High CO₂ Levels Stimulate Growth of Fish Bone

Predictions that ocean acidification driven by high atmospheric levels of CO₂ will slow the growth of fish bones are incorrect, according to researchers at Scripps Institution of Oceanography, in San Diego (Science 2009, 324, 1683). Their study points out limitations in scientists' understanding of the effects of elevated CO₂ concentration on biomineralization in ocean creatures and the need for a clearer grasp of seawater chemistry. High oceanic CO₂ levels increase the concentrations of ocean bicarbonate (HCO₃^-) and hydrogen ions and decrease the concentrations of carbonate ions and calcium carbonate. The interdependence of those chemical species in seawater leads to the prediction that high CO₂ levels should slow bone growth (calcification) in fish. David M. Checkley Jr., Andrew G. Dickson, and coworkers incubated white sea bass eggs and larvae in a series of water samples of various CO₂ concentrations and measured otoliths (ear bones) of sea bass with electron microscopy. Contrary to expectations, otoliths of fish grown in seawater with high CO₂ levels were significantly larger than those of fish grown in water with lower CO₂ levels, the team reports.