Scotia Arc Acari: antiquity and origin

The Scotia Arc comprises South Georgia, South Sandwich, South Orkney and South Shetland Islands together with the Antarctic Peninsula. Free-living Acari of the Scotia Arc contain immigrant and endemic elements. Transport of immigrant species to and within the Maritime Antarctic has been via Holocene storms and ocean currents. Most immigrants are Gamasida, Oribatida and Acaridida while Actinedida dominate the endemic element. Immigrant species on South Georgia share common 'sub-Antarctic' affinities with South Indian and, to a lesser extent, South Pacific Ocean island faunas. In contrast, immigrants to the rest of the Scotia Arc and Bouvetøya on the mid-Atlantic Ridge, form a robust 'Maritime Antarctic' Province group. The endemic component is of largely Tertiary origin and, like that of Continental Antarctica, dominated by a few cosmopolitan families and genera of Actinedida. There are no bona fide pan-Antarctic species and little evidence that Continental and Maritime Antarctic faunas have a common ancestry, indeed the Continental endemic fauna is entirely montane while that of Maritime Antarctica is coastal. The presence of common Maritime Antarctic/South Pacific island genera corroborate the Antarctic Peninsula as being derived from a South Pacific island archipelago which collided with Continental Antarctica during the Tertiary period.     

Diversity, relative abundance, new locality records and population structure of Antarctic demersal fishes from the northern Scotia Arc islands and Bouvetøya

A primary objective of the ICEFISH 2004 cruise was to collect and study notothenioid fishes from remote localities in the Atlantic sector of the Southern Ocean. Nearly 1 month was devoted to bottom trawling for fishes on the shelf and upper slope (to 1,000 m) areas around Shag Rocks, South Georgia, South Sandwich Islands and Bouvetøya. The focus was on the latter two locations, because their faunas are more poorly known. Eight species were collected at Shag Rocks with Patagonotothen guntheri most abundant; 17 at South Georgia with Lepidonotothen nudifrons, L. larseni and Gobionotothen gibberifrons most abundant; 13 at the South Sandwich Islands with L. larseni, L. nudifrons and G. gibberifrons most abundant; and 11 at Bouvetøya with L. larseni, Macrourus holotrachys and L. squamifrons most abundant. Ten new locality records were established: Shag Rocks (1), South Georgia (1), South Sandwich Islands (5), South Sandwich Trench at 5,350 m (1) and Bouvetøya (2). Total known demersal fish diversity on the shelf and upper slope at Shag Rocks/South Georgia, South Sandwich Islands and Bouvetøya is 42, 31 and 17 species, respectively. To examine population structure in the four most abundant notothenioids at Bouvetøya (L. larseni, L. squamifrons, Notothenia coriiceps and Chaenocephalus aceratus), we examined the ND2 portion of mitochondrial DNA. Chaenocephalus aceratus, N. coriiceps and L. larseni exhibited no significant genetic differentiation in comparison with samples from localities in the Scotia Sea and the Antarctic Peninsula. However, L. squamifrons showed significant genetic differentiation between the South Shetlands and Bouvetøya populations (F _ST = 0.189, P = 0.015). Thus, these data combined with previous studies of two other notothenioids suggest that five of the six notothenioid species at Bouvetøya are not genetically differentiated from other localities in the Atlantic sector of the Southern Ocean. The location of Bouvetøya within the Antarctic Circumpolar Current and the long (1–2 years) pelagic stages of the notothenioids at Bouvetøya may be at least partly responsible for this genetic homogeneity.     

Can the chemistry of otolith nuclei determine population structure of Patagonian toothfish Dissostichus eleginoides?

Otolith nucleus chemistry resolved the population structure of Patagonian toothfish Dissostichus eleginoides , an exclusively marine species, along the Patagonian Shelf and North Scotia Ridge out to South Georgia in the Southern Ocean. Concentrations of ⁵⁵Mn, ⁸⁸Sr and ¹³⁷Ba, ratioed to ⁴²Ca, showed a sharp population boundary in the vicinity of the Polar Front, between South Georgia and the North Scotia Ridge. These results validated otolith nucleus chemistry as a technique for examining population structure in Patagonian toothfish, demonstrating that otolith nucleus chemistry can discriminate between populations even in fully marine environments. Moreover, the nucleus chemistry indicated population heterogeneity not previously detected, suggesting the possibility of more than one South American population, and also suggested some South American-caught fish had moved from South Georgia.     

