743 Journal of Oceanography, Vol. 60, pp. 743 to 750, 2004 Review Keywords: ⋅ Rising atmospheric CO 2 concentration, ⋅ CO 2 ocean seques- tration, ⋅ biological impact, ⋅ sub-lethal effects, ⋅ egg production, ⋅ fertilization, ⋅ morphology, ⋅ copepods, ⋅ sea urchins. * Corresponding author. E-mail: harukoku@e-mail.jp Copyright © The Oceanographic Society of Japan. Sub-Lethal Effects of Elevated Concentration of CO 2 on Planktonic Copepods and Sea Urchins HARUKO KURIHARA 1 *, SHINJI SHIMODE 2 and YOSHIHISA SHIRAYAMA 1 1 Seto Marine Biological Laboratory, Kyoto University, Shirahama, Nishimuro, Wakayama 649-2211, Japan 2 Graduate School of Environmental and Information Sciences, Yokohama National University, Tokiwadai, Hodogaya, Yokohama 240-8501, Japan (Received 5 January 2004; in revised form 27 April 2004; accepted 30 April 2004) Data concerning the effects of high CO 2 concentrations on marine organisms are es- sential for both predicting future impacts of the increasing atmospheric CO 2 concen- tration and assessing the effects of deep-sea CO 2 sequestration. Here we review our recent studies evaluating the effects of elevated CO 2 concentrations in seawater on the mortality and egg production of the marine planktonic copepod, Acartia steueri, and on the fertilization rate and larval morphology of sea urchin embryos, Hemicentrotus pulcherrimus and Echinometra mathaei. Under conditions of +10,000 ppm CO 2 in seawater (pH 6.8), the egg production rates of copepods decreased sig- nificantly. The survival rates of adult copepods were not affected when reared under increased CO 2 for 8 days, however longer exposure times could have revealed toxic effects of elevated CO 2 concentrations. The fertilization rate of sea urchin eggs of both species decreased with increasing CO 2 concentration. Furthermore, the size of pluteus larvae decreased with increasing CO 2 concentration and malformed skeletogenesis was observed in both larvae. This suggests that calcification is affected by elevated CO 2 in the seawater. From these results, we conclude that increased CO 2 concentration in seawater will chronically affect several marine organisms and we discuss the effects of increased CO 2 on the marine carbon cycle and marine ecosys- tem. phere and the ocean surface, which is mainly controlled by a “biological pump”. The pump may be defined as the movement of CO 2 that enters into the ocean from the at- mosphere to the deep-ocean floor through biological proc- esses, i.e. photosynthetic fixation of CO 2 by phytoplankton, passive export of organic carbon (e.g. fecal pellets of zooplankton, detritus, and dead organisms) and carbonates (e.g. shells and bones) by gravitation, or through vertical migration of zooplankton to the deep ocean (Fowler and Knauer, 1986; Zhang and Dam, 1997; Rivkin and Legendre, 2002). In the surface ocean, there exists a continuous sea- air gas exchange (Takahashi et al ., 1997); thus, the CO 2 concentration is in equilibrium in respect with the ocean surface and the atmosphere. However, CO 2 in the deep ocean is isolated from the atmosphere because the pycnocline prevents free gas exchange between the at- mosphere and the deep ocean. The deep sea serves, there- 1. Introduction For about 50 million years, the atmospheric concen- tration of CO 2 has been fluctuating between 180 ppm to 280 ppm. However, since the industrial revolution, the atmospheric CO 2 concentration has rapidly increased and recently it has exceeded 365 ppm (Bazzaz, 1990; Houghton et al., 1992; Keeling and Whorf, 1994). Hu- man activity produces approximately 5.0–7.0 Gt C y –1 , about 2.0 Gt y –1 of which is absorbed into the ocean and 3.3 Gt y –1 of which accumulates continuously in the at- mosphere (Keeling et al., 1996; Takahashi et al., 1997; Battle et al., 2000; Sarmiento et al., 2000). CO 2 absorption by the ocean is driven by differences in the partial pressure of CO 2 (PCO 2 ) between the atmos-