are, however, vital for larval krill when water column productivity is limited by light, by providing structures that offer protection from predators and to collect organic material released from the ice. The larvae feed on this sparse ice-associated food during the day. After sunset, they migrate into the water below the ice (upper 20 m) and drift away from the ice areas where they have previously fed. Model analyses indicate that this behaviour increases both food uptake in a patchy food environment and the likelihood of overwinter transport to areas where feeding conditions are more favourable in spring.

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Section: Nature Ecology and Evolutionsupporting

confidence: 92%

The winter pack-ice zone provides a sheltered but food-poor habitat for larval Antarctic krill

et al. 2017

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“…If such a shift in the SACCF occurs about a month after spawning time, the effect may be that very few krill reach South Georgia and the population abundance is reduced. This type of variability may contribute to the strong fluctuations in krill abundance reported for waters around South Georgia (Heywood et al, 1985;Priddle et al, 1988).…”

Section: Key Processes Controlling Krill Transportmentioning

confidence: 99%

Transport of Antarctic krill (Euphausia superba) across the Scotia Sea. Part I: Circulation and particle tracking simulations

Fach

Klinck

2006

Deep Sea Research Part I: Oceanographic Research Papers

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The Harvard Ocean Prediction System (HOPS) is configured to simulate the circulation of the Scotia Sea and environs. This is part of a study designed to test the hypothesis that Antarctic krill (Euphausia superba) populations at South Georgia in the eastern Scotia Sea are sustained by import of individuals from upstream regions, such as the western Antarctic Peninsula. Comparison of the simulated circulation fields obtained from HOPS with observations showed good agreement. The surface circulation, particularly through the Drake Passage and across the Scotia Sea, matches observations, with its northeastward flow characterized by three high-speed fronts. Also, the Weddell Sea and the Brazil Current, and their associated transports match observations. In addition, mesoscale variability, an important component of the flow in this region, is found in the simulated circulation and the model is overall well suited to model krill transport. Drifter simulations conducted with HOPS showed that krill spawned in areas coinciding with known krill spawning sites along the west Antarctic Peninsula continental shelf can be entrained into the Southern Antarctic Circumpolar Current Front (SACCF). They are transported across the Scotia Sea to South Georgia in 10 months or less. Drifters originating on the continental shelf of the Weddell Sea can reach South Georgia as well; however, transport from this region averages about 20 months. Additional simulations show that such transport is sensitive to changes in wind stress and the location of the SACCF. The results of this study show that krill populations along the Antarctic Peninsula and the Weddell Sea are possible source populations that can provide krill to the South Georgia population. However, successful transport of krill to South Georgia is shown to depend on a multitude of factors, such as the location of the spawning area and timing of spawning, and variations in the location of the SACCF. Therefore, this study provides insight into which environmental factors control the successful transport of krill across the Scotia Sea and with it a better understanding of krill distribution in the region. r

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“…Similar seasonal reductions in the biomass of zooplankton have been observed in studies of other regions of the antarctic continental shelf (e.g., copepods; Schnack-Schiel et al, 1998), and for Antarctic krill in particular (Heywood et al, 1985;Siegel 1988Siegel , 1989Lascara et al, 1999;and see review in Siegel, 2000). A seasonal decrease in Antarctic krill biomass may not be a consistent feature across all regions, however, as South Georgia typically supports a strong krill fishery during winter (e.g., Murphy et al, 1997).…”

Section: M)mentioning

confidence: 50%

“…Siegel (2005) and Lascara et al (1999) also recognized the alternate possibility, however, that the apparent seasonal decrease in krill abundance from spring/summer to fall/winter may stem from krill migrating to deeper portions of the water column, beyond the reach of standard survey depths (200 m). In support of this latter view, some studies have suggested that krill may take on a bentho-pelagic existence during winter, based on light trap catches under fast ice in waters shallower than 50 m in depth (Kawaguchi et al, 1986) and acoustic observations supplemented by occasional net samples of krill layers from the bottom to 20 m above near South Georgia (Heywood et al, 1985). Benthic diatom species have also been observed in stomach content analyses of krill collected in winter in Peninsula waters (Ligowski, 2000).…”

Section: 42b Wintermentioning

confidence: 69%

“…There is some evidence, however, that Antarctic krill may on occasion be associated with the bottom, from a bottom-mounted light trap in a shallow water region under fast ice (Kawaguchi et al, 1986), acoustic observations in conjunction with trawl catches (Heywood et al, 1985), and two observations made by a remote-operated vehicle (ROV) within a meter of the bottom (Gutt and Siegel, 1994).…”

Section: 42a Vertical Movementsmentioning

confidence: 99%

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Distribution, patchiness, and behavior of Antarctic zooplankton, assessed using multi-frequency acoustic techniques

Lawson¹

2006

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The physical and biological forces that drive zooplankton distribution and patchiness in an antarctic continental shelf region were examined, with particular emphasis on the Antarctic krill, Euphausia superba. This was accomplished by the application of acoustic, video, and environmental sensors during surveys of the region in and around Marguerite Bay, west of the Antarctic Peninsula, in the falls and winters of 2001 and 2002. An important component of the research involved the development and verification of methods for extracting estimates of ecologically-meaningful quantities from measurements of scattered sound. The distribution of acoustic volume backscattering at the single frequency of 120 kHz was first examined as an index of the overall biomass of zooplankton. Distinct spatial and seasonal patterns were observed that coincided with advective features. Improved parameterization was then achieved for a theoretical model of Antarctic krill target strength, the quantity necessary in scaling measurements of scattered sound to estimates of abundance, through direct measurement of all necessary model parameters for krill sampled in the study region and survey period. Methods were developed for identifying and delineating krill aggregations, allowing the distribution of krill to be distinguished from that of the overall zooplankton community. Additional methods were developed and verified for estimating the length, abundance, and biomass of krill in each acoustically-identified aggregation. These methods were applied to multifrequency acoustic survey data, demonstrating strong seasonal, inter-annual, and spatial variability in the distribution of krill biomass. Highest biomass was consistently associated with regions close to land where temperatures at depth were cool. Finally, the morphology, internal structure, and vertical position of individual krill aggregations were examined. The observed patterns of variability in aggregation characteristics between day and night, regions of high versus low food availability, and in the presence or absence of predators, together reinforced the conclusion that aggregation and diel vertical migration represent strategies to avoid visual predators, while also allowing the krill access to shallowly-distributed food resources. The various findings of this work have important implications to the fields of zooplankton acoustics and Antarctic krill ecology, especially in relation to the interactions of the krill with its predators.

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The absence of krill from the South Georgia zone, winter 1983

Cited by 84 publications

References 8 publications

The winter pack-ice zone provides a sheltered but food-poor habitat for larval Antarctic krill

The winter pack-ice zone provides a sheltered but food-poor habitat for larval Antarctic krill

Transport of Antarctic krill (Euphausia superba) across the Scotia Sea. Part I: Circulation and particle tracking simulations

Distribution, patchiness, and behavior of Antarctic zooplankton, assessed using multi-frequency acoustic techniques

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