Pigment distribution in the Pacific region of the Southern Ocean (autumn 1995)

Phytoplankton distribution patterns are still largely unknown for the Pacific region of the Southern Ocean. Pigment distributions were determined by HPLC on 40-m samples collected from the mixed layer during the ANTXII/4 cruise in March–May 1995 aboard RV “Polarstern”. A transect was covered (90°W, from 51°S to 70°S), crossing the Subantarctic Front in the north, the Polar Front, and the Southern Polar Front in the south. Coinciding with high concentrations of silicate, diatoms dominated in the Antarctic waters south of the Polar Front. North of the Polar Front, silicate concentrations dropped to values less than 10 μM. In this area flagellates (Prymnesiophyceae and green algae) were the dominant phytoplankton group. Nutrient depletion of the surface waters near the Southern Polar Front indicated formerly enhanced productivity. These findings confirmed previous observations by the British Sterna expedition, which described locally elevated chlorophyll a biomass near the southern boundary of the Southern Polar Front. We propose a role for supply of bioavailable iron via the front, and emphasise the importance of frontal systems for phytoplankton productivity in the Southern Ocean. Received: 11 June 1997 / Accepted: 16 November 1997     

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.     

Origin,diversity, and biogeography of Antarctic scale worms (Polychaeta: Polynoidae): a wide‐scale barcoding approach

The Antarctic marine environment hosts diversified and highly endemic benthos owing to its unique geologic and climatic history. Current warming trends have increased the urgency of understanding Antarctic species history to predict how environmental changes will impact ecosystem functioning. Antarctic benthic lineages have traditionally been examined under three hypotheses: (1) high endemism and local radiation, (2) emergence of deep‐sea taxa through thermohaline circulation, and (3) species migrations across the Polar Front. In this study, we investigated which hypotheses best describe benthic invertebrate origins by examining Antarctic scale worms (Polynoidae). We amassed 691 polynoid sequences from the Southern Ocean and neighboring areas: the Kerguelen and Tierra del Fuego (South America) archipelagos, the Indian Ocean, and waters around New Zealand. We performed phylogenetic reconstructions to identify lineages across geographic regions, aided by mitochondrial markers cytochrome c oxidase subunit I (Cox1) and 16S ribosomal RNA (16S). Additionally, we produced haplotype networks at the species scale to examine genetic diversity, biogeographic separations, and past demography. The Cox1 dataset provided the most illuminating insights into the evolution of polynoids, with a total of 36 lineages identified. Eunoe sp. was present at Tierra del Fuego and Kerguelen, in favor of the latter acting as a migration crossroads. Harmothoe fuligineum, widespread around the Antarctic continent, was also present but isolated at Kerguelen, possibly resulting from historical freeze–thaw cycles. The genus Polyeunoa appears to have diversified prior to colonizing the continent, leading to the co‐occurrence of at least three cryptic species around the Southern and Indian Oceans. Analyses identified that nearly all populations are presently expanding following a bottleneck event, possibly caused by habitat reduction from the last glacial episodes. Findings support multiple origins for contemporary Antarctic polynoids, and some species investigated here provide information on ancestral scenarios of (re)colonization. First, it is apparent that species collected from the Antarctic continent are endemic, as the absence of closely related species in the Kerguelen and Tierra del Fuego datasets for most lineages argues in favor of Hypothesis 1 of local origin. Next, Eunoe sp. and H. fuligineum, however, support the possibility of Kerguelen and other sub‐Antarctic islands acting as a crossroads for larvae of some species, in support of Hypothesis 3. Finally, the genus Polyeunoa, conversely, is found at depths greater than 150 m and may have a deep origin, in line with Hypothesis 2. These “non endemic” groups, nevertheless, have a distribution that is either north or south of the Antarctic Polar Front, indicating that there is still a barrier to dispersal, even in the deep sea.     

