Effects of ocean acidification on the calcification of otoliths of larval Atlantic cod Gadus morhua

The growth and development of the aragonitic CaCO₃ otoliths of teleost fish could be vulnerable to processes resulting from ocean acidification. The potential effects of an increase in atmospheric CO ₂ on the calcification of the otoliths were investigated by rearing Atlantic cod Gadus morhua L. larvae in 3 pCO₂ concentrations-control (370 μatm), medium (1800 μatm) and high (4200 μatm)-from March to May 2010. Increased otolith growth was observed in 7 to 46 d post hatch (dph) cod larvae at elevated pCO₂ concentrations. The sagittae and lapilli were usually largest in the high pCO₂ treatment followed by the medium and control treatments. The greatest difference in mean otolith surface area (normalized to fish length) was for sagittae at 11 dph, with medium and high treatments being 46 and 43% larger than the control group, respectively. There was no significant pCO₂ effect on the shape of the otoliths nor were there any trends in the fluctuating asymmetry, defined as the difference between the right and left sides, in relation to the increase in otolith growth from elevated pCO₂.