Trends, cycles, interannual variability for three pelagic species west of the Antarctic Peninsula 1993-2008

Ross, Robin M.; Quetin, Langdon B.; Newberger, Timothy; Shaw, C. Tracy; Jones, Janice L.; Oakes, Stephanie; Moore, Kelly J.

doi:10.3354/meps10965

Cited by 50 publications

(62 citation statements)

References 114 publications

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“…Larval krill abundance was estimated from the amount of larvae caught by the 1 m 2 net with 350 μ m mesh size. For evaluating the condition of larvae in terms of feeding activity (indicated by the digestive gland size), growth rate and stomach content, larvae were sampled in the OW and the MIZ with a RMT or a Bongo net 42 , whereas in the PIZ, larvae were sampled by scientific divers using the plankton pump system MASMA (MAnguera SubMArina) 9 . MASMA consists of a motor-driven centrifugal pump filtering seawater through a zooplankton net with 200 μ m mesh size into a 2 l cod end, which was located inside an airtight container.…”

Section: Nature Ecology and Evolutionmentioning

confidence: 99%

“…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.…”

mentioning

confidence: 94%

“…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 .…”

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confidence: 99%

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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 Evolutionmentioning

confidence: 99%

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confidence: 94%

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confidence: 99%

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

et al. 2017

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“…Krill that over-wintered under the sea ice will have potentially remained in areas of open-ocean as the ice retreated. To be able to predict their distribution would require a dynamic representation of the sea ice field and of spring phytoplankton blooms that establish following its retreat, which are an important food source for krill and will affect their distribution in subsequent months Ross et al, 2014;Schmidt et al, 2014).…”

Section: Methodological Considerationsmentioning

confidence: 99%

Environmental correlates of Antarctic krill distribution in the Scotia Sea and southern Drake Passage

Silk

Thorpe

Fielding

et al. 2016

ICES Journal of Marine Science

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Antarctic krill is a key prey species for many vertebrate and invertebrate predators in the Southern Ocean; it is also an abundant fishery resource in the Scotia Sea and southern Drake Passage. Here, we identify environmental correlates of krill distribution utilizing acoustic data collected during an extensive international survey in January 2000. Separate models (at scales of 10-80 nautical miles) were derived for the full study area and for each of four subregions: northern and southern shelf waters, the seasonally ice-covered open ocean, and the generally ice-free open ocean. Krill distribution was strongly correlated with bathymetry; densities were higher over island shelves and shelf breaks and decreased with increasing distance offshore. Low krill densities occurred in areas of low chlorophyll concentration and high geostrophic velocity. Krill distribution was also related to sea level anomaly but relationships were not consistent between subregions. The models explained a maximum of 44% of the observed deviance in krill density, but did not reliably identify areas of high krill density in the open ocean, and explained a small proportion of the deviance (16%) in offshore areas covered seasonally by sea ice, probably because of the strong, residual influence of retreated ice. The commercial krill fishery is currently concentrated in shelf areas, where high densities of krill are most predictable. As krill are not predictable in the open ocean, the fishery is likely to remain principally a near-shore operation, and should be managed accordingly.

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“…They are important for nutrient cycling and carbon flux through the ecosystem (Laws 1977, Smetacek & Nicol 2005, and their massive biomass supports an important commercial fishery (Nicol et al 2012, Nicol & Foster 2016. A number of studies have shown a strong relationship between seasonal sea-ice extent and recruitment success of krill, emphasizing the importance of physical processes in winter (Loeb et al 1997, Atkinson et al 2004, Ross et al 2014, Saba et al 2014). In the last quarter of the 20th century, krill densities across the Southwest Atlantic sector of the Southern Ocean, near the Antarctic Peninsula, have reportedly declined between 36 and 80%, concomitant with declines in sea-ice extent and duration (Atkinson et al 2004).…”

Section: Introductionmentioning

confidence: 99%

Overwinter habitat selection by Antarctic krill under varying sea-ice conditions: implications for top predators and fishery management

Reiss¹,

Cossio²,

Santora³

et al. 2017

Mar. Ecol. Prog. Ser.

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Climate change will affect Antarctic krill Euphausia superba, krill-dependent predators, and fisheries in the Southern Ocean as areas typically covered by sea ice become ice-free in some winters. Research cruises conducted around the South Shetland Islands of the Antarctic Peninsula during winters with contrasting ice conditions provide the first acoustic estimates of krill biomass, habitat use, and association with top predators to examine potential interactions with the krill fishery. Krill abundance was very low in offshore waters during all winters. In Bransfield Strait, median krill abundance was an order of magnitude higher (8 krill m ), and this pattern was observed in all winters regardless of ice cover. Acoustic estimates of krill biomass were also an order of magnitude higher (~5 500 000 metric tons [t] in 2014) than a 15 yr summer average (520 000 t). Looking at krilldependent predators, during winter, crabeater seals Lobodon carcinophagus were concentrated in Bransfield Strait where ice provided habitat, while Antarctic fur seals Arctocephalus gazella were more broadly distributed. Krill overwinter in coastal basin environments independent of ice and primary production and in an area that is becoming more frequently icefree. While long-term projections of climate change have focused on changing krill habitat and productivity declines, more immediate impacts of ongoing climate change include increased risks of negative fishery−krill−predator interactions, alteration of upper trophic level community structure, and changes in the pelagic ecology of this system. Development of management strategies to mitigate the increased risk to krill populations and their dependent predators over management timescales will be necessary to minimize the impacts of long-term climate change.

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Trends, cycles, interannual variability for three pelagic species west of the Antarctic Peninsula 1993-2008

Cited by 50 publications

References 114 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

Environmental correlates of Antarctic krill distribution in the Scotia Sea and southern Drake Passage

Overwinter habitat selection by Antarctic krill under varying sea-ice conditions: implications for top predators and fishery management

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