Ocean acidification can influence the formation, development and functions of calcified structures in marine organisms, such as otoliths, which are mainly composed of calcium carbonate (CaCO₃) and function in orientation, balance, sensory perception and locomotion in fish. This study investigated the impacts of seawater acidification (pH 8.10, 7.70 and 7.30, roughly corresponding to the ocean acidification under RCP 8.5 scenario predicted by the IPCC) on somatic growth, otolith (aragonite) morphology and microchemistry in the flounder Paralichthys olivaceus at early life stages (ELSs, exposed to acidified seawater via pCO₂ from embryonic to juvenile stages for 52 days). The results demonstrated that seawater acidification promoted otolith growth (mass and size) but did not change their geometric outlines. Seawater acidification did not alter the somatic growth or otolith elemental incorporation (Sr, Ba and Mg) in the flounder. Seawater acidification increased the occurrence of abnormally developed calcitic otoliths (calcite) which considerably differed from the aragonitic otoliths in surface and crystal structures. Additionally, elemental incorporation (Sr:Ca and Ba:Ca) appeared to be higher in aragonitic otoliths than in calcitic otoliths, which was likely related to their unique manners of formation. Our results agreed with the broad literature, in that seawater acidification showed species-specific influences (positive or no effect) on otolith size but did not affect somatic growth, otolith shape or elemental incorporation of fish at ELSs. These findings provide knowledge for evaluating the ecological effects of ocean acidification on the recruitment and population dynamics of fish in the wild.

海洋酸化可影响海洋生物钙化结构的形成、发展和功能，如耳石，其主要成分为碳酸钙（CaCO ₃），在鱼类中具有定向、平衡、感觉和运动等功能。本研究调查了海水酸化（pH 8.10、7.70 和 7.30，大致对应于 IPCC 预测的 RCP 8.5 情景下的海洋酸化）对牙鲆早期生命体细胞生长、耳石（文石）形态和微化学的影响阶段（ELS，通过p CO ₂暴露于酸化海水中从胚胎期到幼年期 52 天）。结果表明，海水酸化促进了耳石的生长（质量和大小），但并未改变其几何轮廓。海水酸化并没有改变比目鱼的体细胞生长或耳石元素掺入（Sr、Ba 和 Mg）。海水酸化增加了异常发育的方解石耳石（方解石）的出现，其在表面和晶体结构上与文石耳石有很大不同。此外，文石耳石中的元素掺入（Sr:Ca 和 Ba:Ca）似乎高于方解石耳石，这可能与其独特的形成方式有关。我们的结果与广泛的文献一致，因为海水酸化显示出对耳石大小的物种特异性影响（正或无影响），但不影响 ELS 中鱼的体细胞生长、耳石形状或元素掺入。这些发现为评估海洋酸化对野外鱼类招募和种群动态的生态影响提供了知识。