Bull. Jpn. Soc. Fish. Oceanogr. 78(4), Page 268-276, 2014   Estimating the occurence of megabenthos for dissolved oxygen concentrations in the bottom water layer during summer in Mikawa Bay, Japan Ryota Sone1†, Satoru Kamohara1, Satoshi Yamada1 and Teruaki Suzuki2 1 Aichi Fisheries Research Institute, 97 Wakamiya, Miya, Gamagori, Aichi 443-0021, Japan 2 Graduate School of Environmental and Human Science, Meijo University, 1-501 Shiogamaguchi, Tempaku, Nagoya, Aichi 468-8502, Japan † E-mail: riyouta_sone@pref.aichi.lg.jp In order to quantify the influences of hypoxia on megabenthos in Mikawa Bay during the summer season, we analyzed the relationships of the occurrence of four megabenthic groups, flounder, swimming crab, prawn, and mantis shrimp, with environmental factors in the bottom water layer, dissolved oxygen concentrations (DO), water temperature, water depth, and bottom sediment types, using generalized linear models (GLM). The selected models in the four groups respectively included DO as an explanatory variable, which showed significant effects on the occurrence of all groups in all cases. Using the resulting model, the DO at 50% probability of occurrence of the flounder, swimming crab, prawn, and mantis shrimp during the summer in the Bay were estimated as 3.9 mg·l−1, 3.5 mg·l−1, 4.7 mg·l−1, and 2.5 mg·l−1, respectively. These figures are substantially higher than the LC50 (50% lethal concentration) of laboratory experiments of previous studies. The results of this study indicate that the distribution of major megabenthos was influenced by DO, which possibly serves as a strategy to avoid death or hypoxia. We suggest that a DO level of >2.5 mg·l−1 was the lowest level that maintains a megabenthic community in Mikawa Bay during the summer. Key words: environmental factors in bottom water layer, generalized linear model, hypoxia, megabenthos, Mikawa Bay, spatial distribution