Contribution of sea ice organic matter in the diet of Antarctic fishes: a diatom-specific highly branched isoprenoid approach

New sets of diatom-specific biomarkers, highly branched isoprenoids (HBIs), have been recently proposed to trace carbon flow from ice algae and pelagic phytoplankton to higher trophic level organisms. In the Antarctic, diene, a HBI of sea ice origin was more abundant in ice-associated species, while triene, a HBI of phytoplanktonic origin, was more abundant in pelagic species. However, this HBI approach has never been applied on Antarctic benthic species. Here, we analyzed diene and triene in the liver and the muscle of eight Antarctic coastal fish species (108 specimens). HBI lipids were detected in all specimens, confirming the contribution of sea ice and pelagic organic matter in coastal benthic fish species. Moreover, HBI markers were much more concentrated in the liver than in white muscle, and the relative concentrations of diene and triene strongly varied among species, as a probable result of species differences in feeding habits and trophic ecology. Seasonal variations in HBI concentrations were detected during the whole year in white muscle, but not in the liver. These findings are consistent with the well-known spring bloom in November–December, just before the annual ice break up, and the second proliferation of ice algae during the land-fast ice formation, in April–May. Therefore, investigation of HBI lipids in white muscle will likely shed new light on seasonal changes in the contribution of ice algal-derived organic matter in higher trophic level organisms.     

Winter aggregations of marine mammals and birds in the north-eastern Weddell Sea pack ice

Summary A seabird and mammal census was carried out in the north-eastern Weddell Sea during the austral winter of 1986. The German research icebreaker Polarstern operated in heavy pack ice along the Greenwich Meridian between the northern sea ice boundary and the Antarctic coast. Crabeater seals (Lobodon carcinophagus), minke whales (Balaenoptera acutorostrata), Adélie penguins (Pygoscelis adeliae), Antarctic petrels (Thalassoica antarctica) and snow petrels (Pagodroma nivea) were found to be more abundant in the vicinity of the submarine Maud Rise, about 700 km north of the continental margin, than in other areas of substantial ice cover traversed during that cruise. The aggregations of birds and mammals are expected to reflect aggregations of their principal food, krill (Euphausia superba) wintering underneath the ice cover. The distribution pattern of krill predators coincides with the course of a warm water belt upwelling near Maud Rise. This upwelling could induce local ice melting which in turn may result in an increased release of sea ice algae.     

Long-term population trends in seven Antarctic seabirds at Pointe Géologie (Terre Adélie) Human impact compared with environmental change

Antarctic seabird populations have been much studied over the last decades as bioindicators of the nature of variability in the Southern Ocean marine ecosystem, and most attention has been focused on the role of food supply and the extent of sea ice. In addition, the rapid spread of tourism and the activities of researchers since the early 1960s have raised questions related to their real and potential impact on bird populations. Our data sets start in 1952 for several species of Antarctic seabirds and this study documents the trends over a 14-year period (1985–1999) in seven species breeding on Pointe Géologie archipelago (Terre Adélie, Antarctica). This is the first study where the direct impact of destruction of breeding sites (for building of an airstrip) is examined and where such long-term populations trends have been assessed in such a number of Antarctic species at one site. Trends from 1985 show that for the whole archipelago and when excluding islands destroyed, Adélie penguins and south polar skuas were the only species to show a significant increase (>3.5% annual change). The others species showed opposite trends, three increasing slightly (southern fulmars +0.4%, cape petrels +2.3%, snow petrels +0.9%) and two decreasing (emperor penguin −0.9%, southern giant petrel −3.9%). Three species particularly affected by the destruction of their breeding habitat (Adélie penguin, cape petrel, snow petrel) showed the capability to restore their populations. The availability of food and nesting sites is discussed in relation to environmental change. Species feeding on krill (Adélie penguins and cape petrels) increased more than other species; however, decrease of ice cover can increase availability of nesting sites. The importance of long-term studies is shown when assessing the role of human activities in Antarctica compared to larger-scale changes. Accepted: 18 September 2000     

Seasonal occurrence and dominance of Centropages congeners in the Middle Atlantic Bight,USA

The distribution and abundance of 15 taxa of birds seen from a vessel in the region of Prydz Bay, Antarctica between November and December 1982 are presented. Antarctic petrels were by far the most frequent in the survey area while Adélie and emperor penguins made up 77% of the observed avian biomass. The distribution and abundance of birds was found to be related to ice conditions, air temperature and wind speed but not to water temperature or air pressure. The extent of species associations at sea are shown and the possibilities of diurnal fluctuations in bird numbers at sea are examined.     

