Seawater carbonate chemistry and otolith development and chemistry in a diadromous fish

Ocean acidification threatens marine ecosystems by altering ocean chemistry and calcification processes in marine organisms. This study investigated the effects of predicted future CO2 levels, under varying temperature levels, on otolith development (size and shape) and chemistry, with the latter aimed at developing a chemical tracer of environmental pCO2. Juvenile barramundi (Lates calcarifer), a diadromous fish species, were reared in ambient (pCO2: 640 µatm; pH: 7.9) and elevated (pCO2: 1490 µatm; pH: 7.5) pCO2 treatments representing current and projected coastal systems crossed with three temperature levels (26 °C, 30 °C and 34 °C) for 42 days. Otolith shape and size parameters (length, width, perimeter and area) were measured and element concentrations (Na, Mg, Sr, Ba, Li, Mn and B) were quantified using Laser Ablation Inductively Coupled Plasma-Mass Spectrometry (LA ICP-MS). There was an interactive effect of elevated pCO2 and temperature on otolith shape and perimeter, whereas otolith chemistry did not vary among treatments. This study demonstrates that combined elevated pCO2 and temperature can affect the development of important internal structures in diadromous fish, but also suggests that otolith elemental chemistry was not a suitable tracer for pCO2 histories in fish. Future climate change conditions affect an important auditory and balance organ; consequently, rising CO2 levels may interfere with sensory function.