Even though the physiological effects of high CO2
in water can be largely ascribed to decreases in body
fluid pH, increased proton concentrations in the ambient
water per se cannot explain the physiological perturbations caused by elevated levels of CO2. The effects of
water acidification by mineral acids such as HCl and
H2SO4 are less than those caused by high CO2, when
tested at the same water pH. This has been demonstrated
clearly by our recent results that compared mortalities of
eggs and larvae of red seabream, Pagrus major,attwo
levels of seawater pH lowered by either CO2 or HCl
[Kikkawa et al., 2004]. Exposure to high CO2 resulted in
far higher mortalities than acid exposure at both pH
levels (Figure 1). This is due to a much higher biomembrane permeability of gaseous CO2compared with that ofH+
[Heisler, 1986; Morris et al., 1989]. Although earlier
studies used mortality data based on acid exposure to
evaluate impacts of CO2 ocean sequestration on marine
animals [e.g., Auerbach et al., 1997], the predicted
impacts based on such studies may be milder than those
caused by hypercapnia.