T6 AM Environmental Hypoxia
Tuesday, 15 November 2005: 8:00 AM - 11:40 AM in 324-326

(KOD-1117-802611) Hypoxia restricts recruitment of the stomatopod Oratosquilla oratoria in Tokyo Bay, Japan.

Kodama, Keita¹, Horiguchi, Toshihiro¹, Kume, Gen¹, Nagayama, Satoshi², Shimizu, Takamichi³, Shiraishi, Hiroaki¹, Morita, Masatoshi¹, Shimizu, Makoto⁴, ¹ National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan² Chiba Prefectural Fisheries Research Center, Awa, Chiba, Japan³ Kanagawa Prefectural Fisheries Research Institute, Miura, Kanagawa, Japan⁴ The University of Tokyo, Bunkyo, Tokyo, Japan

ABSTRACT- We used field surveys to investigate the reproduction and recruitment of the mantis shrimp Oratosquilla oratoria and the spatiotemporal pattern of hypoxia in Tokyo Bay. The spawning seasons of large and small females were May-July and July-August, respectively. More larvae were spawned by small females than by large females, suggesting that there was a low spawning stock abundance of large females. Newly settled juveniles appeared in the northeastern shallow coastal area of the bay in September-October, implying larval transportation from the spawning ground in the southern part of the bay and the successful settling of only those larvae derived from spawning from August onward by small females. Juvenile settlement from spawning before July by large females failed completely, probably because hypoxia (dissolved oxygen concentration of < 2 ml l^-1) persisted in the bottom layer of the north-central part of the bay from May to October. After the hypoxia had abated, the distribution of juveniles expanded to the south-central deep area of the bay, most likely by migration. Hypoxia probably restricts the settlement period and distribution of O. oratoria. Conservation of the spawning stock of small females and regulation to decelerate hypoxia-enhancing eutrophication in the bay are needed for recovery of O. oratoria stocks.

Key words: Hypoxia, Reproduction, Recruitment, Stomatopod