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

The Scotia Sea ecosystem is a major component of the circumpolar Southern Ocean system, where productivity and predator demand for prey are high. The eastward-flowing Antarctic Circumpolar Current (ACC) and waters from the Weddell-Scotia Confluence dominate the physics of the Scotia Sea, leading to a strong advective flow, intense eddy activity and mixing. There is also strong seasonality, manifest by the changing irradiance and sea ice cover, which leads to shorter summers in the south. Summer phytoplankton blooms, which at times can cover an area of more than 0.5 million km2, probably result from the mixing of micronutrients into surface waters through the flow of the ACC over the Scotia Arc. This production is consumed by a range of species including Antarctic krill, which are the major prey item of large seabird and marine mammal populations. The flow of the ACC is steered north by the Scotia Arc, pushing polar water to lower latitudes, carrying with it krill during spring and summer, which subsidize food webs around South Georgia and the northern Scotia Arc. There is also marked interannual variability in winter sea ice distribution and sea surface temperatures that is linked to southern hemisphere-scale climate processes such as the El Ni?o-Southern Oscillation. This variation affects regional primary and secondary production and influences biogeochemical cycles. It also affects krill population dynamics and dispersal, which in turn impacts higher trophic level predator foraging, breeding performance and population dynamics. The ecosystem has also been highly perturbed as a result of harvesting over the last two centuries and significant ecological changes have also occurred in response to rapid regional warming during the second half of the twentieth century. This combination of historical perturbation and rapid regional change highlights that the Scotia Sea ecosystem is likely to show significant change over the next two to three decades, which may result in major ecological shifts.     

Leucistic Antarctic fur seals at Bouvetøya

One leucistic and one partially leucistic Antarctic fur seal Arctocephalus gazella were seen at Bouvetøya during the 1996/97 austral summer. Both likely came from South Georgia, where this colour morph is common. No individuals of this colour morph were sighted during three subsequent expeditions to Bouvetøya. The prevalence of this colour morph in the abundant populations of the Scotia Arc may be due to founder effect, as at least one leucistic animal was present at South Georgia when the Antarctic fur seal was close to extinction.     

Population biology of the myctophid fish Gymnoscopelus nicholsi (Gillbert, 1911) from the western South Atlantic

Thirty-three collections of Gymnoscopelus nicholsi were made between 1976 and 1981 in the South Atlantic using both krill and bottom trawls. In the Antarctic waters the main part of the stock consisted of adult fish 3–7 years old, characterized by a benthopelagic mode of life. Fish of year-class I were observed only in the vicinity of South Georgia, South Sandwich Islands and the Scotia Sea; year-class II individuals were absent from Antarctic samples. In the notal zone of the western South Atlantic, fish aged 1–5 years were found. The existence of only one population in the region is a possible explanation of these findings: this population is divided into a pelagic stock of juveniles and sub-adults which occur in the offshore waters of the western South Atlantic and benthopelagic stocks of adults distributed over the slope regions off Argentina, South Georgia and Antarctic archipelagos.
The computed values of K (von Bertalanffy growth) were 0.48, 0.41 and estimated total annual instantaneous mortality rates (Z) were 0.45, 0.67, and 0.70 for South Georgia, South Shetlands and notal zone of western South Atlantic stocks, respectively.     

Intertidal colonization rates. A matched latitude, north v. south, remote v. near shore island experiment

Colonization of artificial substrata was monitored on sheltered rocky shores at Husvik, South Georgia (54° 11'S; 36° 40'W) and Cumbrae, Scotland (55° 46'N; 4° 55'W) from mid summer to early autumn. South Georgia is a remote island (1,330 km from other land); Cumbrae is only 2 km from nearby coasts. Both islands were heavily glaciated for a period up to about 10,000 ybp, so the intertidal fauna is of geologically recent origin. The South Georgian fauna is depauperate and consists mainly of direct developers; that of Cumbrae is rich and largely larviparous. Colonization rates at Cumbrae were one to four orders of magnitude greater than at Husvik. It is suggested that the fauna of South Georgian shores stems from colonization by rafting from remote sources, while Cumbrae has been supplied predominantly by short-range pelagic larval dispersal. The measured differences in colonization rates reflect the substantial local advantage of larval dispersal over direct development in established communities.     

