排序方式: 共有34条查询结果,搜索用时 15 毫秒
21.
Russell P. Herwig Nancy B. Pellerin Roar L. Irgens James S. Maki James T. Staley 《FEMS microbiology letters》1988,53(2):101-111
Abstract Chitinolytic bacteria were enumerated and isolated from marine waters and sediments along the highly productive Antarctic Peninsula. Chitinolytic bacteria were found in low concentrations (approximately 1 cell per ml) in the water column and at much higher levels in marine surface sediments (104 –105 per g). The predominant chitinolytic bacteria isolated from the water column were identified as psychrophilic Vibrio spp. Rates of chitin mineralization were measured by collection of 14 CO2 respired from 14 C-labeled chitin synthesized from chitosan and [1-14 C]acetic anhydride. Chitin mineralization rates were extremely low in the marine waters analyzed (0.00085–0.0019% of the added label respired in 48 h) and appreciably higher in the marine sediments (0.0039–0.01% per 48 h), suggesting that the sediments are much more important in chitin degradation. Such low mineralization rates suggest that chitin may be accumulating in Antarctic marine sediments, though animals may also play an important role in chitin degradation. 相似文献
22.
The diet of the Weddell seal Leptonychotes weddellii at the South Orkney Islands was investigated by the analysis of 44 and 26 faecal samples collected from the beaches of Laurie
Island from May 1999 to January 2000 and from October to December 2001, respectively. The diet was diverse and both pelagic
and benthic-demersal organisms were represented in the samples. Fish were the most frequent prey of the samples in both seasons,
and fish and krill were the most numerous prey items. Octopods predominated by mass in 1999, whereas krill constituted the
bulk of the diet in 2001, a fact that was not observed previously. Among fish, Gobionotothen gibberifrons was largely the species that contributed mostly to the diet, whereas pelagic fish could not be identified in the samples.
The results are compared with information from other study areas and discussed in relation to the consumption of krill. 相似文献
23.
Karl-Hermann Kock Leonid Pshenichnov Christopher D. Jones Joachim Gröger Rüdiger Riehl 《Polar Biology》2008,31(3):381-393
The most abundant ice fish species observed in catches off the northern tip of the Antarctic Peninsula in the last 25–30 years
has been the spiny ice fish Chaenodraco wilsoni Regan 1914. C. wilsoni has been exploited on a commercial scale from the late 1970s to the end of the 1980s off Joinville–D’Urville Islands (CCAMLR
Statistical Subarea 48.1) and in the Cosmonauts and Cooperation Seas and Prydz Bay in the Indian Ocean sector (CCAMLR Statistical
Division 58.4.2). This paper presents new information on biological features and life history characteristics of C. wilsoni, based on research survey collections along the northern Antarctic Peninsula in 2006 and 2007 and samples taken in the commercial
fishery in 1987. Length frequency compositions from the research surveys demonstrated that fish 21–34 cm long predominated
in the catches. Sexual maturity is attained at 24–25 cm. Absolute fecundity and relative fecundity is low (1,000–2,500 eggs;
6–12 eggs). Oocyte diameter varied from 4.0 to 4.9 mm very close to spawning. Spawning at the tip of the Antarctic Peninsula
is likely to occur in October–November. Remotely operated vehicle deployments in the northern Weddell Sea demonstrated that
C. wilsoni exhibit parental nest guarding where males protect the eggs. The incubation period is likely to be 8 months long. Fish feed
primarily on Antarctic krill (Euphausia superba) in the Antarctic Peninsula region and in the Cosmonauts and Cooperation Seas while fish take ice krill (Euphausia crystallorophias), Pleuragramma antarcticum and myctophids to some extent in other areas. Age determination still awaits validation. Preliminary ageing attempts suggested
a maximum age of about 8–10 years. 相似文献
24.
