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Seasonal variations of the abundance, size structure, and vertical distribution of the population of the hydromedusa Aglantha digitale are studied using the materials collected during multiyear observations in the White Sea from 1961 to 2003. The wide distribution of the species in the Basin of the White Sea and in Kandalaksha, Dvina, and Onega bays is shown. Usually, the maximum bell height of the specimens did not exceed 12 mm, although a few individuals up to 22 mm high were found. The maximum abundance of A. digitale is observed during the reproductive period, which lasts from the second half of June to August. The reproduction starts when the water temperature near the surface reaches 9–11°C. By the onset of winter, specimens with a height of 4–5 mm representing a new generation dominate. By the beginning of the subsequent spring, their average size reaches 5–6 mm, and, by the end of June, specimens with bell heights of 8 mm become mature. During the spring and the summer, the A. digitale population concentrates in the upper 0-to 25-m water layer; during the autumn and winter, it concentrates below the 50-m depth. At the end of the autumn and in the winter, the population is spread over the water column and inhabits all the water layers. At the end of the winter, in April, the ascent of the population starts. An analysis of the seasonal dynamics of the population abundance and size structure indicates that A. digitale in the White Sea has a one-year life cycle. 相似文献
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H.J. Hirche K.N. Kosobokova B. Gaye-Haake I. Harms B. Meon E.-M. Nthig 《Progress in Oceanography》2006,71(2-4):288
After a short introduction to the physical setting and the history of biological research the pelagic ecosystem of the Kara Sea is described. Main emphasis is on regional aspects of the plankton communities and their seasonal dynamics using mostly data collected between 1996 and 2001. In the zooplankton, for which most data were available, four regional aggregations were separated: (1) the rivers and estuaries of the Southern Kara Sea, (2) the south-western and (3) the central Kara Sea, and (4) the northern troughs and slope. The phytoplankton communities had a similar distribution. To provide components for detailed carbon budgets the regional dynamics of bacterial, phytoplankton and zooplankton biomass and production are described and carbon requirements of bacteria and zooplankton are estimated. For completeness a short literature review on higher trophic levels is included. Finally, recent observations of the pelago-benthic coupling are considered. Estimates of the carbon requirements from the plankton and benthos reveal a large underestimation of primary production, which to date, together with seasonal aspects, shows the largest gap in our knowledge. 相似文献
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The results of multiyear observations of the seasonal and inter-annual variability of the population structure, abundance,
and biomass of the arctic calanoids copepod Calanus glacialis in the White Sea are presented. The spring season represents the most crucial period for the population’s seasonal dynamics.
During the spring, the maximal abundance, biomass, and contribution of C. glacialis to the total zooplankton biomass is observed. The interannual variability of the abundance is closely related to the timing
of the spring warming of the upper water column and the respective shifts of the onset of reproduction and the offspring development.
The development of a new generation to the overwintering copepodite stage IV is usually completed three to four weeks later
in the cold years compared to the warm ones. Our multiyear observations suggest that C. glacialis could be more tolerant of Arctic warming than it is usually believed. The high abundance of the C. glacialis population in the White Sea indicates that this arctic species is able to cope with the seasonal surface warming and should
continue to do so, being provided with the cold water “refuge” in the deep sea. 相似文献
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Only a few historical assessments of the zooplankton biomass in the Arctic Ocean exist are difficult to compare due to methodological differences including incomplete sampling of the water column. We present assessments of the zooplankton biomass for 66 locations scattered over the Eurasian and Makarov Basins of the Arctic Ocean and analyze regional variability and factors affecting the biomass distribution. The study is based on material from several summer expeditions of RV Polarstern (1993–1998) that was collected and processed using consistent methods, i.e. stratified sampling of the entire water column from the bottom to the surface with very similar gear and standardized calculation of biomass. Total zooplankton biomass varied strongly from 1.9 to 23.9 g DW m−2 dry mass. Regional variability was mainly related to the circulation pattern, but local food availability was also important. A belt of elevated biomass along the Eurasian continental margin was associated with the advection of Atlantic pelagic populations within the Arctic Ocean Boundary Current along the Siberian shelves and returning branches along mid-ocean ridges. Biomass was highest in the core of the Atlantic inflow and remained rather stable along the continental margins, but species composition changed, pointing to different adaptation levels to local conditions by advected species. Biomass gradually decreased towards the shelves and basins and was lowest in the centers of the basins north of 85°N. In the slope region, three Calanus species (C. hyperboreus, C. glacialis, C. finmarchicus) and Metridia longa contributed most to the biomass, chaetognaths (Eukrohnia hamata) were also important. In the basins, C. hyperboreus was dominant, copepods made up to 97% of total biomass. Vertical distribution was similar at all stations with biomass maxima in the upper 50 m layer except for stations near Fram Strait and northern Kara Sea, the gateways of Atlantic water to the Arctic Ocean, where maxima where between 25 and 100 m. As there was only very little interannual variability of temperature and current velocity in the regions of the Atlantic inflow we suggest that the majority of our samples, collected in 1993 and 1995, represents the phase of the 1990s warm event in the Nordic Seas. 相似文献
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This study examines changes in egg production rates of two co-occurring Pseudocalanus species, P. acuspes and P. minutus, in response to changing temperatures (0, 3, 6, 9 and 12°C) in the White Sea. The boreal P. acuspes (sample size >650 individuals) increased its reproductive rate gradually across the entire range of temperatures from 0 to 12°C. Significant differences in egg production rates and reaction to temperature were also observed between P. acuspes females incubated during the early vs. the mid-summer season. The sample size of the Arctic P. minutus was significantly smaller due to the low numbers at which this species occurred. However, the results suggest that this species increases its egg production rates from 0 to 3°C from 3.3 to 8.5% dry weight female–1 day–1, but at 9° its reproductive rate drops significantly and the animals demonstrate markedly reduced fitness. Our results indicate that closely related co-occurring species, and even different generations within one species, can demonstrate significantly different responses to changes in the physical environment. 相似文献
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Hans-Jürgen Hirche Ksenia Kosobokova 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2729
The distribution of Calanus finmarchicus was studied on a transect across the central Greenland Sea, and on five transects from the Eurasian shelves across the Atlantic Inflow in the Arctic Ocean. Stage composition was used as an indicator for successful growth; gonad maturity and egg production were taken as indicators for reproductive activity. On the Arctic Ocean transects, these parameters were measured simultaneously from the sibling species Calanus glacialis. Response of egg production rate to different temperatures at optimal food conditions was very similar between both species in the laboratory. C. finmarchicus was present at all stations studied, but young developmental stages were only present close to the regions of submergence of Atlantic water under the Polar water. This together with a decreasing abundance and biomass from west to east along the Atlantic Inflow in the Arctic Ocean and reproductive failure indicates that C. finmarchicus is expatriated in the Arctic Ocean. We hypothesize that the late availability of food in the Arctic Ocean, rather than low temperature per se, limits reproductive success. Better reproductive success in the very low temperature regions of the Return Atlantic Current and the marginal ice zone in the Greenland Sea supports this hypothesis. The possibility for a replacement of C. glacialis by C. finmarchicus and consequences for the ecosystem after increasing warming of the Arctic are discussed. 相似文献
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