The biochemical composition of eggs from Macrobrachium rosenbergii in relation to embryonic development

first_img1.1. The proximate (water, protein, lipid, mineral ash) and elemental (carbon, nitrogen, phosphorus) composition of eggs of the freshwater prawn Macrobrachium rosenbergii (de Man, 1879) (Crustacea, Decapoda) were determined in relation to embryonic development. Eggs were sampled at four intervals during development, ranging from day 1 (newly spawned) to day 16 (about to hatch).2.2. Egg dry mass, lipid and carbon content all decreased during development as reserves were utilized; at the same time both water and mineral ash content increased. Although the mean content of both nitrogen and protein declined during development these were not statistically significant due to a high variance. Egg phosphorus content remained constant throughout development.3.3. In the lipid fraction triacylgycerol fatty acids provided the major fuel, although phospholipid was also utilized. The most important substrates were 16:0 and 18:1 fatty acids.4.4. There were strong suggestions of an initial increase in egg lipid content during the first 5 days of development, though this was not statistically significant and the source of the extra material is unknown.last_img read more

Mean thermospheric winds observed from Halley, Antarctica

first_imgThermospheric winds on a total of 237 nights have been studied for the effects due to geomagnetic activity, solar flux, and season. The observations have been made from 1988 to 1992 by a Fabry-Perot interferometer (FPI) operating at Halley (75.5°S, 26.6°W), Antarctica. This is the first statistical study of thermospheric winds near the southern auroral zone. The main factor affecting the wind velocities is the geomagnetic activity. Increases in activity cause an increase in the maximum equatorward wind, and cause the zonal wind in the evening to become more westward. Smaller changes in the mean wind occur with variations in season and solar flux. The small variation with solar flux is more akin to the situation found at mid-latitudes than at high latitudes. Since the geomagnetic latitude of Halley is only 61°, it suggests that the variability of the wind with solar flux may depend more on geomagnetic than geographic latitude. These observations are in good agreement with the empirical Horizontal Wind Model (HWM90). However, comparisons with predictions of the Vector Spherical Harmonic Model (VSH) show that for low geomagnetic activity the predicted phases of the two components of the wind closely resemble the observations but the modelled amplitudes are too small by a factor of two. At high geomagnetic activity the major differences are that modelled zonal velocity is too westward in the evening and too eastward after 04 UT. The modelled ion densities at the F-region peak are a factor of up to 9 too large, whilst the predicted mean value and diurnal variation of the altitude of the peak are significantly lower than those observed. It is suggested that these differences result from the ion loss rate being too low, and an inaccurate model of the magnetic field.last_img read more

Fishery biology of the seven star flying squid Martialia hyadesi at South Georgia during winter

first_imgA scientific research fishing expedition targeting the oceanic/slope ommastrephid squid Martialia hyadesi was undertaken by a Korean-registered squid jigger in CCAMLR area 48.3, near South Georgia, in June 1996, providing the first opportunity to collect data on the fishery biology of this species during the austral winter. Fishing took place over a period of 8 days; a series of eight drifts was undertaken along an approximately east/west transect of about 200 nautical miles to the north and west of South Georgia, over depths ranging from 1,700 to 2,713 m. All fishing was to the south of the Antarctic Polar Front. Data were collected on sea surface temperature, catch per unit of effort, size, sex, maturity status and stomach contents of the catch and a sample of squid was aged by counting putative, daily microgrowth increments in the sectioned statolith. All squid were caught by jigs operating at depths from 80 to 100 m to the surface. Catch per unit of effort per drift varied between 1.0 and 21.9 kg min−1 and there was no by-catch. Greatest numbers of squid were caught at dusk and dawn. Mantle length fell in the range 220–350 mm (males) and 212–370 mm (females). Most males were sexually mature (Lipinski’s stages IV–V) and most females were immature (stage II). The absence of mature females suggests that no spawning takes place in this area during the austral winter. The squid were up to 1␣year of age and had hatched during the previous winter. They were apparently from the same cohort as had been sampled at the Antarctic Polar Front in February 1996. Myctophids were the major prey in the stomach contents and the squid Gonatus antarcticus was also important; crustaceans were relatively unimportant. The results suggest that concentrations of Martialia hyadesi are present in the vicinity of South Georgia, south of the Antarctic Polar Front, during the austral winter. The squid are actively feeding during the austral winter and are susceptible to jigging gear.last_img read more

