Feeding 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.
This 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.
Recent 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.
This 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.
Changes 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.
Amino 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.
In 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 generally
Many shallow water polar communities demonstrate considerable change along a bathymetric gradient. However, it is currently unclear whether community change is generally continuous or discrete. To determine the nature of community change with depth, extensive photographic surveys at three sites at Adelaide Island, West Antarctic Peninsula, were conducted along a bathymetric gradient of 5-35 m depth. Macroalgae were largely absent at the sites, so only distinguishable macrofauna were counted and analysed. Faunal abundance was greatest at the shallowest stations of the depth transects, whilst richness at both species and phylum level increased with depth. Variability in community structure between replicate transects decreased with depth, so that assemblages at > 25 m depth were more homogenous. Depth had a highly significant effect on total abundance, species richness and community structure, and it is likely that the frequency of ice disturbance, which also decreases with depth, drives this pattern. Overall, high variability between transects at each site was recorded, which suggested considerable patchiness at the scale of tens of meters. Community change along the bathymetric gradient was continuous and no evidence of discrete zones of assemblages was recorded.
Quantitative scaling relationships among body mass, temperature and metabolic rate of organisms are still controversial, while resolution may be further complicated through the use of different and possibly inappropriate approaches to statistical analysis. We propose the application of a modelling strategy based on the theoretical approach of Akaike’s information criteria and non-linear model fitting (nlm). Accordingly, we collated and modelled available data at intraspecific level on the individual standard metabolic rate of Antarctic microarthropods as a function of body mass (M), temperature (T), species identity (S) and high rank taxa to which species belong (G) and tested predictions from metabolic scaling theory (mass-metabolism allometric exponent b = 0.75, activation energy range 0.2–1.2 eV). We also performed allometric analysis based on logarithmic transformations (lm). Conclusions from lm and nlm approaches were different. Best-supported models from lm incorporated T, M and S. The estimates of the allometric scaling exponent linking body mass and metabolic rate resulted in a value of 0.696 ± 0.105 (mean ± 95% CI). In contrast, the four best-supported nlm models suggested that both the scaling exponent and activation energy significantly vary across the high rank taxa (Collembola, Cryptostigmata, Mesostigmata and Prostigmata) to which species belong, with mean values of b ranging from about 0.6 to 0.8. We therefore reached two conclusions: 1, published analyses of arthropod metabolism based on logarithmic data may be biased by data transformation; 2, non-linear models applied to Antarctic microarthropod metabolic rate suggest that intraspecific scaling of standard metabolic rate in Antarctic microarthropods is highly variable and can be characterised by scaling exponents that greatly vary within taxa, which may have biased previous interspecific comparisons that neglected intraspecific variability.
Previous studies have revealed that ion drift and neutral wind speeds at ~400 km in the polar cap (>80° magnetic latitude) are on average larger in the Northern Hemisphere (NH) than in the Southern Hemisphere, which is at least partly due to asymmetry in the geomagnetic field. Here we investigate for the first time how these asymmetries depend on season and on solar/geomagnetic activity levels. Ion drift measurements from the Cluster mission show little seasonal dependence in their north-south asymmetry when all data (February 2001–December 2013) are used, but the asymmetry disappears around June solstice for high solar activity and around December solstice for low solar activity. Neutral wind speeds in the polar cap obtained from the Challenging Minisatellite Payload spacecraft (January 2002–December 2008) are always larger in the summer hemisphere, regardless of solar activity, but the high-latitude neutral wind vortices at dawn and dusk tend to be stronger in the NH, except around December solstice, in particular, when solar activity is low. Simulations with the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) more or less capture the behavior of the ion drift speeds, which can be explained as a superposition of seasonal and geomagnetic field effects, with the former being stronger for higher solar activity. The behavior of the neutral wind speed and vorticity is not accurately captured by the model. This is probably due to an incorrect seasonal cycle in plasma density around ~400 km in CMIT, which affects the ion drag force. This must be addressed in future work.