Spatial and temporal variations in phytoplankton biomass and primary productivity in the Southwest Atlantic and the Scotia Sea

Summary Two cruises of the ARA/Islas Orcadas (late winter/early spring 1978 and late summer/early fall 1979) provided data which show that temporal variability of phytoplankton biomass and productivity in the oceanic wates of the Southwest Atlantic and Scotia Sea is insignificant when compared to the influence of geographical variability. Two bloom stations sampled during the late winter/early spring cruise had chlorophyll a concentrations and productivity values an order of magnitude higher than waters sampled from the same locations the following late summer/early fall. However, a comparison of 10 paired stations from the two cruises indicated no seasonal trend, as measured values of chlorophyll a and productivity from the first cruise were randomly larger or smaller than values measured during the second cruise. Consideration of individual stations from both seasons suggests the need to re-examine widely held notions regarding the effect of the Polar Front Zone and the island-mass effect on phytoplankton abundance and productivity. Higher-than-expected standing stock and productivity values at some open-ocean stations and at some stations within the Polar Front Zone indicate that looking for specific factors which promote localized enhancement or impoverishment of phytoplankton would be more useful than continuing with attempts to generalize Antarctic productivity data into broad seasonal or geographical patterns.In memory of Mary Alice McWhinnie (1922–1980)     

Phytoplankton production and biomass at frontal zones in the Atlantic sector of the Southern Ocean

A high resolution study of chlorophyll a and primary production distribution was carried out in the Atlantic sector of the Southern Ocean during the austral summer of 1990–91. Primary production (¹⁴C assimilation) and photosynthetic capacity levels at frontal systems were among the highest recorded during the cruise (2.8–6.3 mgC·m^–3·h^–1, and 1.3–4.7mgC·mgChl a ^–1·h^–1, respectively). Blooms at ocean fronts were strongly dominated by specific size classes and species. This suggests that the increase in biomass was probably the result of an enhancement of in situ production by selected components of the phytoplankton assemblage, rather than accumulation of cells through hydrographic forces. This hypothesis is supported by the high variability of photosynthetic capacities at adjacent stations along the transects. Blooms (ca 2.7–3.5 mg Chl a·m^–3) were found at three oceanic fronts (the Subtropical, Subantarctic and Antarctic Polar Fronts) during the early summer. These were equivalent to, or denser than, blooms in the Marginal Ice Zone and at the Continental Water Boundary. Seasonal effects on phytoplankton community structure were very marked. In early summer (December), netphyto-plankton (>20 m) was consistently the major component of the frontal blooms, with the chain-forming diatoms Chaetoceros spp. and Nitzschia spp. dominating at the Subantarctic and Antarctic Polar Fronts, respectively. During late summer (February), nanophytoplankton (1–20 m) usually dominated algal communities at the main frontal areas. Only at the Antarctic Polar Front did netphytoplankton dominate, with the diatom component consisting almost exclusively of Corethron criophilum. An early to late summer shift of maximum phytoplankton biomass from north to south of the Antarctic Polar Front was observed. Spatial covariance between silicate levels and water-column stability appeared to be the main factor controlling phytoplankton production at the Antarctic Polar Front. Low silicate concentrations may have limited diatom growth at the northern edge of the front, while a deep mixed layer depth reduced production at the southern edge of the front.     

Movement of oceanic fronts south of Australia during the last 10 ka: interpretation of calcareous nannoplankton in surface sediments from the Southern Ocean

Preservation of calcareous nannoplankton in surface sediment samples from the Southern Ocean south of Australia and adjacent to New Zealand record a single assemblage. The dominant species are Emiliania huxleyi, Gephyrocapsa muellerae, Calcidiscus leptoporus, Helicosphaera carteri and Coccolithus pelagicus. The assemblage varies little in abundance and diversity with minor correlation to present-day overlying surface water masses and oceanic fronts. Increase in abundance of H. carteri and C. pelagicus in the region of the Subtropical Front may reflect higher nutrients associated with this front. The assemblage, although altered by dissolution, represents a warmer climatic interval than present-day with the presence of preferentially dissolved, warm-water species preserved as far south as the Polar Front. The presence of warm-water species under sub-Antarctic waters at the Polar Front is interpreted as a relic population from the Holocene climatic optimum of 10–8 ka. The absence of coccoliths in sediments poleward of the Polar Front suggests an equatorward shift of this front following the climatic optimum, resulting in increased productivity of siliceous phytoplankton associated with the colder waters and increased dissolution of coccoliths. Movement of the Subtropical Front for the same interval is not recorded in the preserved coccoliths. The more heavily calcified form of E. huxleyi which dominates the living assemblage north of the Subtropical Front is subject to dissolution in this region and is poorly preserved in the sediment assemblage.     