Cool,cold or colder? Spatial segregation of prions and blue petrels is explained by differences in preferred sea surface temperatures

The Southern Ocean provides one of the largest environmental gradients on Earth that lacks geographical barriers, and small but highly mobile petrels living there may offer fine models of evolution of diversity along environmental gradients. Using geolocation devices, we investigated the winter distribution of closely related petrel species breeding sympatrically in the southern Indian Ocean, and applied ecological niche models to compare environmental conditions in the habitat used. We show that thin-billed prions (Pachyptila belcheri), Antarctic prions (Pachyptila desolata) and blue petrels (Halobaena caerulea) from the Kerguelen archipelago in the southern Indian Ocean segregate latitudinally, sea surface temperature being the most important variable separating the distribution of the species. Antarctic prions spent the winter north of the Polar Front in temperate waters, whereas blue petrels were found south of the Polar Front in Antarctic waters. Thin-billed prions preferred intermediate latitudes and temperatures. Stable isotope values of feathers reflected this near complete niche separation across an ecological gradient that spans large scales, and suggest evolutionary isolation by environment. In pelagic seabirds that exploit large areas of ocean, spatial niche partitioning may not only facilitate coexistence among ecologically similar species, but may also have driven their evolution in the absence of geographical barriers.     

A comparison of Antarctic petrel (Thalassoica antarctica) diets with net samples of Antarctic krill (Euphausia superba) taken from the Prydz Bay region

Samples of the stomach contents of Antarctic petrels (Thalassoica antarctica) were obtained on board ship in the Prydz Bay region of Antarctica from birds which had spontaneously regurgitated. The weight of food and the species composition of the stomach contents were measured. Antarctic krill,Euphausia superba, the sole prey item taken, were compared to krill obtained by nets in the same region as part of a large-scale krill survey. Krill from petrel stomach samples were larger in mean size than those sampled by nets. This may be attributed to selection of the larger sized krill by the petrels, it may be caused by the nets sampling different populations of krill or it may be due to net avoidance by the larger krill.     

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.     

Limited use of sea ice by the Ross seal (<Emphasis Type="Italic">Ommatophoca rossii</Emphasis>), in Amundsen Sea,Antarctica, using telemetry and remote sensing data

To understand the use and importance of the Antarctic sea ice to the Ross seal (Ommatophoca rossii), four adult females were tagged with Argos satellite transmitters in the Amundsen Sea, Antarctica. The Ross seal is the least studied of the Antarctic seal species and nothing was previously known about their behaviour in the Amundsen Sea. During almost 1 year, their movements, haul out behaviour and time spent at different temperatures were logged. By comparing their movements with daily ice maps, distances to the ice edge were calculated, and seals dependence on sea ice for resting, breeding and moulting was analysed. The tagged seals spent on average 70.8 % (range 66.8–77.8 %) of their time in the water and hauled out mainly during the moult in December–January, and in late October–mid-November during breeding. During the pelagic period, they were on average 837.5 km (range 587–1,282 km) from the ice edge indicating a fully pelagic life during several months. Their pelagic behaviour suggests that Ross seals, although being an ice obligate species, may adapt comparatively easy to climate change involving ice melting and recession and thereby potentially being less sensitive to the reduction of sea ice than other Antarctic seal species. Although nothing is known about their mating behaviour, they appear to be relatively stationary during moulting and breeding, hence requiring a small ice surface. Although previous studies in other parts of Antarctica have found similar results, still many questions remain about this peculiar species.     

The biota of Antarctic pack ice in the Weddell sea and Antarctic Peninsula regions

Summary Pack ice surrounding Antarctica supports rich and varied populations of microbial organisms. As part of the Antarctic Marine Ecosystem Research in the Ice Edge Zone (AMERIEZ) studies, we have examined this community during the late spring, autumn, and winter. Although organisms are found throughout the ice, the richest concentrations often occur in the surface layer. The ice flora consists of diatoms and flagellates. Chrysophyte cysts (archaeomonads) of unknown affinity and dinoflagellate cysts are abundant and may serve as overwintering stages in ice. The ice fauna includes a variety of heterotrophic flagellates, ciliates, and micrometazoa. The abundance of heterotrophs indicates an active food web within the ice community. Ice may serve as a temporary habitat or refuge for many of the microbial forms and some of these appear to provide an inoculum for planktonic populations when ice melts. Larger consumers, such as copepods and the Antarctic krill, Euphausia superba are often found on the underside of ice floes and within weathered floes. The importance of the ice biota as a food resource for these pelagic consumers is unknown.     

