Spatial and temporal operation of the Scotia Sea ecosystem: a review of large-scale links in a krill centred food web

Murphy, Eugene J.; Watkins, J. L.; Trathan, Philip N.; Reid, Keith; Meredith, Michael P.; Thorpe, Sally; Johnston, Nadine M.; Clarke, Andrew; Tarling, Geraint A.; Collins, Martin A.; Forcada, Jaume; Shreeve, Rachael S.; Atkinson, Angus; Korb, Rebecca E.; Whitehouse, M. J.; Ward, Peter; Rodhouse, P. G.; Enderlein, Peter; Hirst, Andrew G.; Martin, Anthony R.; Hill, Simeon L.; Staniland, Iain J.; Pond, David W.; Briggs, Dirk R.; Cunningham, Nathan; Fleming, Andrew

doi:10.1098/rstb.2006.1957

Cited by 306 publications

(326 citation statements)

References 294 publications

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“…5d). Our results contribute to existing studies investigating the krill life cycle around Antarctica and/or transport mechanisms that support the highest krill biomass in East Antarctica 30 , western Antarctic Peninsula 31 and Scotia Sea regions 16 .…”

Section: Nature Ecology and Evolutionsupporting

confidence: 61%

“…To examine the implications of our results on the overwinter dispersal of larvae, we undertook a Lagrangian model analysis of the diel vertical migration between the differentially moving ice and upper ocean 16,17 . The advection model indicates the vertical migration is important in determining the overwinter transport pathways and distribution of larvae during late winter.…”

Section: Resultsmentioning

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 Evolutionsupporting

confidence: 61%

Section: Resultsmentioning

confidence: 99%

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

et al. 2017

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“…The Antarctic Peninsula and the mountainous Scotia Arc that connect the Antarctic Peninsula with South America cause deflection of the current to the northeast, with the deeper waters flowing through a number of restricted passages that cut across the Scotia Arc. This also results in upwelling of deeper waters that has important influences on epipelagic ecological processes by disrupting the zonal pattern of the Southern Ocean (Murphy et al, 2007a;Atkinson et al, 2008). Large changes in the latitude of the flow of the Antarctic Circumpolar Current are also apparent in other regions, such as the PacificAntarctic Ridge and the Kerguelen Plateau (Williams et al, 2010;De Broyer and Koubbi, 2014).…”

Section: Physical Conditions and Circulation In The Antarcticmentioning

confidence: 99%

“…The signature of the bloom generated around South Georgia extends downstream over 2700 km to the east in the Antarctic Circumpolar Current (Korb et al, 2004;Murphy et al, 2007a). On the Kerguelen Plateau, natural iron fertilization caused by resuspension of sediments as the Antarctic Circumpolar Current flows past Kerguelen Island fuels one of the largest phytoplankton blooms in the high-nutrient low-chlorophyll Southern Ocean (Pollard et al, 2009;Quéguinér, 2013;Blain et al, 2015).…”

Section: Impacts Of Advection On Primary Production In the Antarcticmentioning

confidence: 99%

“…For example, Montes-Hugo et al (2009) demonstrated that surface chlorophyll maxima along the Antarctic Peninsula have shifted southward as ice duration has decreased and vertical mixing has increased in the northern Peninsula region. Northward advection in the Bellingshausen, Scotia and northern Weddell seas keeps sea ice at relatively low latitudes and therefore in areas of higher irradiance between fall and spring (Murphy et al, 2007a;Smith and Comiso, 2008). This allows a low level of primary production to continue even during winter, thereby providing a food source for larval and juvenile krill (Kottmeier and Sullivan, 1987;Thorpe et al, 2007).…”

Section: Impacts Of Advection On Primary Production In the Antarcticmentioning

confidence: 99%

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Advection in polar and sub-polar environments: Impacts on high latitude marine ecosystems