The influence of some environmental factors on cytological and biometric parameters and chlorophyll content of <Emphasis Type="Italic">Deschampsia antarctica</Emphasis> Desv. in the maritime Antarctic

Under the environmental conditions of the Point Thomas Oasis (King George Island, the South Shetland Islands), we studied the influence of month-long artificial treatment with fresh water, salt water, and guano solution on the biometric characteristics, chlorophyll content, as well as the nuclear area of leaf parenchymal cells and nuclear DNA content, in a maritime Antarctic aboriginal plant Deschampsia antarctica. The modeled factors induced an increase in the generative shoot height and the length of the largest leaf but did not influence the number of flowers. Treatment with guano caused an increase in the chlorophyll a and b contents, while fresh water treatment only led to some increase in chlorophyll a. Fluctuations of physiologically significant traits, such as the nuclear area and DNA content in the leaf parenchyma cells of D. antarctica, have been traced under the influence of the studied factors. Understanding of the hierarchy of influence of these factors as well as and sensitivity of plants of this species to external agents require further investigation.     

Evidence for high iron requirements of colonial Phaeocystis antarctica at low irradiance

We have carried out field and laboratory experiments to examine the iron requirements of colonial Phaeocystis antarctica in the Ross Sea. In December 2003, we performed an iron/light-manipulation bioassay experiment in the Ross Sea polynya, using an algal assemblage dominated by colonial Phaeocystis antarctica, collected from surface waters with an ambient dissolved Fe concentration of ∼0.4 nM. Results from this experiment suggest that P. antarctica growth rates were enhanced at high irradiance (∼50% of incident surface irradiance) but were unaffected by iron addition, and that elevated irradiance mediated a significant decrease in cellular chlorophyll a content. We also conducted a laboratory iron dose–response bioassay experiment using a unialgal, non-axenic strain of colonial P. antarctica and low-iron (<0.2 nM) filtered seawater, both collected from the Ross Sea polynya in December 2003. By using rigorous trace-metal clean techniques, we performed this dose–response iron-addition experiment at ∼0°C without using organic chelating reagents to control dissolved iron levels. At the relatively low irradiance of this experiment (∼20 μE m⁻² s⁻¹), estimated nitrate-specific growth rate as a function of dissolved iron concentration can be described by a Monod relationship, yielding a half-saturation constant with respect to growth of 0.45 nM dissolved iron. This value is relatively high compared to reported estimates for other Antarctic phytoplankton. Our results suggest that seasonal changes in the availability of both iron and light play critical roles in limiting the growth and biomass of colonial Phaeocystis antarctica in the Ross Sea polynya.     

Reproductive response of the copepod Rhincalanus gigas to an iron-induced phytoplankton bloom in the Southern Ocean

The reproductive response of Rhincalanus gigas to the build up of a phytoplankton bloom in the Southern Ocean was studied during the European iron fertilization experiment (EIFEX). Egg production experiments were conducted over a period of approximately 5 weeks during development of a diatom dominated bloom. R. gigas showed a clear response to increasing chlorophyll a concentrations and the total egg production of the R. gigas population was highest just after the peak of the bloom at day 29 after fertilization. The average peak production was 50 eggs female⁻¹ day⁻¹. The percentage of egg producing females increased from about 0 to 90% during the course of the experiment. Accordingly, the maturation of the gonads reflected the positive response towards enhanced chlorophyll a concentrations. The fast reproductive response indicate that R. gigas was food limited during the period of this study in the Antarctic Polar Front region (APF).     