Spatially Extensive Standardized Surveys Reveal Widespread,Multi-Decadal Increase in East Antarctic Adélie Penguin Populations

Seabirds are considered to be useful and practical indicators of the state of marine ecosystems because they integrate across changes in the lower trophic levels and the physical environment. Signals from this key group of species can indicate broad scale impacts or response to environmental change. Recent studies of penguin populations, the most commonly abundant Antarctic seabirds in the west Antarctic Peninsula and western Ross Sea, have demonstrated that physical changes in Antarctic marine environments have profound effects on biota at high trophic levels. Large populations of the circumpolar-breeding Adélie penguin occur in East Antarctica, but direct, standardized population data across much of this vast coastline have been more limited than in other Antarctic regions. We combine extensive new population survey data, new population estimation methods, and re-interpreted historical survey data to assess decadal-scale change in East Antarctic Adélie penguin breeding populations. We show that, in contrast to the west Antarctic Peninsula and western Ross Sea where breeding populations have decreased or shown variable trends over the last 30 years, East Antarctic regional populations have almost doubled in abundance since the 1980’s and have been increasing since the earliest counts in the 1960’s. The population changes are associated with five-year lagged changes in the physical environment, suggesting that the changing environment impacts primarily on the pre-breeding age classes. East Antarctic marine ecosystems have been subject to a number of changes over the last 50 years which may have influenced Adélie penguin population growth, including decadal-scale climate variation, an inferred mid-20th century sea-ice contraction, and early-to-mid 20^th century exploitation of fish and whale populations.     

Spring distribution and ecological role of seabirds and marine mammals in the Weddell Sea,Antarctica

Summary The early spring distribution of seabirds, pinnipeds and cetaceans was quantitatively determined in the northern Weddell Sea during the EPOS 1 cruise of the icebreaking RV Polarstern. Two hundred and ninety-one half hour counts were made in the Antarctic region between October 18 and November 16, 1988 (+94 counts in sub-antarctic and sub-tropical water). The bird populations were dominated by the Adélie Penguin Pygoscelis adeliae, which represented 90% of the birds counted in the closed pack ice (CPI), with a mean density of 31 penguins per km². Crabeater seal Lobodon carcinophagus, the most common pinniped, had a mean density of 1.2/km² in the CPI with local concentrations reaching 14/km². Expressed as biomass, mean values of about 90 kg/km² were found in the whole Antarctic zone for seabirds, 50 for seals, and 35 for baleen cetaceans. Densities were higher in the CPI: 140, 180 and 115 kg/km² respectively, were found for birds, pinnipeds and baleen whales, and lowest in open water (8 kg/km² for the birds, 0.2 for the pinnipeds and no whales). A minimum value of food intake by seabirds and marine mammals was estimated to be 2.7 mg C/m²/day for the Antarctic zone (4.1 in the CPI). Taking into account that pinnipeds density and cetacean food uptake are underestimated, and that Antarctic seabirds consume much more fish than generally suspected, a minimum krill production of 16 mg C/m²/day is proposed for the Antarctic zone: 22.5 in the CPI, 3 in open water, and intermediate values in the marginal ice zones.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Foods of the south polar skua at Hop Island,Rauer Group,East Antarctica

Summary Pellets regurgitated by south polar skuas at Hop Island, in the Rauer Group, East Antarctica, Princess Elizabeth Land were collected and analysed. Individual collections were grouped in relation to the nearest breeding colony of seabirds, but irrespective of their source the frequencies of occurrence of the food items identified in pellets indicated that Adélie penguins were of varying, but major (29%–72%), importance to skuas inhabiting the Island. Though the incidence of Antarctic petrel remains (from adult or chick) was generally low in pellets (<7%), the occurrence of remains of southern fulmars was high (>27%) at all sites near the fulmar breeding colonies. Fish remains, and beaks of cephalopods, were present in few pellets. Whilst indicating the range of foods eaten on Hop Island, and perhaps their relative importance, it is considered that the pellets by themselves do not reflect accurately the level of predation of eggs of Antarctic petrels and southern fulmars, nor do the pellets necessarily include the remains of young of these species.     

