MEPS 324:197-206 (2006)  -  doi:10.3354/meps324197

Effects of hypoxia on early life history of the stomatopod Oratosquilla oratoria in a coastal sea

Keita Kodama1,5,*, Toshihiro Horiguchi1,5, Gen Kume1,6, Satoshi Nagayama2, Takamichi Shimizu3, Hiroaki Shiraishi1,5, Masatoshi Morita1, Makoto Shimizu4

1Endocrine Disrupters and Dioxin Research Project, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan
2Agriculture, Forestry and Fisheries Department, Chiba Prefectural Office, 1-1 Ichibacho, Chuou-ku, Chiba, Chiba 260-8667, Japan
3Resources and Environment Division, Kanagawa Prefectural Fisheries Technology Center, Jogashima, Misaki, Miura, Kanagawa 238-0237, Japan
4Faculty of Agriculture, University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo 113-8657, Japan
5Present address: Research Center for Environmental Risk, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan
6Present address: Faculty of Fisheries, Nagasaki University, Bunkyo-machi, Nagasaki 852-8521, Japan

ABSTRACT: Bottom hypoxia is considered to be one of the factors affecting the recent stock decline of the mantis shrimp Oratosquilla oratoria in Tokyo Bay, Japan. We used field surveys of the bay to investigate the spatiotemporal pattern of bottom hypoxia and the early life history of O. oratoria, and we examined the effects of bottom hypoxia on early life history by nonparametric analyses. Bottom hypoxia in Tokyo Bay began to appear in April, occupied more than half (55 to 67%) of the whole bay area in July and August, and disappeared from November onward. Newly settled juveniles appeared in September–October in the northeastern shallow coastal area, where the hypoxic bottom water had disappeared. After the hypoxia had abated, the distribution of juveniles expanded to the south-central deep area. Classification and regression tree analysis showed that the threshold level of bottom dissolved oxygen concentration for the existence of juveniles was 2.78 ml l–1, implying that hypoxia restricted the spatial distribution of juveniles. A generalized additive model showed that sampling date, bottom dissolved oxygen concentration, depth, latitude, and longitude had significant effects on the occurrence of juveniles, suggesting an adverse effect of hypoxia on the time and location of settlement of O. oratoria. Our results suggest that hypoxia is directly and/or indirectly associated with mass-mortality events during early life history.

KEY WORDS: Hypoxia · Settlement · Recruitment · Juvenile · Oratosquilla oratoria · Tokyo Bay

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