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The distribution of the Recent shallow water Foraminifera in Matsushima Bay on the Pacific coast of northern Japan was studied to analyse the fauna from the view point of taxonomic classification and environment. The foraminifers taken from the top part of the 47 sediment samples obtained by Phleger's bottom sampler, with one exception of a small pipe sampler, were used for the analyses. The living specimens were distinguished by the rose Bengal staining method. Matsushima Bay measures one to three meters in depth except for a few narrow channels at the bay mouth. The larger part of the bay bottom consists of mud overgrown at places with Zostera. The sea water flows in and out of the bay through several narrow channels at the bay mouth area, and a river and two canals drain into the bay. Oceanographic observations, analyses of the bottom sediments, details of chlorinity, temperature and other features of the different areas in the bay and of the different seasons are described. Of the oceanographic data chlorinity seems to be most important with regard to the distribution of the Foraminifera. The approximate variation ranges of the chlorinity and temperature of the bottom water at each station as related with the distribution of the Foraminifera are described. The distribution of the planktonic Foraminifera, number of species, and agglutinated Foraminifera show general correlation with chlorinity distribution, but the living benthonic population and calcareous procellaneous Foraminifera differ somewhat. By the abundancy occurrences of benthonic Foraminifera, three facies and six subfacies are discriminated in the bay. Facies A (outer bay facies) is characterized by the abundant occurrences of Pararotalia nipponica, P.? minuta, Elphidium subarcticum, "E". somaense, Ammonia japonica and many other open shallow-sea species. Facies B (middle bay facies) comprises two subfacies and is a facies transitional between the outer bay and inner bay facies and characterized by a mixed assemblage. Facies C (inner bay facies) comprises four subfacies and is characterized by the abundant occurrences of Trochammina hadai, T. cf. japonica and Ammonia beccarii forma 2, and some brackish-water species such as Miliammina fusca, Goesella iizukae and Quinqueloculina rhodiensis occur at the innermost part. The distribution of these facies is quite analogous to that of the chlorinity-temperature character of the bottom water, but some subfacies diverge because of the influence of other factors. For an attempt for non-specific faunal division, Motomura's law of geometrical progression in animal association was applied to the foraminiferal assemblages of Matsushima Bay in simplified manner. The result correlated well with the facies distribution, general trends of the Foraminifera and bottom water characters, but not with the subfacies. The ratio of the living benthonic Foraminifera in Matsushima Bay of the different facies showed higher value in the inner bay area where the Takagi River drains, and indicates the relative rate of sedimentation. The foraminiferal assemblages of Matsushima Bay are compared with some other bays and brackish-water lakes along the coast of the Japanese Islands, and the general features of the Japanese bay foraminiferal fauna are described. One species is described as new to science. |