Nests of the brown booby (Sula leucogaster) as a potential indicator of tropical ocean pollution by marine debris

Seabirds collect debris primarily nearby breeding sites, and thus they may be used to monitor these pollutants in the ocean. This study aimed to investigate the prevalence of marine debris used as nesting materials by the brown booby (Sula leucogaster) and to test the species selectivity to debris type and color in two coastal islands of Brazil. We found marine debris in 61% of the brown booby nests on both islands. Fishing gear and hard plastic were the most frequent types of debris. Higher prevalence of fishing gear was found on the island with greater fishery activity. Similarly, hard plastic was the most frequent type of debris in nests and adjacent beach environment. The frequency of debris in brown booby nests can be a potential indicator of the abundance of specific items in surrounding marine waters. Monitoring debris in brown booby nests in a long-term may provide a better understanding of the species⿿ selectivity for specific debris. Furthermore, the impacts of debris in seabird nests at population level remain an overlooked threat that may reduce the quality of nesting habitats. We showed that brown booby nests are widely impacted by marine debris and that these organisms are exposed to this form of pollution from the beginning of their life.     

In stark contrast to widespread declines along the Scotia Arc,a survey of the South Sandwich Islands finds a robust seabird community

The South Sandwich Islands, in the South Atlantic Ocean, are a major biological hot spot for penguins and other seabirds, but their remoteness and challenging coastlines preclude regular biological censuses. Here we report on an extensive survey of the South Sandwich Islands, the first since the late 1990s, which was completed through a combination of direct counting, GPS mapping, and interpretation of high-resolution commercial satellite imagery. We find that the South Sandwich Islands host nearly half of the world’s Chinstrap Penguin (Pygoscelis antarctica) population (1.3 million breeding pairs), as well as c. 95,000 breeding pairs of Macaroni Penguins (Eudyptes chrysolophus), and several thousand breeding pairs of Gentoo Penguins (Pygoscelis papua). Despite being at the northern edge of their breeding range, we found an unexpectedly large (≥125,000 breeding pairs) population of Adélie Penguins (Pygoscelis adeliae). Additionally, we report that nearly 1900 pairs of Southern Giant Petrels (Macronectes giganteus) breed in the South Sandwich Islands, 4 % of the global population, almost all of which are found on Candlemas Island. We find that the South Sandwich Islands have not experienced the same changes in penguin abundance and distribution as the rest of the Scotia Arc and associated portions of the western Antarctic Peninsula. This discovery adds important context to the larger conversation regarding changes to penguin populations in the Southern Ocean.     

Stable isotope evidence of diverse species-specific and individual wintering strategies in seabirds

Although there is increasing evidence that climatic variations during the non-breeding season shape population dynamics of seabirds, most aspects of their winter distribution and ecology remain essentially unknown. We used stable isotope signatures in feathers to infer and compare the moulting (wintering) habitat of subantarctic petrels breeding at two distant localities (South Georgia and Kerguelen). Petrels showed species-specific wintering habitat preferences, with a similar pattern of latitudinal segregation for all but one taxon. At both localities, delta13C values indicated that blue petrels (Halobaena caerulea) moult in Antarctic waters, South Georgian diving petrels (Pelecanoides georgicus) in the vicinity of the archipelagos and/or in the Polar Frontal Zone and Antarctic prions (Pachyptila desolata) in warmer waters. In contrast, common diving petrels (Pelecanoides urinatrix) showed divergent strategies, with low and high intrapopulation variation at South Georgia and Kerguelen, respectively. Birds from Kerguelen dispersed over a much wider range of habitats, from coastal to oceanic waters and from Antarctica to the subtropics, whereas those from South Georgia wintered mainly in waters around the archipelago. This study is the first to show such striking between-population heterogeneity in individual wintering strategies, which could have important implications for likely demographic responses to environmental perturbation.     

