Movements of giant petrels Macronectes spp. ringed at South Georgia

first_imgMore than two hundred recoveries of giant petrels Macronectes halli and M. giganteus originally ringed at Bird Island, South Georgia, were analysed to determine the nature of any interspecific differences in the locality, timing and circumstances of recovery. Normally about 3% of the nestlings ringed were recovered within three years of fledging but the recovery rate was significantly lower in nestlings ringed in 1978–80. Eighty percent of the recoveries occurred within 12 months of ringing. Proportionately more M. halli are recovered in South America and the Pacific. The numbers recovered in southern Africa have declined whilst birds were recovered more frequently in New Zealand in 1978–80, compared to earlier years. Most recoveries were of birds found dead or injured on a beach; 9% were involved in fishing incidents and 10% killed by man, mainly in South America. Only one bird ringed as an adult has been recovered away from South Georgia. Details of foreign‐ringed birds and local movements are also included. Differences between the two species are discussed in relation to weather and fledging dates.last_img read more

Oxygen consumption and nitrogen excretion in the Antarctic brachiopod Liothyrella uva (Jackson, 1912) under simulated winter conditions

first_imgThe metabolism of the Antarctic brachiopod Liothyrella uva (Jackson, 1912) has been investigated in the laboratory under simulated winter conditions of low temperature and no food. Under such conditions the metabolic rate measured should approximate to basal or maintenance metabolism. The oxygen consumption of a brachiopod of 35 mm length (210 mg AFDW) was 0.48 μg-at. O · h−1. This is low when compared with other brachiopods, Antarctic invertebrates or starved temperate invertebrates. Ammonia excretion was also low, 0.056 μg-at. NH3-N · h−1 in a 35-mm animal. The slopes of the allometric relationships against ash-free dry weight were 0.72 for oxygen consumption and 0.75 for ammonia excretion. These slopes were not significantly different from each other, or from 0.75. The mean overall oxygen: nitrogen ratio was 9.3, which suggests that protein was being used as the main metabolic substrate. A preliminary biochemical study of brachiopods collected from Signy Island, Antarctica, showed only small seasonal changes in lipid and carbohydrate, but there were marked changes in protein content in the later stages of winter. This confirms that, at least in late winter, L. uva survives primarily by the utilization of protein.last_img read more

Physiological constraints on living and fossil brachiopods

first_imgAsh-free-dry-weight determinations for a representative range of living brachiopod genera have revealed that a consistently high proportion of total organic mass is contained within the shell, partly as the organic matrix for biomineralisation and partly as minute extensions of the mantle tissues (caeca) housed within hollow endopunctae permeating the shell. On average 40% to 50% of the total organic mass of both articulate and inarticulate brachiopods is situated within the shell. This is true even for a rhynchonellid brachiopod which does not possess endopunctae, but which has a more dense protein matrix in its shell. The effectively hidden constituent of brachiopod tissue mass which is included in this component has often been overlooked, and as a result total metabolic tissue mass has been underestimated. This throws into question some previous interpretations of brachiopod respiratory and metabolic data. The oxygen consumption rates of several living brachiopods have been measured, and when respiring tissue in caeca in the shell is taken into consideration, it is clear that brachiopod metabolic rates are low when compared with other marine invertebrates (e.g. between 10% and 50% of the oxygen uptake of comparable gastropods and bivalve molluscs held in similar conditions). This low rate cannot be attributed to a slower pumping rate by the brachiopod lophophore, as has been suggested, because the rate of water movement is comparable to that across the bivalve gill. Nitrogen excretion rates have also been measured for a few living brachiopods, allowing a comparison with rates of oxygen consumption and providing an indication of the metabolic substrates used. These data on oxygen: nitrogen ratios suggest that one Antarctic brachiopod utilises exclusively protein as a metabolic substrate, while a temperate latitude species uses mainly protein during winter but lipids and carbohydrates during summer months. Histological observations, particularly of Terebratulina retusa from temperate waters, show that a specialised tissue layer in the brachiopod outer mantle epithelium proximal to the shell may be the site of storage of the protein that is metabolised during winter, and of carbohydrate mobilised during gonadal development in summer. The caeca have also been suggested as sites of storage of metabolites, and the possible relationships between these areas of mantle are discussed. It seems that the ability to store nutrients in the mantle, combined with flexibility of substrate utilisation and an inherently low metabolic rate, have been important factors in brachiopod evolution.last_img read more

Diving depths of albatrosses

first_imgStudies of diving in seabirds have mainly been confined to penguins, alcids and cormorants. There are few data on the depths to which other seabirds dive although some species are known to have considerable abilities for diving and swimming underwater e.g. shearwaters (Kuroda 1954, Brown et al. 1978), diving petrels (Prince & Jones 1992) and gannets (Adams & Walter 1993).last_img

