Copyright © The Oceanographic Society of Japan. Deep-Sea Eukaryote Ecology of the Semi-Isolated Basins off Japan

The Japanese archipelago is surrounded by the Pacific to the east, the Okhotsk Sea to the north, the Sea of Japan to the west and the Okinawa Trough to the south. The last three seas form semi-isolated deep basins, all with potentially tectonic origin but a different primary energy source as well as hydrographic and faunistic history. The Okhotsk Sea is connected to the Pacific through the deep straits between the Kurile Islands. As a result much of the fauna has links with that fauna found at similar depths in the Pacific. By contrast, the Sea of Japan was isolated from the main Pacific during the last ice age and became anoxic. Even today the link is only through nar-row shallow straits. As a result the fauna is impoverished and is believed to be com-posed of cold-adapted eurybathic species rather than true deep-sea species. The deep-water fauna of both these seas derive their energy from sinking surface primary pro-duction. The Okinawa Trough has a much younger tectonic history than the Okhotsk Sea or the Sea of Japan. In the Okinawa Trough the most noticeable fauna is associ-ated with hydrothermal activity and chemosynthesis forms the base of the food chain for the bathyal community. The variable nature of these three basins offers excellen