Patterns of marine bacterioplankton biodiversity in the surface waters of the Scotia Arc, Southern Ocean

Spatial patchiness in marine surface bacterioplankton populations was investigated in the Southern Ocean, where the Antarctic Circumpolar Current meets the islands of the Scotia Arc and is subjected to terrestrial input, upwelling of nutrients and seasonal phytoplankton blooms. Total bacterioplankton population density, group-specific taxonomic distribution and six of eight dominant members of the bacterioplankton community were found to be consistent across 18 nearshore sites at eight locations around the Scotia Arc. Results from seven independent 16S rRNA gene clone libraries (1223 sequences in total) and fluorescent in situ hybridization suggested that microbial assemblages were predominantly homogeneous between Scotia Arc sites, where the Alphaproteobacteria, Gammaproteobacteria and the Cytophaga-Flavobacterium-Bacteroidetes cluster were the dominant bacterial groups. Of the 1223 useable sequences generated, 1087 (89%) shared ≥?97% similarity with marine microorganisms and 331 (27%) matched published sequences previously detected in permanently cold Arctic and Antarctic marine environments. Taken together, results suggest that the dominant bacterioplankton groups are consistent between locations, but significant differences may be detected across the rare biodiversity.     

The Impact of Predation by Marine Mammals on Patagonian Toothfish Longline Fisheries

Predatory interaction of marine mammals with longline fisheries is observed globally, leading to partial or complete loss of the catch and in some parts of the world to considerable financial loss. Depredation can also create additional unrecorded fishing mortality of a stock and has the potential to introduce bias to stock assessments. Here we aim to characterise depredation in the Patagonian toothfish (Dissostichus eleginoides) fishery around South Georgia focusing on the spatio-temporal component of these interactions. Antarctic fur seals (Arctocephalus gazella), sperm whales (Physeter macrocephalus), and orcas (Orcinus orca) frequently feed on fish hooked on longlines around South Georgia. A third of longlines encounter sperm whales, but loss of catch due to sperm whales is insignificant when compared to that due to orcas, which interact with only 5% of longlines but can take more than half of the catch in some cases. Orca depredation around South Georgia is spatially limited and focused in areas of putative migration routes, and the impact is compounded as a result of the fishery also concentrating in those areas at those times. Understanding the seasonal behaviour of orcas and the spatial and temporal distribution of “depredation hot spots” can reduce marine mammal interactions, will improve assessment and management of the stock and contribute to increased operational efficiency of the fishery. Such information is valuable in the effort to resolve the human-mammal conflict for resources.     

Species identification and likely catch time period of whale bones from South Georgia

Skeletal remains of baleen whales killed during the onset of 20th century commercial whaling lie scattered across the shores and abandoned whaling stations of the subantarctic island of South Georgia. Here we report on genetic species identification of whale bones collected from South Georgia using standard historical DNA protocols. We amplified and sequenced short fragments of the mitochondrial DNA (mtDNA) control region from 281 available bone samples. Of these, 231 provided mtDNA sequences of sufficient quality and length (174–194 bp) for species identification: 158 bones were identified as humpback whale (Megaptera novaeangliae), 51 bones were identified as fin whale (Balaenoptera physalus), 18 bones were identified as blue whale (B. musculus), two bones were identified as sei whale (B. borealis), one bone was identified as a southern right whale (Eubalaena australis), and one bone was identified as a southern elephant seal (Mirounga leonina). The prominence of humpback, fin, and blue whale bones in the sample collection corresponds to the catch record of the early years of whaling on the island of South Georgia (pre‐1915), prior to the depletion of these populations.     

Distribution,habitat and trophic ecology of Antarctic squid Kondakovia longimana and Moroteuthis knipovitchi: inferences from predators and stable isotopes

Cephalopods have a key role in the marine environment though knowledge of their distribution and trophic ecology is limited by a lack of observations. This is particularly true for Antarctic species. Toothfish species are key predators of cephalopods and may be viewed as ideal biological samplers of these species. A total of 256 cephalopod lower beaks were identified from the stomachs of Patagonian toothfish (Dissostichus eleginoides) and Antarctic toothfish (Dissostichus mawsoni), captured in fisheries of South Georgia and the South Sandwich Islands in the South Atlantic between March and April 2009. Long-armed octopus squid (Kondakovia longimana) and smooth-hooked squid (Moroteuthis knipovitchi) were the main cephalopod prey and both were predated upon wherever toothfish were captured, though this cephalopod species appear to inhabit deeper waters at the South Sandwich Islands than at South Georgia. Measurements of δ¹³C from beak material indicated a clear segregation of habitat use comparing adult and sub-adult sized K. longimana. Variation in δ¹⁵N with size indicated an ontogenetic shift in the diet of cephalopods and also suggested some trophic plasticity among years. This study provides new insights into the private life of some elusive Antarctic cephalopods in an underexplored region of the South Atlantic.     