Yuka Unno Hirona Yamamoto Shuto Takatsuki Yoshinori Sato Takefumi Kuranaga Kazunaga Yazawa Yasuo Ono Toshiyuki Wakimoto 《Biochimica et Biophysica Acta (BBA)/Molecular and Cell Biology of Lipids》2018,1863(7):772-782
Brown adipose tissue is specialized to generate heat by dissipating chemical energy and may provide novel strategies for obesity treatment in humans. Recently, advances in understanding the pharmacological and dietary agents that contribute to the browning of white adipose tissue have been made to alleviate obesity by promoting energy expenditure. Krill oil is widely used as a health supplement in humans. In this study, the components from krill oil that promote adipogenesis of 3T3-L1 cells were screened to reveal palmitoyl lactic acid (PLA) as a promoter of adipogenesis. The PLA-induced adipocytes contained large number of small lipid droplets. Moreover, similar to the peroxisome proliferator-activated receptor (PPAR)γ agonists, pioglitazone and rosiglitazone, PLA significantly enhances adipogenesis in the presence of dexamethasone compared with PLA alone. Treatment with PLA causes a brown fat-like phenotype in 3T3-L1 cells by enhanced expression of various brown/beige cell-specific genes, such as PR domain containing 16 (Prdm16) and peroxisome proliferative activated receptor, gamma, coactivator 1 alpha (Pgc1a), as well as adiponectin gene. The expression profile of the brown/beige cell-specific genes induced by PLA was similar to that of the PPARγ agonist in 3T3-L1 cells. Our findings suggest that PLA induces a brown fat-like phenotype and, thus, likely has therapeutic potential in treating obesity. 相似文献
25.
Jeannette Yen Jason Brown Donald R. Webster 《Marine and Freshwater Behaviour and Physiology》2013,45(4):307-319
Velocity measurements were performed for the flow field generated by tethered krill Euphausia pacifica. The particle image velocimetry (PIV) technique was used to measure the velocity field in vertical planes aligned with the krill body axis. The krill generates a narrow jet-like flow behind and below the pleopods (roughly 25° below horizontal). The volume of fluid moving at greater than 10% of the maximum velocity near the pleopods is roughly 18 times larger than the volume of the krill. Thus, the hydrodynamic disturbance occupies a significantly larger region than the animal body. Other krill, sensing the flow disturbance, may take advantage of the flow induced by a neighbor to locate a mate or to draft for efficient propulsion. 相似文献
26.
Yasuo Hirano Tsuyoshi Matsuda So Kawaguchi 《Marine and Freshwater Behaviour and Physiology》2013,45(4):259-269
Antarctic krill were maintained in large aquaria at Port of Nagoya Aquarium, Japan, under controlled photoperiod and were fed on phytoplankton and enriched animal feed. Maturation and spawning were induced after the light?:?dark (L?:?D) cycle was increased from 8?:?16 or 12?:?12 to 24?:?0, or when the L?:?D cycle was held constant at 14?:?10. This study is one of the first studies that demonstrate initiation of maturation and spawning events of krill under controlled photoperiod. Out of three experimental batches of krill, a total of 28 spawning events were observed. The mean number of eggs per event was 1424 with a range between 139 and 3458. The mean hatching success per batch was 19.1%. The relation between photoperiod and maturity/spawning is discussed. Furthermore, hatching is compared to previous studies and the reason for the low success is discussed. 相似文献
27.
Six out of ten adult Ross seals that were tagged with Argos satellite-linked dive recorders off Queen Maud Land, just after
the moult in February, provided data on location and diving activity throughout a year. Shortly after tagging, the animals
headed 2,000 km north and stayed pelagic in the area south of the Antarctic Polar Front, until October when they went south into the pack-ice. Throughout the year
they made about 100 dives a day, most to a depth of 100–300 m, the deepest dive on record being 792 m, while some dives were
very shallow during their stay in the pack-ice. Most dives, outside the breeding and moulting period, lasted for 5–15 min
throughout the year. This diving behaviour is consistent with feeding on mid-water fish, like Pleurogramma antarcticum, squid, and to some extent krill (Euphausia superba), when in the pack-ice, and myctophid fish and several species of squid, when in the open ocean. The nursing period was 13 days
in mid-November, and moulting occurs in late January–early February, which is the period when sightings surveys for this species
should be done. 相似文献
28.
