Some aspects of feeding in the Antarctic krill,Euphausia superba

Polar Biology - The interaction between feeding activity, swarming behaviour and vertical migration in Antarctic krill, Euphausia superba Dana, was examined by a combination of laboratory...     

Distribution of Euphausia crystallorophias within Prydz Bay and its importance to the inshore marine ecosystem

Summary Within Prydz Bay (Antarctica) Euphausia crystallorophias was found to be restricted to the continental shelf (<1000 m). Densities greater than 1000 indiv. 1000 m^-3 were observed nearer the coast, while lower densities were seen further offshore. E. crystallorophias was the dominant euphausiid in the shelf region with the occurrence of Euphausia superba increasing close to the continental shelf break and further off the shelf. E. crystallorophias was found to be an important component of the diet of Adelie penguins (Pygoscelis adeliae) breeding on Magnetic Island in Prydz Bay. The importance of E. crystallorophias as a dietary item for other predators in the region is discussed.     

Mesozooplankton distribution patterns and grazing impacts of copepods and Euphausia crystallorophias in the Amundsen Sea, West Antarctica, during austral summer

The rapid melting of glaciers as well as the loss of sea ice in the Amundsen Sea makes it an ideal environmental setting for the investigation of the impacts of climate change in the Antarctic on the distribution and production of mesozooplankton. We examined the latitudinal distribution of mesozooplankton and their grazing impacts on phytoplankton in the Amundsen Sea during the early austral summer from December 27, 2010 to January 13, 2011. Mesozooplankton followed a latitudinal distribution in relation to hydrographic and environmental features, with copepods dominating in the oceanic area and euphausiids dominating in the polynya. Greater Euphausia crystallorophias biomass in the polynya was associated with lower salinity and higher food concentration (chlorophyll a, choanoflagellates, and heterotrophic dinoflagellates). The grazing impact of three copepods (Rhincalanus gigas, Calanoides acutus, and Metridia gerlachei) on phytoplankton was low, with the consumption of 3 % of phytoplankton standing stock and about 4 % of daily primary production. Estimated daily carbon rations for each of the three copepods were also relatively low (<10 %), barely enough to cover metabolic demands. This suggests that copepods may rely on food other than phytoplankton and that much of the primary production is channeled through microzooplankton. Daily carbon rations for E. crystallorophias were high (up to 49 %) with the grazing impact accounting for 17 % of the phytoplankton biomass and 84 % of primary production. The presence of E. crystallorophias appears to be a critical factor regulating phytoplankton blooms and determining the fate of fixed carbon in the coastal polynyas of the Amundsen Sea.     

Electrophoretic investigation of genetic variation in two krill species Euphausia superba and E. crystallorophias (Euphausiidae)

Summary Specimens of Euphausia superba and of E. crystallorophias from different locations were analyzed electrophoretically for protein variation. The present study extends previous genetic studies on E. superba by analyzing samples from the East Wind Drift and repeat samples from the Bransfield Strait, Elephant Island and the Weddell Sea. E. crystallorophias was collected in the Weddell Sea and around the Antarctic Peninsula in order to provide information on the breeding structure of the species in this region. For all loki taking all sampling sites together for both species except GPI in E. crystallorophias no significant deviation of phenotype distributions from random mating expectations was observed. Furthermore, the allele distributions in all polymorphic loci for both species were found to be homogeneous. Estimates of genetic distance between samples within each species are low (0.0001 to 0.0003 in E. superba and 0.0001 to 0.0002 in E. crystallorophias), and are consistent with results expected for samples from a single interbreeding population. Estimate of genetic distance between these two species was 0.9729. These results suggest that for each species specimens from all locations investigated in the Bransfield Strait and Weddell Sea belong to a single genetically homogeneous population. A possible mechanism for maintaining such homogeneity and the implications for fishery management are discussed.     

Functional biodiversity of lipids in Antarctic zooplankton: Calanoides acutus, Calanus propinquus, Thysanoessa macrura and Euphausia crystallorophias