Temporal variation in Antarctic sea-ice: analysis of a long term fast-ice record from the South Orkney Islands

first_imgDetection of climate-induced change in marine ecosystems requires a knowledge of the underlying variability of the environment. This paper uses a range of datasets to investigate the interannual variability in Southern Ocean sea-ice dynamics. We present the first analysis of a series of fast-ice duration data from Signy Island, which we have cross-calibrated and combined with an earlier series from the same island group. The combined series covers the period from 1903 to the present day. The analyses indicate that there has been a long term decline in the duration of sea-ice at the South Orkney Islands in the north-west Weddell Sea. This change has not been a simple linear decline but appears to have been the result of a reduction in the duration of fast-ice during the 1940s and 1950s. There was a pronounced sub-decadal year cycle in fast-ice duration at the South Orkney Islands from the mid-1960s to 1990. In recent years this cyclicity has broken down and fast-ice duration has been greater than expected. Analyses of satellite data have shown that fast-ice duration at Signy Island reflects the larger-scale ice dynamics of the Weddell Sea. Investigation of the Weddell Sea ice dynamics in relation to circumpolar ice extents indicates that the position of anomalies in the maximum sea-ice extent field precesses around the Antarctic continent with a period of approximately 7–9 years. Analysis of atmospheric and oceanic connections with the sea ice variability show that there are signals in both regimes. This environmental variability has significant implications for ecosystem function and the detection of short-term and long-term ecological change.last_img read more

Phosphatase activities of endolithic communities in rocks of the Antarctic Dry Valleys

first_imgPhosphorus is scarce in Beacon Sandstone of the McMurdo Dry Valleys, Antarctica, and any input from precipitation is minimal. In endolithic microbial communities recycling of P by the action of phosphatases may therefore be important. The phosphatase activities of three different types of endolithic communities in the McMurdo Dry Valley, Antarctica, were studied in the laboratory. The dominant phototrophs were Chroococcidiopsis, mixed Gloeocapsa and Trebouxia, and Trebouxia. Bacteria were also visually conspicuous in the latter two communities, and the Trebouxia in both cases formed a lichenized association with fungal hyphae. In each case marked phosphomonoesterase (PMEase) activity was found in assays with 4-methylumbelliferyl phosphate (MUP) or p-nitrophenyl phosphate as substrate, and phosphodiesterase activity with bis-p-nitrophenyl phosphate as substrate. The pH optimum of PMEase (assayed at 0.5 pH intervals) of the Chroococcidiopsis, Gloeocapsa–Trebouxia, and Trebouxia communities was 9.5, 5.5, and 8.0, respectively. These values are similar for aqueous extracts of the respective rocks (pH 9.2, 6.2, 7.5). All three communities showed significantly higher PMEase activity at 5° than 1°C, and the first two also showed much higher activity at 5° than 10°C. All three communities also showed slightly lower activity in the light (7 μmol photon m-2 s-1) than the dark; this was found with all substrates and substrate concentrations. Prior exposure of a moistened sample to light for 2 h led to a reduction in activity even when the subsequent assay was done in the dark. The rate of PMEase activity (using 100 μM MUP) in the Gloeocapsa–Trebouxia and Trebouxia communities was approximately linear with time up to 24 h, whereas the Chroococcidiopsis community showed a marked decrease after 6 h. At least part of this was due to retention of the 4-methylumbelliferone (MU) hydrolysis product. In spite of the assays being conducted on a whole community, the activity–substrate relationship in each case quite closely resembled a typical Michaelis–Menten relationship. Estimates were made of the apparent half-saturation value and the concentration of MUP required to support half-maximal rates. The apparent K m values were: Chroococcidiopis, 230 μM; Gloeocapsa–Trebouxia 169 μM; Trebouxia, 135 μM. The respective values for apparent V max were 0.053, 0.55, and 0.35 μmol MU g-1 h-1. In view of the greater dependence of these communities on the rock for their sole supply of P than for C and probably N, it is suggested that the cycling of P within the communities is a key factor influencing their overall metabolic activity when moisture permits their activation.last_img read more

Integrated chronostratigraphic calibration of the Oligocene-Miocene boundary at 24.0 +/- 0.1 MA from the CRP-2A drill core, Ross Sea, Antarctica