Shearwater Foraging in the Southern Ocean: The Roles of Prey Availability and Winds

Background

Sooty (Puffinus griseus) and short-tailed (P. tenuirostris) shearwaters are abundant seabirds that range widely across global oceans. Understanding the foraging ecology of these species in the Southern Ocean is important for monitoring and ecosystem conservation and management.

Methodology/Principal Findings

Tracking data from sooty and short-tailed shearwaters from three regions of New Zealand and Australia were combined with at-sea observations of shearwaters in the Southern Ocean, physical oceanography, near-surface copepod distributions, pelagic trawl data, and synoptic near-surface winds. Shearwaters from all three regions foraged in the Polar Front zone, and showed particular overlap in the region around 140°E. Short-tailed shearwaters from South Australia also foraged in Antarctic waters south of the Polar Front. The spatial distribution of shearwater foraging effort in the Polar Front zone was matched by patterns in large-scale upwelling, primary production, and abundances of copepods and myctophid fish. Oceanic winds were found to be broad determinants of foraging distribution, and of the flight paths taken by the birds on long foraging trips to Antarctic waters.

Conclusions/Significance

The shearwaters displayed foraging site fidelity and overlap of foraging habitat between species and populations that may enhance their utility as indicators of Southern Ocean ecosystems. The results highlight the importance of upwellings due to interactions of the Antarctic Circumpolar Current with large-scale bottom topography, and the corresponding localised increases in the productivity of the Polar Front ecosystem.     

Spectral Properties of the Green Alga Trebouxia,a Phycobiont of Cryptoendolithic Lichens in the Antarctic Dry Valley

An algologically pure culture of the green alga Trebouxia, a phycobiont of cryptoendolithic lichens, was isolated from sandstone samples collected in the high-altitude polar regions of Antarctica. The absorption and second-derivative absorption spectra of acetone extract of the Antarctic phycobiont cells were studied in comparison with those of a Trebouxia phycobiont isolated recently from a Parmeliaceae lichen in the Mid-European climatic zone. The cells of the Antarctic phycobiont were characterized by a lower content of chlorophyll a and a higher ratio of chlorophyll b and carotenoids to chlorophyll a as compared to the Mid-European phycobiont. Furthermore, the carotenoids of the Antarctic phycobiont were more diverse. The low-temperature fluorescence spectra of the Antarctic phycobiont were characterized by an increased intensity of the short-wavelength fluorescence peak of chlorophyll aand a diminished intensity of fluorescence in the long-wavelength spectral region.     

Vertical distribution and dietary preferences of deep-sea copepods (Euchaetidae and Aetideidae; Calanoida) in the vicinity of the Antarctic Polar Front

Four Paraeuchaeta species and three aetideids were frequently encountered along 51°30′S in the Atlantic sector of the Southern Ocean. Paraeuchaeta antarctica was most abundant close to the Antarctic Polar Front. Within the genera Paraeuchaeta and Gaetanus, congeners usually partitioned the water column. Euchaetidae had high lipid (≤37% dry mass, DM in adult females) and wax ester contents (≤22% DM). Fatty acid composition of Paraeuchaeta spp. was dominated by monounsaturated moieties, especially 16:1(n-7) and 18:1(n-9), while fatty alcohols were mainly saturated. Surprisingly, only the bathypelagic P. barbata contained moderate amounts of 20:1(n-9) and 22:1(n-11) fatty acids (≤14%) and high levels of the respective fatty alcohols (≤50%), generally considered trophic biomarkers for calanid copepods as prey. Thus, herbivorous calanid copepods seem to be a readily available prey source at bathypelagic depths, indicating that their seasonal vertical migration provides a “trophic shortcut” from primary production at the surface to the interior of the ocean. Aetideidae also contained substantial levels of total lipid (14–36% DM), but wax esters contributed only up to 12% DM in copepodite stages C5 of Gaetanus spp., whereas other stages of Gaetanus and Aetideopsis minor only contained ≤6% DM of wax esters. The fatty acid compositions of Aetideidae were more balanced with 16:0, 18:1(n-9), 20:5(n-3), and 22:6(n-3) as important components, indicating a generally omnivorous feeding behaviour.     