Zooplankton samples were collected in January 1993 off Dronning Maud Land along a transect from open waters to the marginal ice zone close to the Antarctic ice shelf. Thysanoessa macrura was caught in open waters while Calanoides acutus and Calanus propinquus were mainly sampled between ice floes in the marginal ice zone. The “ice-krill”Euphausia crystallorophias was found over the shelf directly associated with ice floes. T. macrura had a lipid content up to 36% of its dry weight with the dominant lipid class, wax ester, accounting for 45–50% of the total lipid. The predominance of 18:1 fatty alcohols is the striking characteristic of the wax esters. Small specimens of E. crystallorophias had lipid levels up to 26% of their dry weight with, unexpectedly, triacylglycerols being the dominant lipid (up to 41% of total lipid). The small levels of wax esters in these animals (3–6% of total lipid) had phytol as a major constituent. Large specimens of E. crystallorophias had up to 34% of their dry weight as lipid, with wax esters (47% of total lipid) dominated by 16:0 and 14:0 fatty alcohols as the major lipid. Calanus propinquus had lipid levels of up to 34% of their dry weight, with triacylglycerols (up to 63% of total lipid) being the dominant lipid. High levels of 22:1 (n-9) fatty acid were present in the triacylglycerols. Calanoides acutus had lipid levels up to 35% of the dry weight with wax esters accounting for up to 83% of total lipid. High levels of (n-3) polyunsaturated fatty acids were recorded with 20:5(n-3), 22:6(n-3) and 18:4(n-3) being the dominant moieties. On the basis of their lipid compositions we deduce that: (1) Calanoides acutus is the strictest herbivore among the four species studied, heavily utilizing the typical spring bloom; (2) T. macrura is essentially omnivorous, probably utilizing the less defined bloom situations found in oceanic waters; (3) E. crystallorophias is an omnivore well adapted to utilize both a bloom situation and to feed on ice algae and micro-zooplankton associated with the ice; (4) Calanus propinquus seems to be the most opportunistic feeder of the four species studied, probably grazing heavily on phytoplankton during a bloom and, during the rest of the year, feeding on whatever material is available, including particulates, flagellates and other ice-associated algae. We conclude that the different biochemical pathways generating large oil reserves of different compositions, enabling species to utilize different ecological niches, are major determinants of biodiversity in polar zooplankton. Accepted: 22 June 1998     

Some aspects of the seasonal distribution of flagellates in mountain lakes

In a larger regional survey in Tyrol, phytoplankton species composition and biovolume of mid-altitude and high-mountain lakes was studied. Results from eight lakes showed that flagellates (mainly Chrysophyceae, Dinophyceae, and Cryptophyceae) are important components of the phytoplankton.In the mid-altitude lakes a spring and an autumn maximum of Chrysophyceae as well as a summer maximum of large dinoflagellates are observed, whereas Cryptophyceae and Dinophyceae show irregular distributions. In the high-mountain lakes the seasonal variations of phytoplankton, including flagellates, are limited by the long duration of the winter situation. However similar sequences of phytoplankton assemblages as in the midaltitude lakes can be observed. Flagellates in high-mountain lakes are important to sustain phytoplankton standing crop under the winter snow and ice cover.In order to show similarities and differences of high-mountain and mid-altitude lakes, vertical profiles of phytoplankton from three lakes and seasonal patterns of Gymnodinium uberrimum from two lakes are compared. In addition the patterns of cryptomonads differing in their ecological requirements (Cryptomonas spp. and Rhodomonas minuta) are shown for a meromictic mid-altitude lake.     

Use of oxygen microsensors to measure the respiration rates of five dominant copepods and Euphausia crystallorophias furcilia from the Amundsen Sea,West Antarctica

The individual respiration rates of five biomass-dominant copepods (Calanoides acutus, Rhincalanus gigas, Metridia gerlachei, Calanus propinquus and Paraeuchaeta antarctica), and Euphausia crystallorophias furcilia, from the Amundsen Sea, West Antarctica, were determined using a Clark-type oxygen microsensor affording high temporal resolution. Measurements were conducted on specimens collected from waters exhibiting a very narrow temperature range (?1.68 to ?1.32 °C), at sites located between 71 and 75°S, during the summer (31 January–20 March 2012). A short incubation time (3 h) was sufficient to reveal significant declines in dissolved oxygen concentrations by 12–45%. The respiration rates of the copepods and E. crystallorophias furcilia were within the ranges of previously reported values. The respiration rates of relatively large-bodied species were rather low, whereas the smaller species generally exhibited higher respiration rates. The data show that this simple microsensor technique is a useful high-resolution non-invasive means of investigating the metabolism of zooplankton in the Southern Ocean. The method could be used in other situations when such information is required.     

Some aspects of the morphology and distribution of Microsoriurn linguaeforrne (Polypodiaceae)

Microsorium linguaeforme is reported for the first time from India. Its rhizome is slender, much elongated with a highly dissected stele and leaf gaps in a single median dorsal row. The characteristic branching pattern is a modification of the common pattern in Polypodiaceae, resulting from the displacement of leaf-associated branches and the precocious development of the most basal secondary branch of each primary branch. The first two or three leaves of juvenile plants have no associated branches; thereafter, abaxially-originating traces t o solitary branches are progressively displaced so that the branch trace is close to the preceding leaf trace. Stomata of adult leaves are Copolomesoperigenous and of juvenile leaves Eupolomesoperigenous. The spores are monolete and with a smooth exine. Spore germination is of the Vitiariatype and prothallial development of the Kauliniatype. It is concluded that M. linguaeforme is closely allied to Leptochilus and is probably parental to it.     