Importance of seasonal and annual layers in controlling backscatter to radar altimeters across the percolation zone of an ice sheet

first_imgRadar altimeters are one of the main tools for measuring elevation changes across the Antarctic and Greenland ice sheets and larger ice caps. A ground-based radar was deployed in autumn 2004 and spring 2006 in the percolation zone of the Greenland Ice Sheet. This radar is a high bandwidth system operating in the Ku band, the same frequency as several satellite altimeters. Measurements were made over an elevation range of 1795 to 2350 m, along with snow pit and shallow core studies. These measurements demonstrate the spatial and temporal variations in the backscatter. Relative strengths of surface and volume reflections change dramatically between spring and autumn and there is also high spatial variability across the percolation zone. The extent of percolation will affect elevation estimates made by radar altimeters.last_img read more

Origins of plasmaspheric hiss

first_imgPlasmaspheric hiss is an electromagnetic wave emission responsible for electron loss from the radiation belts, particularly in the slot region (2 < L < 3). There are two leading theories for the origin of plasmaspheric hiss: in situ amplification of wave turbulence in space and lightning-generated whistlers. Here we analyze CRRES wave data together with the global distribution of lightning to test both theories. Using the entire CRRES wave database, we split the data into seven frequency bands between 0.1 and 5 kHz and examine the ionospheric mapping of the wave intensities in the slot region as a function of season, magnetospheric location, and magnetic activity. The wave intensities peak in the frequency range 0.2–0.5 kHz and become progressively smaller at higher frequencies. The wave intensities at low frequencies, f 2 kHz, increase with flash rate, are stronger on the nightside, and peak during the boreal summer. The wave intensities increase with magnetic activity for all frequencies on the dayside but are independent of magnetic activity on the nightside. The data suggest that in situ amplification of wave turbulence in space is the main source of wave power below 1 kHz, whereas wave power above 2 kHz is more related to lightning-generated whistlers. The results suggest that natural plasma turbulence should dominate the loss of relativistic (approximately MeV) electrons in the slot region 2 < L < 3.last_img read more

Size and structure of bacterial, fungal and nematode communities along an Antarctic environmental gradient

first_imgThe unusually harsh environmental conditions of terrestrial Antarctic habitats result in ecosystems with simplified trophic structures, where microbial processes are especially dominant as drivers of soil-borne nutrient cycling. We examined soil-borne Antarctic communities (bacteria, fungi and nematodes) at five locations along a southern latitudinal gradient from the Falkland Islands (51 degrees S) to the base of the Antarctic Peninsula (72 degrees S), and compared principally vegetated vs. fell-field locations at three of these sites. Results of molecular (denaturing gradient gel electrophoresis, real-time PCR), biochemical (ergosterol, phospholipid fatty acids) and traditional microbiological (temperature- and medium-related CFU) analyses were related to key soil and environmental properties. Microbial abundance generally showed a significant positive relationship with vegetation and vegetation-associated soil factors (e.g. water content, organic C, total N). Microbial community structure was mainly related to latitude or location and latitude-dependent factors (e.g. mean temperature, NO3, pH). Furthermore, strong interactions between vegetation cover and location were observed, with the effects of vegetation cover being most pronounced in more extreme sites. These results provide insight into the main drivers of microbial community size and structure across a range of terrestrial Antarctic and sub-Antarctic habitats, potentially serving as a useful baseline to study the impact of predicted global warming on these unique and pristine ecosystems.last_img read more

Antarctic subglacial lake exploration: a new frontier in microbial ecology

first_imgTo date, wherever life has been sought on Earth, it has almost always been found—from high in the stratosphere (Imshenetskii et al., 1975, 1978, 1986; Wainwright et al., 2003) to deep in the ocean trenches (Takamia et al., 1997; D’Hondt et al., 2004) and even within the Earth’s crust itself (Pedersen, 2000). Microorganisms have also been found in some of the most extreme environments. They have been found to exist in ice, boiling water, acid, salt crystals, toxic waste and even in the water cores of nuclear reactors (Rothschild and Mancinelli, 2001).Antarctic subglacial lake ecosystems have the potential to be one of the most extreme environments on Earth, with combined stresses of high pressure, low temperature, permanent darkness, low-nutrient availability and oxygen concentrations derived from the ice that provided the original meltwater (Siegert et al., 2003), where the predominant mode of nutrition is likely to be chemoautotrophic. Yet, to date, the identification of significant subglacial bacterial activity in the Arctic, beneath glaciers (Skidmore et al., 2000, 2005) and in subglacial lakes (Gaidos et al., 2004), as well as extensive work on permafrost communities and work in the deep sea, suggests that life can survive and potentially thrive in these types of environment. Microbial life has been shown to function at gigapascal pressures (Sharma et al., 2002) and bacteria recovered from the deep ocean at around 4000 m have been shown to retain both structural integrity and metabolic activity. They have shown activity in the Antarctic at −17 °C (Carpenter et al., 2000) and to exist in the pore spaces between ice crystals (Thomas and Dieckmann, 2002).last_img read more