Spatial-temporal variability of ultraplankton vertical distribution in the Antarctic frontal zones within 60–66°E, 43–46°S

The vertical distribution of heterotrophic bacteria and four ultraphytoplanktonic (<10 µm) groups (Prochlorococcus, Synechococcus, pico- and nanoeukaryotes) was investigated by flow cytometry at three process stations located in three different sub-systems belonging to the Antarctic Circumpolar Current frontal zone and to the Southern Indian Ocean (60–66°E, 43–46°S; ANTARES 4 cruise, January-February 1999): the Subtropical Zone (STZ), the Convergence Zone and the Polar Frontal Zone (PFZ). In each sub-system, short-term variability of cell abundance and flow cytometric parameters (right-angle light scatter and chlorophyll autofluorescence) was assessed through a times series of up to 24 h with a 2 h sampling frequency. The ultraphytoplankton vertical distribution exhibited a high spatial variability, with dominance of Prochlorococcus in the STZ (mean: 762.85×10¹⁰ cells m^–2), whereas picoeukaryotes (<3 µm) were dominant in the PFZ (55.46×10¹⁰ cells m^–2), a typically high-nutrient low-chlorophyll zone. Heterotrophic bacteria abundance was maximum (9.84×10¹³ cells m^–2) in the frontal zone, between the Agulhas Front and the Subtropical Front. Nanoeukaryotes showed the largest (up to 80%) variations between two consecutive sampling periods (2 h). Abundance variations could not be assigned to the same water mass during the time series due to the highly variable hydrodynamics of the study area. Trends of short-term abundance variations were opposite between the PFZ (lowest at night) and north of the Subtropical Front (highest at night). The observed spatial and short-term variations illustrate the complexity of the water masses in the Indian sector of the Southern Ocean, and highlight the challenge of extrapolating discrete measurements over space and time for use in evaluating carbon budgets in such dynamic areas.     

Day and night mesopelagic fish assemblages off the Kerguelen Islands (Southern Ocean)

Mesopelagic fish assemblages were investigated in the Polar Frontal Zone off the Kerguelen Islands during summer 1995, in parallel with a king penguin tracking study. During the day, the upper offshore water layers (0–200 m) have low potential prey diversity and abundance with only three fish species: a lanternfish, Krefftichthys anderssoni, a member of the Muraenolepididae, Muraenolepis marmoratus, and the early stages of the nototheniid, Lepidonotothen squamifrons. The mesopelagic fish community, including the typical myctophids, first appears in the deeper layer (300 m). At night, the surface layer (50 m) is invaded by the mesopelagic Myctophidae Electrona antarctica, Gymnoscopelus braueri, G. piabilis, G. fraseri, G. nicholsi, Protomyctophum bolini and P. tenisoni. Deeper (>100 m), a cline of species assemblages from the coast to offshore is observed. Accepted: 4 August 1999     

Effects of iron concentration on pigment composition in Phaeocystis antarctica grown at low irradiance

