Bull. Jpn. Soc. Fish. Oceanogr. 76(4), Page 187-196, 2012   Distribution of dead zones in the coastal waters: A model study in Mikawa Bay, Japan Mitsuyasu Waku1 ‡, Kenji Kaneko2 *, Teruaki Suzuki3 and Teruhiro Takabe4 1 Aichi Fisheries Research Institute, 97 Wakamiya, Miya, Gamagori, Aichi 443-0021, Japan 2 Chubu branch, Marine Biological Research Institute of Japan Co., Ltd., 3-9-2 Koubai, Showa, Nagoya, Aichi 466-0031, Japan 3 Graduate School of Environmental and Human Science, Meijo University, 1-501 Shiogamaguchi, Tempaku, Nagoya, Aichi 468-8502, Japan 4 Research Institute of Meijo University, 1-501 Shiogamaguchi, Tempaku, Nagoya, Aichi 468-8502, Japan ‡ Present address: Ama Agriculture, Forestry, and Fisheries Office Aichi Prefectural Government, 1-14 Nishiyanagihara, Tsushima, Aichi 496-8532, Japan * Present address: Graduate School of Agricultural Science, Tohoku University, 1-1 Amamiya-machi, Tsutsumidori, Aoba, Sendai, Miyagi 981-8555, Japan mitsuyasu_waku@pref.aichi.lg.jp Dead zones are determined as areas where few organisms can survive. The extent of dead zones was estimated in the coastal waters of Mikawa Bay, Japan, to estimate its adverse effects on the bay-wide ecosystem function. Fisherpersons of the fisheries cooperatives holding common fishery rights in the coastal area of Mikawa Bay, were surveyed using a questionnaire to ask opinions as to the type of waters where few organisms can survive. From the survey results, 174 areas were extracted as potential dead zones from the coastal waters of Mikawa Bay. Field observations of macroben- thos biomass were conducted at 44 of the 174 areas. In areas where the number of macrobenthos species was <5, its biomass was very low (4.13 g⋅m−2, on an average). The macrobenthos community in these areas was mainly composed of pollution indicator species, such as polychaetes Paraprionospio patiens and Sigambra hanaokai, and bivalves Macoma tokyoensis, Macoma incongrua and Theora fragilis. These areas were thus defined as dead zones. Multiple linear regression analysis indicated a significant relationship between the number of macrobenthos species and environmental factors. These factors included not only local ones（such as degree of closeness to the coastline, the depth, presence of influent water, presence of near-by tidal flat, and speed of tidal flow）, but also large-scale hypoxia. The number of macrobenthos species was estimated based on a multiple linear regression analyses of the 174 potential dead zones. The estimated number of macrobenthos species was <5 at 80 out of the 174 areas. These 80 areas, comprising of 27.8 km2, were designated as dead zones. Overall, 79.2% of the total dead zones was represented by large-scale ports, and waterways created at closed-off section of the bay. Our results suggest that environmental restoration of the dead zones is essential to the recovery of the bay-wide ecosystem function. Key words: dead zone, coastal waters, macrobenthos, multiple linear regression analysis, Mikawa Bay