Although Antarctic rocky intertidal belt and shallowwater area had been dealt with in numerous publications, but few of them refer to soft substratum.Based on field work carried out during Nov.,1985-Mar.,1986,intertidal ecosystems in gravel beach of Great Wall Bay and exposed rocky shores of Marsh Base(62°12′S,58°55′W),the South Shetland Islands, Antarctica are described and studied in this paper. Species composition, ecological distribution, biomass, and density are described and their probable ecological role in the population structure and dynamics of intertidal communities discussed. Great Wall Bay and Marsh Base are situated at King George Island and about two kilometers apart. The temperature there is rather varied, the monthly mean for February is about 1.5℃, while that for August is about -7.8℃. The tides are of irregular semidiurnal types,with a tidal range of not over 2.02 meters usually. The survey method involved the use of both biomass and density using field quadrat (50×50). Two randomly selected intertidal transects were studied. A station was set every xmeters along the transect and a nondestructive method was used to evaluate the community. The degree of dominance was measured in every station. The supralittoral zone is extremely poor in organisms. only Capitella exists. The thick crust of ice covering the surface of the sea for 8-9 months each year changes into a stabilized brackish or freshwater layer when the thawsets in, and makes the tidal zone nearly impossible as a permanent habitat for plants and animals. Here ice and cold are the "controlling factors" and out-weighs all other factors. Toward the littoral the increase of marine species becomes more gradual. The supralittoral fringe, is characterized by a green belt of Urospora penicilliformis and Ulothrix sp. Porphyra endiviifolium,Enteromorpha bulbosa, Spongomorpha arcta and yellow lichens are also found in this belt. Nacella concinna was the dominant species at midlittoral, its density reached 14670 individual/m 2. Harpacticus sp. also exists in this region.The gastropod Laevilittorina antarctica and L.caliginosa are present all along this belt. At the sublittoral fringe, a great number of organisms occur such as Neobvuccinum eatoni,Necella concinna,Laevilittorina antarctica,L.caliginosa,Iridaea obovata and Monostroma applanatum etc. among which Necella concinna and Laevilittorina antarctica were dominant, their biomass averaged 2195g/m 2and 845g/m 2, their density averaged 117 individuals per square meter and 3700 individuals per square meter respectively. Infralittoral belt, was characterized mainly by dense concentrations of the common animals sterechinus new mageri, Magellanea joubini, Glytonotus antarcticus, Cheirimedon femoratus,Philine alatu, Priapulus tuberculatospinosus, and the presence of several species of macroalgae, i.e. Desmarestia anceps, D.menziesii, Gigartina papillosa, Iridaea obovata, Cystosphaera jacquinotii, Adenocystis utricularis,Ascosseira mirabilis. Toward the sublittoral the annual temperature becomes more nearly constant than other zones. Accordingly, the selective effect of each single microhabitation in the sublittoral zone acts upon those organisms which find their optimal conditions there. The sublittoral is a suitable habitat for more species. Benthic marine animals can be differentiated into two principal and ecologically different groups: 1). The epifauna, comprising all animals living upon or associated with rocks, stones, shells, piling, and vegetation. 2).The infauna comprising all animals inhabiting the sandy or muddy surface layers of the sea bottom. The infauna is most fully developed below the intertidal zone. Such constantly submerged infaunas are associated with a level bottom and are exposed to nearly the same types of environmental conditions. In antarctic as in tropical seas, the only factor that is really different is the t