Interpretation of photosynthetic pigment data using iterative programs such as CHEMTAX are widely used to examine algal community structure in the surface ocean. The accuracy of such programs relies on understanding the effects of environmental parameters on the pigment composition of taxonomically diverse algal groups. Phaeocystis antarctica is an important contributor to total autotrophic production and the biogeochemical cycling of carbon and sulfur in the Southern Ocean. Here we report the results of a laboratory culture experiment in which we examined the effects of ambient dissolved iron concentration on the pigment composition of colonial P. antarctica, using a new P. antarctica strain isolated from the southern Ross Sea in December 2003. Low-iron (<0.2 nM dissolved Fe) filtered Ross Sea seawater was used to prepare the growth media, thus allowing sub-nanomolar iron additions without the use of EDTA to control dissolved iron concentrations. The experiment was conducted at relatively low irradiance (∼20 μE m⁻² s⁻¹), with P. antarctica primarily present in the colonial form—conditions that are typical of the southern Ross Sea during austral spring. Relative to the iron-limited control treatments (0.22 nM dissolved Fe), iron addition mediated a decrease in the ratio of 19′-hexanoyloxyfucoxanthin to chlorophyll a, and an increase in the ratio of fucoxanthin to chlorophyll a. Our results also suggest that the ratio of 19′-hexanoyloxyfucoxanthin to chlorophyll c₃ (Hex:Chl c₃ ratio) may be a characteristic physiological indicator for the iron-nutritional status of colonial P. antarctica, with higher Hex:Chl c₃ ratios (>3) indicative of Fe stress. We also observed that the ratio of fucoxanthin to 19′-hexanoyloxyfucoxanthin (Fuco:Hex ratio) was highly correlated (r ² = 0.82) with initial dissolved Fe concentration, with Fuco:Hex ratios <0.05 measured under iron-limited conditions (dissolved Fe <0.45 nM). Our results corroborate and extend the results of previous experimental studies, and, combined with pigment measurements from the southern Ross Sea, are consistent with the hypothesis that the interconversion of fucoxanthin and 19′-hexanoyloxyfucoxanthin by colonial P. antarctica is used as a photo-protective or light-harvesting mechanism, according to the availability of dissolved iron.     

Photosynthetic responses in Phaeocystis antarctica towards varying light and iron conditions

The effects of iron limitation on photoacclimation to a dynamic light regime were studied in Phaeocystis antarctica. Batch cultures were grown under a sinusoidal light regime, mimicking vertical mixing, under both iron-sufficient and -limiting conditions. Iron-replete cells responded to changes in light intensity by rapid xanthophyll cycling. Maximum irradiance coincided with maximum ratios of diatoxanthin/diadinoxanthin (dt/dd). The maximum quantum yield of photosynthesis (F _v /F _m ) was negatively related to both irradiance and dt/dd. Full recovery of F _v /F _m by the end of the light period suggested successful photoacclimation. Iron-limited cells displayed characteristics of high light acclimation. The ratio of xanthophyll pigments to chlorophyll a was three times higher compared to iron-replete cells. Down-regulation of photosynthetic activity was moderated. It is argued that under iron limitation cells maintain a permanent state of high energy quenching to avoid photoinhibition during exposure to high irradiance. Iron-limited cells could maintain a high growth potential due to an increased absorption capacity as recorded by in vivo absorption, which balanced a decrease in F _v /F _m . The increase in the chlorophyll a-specific absorption cross section was related to an increase in carotenoid pigments and a reduction in the package effect. These experiments show that P. antarctica can acclimate successfully to conditions as they prevail in the Antarctic ocean, which may explain the success of this species.     

Inter-annual variability in the breeding performance of seabirds in relation to oceanographic anomalies that affect the Crozet and the Kerguelen sectors of the Southern Ocean

Global warming is expected to increase the frequency and intensity of inter-annual variation in Sea-Surface Temperatures (SST) associated with a latitudinal shift of frontal structures in the Southern Ocean. However, the long-term consequences of these major climatic events on the biotic environment remain poorly understood. We studied the effect of SST anomalies in the southern Indian Ocean on the breeding success of eight seabird species, and found these temperature anomalies to have different effects depending on the foraging habitat of the species. The breeding success of four seabird species foraging mainly south of the Polar Front in Antarctic waters was significantly depressed by warm SST occurring mainly in winter and spring, prior to breeding. Conversely, warm SST anomalies were associated with a higher breeding success for species foraging mainly north of the Polar Front, while no significant effect was found for two species that forage on the Kerguelen plateau. These different responses to changes in the SST were also observed for two closely related species (sooty albatross Phoebetria fusca and light-mantled sooty albatross P. palpebrata ) breeding at Kerguelen. These observations highlight the importance of multi-species long-term monitoring programs for understanding the ecological consequences of environmental variability. Our results suggest that the predicted southward shift of the Polar Front caused by oceanic warming could lead to an important decrease in the breeding performance of top predator seabirds depending on the location and changes of their foraging habitat in relation the Polar Front.     

