Ecophysiological investigations on the oyster, Crassostrea gigas, in Flensburg Fjord
The growth, mortality and chemical composition of Crassostrea gigas in Flensburg Fjord (Western Baltic) were followed over an annual cycle. Water temperature, salinity, pH, oxygen levels, total seston content, and chlorophyll a and phaeopigment levels were monitored during the same period. The oyste...
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| Format: | Thesis |
| Language: | English |
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1985
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| Online Access: | https://oceanrep.geomar.de/id/eprint/50455/ https://oceanrep.geomar.de/id/eprint/50455/1/Dipl.%201985%20Seaman,M.pdf |
| Summary: | The growth, mortality and chemical composition of Crassostrea gigas in Flensburg Fjord (Western Baltic) were followed over an annual cycle. Water temperature, salinity, pH, oxygen levels, total seston content, and chlorophyll a and phaeopigment levels were monitored during the same period. The oysters grew from 7 to 24 g total wet weight (230 to 890 mg dry meat weight) during the sampling period. The main growth phase was from April to September. The combination of strongly reduced salinity (about 15%) and salinity fluctuations during the summer are considered primarily responsible for the oysters' slow growth. Mortality reached almest 50% in spring, probably due to the coincidence of salinity changes and freezing temperatures during the preceding winter; otherwise, mortality was zero. Most oysters formed gel blisters during the summer, presumably because of salinity stress and toxic effects of tributyl tin compounds. Protein levels were about 40% of the ash-free dry meat weight during most of the year, with a peak of almost 60% in August. Glycogen levels were nearly constant at about 30% most of the time, dropping to 9% during gametogenesis from late spring until midsummer, and recovering immediately afterwards. Lipid levels were around 15% in summer and 11% the rest of the year. The oysters apparently failed to spawn, because of a sharp temperature decline in August, before gonad formation had been completed. The oysters did not present any physiological anomalies. The fluctuating and excessively low summer salinities, and perhaps low levels of primary production in late spring, present the main obstacles to commercial cultivation of C. gigas, as well as the risk of high spring mortalities after ice-winters. Oyster cultivation sites in the Baltic should be placed at locations where currents can be expected, and the immediate vicinity of heavily frequented ports should be avoided. |
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