open access

https://hdl.handle.net/2115/68442

The Zoological Environs of the Akkeshi Marine Biological Station (With 7 text-figures and 4 plates)

英語

1963-07

Akkeshi Marine Biological Station

Publications from the Akkeshi Marine Biological Station

13

2-36

The Akkeshi Marine Biological Station of the Hokkaido University is located in Akkeshi on the Pacific coast of the easternmost part of Hokkaido, on 43°00'N. and 144°50'E. It was founded in 1931 for the biological research of marine animals and plants at that region and its vicinity, and since that time a number of works were made in different fields of research. The main reason why this place was chosen for institution of this station lies in the fact that the station has the rich fauna and flora which are distinctly different from those of other marine biological stations as will be stated below. It is well known that the two different main currents flow along the Japanese coast, i. e. the Oyashio, a cold current from the north and the Kuroshio, a warm current from the south. The eastern part of the Pacific coast of Hokkaido is chiefly washed by the cold Oyashio and influence of the warm Kuroshio from the south is very little in this coast. Most of the animal species found in Akkeshi Bay are boreal forms as is shown in the later pages. Clear from its high latitude it is natural that the marine fauna of the coasts of Hokkaido is generally different from that of the coasts of Honshu, Shikoku or Kyushu, comprising many boreal forms. Concerning the faunal nature of the coasts of Hokkaido itself, however, remarkable differences can be seen between different coasts. The southwestern coast of Hokkaido facing to the Pacific Ocean is mainly washed by the cold Oyashio but fairly influenced by the warm Kuroshio. A considerable number of temperate forms are distributed in this area. On the west coast of Hokkaido facing to the Japan Sea the boreal forms Publ. Akkeshi are mixed with temperate ones, like on the southwestern coast above. On the northeastern coast of Hokkaido facing to the Okhotsk Sea we can see also two different elements of current, the cold one coming down from the north along the Kurile Islands and the warm one coming into through the Soya Strait from the Japan Sea. As is clear from above, boreal forms are always more or less mixed with temperate ones in most part of the coasts of Hokkaido, while the southeastern coast including Akkeshi Bay is scarcely influenced by the warm current though only a few temperate forms can be found as temporary visitors there. As is seen in Fig. 1 Akkeshi Bay is of roughly round shape, about 10 km in diameter, and opens to the Pacific Ocean south- and southeasternwards. Two small inlets, Daikokujima and Kojima lie in the mouth of the Bay. Akkeshi Bay is connected at its northern end with a shallow lagoon named Akkeshi Lake by a narrow channel. The bay is about 30 m deep at its mouth and becomes shallower toward the inner part gradually. Akkeshi Lake is very shallow and is less than 2m deep. Most of the coast of Akkeshi Bay is of rocky shore, but sandy and muddy shores are also found. Sandy shore is found in Daikokujima and in Tsukushikoi between Aikappu and Aininkappu, and muddy shore is in Shinryu. Akkeshi Lake is a lagoon and is connected with Akkeshi Bay by a narrow channel. Bekambeushi and some other rivers pour into the Lake and the Lake is brackish showing low salinity. These natural features of environment give many diverse habitats to the marine fauna of the Bay. It is true that the marine fauna is richer in Akkeshi Bay than in the regions little apart from the Bay. The surface water temperature in front of the Station is shown in the following table which indicates the mean value in each month for these three years, 1960-1962.

紀要論文

Version of Record

0439-349X

AA00795172