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The community of Phyllospadix iwatensis is studied using materials from expeditions of A.V. Zhirmunsky Institute of Marine Biology (National Scientific Center of Marine Biology, Far Eastern Branch, Russian Academy of Sciences) and archive data (1949-2013) of the Laboratory of Chorology covering the species habitat area from Peter the Great Bay in the south to middle Kuril Islands in the north. The core of the community is identified. It has changing species composition; the changes correspond to geographical boundaries of the cenotic systems of Peter the Great Bay, the Lesser Kuril Islands, and Iturup Island. However, these boundaries do not coincide with the boundaries of the species-edificator habitat that embraces several cenotic systems. Spatial alterations of the cenotic systems are caused by landscape changes conditioned by general geomorphological situation and ecological conditions in the intertidal zone.

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Characteristics of vertical distribution, species composition and biogeographical structure of macrobenthos of the intertidal communities of Kunashir Island (South Kurile Islands) are described. In the rocky and bouldery intertidal zones, communities dominated by barnacle Chthamalus dalli and a gastropod species Littorina sitkana with the poor species composition of the macrobenthos are typical for the upper intertidal subzone. The middle intertidal subzone is occupied by fucoid assemblages. The dense beds of laminarian algae dominate in the lower intertidal subzone with the total macrobenthic biomass up to 100 kg wet wt m −2 . On wave-exposed sandy beaches formed by clean sand, populations of the macrobenthic organisms are very poor, and macrophytes and the other attached forms are absent. The communities dominated by eelgrass Zostera japonica and a gastropod species Batillaria cumingii are found only in the sandy intertidal zones of the southern coast of Kunashir Island, in Izmeny Bay. Reduction of species richness and increase of biomass of macrobenthos have been recorded from 1963 to 1991 in Izmeny Bay, and it is due to the fact that this area has been exposed to anthropogenic impact. At least, 563 species of macrobenthos are found in the intertidal zone of Kunashir Island. Pacific low-boreal and Pacific wide-boreal species are dominant. Warm-water species are more abundant in the intertidal zones of Izmeny Bay and on the Sea of Okhotsk coast as compared to those on the Pacific coast of Kunashir Island. It is probably associated with the flow patterns of the Soya Warm Current. Species composition and distribution of the intertidal macrobenthos of Kunashir Island are typical for the low-boreal intertidal zone with irregular diurnal and semi-diurnal tides. The intertidal zones of Kunashir Island and neighboring Shikotan Island have similar species composition and distribution patterns of the macrobenthic communities.

The intertidal zone of the Gizhiginskaya Guba and Yamskaya Guba inlets located in the Shelikhov Bay is surveyed and 179 species are found in its macrobenthos (66 plants and 113 animals). They form 25 communities, including 7 ones on soft bottom sediments, 12 - on hard substrates, and 6 transitional (mixed) communities. The community of Lyonsia cucumerina is endemic of the Shelikhov Bay, it occupies the mixed substrate, namely flat rocks covered with silty sand that occur in the Gizhiginskaya Guba and at Ust’-Palana.