first_imgAn expanded Oligocene-Miocene boundary interval recovered in the Cape Roberts Project CRP-2A core from beneath the Ross Sea, Antarctica, has yielded a high-resolution integrated chrono stratigraphy that has, in turn, enabled a new, more direct, calibra tion of magnetic polarity and biostratigraphic events. The Oligocene-Miocene boundary interval in the CRP-2A core comprises three ∼60-m-thick, rapidly deposited (>0.5 m/k.y.) sedimentary sequences (sequences 9, 10, and 11). In sequences 10 and 11, single-crystal, laser-fusion 40Ar/39Ar analyses of anorthoclase phenocrysts from two tephra horizons independently calibrate the CRP-2A magnetic-polarity stratigraphy and age model. Sequences 10 and 11 encompass subchron C6Cn.3n, which is dated as 24.3 ± 0.1 to 24.16 ± 0.1 Ma. Sequence 9 is interpreted to encompass subchron C6Cn.2n and the Oligocene-Miocene boundary, which is dated as 24.0 ± 0.1 Ma. These ages are ∼0.2 m.y. older than those of the geomagnetic polarity time scale calibrated from seafloor-spreading ridges and ∼0.9–1.3 m.y. older than the newly proposed astronomically calibrated ages. We contend that the discrepancy with the astronomically calibrated ages arises from a mismatch of three 406 k.y. eccentricity cycles or a 1.2 m.y. modulation of obliquity amplitude in the astronomical calibration of the Oligocene–Miocene time scale.last_img read more

Airborne measurements in a stable boundary layer over the Larsen Ice Shelf, Antarctica

first_imgWe present aircraft measurements of boundary-layer structure and surface turbulent fluxes from a flight over the Larsen Ice Shelf, Antarctica. Warm advection, associated with föhn flow, led to the formation of a stable boundary layer over the ice shelf, with a well-defined low-level jet at the top of the surface inversion. The strong shear associated with the jet kept the gradient Richardson number small and maintained a turbulent boundary layer over a depth of at least 600 m. The net surface energy balance amounted to 52 Wm−2, equivalent to a melt rate of 13 mm water per day, with net radiation (48 Wm−2) making the largest contribution to melt. The contribution from the sensible heat flux (13 Wm−2) was largely balanced by an upwards latent heat flux (−9 Wm−2). These measurements provide insight into the processes that control surface melt rates in an area that has experienced recent rapid warming and deglaciation.last_img read more

Seasonal patterns of prolactin and corticosterone secretion in an Antarctic seabird that moults during reproduction

first_imgIn avian species that have evolved life-history strategies wherein molt and breeding overlap, there arepotential conflicts between the regulatory roles of baseline prolactin and corticosterone in parental care(positive) and moult (negative). We describe seasonal patterns of hormonal secretion, moult, and parentalbehaviour in sibling species of giant petrels (Macronectes spp.) which begin moult during the incubation/early chick-rearing stage of reproduction. With the exception of male Southern giant petrels(Macronectes giganteus), prolactin secretion and moult in Northern (Macronectes halli) and female Southerngiant petrels conformed to those observed in all other avian species, with the initiation of moult coincidentwith decreases from peak prolactin levels. However, male Southern giant petrels began moultingearly in incubation when prolactin was increasing and had not yet peaked, which suggests a requirementof prolactin for incubation behaviour and a dissociation of prolactin from moult. Corticosterone showedlittle seasonal variation and no relationship with moult. When comparing prolactin, corticosterone, andmoult in failed vs. active breeders, we found that failed breeding enabled a more rapid down-regulationof prolactin, thus facilitating a more rapid moult. We present specific examples of the behavioural ecologyof giant petrels which we conclude help mediate any potential hormonal conflicts between parentalcare and moult.last_img read more

Changing circumpolar distributions and isoscapes of Antarctic krill: Indo‐Pacific habitat refuges counter long‐term degradation of the Atlantic sector

first_imgThe Southern Ocean provides strong contrasts in rates and directions of change in temperature and sea ice between its sectors, but it is unknown how these affect plankton species that are distributed right around Antarctica. Here, we quantify the changing circumpolar distributions of Antarctic krill, based on the CHINARE 2013/14 circum‐Antarctic expedition, plus independent analyses of compiled abundance data (KRILLBASE: 1926–2016). In the 1920s–1930s, average krill densities in the Atlantic‐Bellingshausen sector were eight times those in the other sectors. More recently, however, the concentration factor has dropped to only about twofold. This reflects a rebalancing broadly commensurate with climatic forcing: krill densities declined in the Atlantic‐Bellingshausen sector which has warmed and lost sea ice, densities may have increased in the Ross‐Pacific sector which showed the opposite climatic trend, while densities showed no significant changes in the more stable Lazarev‐Indian sectors. Such changes would impact circumpolar food webs, so to better define these we examined circumpolar trends of isotopic values in krill and other zooplankton based on the CHINARE cruise and a literature meta‐analysis. Krill δ15N values ranged significantly between sectors from 2.21‰ (Indian) to 3.59‰ (Ross‐Pacific), about half a trophic level lower than another key euphausiid, Thysanoessa macrura. These isoscapes form a baseline for interpreting the reliance of predators on euphausiids, within the varying food webs around the continent. Overall, we suggest that the Indo‐Pacific sector has acted as a refuge for the circumpolar krill stock while conditions for them deteriorated rapidly in the Atlantic sector.last_img read more