Abstract
The effects of ocean acidification on otolith crystallization and growth rates were investigated in gilthead sea bream (Sparus aurata) larvae. Larvae were exposed to three different pH levels: pH8.2, pH7.7 and pH7.3 for a period of 18 days post-fertilization. For the first time, we demonstrate that pH has a significant impact on the carbonate polymorph composition, showing calcite in a significant percentage of individuals at low pH. Around 21% of the larvae exposed to pH7.3 showed irregular calcitic otoliths rather than commonly found round aragonitic otoliths. Calcitic otoliths showed a moderate level of heritability suggesting an important role of genetic factors. We also observed significantly larger otoliths in larvae reared at pH7.7 and pH7.3 compared to pH8.2 in both sagittae and lapilli. Our results demonstrate that otolith growth rates in gilthead sea bream larvae increase at low pH while a significant proportion of larvae are prone to the formation of calcitic otoliths at pH7.3.
Highlights
Ocean acidification is a major consequence of rising levels of atmospheric carbon dioxide (CO2)
The otoliths’ area (OA), otoliths’ perimeter (OP) and the larval body length were measured for a total of 111 (13–14 individuals per tank), 174 (23–26 individuals per tank) and 186 (25–30 individuals per tank) larvae exposed to water at pH8.2, pH7.7 and pH7.3, respectively
We found that the pH treatment had a significant impact on the average Otolith area (OA) (p < 0.001) and OP (p < 0.001) for both sagittae and lapilli
Summary
Ocean acidification is a major consequence of rising levels of atmospheric carbon dioxide (CO2). The impact of ocean acidification on marine ecosystems has been the focus of intensive research[2] This pH decline is predicted to affect the saturation states of the different calcium carbonate (CaCO3) polymorphs (aragonite, calcite and vaterite)[3] altering the formation and dissolution rates of carbonate-based structures in marine organisms including shells and exoskeletons[4]. To increase our knowledge of ocean acidification impact on otolith formation in Mediterranean fish we studied how different levels of pCO2 affect otolith growth during the first stages of gilthead sea bream development. At these early stages of development fish are more vulnerable to environmental factors due to their reduced acclimation capacity and limited ability to avoid unfavourable conditions. The effects of otolith formation in gilthead sea bream were studied following exposure to three different levels of pCO2 with corresponding changes in pH: 287 μatm (pH8.2; pre-industrial levels), 1159 μatm (pH7.7) and 2650 μatm (pH7.3) for 18 days after egg fertilization
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