Palaeomagnetic and biostratigraphic dating of marine sediments from the Scotia Sea, Antarctica: First identification of the Laschamp excursion in the Southern Ocean

first_imgEstablishing accurate chronologies for Late Quaternary Antarctic marine sediments is often a challenge due to variable radiocarbon reservoir effects, the presence of coarse-grained glacial material and a lack of carbonate preservation. Without accurate age control the scope for precise comparison of palaeoenvironmental records is severely limited. In order to address this, we combined diatom abundance stratigraphy, magnetic and radiocarbon methods to build an accurate chronology for two late glacial marine sedimentary sequences, from cores TPC063 and TPC286 from the Scotia Sea, SW Atlantic. Palaeomagnetic data provide the first evidence for the Laschamp geomagnetic excursion (similar to 41 cal ka B.P.) in Antarctic marine sediments and a relative palaeointensity curve that is tuned to the independently dated SAPIS relative palaeointensity reference stack. Together, these key findings provide an accurate age model between 43.7 cal ka B.P. and 25.3 cal ka B.P. The age model was further extended to 17.3 cal ka B.P. through identification of the diatom Eucampia antarctica 2Ea(1) abundance stratigraphy datum. Radiocarbon dating did not provide dates that were in stratigraphic order, and magnetic susceptibility only identified glacial interglacial transitions in one core. We demonstrate that combining geomagnetic and diatom abundance data can enable generation of high-resolution geochronologies for glacial sediments from the Scotia Sea, and offers the potential for more widespread comparison and correlation of Antarctic and Southern Ocean palaeoenvironmental records. (C) 2011 Elsevier B.V. All rights reserved.last_img read more

Anomalous mid-twentieth century atmospheric circulation change over the South Atlantic compared to the last 6000 years

first_imgDetermining the timing and impact of anthropogenic climate change in data-sparse regions is a considerable challenge. Arguably, nowhere is this more difficult than the Antarctic Peninsula and the subantarctic South Atlantic where observational records are relatively short but where high rates of warming have been experienced since records began. Here we interrogate recently developed monthly-resolved observational datasets from the Falkland Islands and South Georgia, and extend the records back using climate-sensitive peat growth over the past 6000 years. Investigating the subantarctic climate data with ERA-Interim and Twentieth Century Reanalysis, we find that a stepped increase in precipitation across the 1940s is related to a change in synoptic atmospheric circulation: a westward migration of quasi-permanent positive pressure anomalies in the South Atlantic has brought the subantarctic islands under the increased influence of meridional airflow associated with the Amundsen Sea Low. Analysis of three comprehensively multi-dated (using 14C and 137Cs) peat sequences across the two islands demonstrates unprecedented growth rates since the mid-twentieth century relative to the last 6000 years. Comparison to observational and reconstructed sea surface temperatures suggests this change is linked to a warming tropical Pacific Ocean. Our results imply ‘modern’ South Atlantic atmospheric circulation has not been under this configuration for millennia.last_img read more

Classification of Southern Ocean krill and icefish echoes using random forests

first_imgTarget identification remains a challenge for acoustic surveys of marine fauna. Antarctic krill, Euphausia superba, are typically identified through a combination of expert scrutiny of echograms and analysis of differences in mean volume backscattering strengths (SV; dB re 1 m−1) measured at two or more echosounder frequencies. For commonly used frequencies, however, the differences for krill are similar to those for many co-occurring fish species that do not possess swimbladders. At South Georgia, South Atlantic, one species in particular, mackerel icefish, Champsocephalus gunnari, forms pelagic aggregations, which can be difficult to distinguish acoustically from large krill layers. Mackerel icefish are currently surveyed using bottom-trawls, but the resultant estimates of abundance may be biased because of the species’ semi-pelagic distribution. An acoustic estimate of the pelagic component of the population could indicate the magnitude of this bias, but first a reliable target identification method is required. To address this, random forests (RFs) were generated using acoustic and net sample data collected during surveys. The final RF classified as krill, icefish, and mixed aggregations of weak scattering fish species with an overall estimated accuracy of 95%. Minimum SV, mean aggregation depth (m), mean distance from the seabed (m), and geographic positional data were most important to the accuracy of the RF. Time-of-day and the difference between SV at 120 kHz (SV 120) and that at 38 kHz (SV 38) were also important. The RF classification resulted in significantly higher estimates of backscatter apportioned to krill when compared with widely applied identification methods based on fixed and variable ranges of SV 120–SV 38. These results suggest that krill density is underestimated when those SV-differencing methods are used for target identification. RFs are an objective means for target identification and could enhance the utility of incidentally collected acoustic data.last_img read more