To Eat or Not to Eat? Debris Selectivity by Marine Turtles

Marine debris is a growing problem for wildlife, and has been documented to affect more than 267 species worldwide. We investigated the prevalence of marine debris ingestion in 115 sea turtles stranded in Queensland between 2006-2011, and assessed how the ingestion rates differ between species (Eretmochelys imbricata vs. Chelonia mydas) and by turtle size class (smaller oceanic feeders vs. larger benthic feeders). Concurrently, we conducted 25 beach surveys to estimate the composition of the debris present in the marine environment. Based on this proxy measurement of debris availability, we modeled turtles' debris preferences (color and type) using a resource selection function, a method traditionally used for habitat and food selection. We found no significant difference in the overall probability of ingesting debris between the two species studied, both of which have similar life histories. Curved carapace length, however, was inversely correlated with the probability of ingesting debris; 54.5% of pelagic sized turtles had ingested debris, whereas only 25% of benthic feeding turtles were found with debris in their gastrointestinal system. Benthic and pelagic sized turtles also exhibited different selectivity ratios for debris ingestion. Benthic phase turtles had a strong selectivity for soft, clear plastic, lending support to the hypothesis that sea turtles ingest debris because it resembles natural prey items such as jellyfish. Pelagic turtles were much less selective in their feeding, though they showed a trend towards selectivity for rubber items such as balloons. Most ingested items were plastic and were positively buoyant. This study highlights the need to address increasing amounts of plastic in the marine environment, and provides evidence for the disproportionate ingestion of balloons by marine turtles.     

The biodiversity and biogeography of the free-living nematode genera Desmodora and Desmodorella (family Desmodoridae) at both sides of the Scotia Arc

Samples taken at two stations in the northern and southern parts of the Scotia Arc, at depths of 277 and 307 m, respectively, were analysed for metazoan meiofauna with special attention to the nematodes. Identification to species level was performed for two closely related subdominant nematode genera (Desmodora and Desmodorella) in samples from the two Scotia Arc stations and in other available samples from adjacent areas (Magellan Region, Drake Passage, Weddell Sea). Seven Desmodora species and three Desmodorella species were found, of which, respectively five and two species are new to science. The Scotia Arc stations show relatively high densities and average diversity on meiofauna and nematode level compared to adjacent areas. The distribution patterns of the various Desmodora and Desmodorella species suggest the Scotia Arc as a shallow bridge and a possible exchange route for meiofauna between the Antarctic and South America, especially since these species seem to be constrained by water depth.     

Polychaete diversity in the Scotia Arc benthic realm: Are polychaetes tracers for faunal exchange?

The Scotia Arc is the only shallow-water and island bridge linking nowadays Patagonia and the Antarctic. The Antarctic Circumpolar Current as an oceanographic peculiarity makes this region an interesting biogeographic transition zone, because this frontal system traditionally is said to isolate the Antarctic fauna from that of the adjacent northern ecosystems. Based on benthos samples from three expeditions onboard R/V Polarstern, we studied distribution patterns of 200 polychaete species and 34 major benthic taxa in order to evaluate the role of polychaetes in the benthic realm of this part of the Southern Ocean. ANOSIM test distinguished three station groups: the central eastern Scotia Sea, the continental shelf off South America and stations at the tip of the Antarctic Peninsula. These station groups differed in organism densities and diversities with stations at the tip of the Antarctic Peninsula hosting the most diverse and dense community. The polychaete diversity patterns in the three assemblages evidenced closer connectivity between the tip of the Antarctic Peninsula and the central eastern Scotia Sea than between the continental shelf off South America with either the stations off the tip of the Peninsula or the central eastern Scotia Sea. This is probably supported by the Polar Front, which divides the island chain into two branches. Species distribution and community patterns of polychaetes appear to be associated with oceanographic and sediment conditions in this region. Most of the shared species showed the capability to tolerate differences in hydrostatic pressure. We suggest that the islands of the Scotia Sea may constitute a bridge for exchange of benthic species, particularly for polychaetes with eurybathic distribution and high dispersal capabilities.     