Some general aspects of the distribution and epidemiology of bovine trypanosomosis in southern Africa

Bovine trypanosomosis occurs in vast areas of southern Africa. Its epidemiology and impact on cattle production is determined largely by the level of interaction between tsetse and cattle. Four situations can be distinguished. First, areas where cattle are absent. Second, zones where cattle have been introduced in game areas but where game is still abundant and constitutes the major source of food for tsetse. Third, areas where, often because of human interference, the density of game animals is low and cattle constitute the main source of food and finally, areas where cattle occur at the edge of tsetse-infested zones. In southern Africa, the impact of the disease on cattle production varies according to the epidemiological circumstances. The disease has an epidemic character with significant impacts on production in areas where cattle have been introduced recently or along the interface between tsetse-infested game areas and tsetse-free cultivated areas. Bovine trypanosomosis has an endemic character, with little impact on production, in areas where tsetse mainly feed on cattle and where the invasion of tsetse is low. Options for the control of bovine trypanosomosis will vary according to the epidemiological circumstance. In particular, the control of tsetse with insecticide-treated cattle will only be effective when a large proportion of feeds are taken from cattle over a large area and when the invasion of tsetse can be reduced sufficiently.     

Small-scale spatial distribution of the euphausiid Euphausia pacifica and overlap with planktivorous fishes

The spatial distribution of zooplankton and planktivorous fishin Saanich Inlet, British Columbia was characterized with a445 kHz multibeam sonar capable of localizing individual animalsin three dimensions. Numerical simulation of data processingprocedures indicates that this instrument has sufficient resolutionto characterize zooplankton spatial distributions using Lloyd’sindex of patchiness and nearest neighbour distance (NND) measures.Zooplankters at this site were dominated by the euphausiid Euphausiapacifica which underwent diel vertical migration (DVM). Fish(mainly herring and walleye pollock) were only abundant at thisdeep-water station at night. Analysis of 4 m³ volumes over scalesof     

Spatial distribution of Euphausia pacifica (Euphausiacea: Crustacea) in the Yellow Sea

Euphausia pacifica were collected in the Yellow Sea in summer(August, 1997) and winter (February, 1998), and their distributionwas investigated in terms of the developmental stages in relationto environmental factors (temperature, salinity and chlorophylla). In summer, the water column was highly stratified with athermocline between 10–30 m depth, whereas the water columnwas well mixed in winter. Seasonal variation in temperaturewas large, ranging between 6.3 and 28.8°C in summer and3.9 and 12.2°C in winter. Chlorophyll a concentration changedlittle seasonally but a high concentration was observed in coastalareas. Salinity in the two seasons varied little spatio-temporally.In the studied area and sampling period, E.pacifica was themost dominant euphausiid species (99.7 and 99.8% in summer andwinter, respectively), and comprised adults and juveniles (74.6%in summer and 41.9% in winter), furcilia (17.5 and 44.9%) andcalyptopis (7.9 and 13.1%). The spatial distribution of theE.pacifica population varied seasonally depending on developmentalstage and appeared to be related primarily to the seawater temperatureand secondly to the chlorophyll a concentration, but not tosalinity. In summer, adults were abundant in areas below 10°C,and furcilia and calyptopis above 9°C. In winter, adultswere confined to areas between 7 and 10°C, and furciliaand calyptopis, to areas between 6 and 8°C. Furcilia andcalyptopis were concentrated in the vicinity, or at the centerof chlorophyll a-rich water masses, whereas adults seemed toavoid those water masses.     

Some aspects of the plant radioresistance

Mutant strains of unicellular green algae--Chlorella and Chlamydomonas which differ in their radioresistance have been investigated at different levels: cellular, molecular, biochemical and ultrastructural. It is obtained that several futures are typical for investigated strains. There are several features typical for radioresistant mutant strains investigated by us: in some cases a relationship was found between radioresistance and ssb-DNA repair efficiency; a high level of SH-groups; SOD; pigments content, especially carotenoids and chlorophyll a; a lower level of Pro content; a stability of the ultrastructural cell components or/and of the presence and structure of the cell envelope.     

Quantitative aspects of the distribution of invertebrates in the benthos of a small stream system in western Ireland

The invertebrate community of a small stream system in western Ireland is described from the results of two sampling programmes. The investigation was conducted at four sites which occurred within the same range of altitude (between 60 and 130 m O.D.) and the greatest differences between them were rock size, current intensity and the amount and type of detritus in the substratum. Approximately 60,000 invertebrates were identified and almost 100 taxa were listed. Attempts which were made to relate the occurrence of certain taxa to three factors (rock size, current intensity and detrital content) showed that detrital content was the most significant. Using empirical clustering techniques efforts were made to demonstrate zonation of the invertebrates taken during one of the two sampling programmes and the groups which were so obtained were further amalgamated subjectively. The resemblance of the resulting pattern to lotic zonation is briefly discussed.