185 Journal of Oceanography, Vol. 62, pp. 185 to 196, 2006 Keywords: ⋅ Lethality, ⋅ pCO 2 , ⋅ epipelagic, ⋅ mesopelagic, ⋅ copepod, ⋅ pH. * Corresponding author. E-mail: watanabe_yuji@kanso.co.jp Copyright © The Oceanographic Society of Japan. Lethality of Increasing CO 2 Levels on Deep-Sea Copepods in the Western North Pacific YUJI WATANABE 1,2 *, ATSUSHI YAMAGUCHI 3 , HIROSHI ISHIDA 1 , TAKASHI HARIMOTO 1 , SHINYA SUZUKI 1 , YOSHIO SEKIDO 1 , TSUTOMU IKEDA 3 , YOSHIHISA SHIRAYAMA 4 , MASAYUKI MAC TAKAHASHI 5 , TAKASHI OHSUMI 6 and JOJI ISHIZAKA 7 1 The General Environmental Technos Co., Ltd., Azuchimachi, Chuo-ku, Osaka 541-0052, Japan 2 Graduate School of Marine Science and Engineering, Nagasaki University, Bunkyo-machi, Nagasaki 852-8521, Japan 3 Graduate School of Fisheries Sciences, Hokkaido University, Minato-cho, Hakodate 041-8611, Japan 4 Field Science Education and Research Center, Kyoto University, Shirahama, Nishimuro, Wakayama 649-2211, Japan 5 Graduate School of Kuroshio Sciences, Kochi University, Nangoku, Kochi 783-8502, Japan 6 Research Institute of Innovative Technology for the Earth (RITE), Kizu, Soraku, Kyoto 619-0292, Japan 7 Faculty of Fisheries, Nagasaki University, Bunkyo-machi, Nagasaki 852-8521, Japan (Received 17 May 2004; in revised form 29 November 2005; accepted 30 November 2005) The first CO 2 exposure experiments on several species of pelagic copepods inhabiting surface and deep layers in the western North Pacific were conducted. Living organ- isms were collected from two layers between the surface and 1,500 m between lati- tudes of 11 and 44°N, and they were exposed aboard ship to various pCO 2 up to about 98,000 μ μ μatm. Mortality of copepods from both shallow and deep layers in subarctic to subtropical regions increased with increasing pCO 2 and exposure time. Deep-living copepods showed higher tolerance to pCO 2 than shallow-living copepods. Further- more, deep-living copepods from subarctic and transitional regions had higher toler- ances than the subtropical copepods. The higher tolerances of the deep-living copepods from subarctic and transitional regions may be due to the adaptation to the natural pCO 2 conditions in the subarctic ocean. exterminated because of the effects of high CO 2 concen- trations. The option of dissolving CO 2 in the bathypelagic zone, such as 1,000 to 3,000 m, may possibly minimize the impact, if the CO 2 is adequately diluted (Handa and Ohsumi, 1995; Drange et al., 2001). At present only limited information about the effect of CO 2 on marine organisms is available (Shirayama, 1997; Omori et al ., 1998). Auerbach et al . (1997) used data from experiments of lowering pH by hydrochloric or sulfuric acids to estimate the effects of CO 2 ocean se- questration on marine organisms. Some CO 2 exposure experiments have been conducted recently. Effects of CO 2 on the phytoplankton (Riebesell et al., 2000; Riebesell, 2004), fishes (Kikkawa et al., 2003), invertebrates includ- ing copepods (Kurihara et al ., 2004) and foraminifera (Takeuchi et al., 1997) have been reported; however, those organisms were from coastal or epipelagic regions and not from the deep sea. Bacteria isolated from the deep sea (Takeuchi et al., 1997) have been examined for the 1. Introduction Sequestration of carbon dioxide (CO 2 ) in the deep ocean, which has a potentially large storage capacity (Hoffert et al ., 1979; Lackner, 2003), has been proposed as one of the mitigation options for slowing down the increase in atmospheric CO 2 —the most influential green- house gas (Houghton et al ., 2001). Several options have been considered for CO 2 storage in oceans (Haugan and Drange, 1992; Herzog and Edmond, 1994; Handa and Ohsumi, 1995; Ormerod and Angel, 1996), such as stor- ing in deep-sea basins as hydrates and in the bathypelagic zone as dissolved CO 2 . The option of storing in a deep- sea basin should enable storage of CO 2 in a narrow area for a long period of time and localizes the impact (Omori et al ., 1998); however, the organisms living there will be