Age and growth of the Antarctic dragonfish Parachaenichthys charcoti (Pisces, Bathydraconidae) from the southern Scotia Arc

The Antarctic dragonfish Parachaenichthys charcoti is commonly found in shelf waters of islands in the southern Scotia Arc. Its northern congener P. georgianus is distributed on the shelves of South Georgia and the South Sandwich Islands. Biological information on P. charcoti is limited and restricted largely to reproductive traits and feeding habits. The present study fills this gap, providing the first data on age and growth of this species by otolith reading. Age was estimated in juveniles and adults by counting annuli on otoliths. Age of early juveniles was determined by microincrement counts (considered to be daily rings). Age estimates of juveniles and adults ranged from 1 to 9?years, with a high percentage agreement between readings and low values of counting variability indices APE (3.3?%) and CV (4.7?%). Age of early juveniles ranged from 160 to 204?days, all showing an evident check at 32–35?days of age, tentatively linked to the first larval exogenous feeding. The estimated values of von Bertalanffy growth parameters L _∞ and k were 53.55?cm and 0.22, respectively, and the index of growth performance P was 2.33. Hatching in P. charcoti takes place in late winter, from August to September. Compared to other notothenioids inhabiting the Seasonal Pack-ice Zone, P. charcoti is a relatively fast growing species with moderate longevity, sharing several biological characteristics with its sister species P. georgianus.     

Field comparison of an LHPR net sampling system and an Optical Plankton Counter (OPC) in the Southern Ocean

A field comparison of an optical plankton counter (OPC) anda Longhurst-Hardy Plankton Recorder (LHPR) was undertaken aroundthe sub-Antarctic island of South Georgia during austral spring,1997, to investigate the capacity of the OPC to accurately describefine-scale plankton distributions. Initially, formalin-preserveddevelopmental stages of representative zooplankton were passedthrough a benchtop OPC and a relationship established betweenmaximum cross sectional area (CSA) of the plankton and the digitaloutput value (DOV) of the OPC. The LHPR with an OPC attachedto the net frame was then deployed at two stations representingcontrasting plankton abundances. Outputs from two oblique haulstaken at a shelf station, and one at an oceanic station, werecompared. Following corrections for volume swept by both instruments,and standardization of OPC particle and net plankton countson the basis of sampler mouth area, the OPC was found to ‘overestimate'relative to the net by up to several orders of magnitude. However,following the correction for rate of flow though the OPC, andthe application of a size threshold to the OPC data excludingthe proportion of particles <0.25 mm² CSA, based on the expectedretention of plankton by the net there was a greatly improvedand significant correlation. Overall there was no consistentover- or undersample by the OPC relative to the net, with meanOPC:net ratios being 1–1.8 for net plankton densitiesof up to 6000 ind. m^–3. There was also a generally goodagreement between the abundances of the rarer large biomassdominant calanoid copepods estimated by both samplers. An OPCoverestimate of 2–3x relative to the net was seen on theascent portion of the haul at the oceanic station, attributableto the presence of high abundances (estimated density     

Climatically driven fluctuations in Southern Ocean ecosystems

Determining how climate fluctuations affect ocean ecosystems requires an understanding of how biological and physical processes interact across a wide range of scales. Here we examine the role of physical and biological processes in generating fluctuations in the ecosystem around South Georgia in the South Atlantic sector of the Southern Ocean. Anomalies in sea surface temperature (SST) in the South Pacific sector of the Southern Ocean have previously been shown to be generated through atmospheric teleconnections with El Niño Southern Oscillation (ENSO)-related processes. These SST anomalies are propagated via the Antarctic Circumpolar Current into the South Atlantic (on time scales of more than 1 year), where ENSO and Southern Annular Mode-related atmospheric processes have a direct influence on short (less than six months) time scales. We find that across the South Atlantic sector, these changes in SST, and related fluctuations in winter sea ice extent, affect the recruitment and dispersal of Antarctic krill. This oceanographically driven variation in krill population dynamics and abundance in turn affects the breeding success of seabird and marine mammal predators that depend on krill as food. Such propagating anomalies, mediated through physical and trophic interactions, are likely to be an important component of variation in ocean ecosystems and affect responses to longer term change. Population models derived on the basis of these oceanic fluctuations indicate that plausible rates of regional warming of 1^oC over the next 100 years could lead to more than a 95% reduction in the biomass and abundance of krill across the Scotia Sea by the end of the century.