排序方式: 共有19条查询结果,搜索用时 426 毫秒
1.
Gut clearance rates of starving and continuously feeding Acartiatonsa were estimated. During the initial 30 min the rates weresimilar (0.045 and 0.048 min1, respectively; 14°C)but thereafter starving animals expelled the remains of theirgut contents at half the rate (0.019 min1) of fed ones(0.048). Pigment destruction was estimated by (i) incubationexperiments over 34 days, (ii) silica to pigment ratioin algae and faeces and (iii) by gut filling experiments. Theincubations showed that 8% of the ingested pigments were destroyedto nonfluorescent residues during gut passage. The silica topigment ratio method gave an average of 11 % (1 24) destructionand gut-filling experiments showed no systematic differencebetween ingestion measured as gut filling rate (fluorescence)and particle reduction.
1Present address: Kristineberg Marine Biological Station, S-45034 Fiskebäckskil, Sweden 相似文献
2.
During the spring of 1994, we determined the factors responsiblefor the decline of the seasonal diatom bloom in the Gullmarfjord, on the west coast of Sweden. Four species constituted>75% of the biomassDetonula confervacea, Chaetocerosdiadema, Skeletonema costatum and Thalassiosira nordenskioeldiireachingconcentrations of 4900, 350, 8200 and 270 cells ml1,respectively. Growth of phytoplankton was exponential (growthrate = 0.12 day1) from 3 to 21 March, after which a galewith winds >15 m s1 caused massive aggregation. Amaximum of 130 p.p.m. (v/v) of marine snow aggregates was observedby in situ video at the peak of the bloom. Critical concentrations(Jackson, Deep-Sea Res., 37, 11971211, 1990) were similarto observed showing that coagulation theory could explain thesudden decline of the bloom. The heterotrophic dinoflagellateGyrodinium cf. spirale increased exponentially after the peakof the bloom with maximum (temperature-adjusted) growth rates.After the rapid aggregation and sedimentation of the bloom,they were able to control any further growth of diatoms. Nitrateand silicate were never depleted, but phosphate may have beenlimiting by the end of the study period. We conclude that massaggregation during a gale marked the end of the bloom, and thatintense grazing by heterotrophic dinoflagellates prevented anysubsequent increase of diatoms. 相似文献
3.
Life history and population dynamics of the chaetognath Sagitta elegans in central Long Island Sound
One chaetognath species is found in Long Island Sound. Sagittaelegans. Individuals ranging in length from 1.5 to 22 mm werefound from March through August. Length at maturity ranged from13 to 22 mm. Maximum abundances. 67 ind m3 in 1982 and106 md m in 1983. occurred in early summer Two cohorts wereseen during both years, beginning as eggs produced in April-May.and in late June. The population is not endemic to Long IslandSound because temperatures during summer exceed 19C, whichseems to be lethal. The appearance of the first cohort in springis due to advection of animals from shelf waters. The secondcohort, however, is produced locally. The S. elegans populationin Long Island Sound is unique in two ways. First, the adultsare considerably longer than predicted by McLaren's (1963) Belhrdekfunction, and second, the total abundance of eggs, juvenilesand adults is at least two times higher than anywhere else. 相似文献
4.
Metabolism of tritium-labelled pyridoxine and pyridoxine 5'-phosphate in the central nervous system 总被引:1,自引:1,他引:0
H G Tiselius 《Journal of neurochemistry》1973,20(4):937-946
Abstract— [3H]Pyridoxine and [3H]pyridoxine 5′-phosphate have been injected into rats and mice. The uptake in brain tissue has been studied by comparing the concentrations of labelled compounds in serum, cerebrospinal fluid and brain tissue. Labelled pyridoxine passes rapidly into brain tissue, whereas the uptake of pyridoxine 5′-phosphate occurs at a much slower rate. Perchloric acid extracts of brain have been fractionated by ion-exchange chromatography and the distribution of isotope between the different forms of the vitamin has been determined at different times after the administration. The time sequence of the metabolic transformation is: pyridoxine+→ pyridoxine 5′-phosphate → pyridoxal 5′-phosphate → pyridoxamine 5′-phosphate. After the initial transformation period about 40 per cent of the isotope is recovered in each of the pyridoxal 5′-phosphate and pyridoxamine 5′-phosphate fractions. 相似文献
5.
6.
Metabolic interconversions of different forms of vitamin B6 总被引:2,自引:0,他引:2
7.
8.
Knowledge of how energetic parameters relate to fluctuating factors in the natural habitat is necessary when evaluating the
role of gelatinous zooplankton in the carbon flow of coastal waters. In laboratory experiments, we assessed feeding, respiration
and growth of the ctenophore, Pleurobrachia pileus, and constructed carbon budgets. Clearance rates (F, l d−1) of laboratory-reared Acartia tonsa as prey increased as a function of ctenophore polar length (L, mm) as F = 0.17L
1.9. For ctenophores larger than about 11 mm, clearance rate was depressed in containers of 30–50 l volume. Clearance rates on
field-collected prey were highest on the copepod, Centropages typicus, intermediate on the cladoceran, Evadne
nordmanni and low on the copepods, Acartia clausi and Temora longicornis. Specific growth rates of 8–10 mm P. pileus increased with increasing prey concentrations to a maximum of 0.09 d−1 attained at prey carbon densities of 40 and 100 μg C l−1 of Artemia salina and A. tonsa, respectively. Weight-specific respiration rates increased hyperbolically with prey concentration. From experiments in which
growth, ingestion and respiration were measured simultaneously, a carbon budget was constructed for individuals growing at
maximum rates; from the measured parameters, the assimilation efficiency and net growth efficiency were estimated to be 22
and 37%, respectively. We conclude that the predation rates of P. pileus depend on ctenophore size, prey species, prey density and experimental container volume. Because the specific growth rates,
respiration, assimilation and net growth efficiencies all were affected by food availability, knowledge of the ambient prey
field is critical when evaluating the role of P.
pileus in the carbon flow in coastal waters. 相似文献
9.
10.
Sérgio Miguel Leandro Peter Tiselius Sónia Cotrim Marques Francisco Avelelas Catarina Correia Pedro Sá Henrique Queiroga 《Hydrobiologia》2014,730(1):139-152
Although growth in adult copepods is frequently assumed to be similar to juvenile growth, some evidence have pointed out that under in situ conditions, it can be lower, with, as a consequence, underestimation of secondary production. In addition, under field conditions, juvenile growth in copepods is close to maximum rates estimated at food-saturated conditions. Based on previous assumptions, this study aimed to test the applicability of a new approach for copepod production estimate, derived from temperature-dependent growth models and in situ data, such as seawater temperature and copepod biomass. For this purpose, site-specific copepod juvenile growth models, defined for Acartia tonsa and A. clausi populations from a Southern European estuary (Canal de Mira, Ria de Aveiro, Portugal), were used and copepod biomass was taken from zooplankton samples collected during 2 years at six sampling stations. By comparing the obtained results with published data, the feasibility of the approach for copepod secondary production estimates and its applicability in worldwide marine ecosystems was confirmed. Future studies should combine the estimates of adult and juvenile production in order to evaluate its relative contribution and to obtain a more precise estimate of secondary production. 相似文献