On the Planktology of Okhotsk Sea in Autumn
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概要
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Autumnal plankton associations observed in Okhotsk Sea in 1923, '29, and '32 may be referred to three main water masses, riz, (1) Oyasio water, (2) Tusima current water, and (3) the neritic water in the northern part of Okhotsk Sea. (1) Oyasio water passes through somewhere between the Northern Kurile Islands to spread in the middle part of Okhotsk Sea. My observations show that (1) Plankton association is zooplanktonic, (2) Thal. long. and Coscinodisczus sp. are so rich as to call the diatom community by the name of Disco-plankton, (3) Calanus pulmchrus is always predominant, and (4) Tintinnodes form a significant part of the association consisting mainly of G. parafarella and Ptychocylis obtusa. Being different from the plankton association in the north Pacific Ocean in far richer animal constituents but a little poorer plant elements, subsidiary diatom species of this association are common to the latter to be referable to the same category of the diatom community with it. (2) Due to Tusima current coming into Okhotsk Sea through Soya Strait, the plankton association from Japan Sea covers either an extensive (1928) or a narrow (1929 and 1932) are in the southern part of Okhotsk Sea with the following characteristics: -(l) the plankton association is phytoplanktonic, (2) microcalanids are abundant, but macrocalanids such as Calanus pulmchrus and Eucalanus elongatus are scarcely observable, (3) diatom community is Styli-plankton (1928) or Chaeto-plankton (1929 and 1932), (4) Tintinnodes consist of G. Parafazella and Ptychocylis obtusa, which are rich in Okhotsk waters on the one hand, and of Uadella sp. and some others rich in Japan Sea on the other. Needless to say that the plankton as ?? whole is richer in species here than in Okhotsk water. (3) The neritic water in the northern part of Okhotsk Sea is characterized by the monotonous dominance of Chaetoceros spp. The diatom communities are similarly rich in fine Chaeloceros-species in 1928 and '29, and especially so around Cape Lopatka in 1928. Considered from these data, the diatom community of Oyasio water is probably modified around Cape Lopatka or on passingthrough the North Kurile Islands to be brought all around the northern partof Ok Thisdiatomcommunity appears along the coast north from Kitasiretoko Saki (Cape of Patience) being carried by vita Karahuto cold current. The extension of this neritic plankton association is dependent upon the intensity and directionof Oyasio water pouring into Okhotsk Sea, being wide in 1928 but narrow in 1929 and 1932. (4) In the region north from the Near Islands and around Komandorski Island, Denticula-plankton is observed and in its southern region Chaeto-plankton (Chaet. crioph. and C. atl.) is present. In the northern part of the Rat Islands Disco-plankton is present, while in its southern part Nitzschia-plankton is present. All these categories of diatom communities in the West Aleutian Islands Sea differ from each other in their leading species, although they are quite similar in their constituents of diatoms. Nitzschia-plankton spreads toward the southern coast of Kamtehatka, and Denticula-plankton invades into this region along the coast of Kamtchatka from the Near Islands and Komandorski Island. Nitzsehia-plankton includes a fairly large number of Thal. long., Cos. sp., Chaet. crioph. and Chaet. atl. in addition to Nitz. ser. This plankton association becomes zooplanktonic and Disco-plankton in Okhotsk Sea, after passing through the North Kurile Islands.