|Decalcification of a Pteropod shell exposed over a two month period to|
seawater with expected CO2 levels at century's end (Credit).
reduce calcification and growth rates of shell-forming marine organisms such as plankton, molluscs, echinoderms, and corals.
|Picture of an otolith cross-section|
|Dorsal view of sagittal otoliths of 7-day-old white sea bass grown at (A) 430, (B) 1000, and (C) 2500 µatm p(CO2) seawater. Scale bars indicate 10 µm. (D) Ratio (treatment/control) of otolith area in relation to p(CO2)seawater. Mean ratios and their associated uncertainties (3) are plotted. The control level p(CO2) seawater was ~430 µatm [p(CO2) atmosphere ~ 380 µatm], for which otolith area ratio = 1. Checkley et al. 2009.|
These results suggest that young fish can control the concentration of ions (H+ and Ca2+) in the endolymph surrounding the otoliths. If there is constant pH (from the regulation of ions) and increased CO2 (from the water) in the endolymph this would result in an increase in carbonate and thus an increase in the saturation state of CaCO3, therefore accelerating otolith formation. It is still unknown whether this increase in size could cause any ill effects in the fish or on our estimates of age and growth.
Further, other potential effects of ocean acidification include acidification of body fluids (hypercapnia), decreased growth and increased stress as organisms reallocate resources to maintain calcification, and cascading affects on the ecosystem as calcified organisms are adversely effected. Global warming is complicated and can have unexpected affects. Studies like Checkley et al. (2009) and others (i.e. Ries et al. 2009) are good reminders of how difficult it can be to predict the complex bio-physical relationships that exist in a dynamic ocean environment.
Checkley Jr. DM, Dickson AG, Takahashi M, Radich JA, Eisenkolb N, Asch R. 2009. Elevated CO2 enhances otolith growth in young fish. Science 324:1683.
Doney SC, Fabry, VJ, Feely RA, Kleypas JA. 2009. Ocean acidification: the other CO2 problem. Annual Review of Marine Science 1:169-192.
Ries JB, Cohen AL, McCorkle DC. 2009. Marine calcifiers exhibit mixed responses to CO2-induced ocean acidification. Geology 37:1131-1134.