The intertidal zonation of marine algae along the coasts of Sagami Bay was studied. The field work which forms the basis of this paper was commenced in March, 1957 and continued to March, 1958. As the results of the investigations, all the marine algal communities found along the coasts proved to be the open-sea type. No inland-sea community, e.g. Monostroma nitidum-Scytosiphon lomentarius community of Ulva pertusa-Grate. loupia filicina community, were found. The open-sea communities are divided into Gloiopeltis furcata-Myelophycus caespitosus-Hizikia fusifor-me-Eisenia bicyclis community which are found on the eastern part of the bay (Enoshima, Hayama, Aburatsubo), and the Gigartina intermedia-Sargassum sagamianum community on the western part (Oiso, Manazuru, Izusan, Ito, Yatano, Kitagawa). In the former community there can be recognized four belts which are named after the dominant species occurring there. They are, from above downwards, Gloiopeltis furcata belt, Myelophycus caespitosus belt, izikia fusiforme belt and Eisenia bicyclis belt. In the first belt, Gloiopeltis furcata and Gloiopeltis complanata are found. The dominant alga of the second belt is Myelophycus caespitosus and it is associated with the following forms : Ishige Okamurai I. foliacea, Petrospongium rugosum, Porphyra suborbiculata, Endarachne binghamiae and Caulacanthus okamurai. The dominant alga of the third belt is Hizikia fusiforme and it is associated with the following forms : Chondrus ocellatus f. typicus, Gigartina intermedia, Colpomenia sinuosa and Laurencia sp. The dominant alga of the last belt is Eisenia bicyclis and it is associated with the following forms : Sargassum hemiphyllum, S. Ringgoldianum, S : nigrifolium, S. Thunbergii, S. patens and S. sagamianum. The community is distributed over Onahama, Boso Pen., Izu Pen., Ise Bay, Shima Pen. and Hyuganada etc., and it is the characteristics of the Pacific coasts. In the latter community there can be recognized two belts. They are, from above downwards, Gigartina intermedia belt and Sargassum sagamianum belt. The dominant alga of the first belt is Gigartina intermedia and it is associated with the following forms : Gloiopeltis furcata, Gelidium divaricatum, Chondrus ocellatus f. typicus. C. ocellatus f. canariculatus. Carpopeltis flabellata, Nemalion pulvinatum, Grateloupia livida, Myelophycus caespitosus and Ishige Okamurai. The dominant alga of the second belt is Sargassum sagamianum and it is associated with the following forms : Sargassum nigrifolium, Lomentaria catenata, Corallina pilulifera and Grateloupia elliptica. In the community, some of the marine algae are discolored whitish. This community is also distributed over the Kiisuido and Tosa Bay, which is of a special feature. The return current of the sea, the inflow of rivers and the shape of the bay have significance with the distribution of the community.
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