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The paper describes the modelling ofeg g production in Acartia spp. under changing environmental conditions in the southern Baltic Sea (Gdańsk Deep). The hypothesis (Sekiguchi et al. 1980) that the food-saturated rate of egg matter production is equivalent to specific growth rate ofco pepods is applied. The average number ofeggs produced per day by one Acartia female is obtained as a function ofg rowth rate, i.e. by multiplying exp gN3 − 1 from the growth rate of the nauplius stage equation by Wfemale/Wegg. The copepod model, reduced to a zerodimensional population model calibrated for Acartia spp. under the environmental conditions typical ofthe southern Baltic Sea, was used to determine the effects of temperature and food concentration on the growth rate ofeac h oft he model stages (see Part 1 – Dzierzbicka-Głowacka et al. 2009 – this issue). In this part, egg production as a function of the above parameters is evaluated. The rate of reproduction during the seasons in the upper layer ofthe Gdańsk Deep is also determined.
The copepod model (see Dzierzbicka-Głowacka 2005b),red uced to a zero-dimensional population model (Fennel 2001,S tegert et al. 2007),i s calibrated for Acartia spp. under the environmental conditions typical of the southern Baltic Sea. Most of the coefficients used in the model are taken from the literature,co ntaining values from various published studies and parameters derived for similar species. The parameters for growth are presented in Part 1; those for population dynamics are given in Part 2. Ingestion rates,whic h are dependent on developmental stage, food supply,temp erature and weight of the animals, are estimated for Acartia bifilosa at 15◦C from the Gdańsk Deep after the experimental data of Ciszewski & Witek (1977). In Part 1 the model presents the change in mean individual mass in successive stages. Quantitative formulae are obtained describing the effects of temperature and food concentration on the development time of Acartia spp. for each of the model stage groups. The generation time during the seasons in the upper layer of the Gdańsk Deep is also determined. The simulations computed here are similar to the experimental results. Part 2 (Dzierzbicka-Głowacka et al. 2009 – this issue) will evaluate egg production as a function of the above-mentioned parameters,temp erature and food availability.
The aim of this paper is to determine the current biological state of life in the pelagic zone of the Gulf of Gdańsk in relation to the planned start-up of an underwater outfall which will discharge sewage from the Gdańsk–Wschód (Gdańsk–East) sewage treatment plant. The plankton material was collected during two research cruises in July and October 1998. The samples were taken at 15 stations in four profiles located near Wyspa Sobieszewska (Sobieszewo Island), perpendicular to the coastline. Both the taxonomic and numerical structure of phytoplankton and zooplankton were typical of the coastal area of the Gulf of Gdańsk. The species diversity depends on hydrological conditions, mainly input from the River Wisła (Vistula). The abundance and biomass of phytoplankton in 1998 were several times lower than in 1994 and 1995 in the area off Górki Wschodnie, the profile located closest to the planned construction site. This could have been caused by generally lower temperatures in 1998 in comparison to previous years. In the investigated area only traces of algal eutrophication indicator species were noted. However, potentially toxic species were confirmed and were most abundant near the Wisła mouth. The highest concentrations of pelagic fauna occur in the shallowest area closest to the shoreline. Long-term observations of the dynamics of the variations in abundance and species composition indicate the increasing significance of one particular species – Acartia bifilosa.
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