融雪プールの動物プランクトン : 石狩砂丘地帯を例として
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概要
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In every spring, temporary pools are widely distributed on the Ishikari coastal sand dune area after thawing. The present study is intended to clarify the relationship between aquatic organisms and their habitats ; especially water temperature, pH, salinity, and period of continuous existence of pools. Five temporary pools, which were formed on the shallow depressions between sand dunes and emerged sand bars, were taken and the field works were carried on from November 1976 to January 1978. Maximum depth of snow cover was 150 cm during the observation period. The main results obtained by this study are as follows : 1) Northern species such as Nordodiaptomus alaskaensis occurred in these pools. Three stages were distinguished on the basis of the changes of fauna, which were affected by the temporal changes of water temperature. 2) The waters of the studied pools showed weak acidity ; pH 6. Rotifer, Rotaria rotatoria, Lecane luna and Lecane lunaris, Cladocera, Chydorus sphaericus, the common species in acidic waters, were found in these pools. 3) Chlorinity in these nools was 5 to 40 times as much as that in inland lakes under the natural conditions, and was increased towards the shoreline, attaining 100mg/l at Pool 1 situated 250m from the shore-line. Accumulated number of species became greater in proportion to the increase of period of continuous existence of pool. The rate ot increase ofaquatic species living in Pool 1 was pmaller than that for the other pools. This may be caused due to the higher chlorinity of Pool 1. 4) Aquatic organisms living in the studied pools had to bear the deterioration of their habitat ; especially dryness and both low and high temperature. From the results of field survey, the stage of tolerance to such extreme environmental conditions was clarified for three species ; adult of R. rotatoria, embryonated egg of Chirocephalopsis uchidai and egg of N. alaskaensis. In the case of R. rotatoria, the laboratory experiments also showed that adult was in the stage of tolerance. 5) Judging from the relationship between aquatic organisms and their environmental conditions, these temporary pools fall on the type of dystrophic β-mesotrophy, cold-temperate water and "Kleingewasser" 6) It should be emphasized that a lot of female C. uchidai which has never been reported before were collected from the studied pools, the diameter of the resting eggs produced being 450-500μm.
- 1979-03-25