Food and feeding ecology of emperor penguins in the eastern Weddell Sea

Summary The diet of the emperor penguin Aptenodytes forsteri in the eastern Weddell Sea, Antarctica was studied during October and November 1986 by stomach content analysis. Emperor penguins fed mainly on Antarctic krill Euphausia superba, Antarctic silverfish Pleuragramma antarcticum and squid Psychroteuthis glacialis. Benthic prey was not found. The prey composition suggests two different feeding strategies, shallow dives exploring the rugged underside of sea ice where krill is taken, and deep dives when mesopelagic fish and squid are consumed. Chicks were fed on average every 1.44 days.     

Status,trends, and patterns of covariation of breeding seabirds at St Lazaria Island,Southeast Alaska, 1994–2006

Aim We examined patterns of covariation among piscivorous and planktivorous seabirds breeding at St Lazaria Island in order to evaluate their responses to interannual changes in sea surface temperature, a variable that affects marine food webs. In addition, we evaluated seabird population trends for responses to decadal‐scale changes in the marine ecosystem. Location St Lazaria Island, Sitka Sound, Alaska. Methods Established seabird monitoring protocols for the Alaska Maritime National Wildlife Refuge were followed in estimating population trends, the timing of nesting events and the reproductive success of eight species of seabirds between 1994 and 2006. Results  Population increases were noted for storm‐petrels (Oceanodroma furcata and O. leucorhoa), rhinoceros auklets (Cerorhinca monocerata) and glaucous‐winged gulls (Larus glaucescens). We found no population trend for pelagic cormorants (Phalacrocorax pelagicus), but it appeared that populations of common (Uria aalge) and thick‐billed (U. lomvia) murres and of tufted puffins (Fratercula cirrhata) declined. We detected no linear trends in either breeding chronology or reproductive success over the study period for any seabird. All species of piscivorous seabirds apparently responded similarly to environmental cues as there was a positive covariation among species in the timing of nesting. Piscivores tended to nest earlier, and most species had higher rates of reproductive success in years with relatively warm spring sea temperatures. In contrast, planktivorous Leach’s storm‐petrels (O. leucorhoa) tended to nest earlier when spring and summer sea temperatures were relatively cool. Clearly, seabirds at St Lazaria were responding to interannual changes in sea temperatures near the breeding colony, probably as a result of effects on the food webs. Main conclusions Every seabird species we monitored at St Lazaria exhibited significant population trends between 1994 and 2006. For most species there appeared to be a relationship between both the timing of nesting and reproductive rates and spring or summer sea surface temperatures. Responses at both decadal (populations) and interannual (timing and reproductive success) scales make seabirds useful candidates for helping to monitor change in the marine environment.     

南极Gerlache海峡海鸟的取食集群及食性

1997年12月至1998年2月,我们对南极半岛席尔瓦角善于飞翔海鸟与企鹅的取食关联性进行了研究,同时调查了取食集团中主要鸟种的食性.发现每个取食集团中有35.6-37.0只善于飞翔的海鸟,其中几乎都有纹颊企鹅群 (Pygoscelis antarctica),黑背鸥(Larus dominicanus)、灰贼鸥(Catharacta maccormicki)、花斑鹱(Daption capensis)和巨鹱(Macronectes giganteus)是各集团中最常见的鸟类.各取样单元内有相关性的种数随季节变化而减少,一些种类的减少与特定的物候期有关.南极磷虾(Euphausia superba)是绝大部分飞翔海鸟的主要食物,研究发现黑背鸥与纹颊企鹅所捕食的南极磷虾的大小最为接近.飞翔海鸟的觅食行为表明:在海面上短时停留的飞翔海鸟也能够成功捕捉到磷虾,这可能与磷虾躲避企鹅的捕食有关[动物学报 53(3):425-430,2007].     

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.     

Sea ice seasonality during the Holocene, Adélie Land, East Antarctica

Thin sections of laminated cores from different Antarctic coastal areas have demonstrated the potential of diatom species to document climate change at the seasonal scale. Here we present the relative abundances of four diatom species and species groups (Fragilariopsis curta group as a proxy for yearly sea ice cover, F. kerguelensis as a proxy for summer sea-surface temperature, Chaetoceros Hyalochaete resting spores as a proxy for spring sea ice melting and the Thalassiosira antarctica group as a proxy for autumn sea ice formation) in core MD03-2601 retrieved off Adélie Land on the Antarctic continental shelf. These abundances were compared to surface temperatures and sea ice cover modelled over the last 9000 years. Both the marine records and the simulated climate demonstrated a cooler Early Holocene (9000–7700 years BP), a warmer Mid-Holocene (7700–4000 years BP) and a colder Late Holocene (4000–1000 years BP). Yearly sea ice cover followed an inverse pattern to temperatures with less sea ice during the Mid-Holocene Hypsithermal than during the Late Holocene Neoglacial. However, diatom census counts and model output indicate that sea ice spring melting happened earlier in the season, as expected, but that autumn sea ice formation also occurred earlier in the season during the Hypsithermal than during the colder Neoglacial, thereby following seasonal changes in local insolation.     