Seasonal use of oceanographic and fisheries management zones by juvenile southern elephant seals (<Emphasis Type="Italic">Mirounga leonina</Emphasis>) from Macquarie Island

The foraging distribution of marine predator populations is important for effective modelling and management of pelagic marine systems. We tracked 31 juvenile southern elephant seals from Macquarie Island (158°57E, 54°30S) over their annual post-moult and mid-year trips to sea. We calculated the amount of time spent in regional fisheries management areas and within bounded oceanographic regions. During the austral summer, juvenile seals spent over 90% of their time south of the Antarctic Polar Front and ~80% within fisheries management regions [Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) and exclusive economic zones]. In winter, seals spent ~75% of their time in the region bounded by the Antarctic Polar Front and the southern boundary of the Antarctic Circumpolar Current, and ~60% within fisheries management regions. The time spent per region differed significantly between summer and winter. Our results demonstrate that juvenile southern elephant seals from Macquarie Island spent more time south of the Antarctic Polar Front and within fisheries management areas than previously suspected.     

Metabolic recovery of the Antarctic liverwort <Emphasis Type="Italic">Cephaloziella varians</Emphasis> during spring snowmelt

We measured the responses of pigments and chlorophyll a fluorescence parameters of the Antarctic leafy liverwort Cephaloziella varians to snowmelt during austral spring 2005 at Rothera Point on the western Antarctic Peninsula. Although no changes to the concentrations of UV-B photoprotective pigments were detected during snowmelt, chlorophyll and carotenoid concentrations and maximum photosystem (PS)II yield (F _v /F _m) were respectively 88, 60 and 144% higher in the tissues of the liverwort that had recently emerged from snow than in those under a 10 cm depth of snow. A laboratory experiment similarly showed that effective PSII yield increased rapidly within the first 45 min after plants sampled from under snow were removed to an illuminated growth cabinet. The pigmentation and PSII yields of plants during snowmelt were also compared with those of plants in January, during the middle of the growing season at Rothera Point. During snowmelt, plants had lower F _v /F _m values, chlorophyll a/b ratios and concentrations of UV-B photoprotective pigments and carotenoids than during mid-season, suggesting that although there is some recovery of PSII activity and increases in concentrations of photosynthetic pigments during snowmelt, the metabolism of C. varians is restricted during this period.     

Low-temperature limitation of primary photosynthetic processes in Antarctic lichens <Emphasis Type="Italic">Umbilicaria antarctica</Emphasis> and <Emphasis Type="Italic">Xanthoria elegans</Emphasis>

Temperature response curves of chlorophyll a fluorescence parameters were used to assess minimum sub-zero temperature assuring functioning of photosynthetic photochemical processes in photosystem II (PS II) of Antarctic lichens. Umbilicaria Antarctica and Xanthoria elegans were measured within the temperature range from −20 to +10°C by a fluorometric imaging system. For potential (F _V/F _M) and actual (Φ _II) quantum yields of photochemical processes the minimum temperature was found to be between −10 and −20°C. Non-photochemical quenching (NPQ) of absorbed excitation energy increased with temperature drop reaching maximum NPQ at −15°C. Image analysis revealed intrathalline heterogeneity of chlorophyll a fluorescence parameters with temperature drop. Temperature response of Φ _II exhibited an S-curve with pronounced intrathalline differences in X. elegans. The same relation was linear with only limited intrathalline difference in U. antarctica. The results showed that Antarctic lichen species were well adapted to sub-zero temperatures and capable of performing primary photosynthesis at −15°C.