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et al. 2016

Progress in Oceanography

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a b s t r a c tWe compare and contrast the ecological impacts of atmospheric and oceanic circulation patterns on polar and sub-polar marine ecosystems. Circulation patterns differ strikingly between the north and south. Meridional circulation in the north provides connections between the sub-Arctic and Arctic despite the presence of encircling continental landmasses, whereas annular circulation patterns in the south tend to isolate Antarctic surface waters from those in the north. These differences influence fundamental aspects of the polar ecosystems from the amount, thickness and duration of sea ice, to the types of organisms, and the ecology of zooplankton, fish, seabirds and marine mammals. Meridional flows in both the North Pacific and the North Atlantic oceans transport heat, nutrients, and plankton northward into the Chukchi Sea, the Barents Sea, and the seas off the west coast of Greenland. In the North Atlantic, the advected heat warms the waters of the southern Barents Sea and, with advected nutrients and plankton, supports immense biomasses of fish, seabirds and marine mammals. On the Pacific side of the Arctic, cold waters flowing northward across the northern Bering and Chukchi seas during winter and spring limit the ability of boreal fish species to take advantage of high seasonal production there. Southward flow of cold Arctic waters into sub-Arctic regions of the North Atlantic occurs mainly through Fram Strait with less through the Barents Sea and the Canadian Archipelago. In the Pacific, the transport of Arctic waters and plankton southward through Bering Strait is minimal.In the Southern Ocean, the Antarctic Circumpolar Current and its associated fronts are barriers to the southward dispersal of plankton and pelagic fishes from sub-Antarctic waters, with the consequent evolution of Antarctic zooplankton and fish species largely occurring in isolation from those to the north. The Antarctic Circumpolar Current also disperses biota throughout the Southern Ocean, and as a result, the biota tends to be similar within a given broad latitudinal band. South of the Southern Boundary of the ACC, there is a large-scale divergence that brings nutrient-rich water to the surface. This divergence, along with more localized upwelling regions and deep vertical convection in winter, generates elevated nutrient levels throughout the Antarctic at the end of austral winter. However, such elevated nutrient levels do not support elevated phytoplankton productivity through the entire Southern Ocean, as iron concentrations are rapidly removed to limiting levels by spring blooms in deep waters. However, coastal http://dx

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Variability in transport pathways on and around the South Georgia shelf, Southern Ocean: Implications for recruitment and retention

et al. 2014

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The waters around South Georgia are among the most productive in the Southern Ocean, with zooplankton populations close to the island, in particular Antarctic krill, supporting vast colonies of higher predators. However, our understanding of the processes governing variability in the supply of these food resources is limited by the poor spatial and temporal resolution of available data. Here, we use a numerical modeling approach to examine the underlying physical processes driving the recruitment and retention of zooplankton to the South Georgia shelf. Variability in the magnitude and spatial distribution of recruitment was dominated by the proximity and orientation of the southern Antarctic Circumpolar Current front to the shelf edge. Shelf retention was highest for source sites on the southwest shelf, with the main transport routes off the shelf to the north and northwest. Retention was lowest in the austral summer and winter; in summer increased glacial melt drives stronger off‐shelf near‐surface currents, while in winter, stronger winds lead to an increase in off‐shelf transport. Of particular note was the prediction of a significant increase in retention for particles released throughout the shelf in April and July 2000. This period coincided with the development of pronounced anticlockwise shelf flows, associated with horizontal density gradients due to reduced wind mixing of shelf waters, and differences between shelf and oceanic waters, which significantly reduced off‐shelf transport rates. Such findings are crucial for understanding the influence of variability in physical processes on the ecosystem at South Georgia.

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Spatial and temporal operation of the Scotia Sea ecosystem: a review of large-scale links in a krill centred food web

Cited by 306 publications

References 294 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

Advection in polar and sub-polar environments: Impacts on high latitude marine ecosystems

Variability in transport pathways on and around the South Georgia shelf, Southern Ocean: Implications for recruitment and retention

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