Interactive effects of body mass changes and species‐specific morphology on flight behavior of chick‐rearing Antarctic fulmarine petrels under diurnal wind patterns

For procellariiform seabirds, wind and morphology are crucial determinants of flight costs and flight speeds. During chick‐rearing, parental seabirds commute frequently to provision their chicks, and their body mass typically changes between outbound and return legs. In Antarctica, the characteristic diurnal katabatic winds, which blow stronger in the mornings, form a natural experimental setup to investigate flight behaviors of commuting seabirds in response to wind conditions. We GPS‐tracked three closely related species of sympatrically breeding Antarctic fulmarine petrels, which differ in wing loading and aspect ratio, and investigated their flight behavior in response to wind and changes in body mass. Such information is critical for understanding how species may respond to climate change. All three species reached higher ground speeds (i.e., the speed over ground) under stronger tailwinds, especially on return legs from foraging. Ground speeds decreased under stronger headwinds. Antarctic petrels (Thalassoica antarctica; intermediate body mass, highest wing loading, and aspect ratio) responded stronger to changes in wind speed and direction than cape petrels (Daption capense; lowest body mass, wing loading, and aspect ratio) or southern fulmars (Fulmarus glacialoides; highest body mass, intermediate wing loading, and aspect ratio). Birds did not adjust their flight direction in relation to wind direction nor the maximum distance from their nests when encountering headwinds on outbound commutes. However, birds appeared to adjust the timing of commutes to benefit from strong katabatic winds as tailwinds on outbound legs and avoid strong katabatic winds as headwinds on return legs. Despite these adaptations to the predictable diurnal wind conditions, birds frequently encountered unfavorably strong headwinds, possibly as a result of weather systems disrupting the katabatics. How the predicted decrease in Antarctic near‐coastal wind speeds over the remainder of the century will affect flight costs and breeding success and ultimately population trajectories remains to be seen.     

Proximity of krill and salps in an Antarctic coastal ecosystem: evidence from penguin-mounted cameras

Antarctic krill (Euphausia superba) and salps (mainly Salpa thompsoni) are main components of Southern Ocean ecosystem, but little is known about their coastal distribution at a fine scale (<1 km). We deployed miniaturised cameras on breeding chinstrap (n = 9 birds) and gentoo penguins (n = 9 birds) in the Antarctic Peninsula region and obtained 2,333 krill images, 93 salp images and 609 sea floor images from 1,843 dives. 51.2 % of penguin dives that had salps present in the images occurred near the dives with krill images (within 5 min). The vertical distribution of salp images showed overlap with the upper depth zone of krill images. While 16.3 % of dives with krill images were associated in time with the sea floor, only 1.2 % of dives with salp images did. These results revealed close proximity between krill and salps within the penguin’s foraging range in an Antarctic coastal ecosystem. These results also imply that krill patches were common in both pelagic and benthic habitat, whereas salps were common mainly in pelagic habitat. If the effects of deployments are similar between the years or regions, inter-annual or regional comparison using the penguin-mounted camera will be valid for characterising prey environment in the penguin foraging area.     

The overwintering strategy of Antarctic krill under the pack-ice of the Weddell Sea

Summary Antarctic krill (Euphausia superba Dana) occurs in enormous swarms in Antarctic waters during the ice-free summer months. The winter whereabouts of this stock were hitherto unknown. Evidence collected during the Winter Weddell Sea Project 1986 (WWSP'86, G. Hempel 1988) covering a large area of the eastern and southern Weddell Sea indicates that the seasonal sea ice cover sustains the bulk of the krill population. Results presented here, show that known aspects of krill morphology and behavior are actually adaptations to the ice habitat, suggesting that the dominance of krill in the Antarctic marine ecosystem is a result of its capacity to grow and reproduce in the water column in summer, and find both food and shelter in the ice cover during the rest of the year. This conclusion has far-reaching implications for our understanding of Southern Ocean biology and ecology.