Abstract
To date the study of ocean acidification on fish otolith formation has been mainly focused on larval and juvenile stages. In the present pilot study, wild-captured adult Atlantic cod (Gadus morhua) were exposed to two different levels of pCO(2,) 422µatm (ambient, low pCO(2)) or 1091µatm (high pCO(2)), for a period of 30 weeks (from mid-October to early April 2014-2015) in order to study the effects on otolith size, shape and CaCO(3) crystallization amongst other biological parameters. We found that otoliths from cod exposed to high pCO(2) were slightly smaller (- 3.4% in length; - 3.3% in perimeter), rounder (- 2.9% circularity and + 4% roundness) but heavier (+ 5%) than the low pCO(2) group. Interestingly, there were different effects in males and females; for instance, male cods exposed to high pCO(2) exhibited significant changes in circularity (- 3%) and roundness (+ 4%) compared to the low pCO(2) males, but without significant changes on otolith dimensions, while females exposed to high pCO(2) had smaller otoliths as shown for length (- 5.6%), width (- 2%), perimeter (- 3.5%) and area (- 4.8%). Furthermore, while the majority of the otoliths analysed showed normal aragonite deposition, 10% of fish exposed to 1091µatm of pCO(2) had an abnormal accretion of calcite, suggesting a shift on calcium carbonate polymorph crystallization in some individuals under high pCO(2) conditions. Our preliminary results indicate that high levels of pCO(2) in adult Atlantic cod might affect otolith growth in a gender-specific way. Our findings reveal that otoliths from adult cod are affected by ocean acidification, and we believe that the present study will prompt further research into this currently under-explored area.