A LIST OF THE MACROFAUNA IN THE INTERTIDAL ZONE OF THE KURILE ISLANDS, WITH REMARKS ON ZOOGEO-GRAPHICAL STRUCTURE OF THE REGION

Abstract

The Kurile Islands extending over vast stretches from north to south in the western North Pacific are particularly interesting to hydrobiologists and biogeogra- phers. Here a complex interaction of currents along with the effects of the latitudinal climatic change and a number of other factors are responsible for an extremely complicated biogeographical and hydrobiological picture. On the one hand, the two faunas and floras of different origins meet each other in this region. One of them is relatively warm-water (low-boreal with the admixture of subtropical elements), and reaches the Kuriles from the south along the coast of Japan. The other is relatively cold-water (high-boreal) and arrives here from the north with cold waters of the Bering Sea and the northern part of the Pacific. On the other hand, due to a complicated hydrological regime, a number of unistic areas considerably different from one another can be marked within each of the two clearly distinguished biogeographical subdivisions (low- and high-boreal) . On the southern Kurile Islands, including Iturup, the Okhotsk and Pacific coasts of one and the same island significantly differ from each other. Proceeding northwards, this contrast is smoothing out. The local ecological factors and biono- mic peculiarities of the areas (for example, bays with muddy sand protected from surf as observed on Shikotan Island and in the south of Kunashir Island are missing on the islands further north) no doubt play an important part in faunistic differencia- tion in various areas of the Kurile Islands. However, even in bionomically similar places the above faunistic difference is still rather noticeable. Straits can hardly be regarded as actual faunistic barriers since most of them are narrow, the widest being no more than 70 km in width. The present paper is intended to show the close connection of differences in the fauna1 composition with the correlation of certain biogeographical components which in turn changes in full accordance with the distribution of summer temperature of the waters skirting the Kurile Islands. During warm seasons the water temperature of the upper layers in different areas of the archipelago fluctuates so greatly that within a narrow latitudinal range between the warmest Kunashir Island and the coldest middle Kuriles (only 4') these fluctuations often reach 12-13OC. The above temperature regime is responsible for a considerable difference in the population of these regions.