May 2021

first_imgNine species of marine littoral Halacaridae were collected from Husvik Harbour, South Georgia, all of which are new to the fauna of the island. These include Isobactrus microdens Newell, Rhombognathus auster Bartsch, R. multisetosus Newell, R. plumifer Trouessart, Agauopsis inflatus Newell, Halacarellus novellus Bartsch and Pugh, H. porellus Bartsch and Pugh, Lohmannella bihamata Viets and L. grandipora Newell. The halacarid fauna is similar to that of southern South America, though depauperate and dominated by a single species, R. auster , which was found in large numbers and at all levels of the littoral zone. Low diversity probably results from isolation and/or severe climatic factors. Isolation includes both that of suitable habitable shores and the remoteness of South Georgia itself. The main climatic limitation is exposure to freezing air and icing during winter non-submergent neap tides.last_img read more

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first_imgThe Antarctic Peninsula region has exprienced a long-term warming trend over the twentieth century, with the 1971-90 mean at Faraday being 1.9°C warmer than the mean over 1903-41 based on expedition reports. For the period prior to 1900, there is conflicting evidence from different data sources. An initial interpretation of isotopic data from ice cores suggests that the nineteenth century was warmer than the twentieth century. In contrast, snow accumulation rate data for the nineteenth century from the same ice cores suggest lower temperatures. Here we investigate these facts by studying the links between atmospheric temperature over the Antarctic Peninsula, circulation parameters and isotopic data over the period of instrumental records. We show that the relationships between these variables are complex and highly spatially variable. In particular, the correlations between temperature and δ 18O and δD are generally of the order r = 0.5 or less on timescales of one to five years. Conflicts between evidence from accumulation rate and isotopic data appear to reflect the influence of source-region effects on the isotope records. To unravel the complex isotopic records available for the Peninsula region better; additional cores must be analysed for both δ 18O and 8D at the same site.last_img read more

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Some thoughts on precautionary measures for the krill fishery

first_imgThe concept of precautionary measures for krill is discussed. A precautionary catch limit, based on the potential yield model developed by the CCAMLR Scientific Committee’s Working Group on Krill (WG-Krill) is discussed and it is concluded that such a method is appropriate in setting an overall precautionary catch limit in large areas, such as Statistical Area 48, but the approach requires considerable refinement to provide a sufficient safeguard for land-based predators. A new approach is described which takes account of the requirements of land-based predators. Implementation of the approach is discussed and the question of how the method relates to the current CCAMLR Ecosystem Monitoring Program (CEMP) is considered.last_img read more

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first_imgFeeding by juvenile Antarctic krill Euphausia superba near South Georgia was assessed during the austral summer of 1995/1996. Gut fluorescence results were compared with those from incubations in natural seawater and seawater enriched with phytoplankton and zooplankton. In natural seawater, with typically low food concentrations (median 56 mg C m-3) the median ration was 0.68% of krill carbon d-1. Phytoplankton dominated carbon in the natural incubation water but dinoflagellates, ciliates and small calanoid copepods dominated the carbon intake of krill. In both natural and enriched water, maximum clearance rates were on 1 to 3 mm calanoid copepods. Copepods larger than this (e.g. late copepodite stages of Calanoides acutus and Rhincalanus gigas) were cleared more slowly despite dominating the carbon in the enriched incubations. Oithona spp. were cleared more slowly than calanoids of similar size, despite their greater abundance and their similar contributions to available carbon. These trends could reflect detection/escape interactions between krill and copepods. With enriched food, copepods dominated krill diet, krill rations exceeded 10% of body carbon d-1 and rations did not appear to reach a plateau even at food concentrations of ~1 g C m-3. This suggests that krill could feed rapidly during periodic encounters with layers or patches of zooplankton. Gut fluorescence revealed gut passage times of 3.7 to 6.3 h and an algal carbon ration of 0.43% d-1, thus supporting the low algal carbon rations derived from the incubations. Published acoustic values of mean krill biomass north of South Georgia that summer of 8.3 g dry mass m-2 were combined with their clearance rates to give estimates of krill removing daily 0.2% of phytoplankton standing stocks, 0.6% of protozoans and 1.6% of small calanoid copepods. This impact on copepods is much higher than previous estimates from Antarctic amphipods and chaetognaths. The long generation times of Antarctic copepods mean that krill were potentially important predators of small copepods during our study.last_img read more

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first_imgThis report is the first seasonal study of anthropogenic pollutant biodegradation rates in Antarctic coastal waters. The capacity of surface waters from Rothera Research Station, Adelaide Island, Antarctica, to biodegrade the anionic surfactant sodium dodecyl sulphate (SDS) was quantified in biodegradation tests from April 1988 to January 1999. Large temporal differences in the persistence of SIDS were observed. In mid-winter (July), the SDS-biodegradation half life was twice that measured in mid-summer (January), despite small temperature differences (up to 2.45 degreesC). Comparisons between water from a pristine site and a site receiving grey-waste water from the station showed that some acclimation to SDS was occurring in the contaminated water. This resulted in SDS half lives up to similar to80 h shorter in the polluted water compared with the pristine site in the summer months when a large population of SDS-degrading bacteria had developed. Biodegradation half lives in Antarctic coastal waters (160-460 h) were generally far higher than those observed in temperate waters.last_img read more

