2006 年 10 巻 2 号 p. 189-199
The IPCC report published in April 2001, predicted sea surface water temperatures to increase by 3°C or so by 2100. This rise in seawater temperature is expected to have a significant impact on marine organisms distributed around Japan. In order to estimate the influence of warmer water, we performed a simulation study based on the assumption that sea surface water temperatures will increase by 1.0°C in 30 years (short-term), 1.4°C in 50 years (medium-term), and 2.9°C in 100 years (long-term). Data on the range of water temperatures marine organisms can inhabit were collected from previous studies and reports, and those data were applied to maps of seawater temperatures predicted over the short, medium, and long-term to study the changes in the distribution of areas of inhabitation.
The results showed that a shift in the 29°C isothermal line (i.e., the line at which the maximum annual sea water temperature is 29°C) significantly influences the distribution of marine organisms, because the line coincides with the boundary between the zone of temperate marine organisms and that of sub-tropical ones. Though the isothermal line currently stays south of the island of Kyushu, it will supposedly move north as global warming proceeds, reaching the coasts of the Chugoku district and the island of Shikoku in 50 years, and those of the Kanto and Hokuriku districts in 100 years. The north-ward-shift of the 29°C isothermal line will not affect pelagic fish, such as mackerel, bonito, and Pacific saury, because they have strong swimming abilities, although their catch and fishing seasons will have to change somewhat, Demersal organisms like Alaska pollock and tanner crab will also not be influenced because water temperatures will rise only slightly in water deeper than 100 m.
However, our simulation showed that the number of coastal marine organisms such as bastard halibut, red sea bream, abalone, and sea urchin will decrease significantly and the cultivation of Japanese amberjack, puffer, and seaweeds will also be impacted, especially in southern Japan, where these bad influences will be observed early in the future. These results indicate that we must urgently consider plans to protect fishery resources against global warming.