Syuhei Ban Nobuaki Ohi Sandric Chee Yew Leong Kunio T. Takahashi Christian W. Riser Satoru Taguchi 《Polar Biology》2007,30(10):1295-1302
The effect of solar ultraviolet radiation on the survival rate of Antarctic zooplankton was examined in February–March in
2002. We investigated survival rate of calyptopis larvae of Euphausia superba and late copepodite stages (IV and V) of large dominant calanoid species, Calanoides acutus and Calanus propinquus reared in quartz jars with three different radiation regimes (total radiation, exclusion of UVB, exclusion of UVA and UVB)
and a dark control. The survival rates of the krill larvae decreased after 3 days from start of the experiment, being below
50% at 4 days in the treatments with total radiation and exclusion of UVB, although most individuals could survive until the
end of the experiments in the treatments with exclusion of both UVA and UVB and dark control. The calanoid juveniles showed
almost same pattern of survival curves as the krill larvae did, but survived slightly longer. Although >10% of surface UVA
radiation at 340 and 380 nm penetrated down to 30 m, both C. acutus and C. propinquus were mostly distributed above 20 m. Surface swarm of the krill larvae can be often recognized in the previous studies. These
results suggest that not only solar UVB but also UVA radiation potentially lower the survival rate of Antarctic zooplankton
at depth less than 20 m. 相似文献
29.
Friedrich Buchholz 《Marine and Freshwater Behaviour and Physiology》2003,36(4):229-247
Physiological data are needed for life history studies on krill, and as parameters for input into energy budgets and models. In conjunction with moult and growth data, these may also prove useful for assessing the fishable biomass of krill. Here, the development of physiological concepts in experimental krill research is briefly evaluated, with emphasis on the gaps to be filled. Krill growth is very flexible, as well as strongly temperature and nutrition dependent. The polar Antarctic krill Euphausia superba grows as fast as the boreal species Meganyctiphanes norvegica, at least during the first 2.5 years, and the species are comparable in terms of physiological plasticity. Accordingly, as krill appear to adjust quickly to specific laboratory conditions, short-term experiments are essential if field conditions are to be reflected as closely as possible. Furthermore, direct comparisons between laboratory experiments and swarming studies in the field are advantageous. For these, M. norvegica is particularly well-suited, as swarms can be followed over longer times and more easily than in E. superba. For example, processes of moult and reproduction were found to be highly coordinated in swarms and populations of Northern krill. For this species a conceptual model of reproduction was developed based on a combination of short-term laboratory observations coupled with field data on moult and ovary stages. In further physiological experiments krill should be studied as groups when swarming. Using proxies, that is applying physiological and/or biochemical methods side by side, is a promising way to enhance the reliability of life history data. 相似文献
30.
John I. Spicer Jarl-Ove Strömberg 《Journal of experimental marine biology and ecology》2003,295(2):207-218
The effect of exposure to acutely declining oxygen tensions on O2 uptake (MO2) and ventilation has been investigated in different larval stages of Northern krill Meganyctiphanes norvegica (calytopis III/early furcilia I, late furcilia I, furcilia III and V). An ability to regulate MO2 during acutely declining PO2 began to appear about furcilia III (critical O2 tension or Pc=15.4±0.73 kPa) and had improved by furcilia V (Pc=12.6±0.39 kPa). Hypoxia-related hyperventilation was achieved by an increase in pleopod (but not thoracic limb) activity (Pc∼11 kPa), a sensitivity which also appeared at, or just before, furcilia V even though an earlier stage (furcilia III) had a full compliment of functional setose pleopods. While this regulatory ability appeared as the gills were beginning to form, furcilia V is still early in gill ontogeny compared with adults. Preexposure to very moderate hypoxia (60% and 70% O2 saturation) of furcilia III and V resulted in substantial mortality, but where it did not (furcilia V, 80% O2 saturation), there was no effect of keeping krill at this PO2 on either MO2 or ventilation, suggesting that the development of respiratory regulation in M. norvegica is not open to environmental influence in the same way as for other crustaceans. We suggest that ontogeny of pleopod control provides furcilia V+ with both a stronger means of propulsion, allowing the ontogeny of DVM but also with an ability to regulate MO2 during exposure to acutely declining PO2s. The onset of respiratory regulation (furcilia V) preceded the onset of DVM (furcilia VI+). As pleopod ontogeny is associated intimately with the ontogeny of DVM and respiratory regulation, in the Gullmarsfjord this co-occurrence is fortuitous as krill can be required during DVM to migrate into hypoxic water which they are not equipped to deal with, in physiological terms, before furcilia V. 相似文献