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Environmental change and Antarctic seabird populations

first_imgRecent changes in Antarctic seabird populations may reflect direct and indirect responses to regional climate change. The best long-term data for high-latitude Antarctic seabirds (Adelie and Emperor penguins and snow petrels) indicate that winter sea-ice has a profound influence. However, some effects are inconsistent between species and areas, some in opposite directions at different stages of breeding and life cycles, and others remain paradoxical. The combination of recent harvest driven changes and those caused by global warming may produce rapid shifts rather than gradual changes.last_img read more

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first_imgThis paper presents Maximum Entropy (MaxEnt) reconstructions of krill distribution and estimates of mean krill density within two survey boxes (dimensions 80 km x 100 km) north of South Georgia. The reconstructions were generated from line-transect acoustic survey data gathered in the boxes during austral summers from 1996 to 2000. Krill densities had previously been determined at approximately 0.5 km intervals along each of the ten 80 km transects in each box, providing about 1600 density estimates per box. The MaxEnt technique uses an iterative Bayesian approach to infer the most probable krill density for each of the 32 000 0.5 x 0.5 km cells in each box, taking explicit account of the spatial relationship between densities in the observed data. Despite some very large interannual and regional differences in mean krill density, the MaxEnt approach works well, providing plausible maps of krill distribution. The maps reveal some consistent ‘hot spots’ of krill distribution, knowledge of which could aid the understanding of mechanisms influencing krill distribution, and hence krill/predator interactions. The MaxEnt technique also yields mean krill densities for each survey, for which the confidence limits are often narrower than those determined from conventional statistical analyses.last_img read more

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first_imgChanges to the radiative environment arising from stratospheric ozone (O3) depletion and subsequent associations between these changes and the pigmentation of the moss Andreaea regularis were measured in late austral spring and early summer 1998 at Rothera Point on the western Antarctic Peninsula (67 S, 68 W). A strong relationship between O3 column depth and the ratio of UV-B to PAR irradiance (FUV-B/FPAR) was recorded at ground level (r2 = 92%, P<0.001). Weaker, but significant, associations between O3 column depth and ground level unweighted and biologically effective UV-B radiation (UV-BBE) were also found. Regression analyses indicated that FUV-B/FPAR was the best predictor for concentrations of UV-B screening pigments and total carotenoids extracted from plant tissues. Concentrations of these pigments were loosely (r2 = c. 30%) but significantly (P<0.01) positively associated with FUV-B/FPAR. Concentrations of UV-B screening pigments were also positively associated with irradiances and daily doses of unweighted UV-B and UV-BBE radiation. The concentrations of chlorophylls a and b were apparently unaffected by O3 depletion. The data derived from this study suggest that changes to the radiative environment associated with stratospheric O3 depletion influence the pigmentation of A. regularis. As a corollary, flavonoids are shown to be present in tissues of A. regularis.last_img read more

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Rapid amino acid cycling in arctic and antarctic soils

first_imgAmino acids constitute one of the largest inputs of organic nitrogen (N) to most polar soils and have been hypothesized to be important in regulating vegetational succession and productivity in Arctic ecosystems. Our understanding of amino acid cycling in these soils, however, is poor. The aim of this study was to investigate the size and rate of turnover of the amino acid pool in a range of Arctic and Antarctic soils. Our results indicate that in polar soils with either high or low ornithogenic inputs the amino acid pool is small in comparison to the inorganic N pool (NO 3 – and NH 4 +). The free amino acid pool constituted only a small proportion of the total dissolved organic nitrogen (DON) pool in these soils. Here we show that these low concentrations may be due to rapid use by the soil microbial community in both Arctic and Antarctic soils. The turnover of the amino acid pool in soil was extremely rapid, with a half-life ranging from 2 to 24 h, indicating that this N pool can be turned over many hundred times each summer when polar soils are frequently unfrozen. The implications of amino acids in N cycling and plant and microbial nutrition are discussed.last_img read more

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first_imgIn this study we report the abundance, fecundity and an index of mortality of Oithonasimilis across a large latitudinal and temperature range within the Southern Ocean.The abundance of O. similis was strongly related to temperature and to depthintegrated(0-100m) chorophyll a (Chl a), abundance increasing with increasing temperature (and therefore increasing latitude) and Chl a. In situ total egg production rates and fecundity per female were significantly and positively related to temperature and Chl a. Egg hatch times lengthen as temperature decreases and in sac spawning species the next batch of eggs cannot be produced until the previous clutch hatch.Consequently, O. similis fecundity rates must rapidly decline at low temperatures,especially below 5oC. In situ fecundity rates were compared with a model ofmaximum fecundity, and were generally much lower, thus suggesting strong foodlimitation across the region studied. However the relationships of in situ andmaximum rates to temperature were similar, confirming the importance oftemperature. Further, as time taken to develop from egg to adult also rapidly extendswith declining temperature, it is increasingly unlikely that O. similis will be able to2maintain its population against typical field mortality. Our findings have broadimplications for the lower temperature range and hence geographic limits of O.similis, but also for the distribution of other sac spawning copepods and planktonicspecies generallylast_img read more

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