[BPT04-P01] Variation of geochemistry in sea urchins cultured under the long-term acidification experiment
Keywords:sea urchin, ocean acidification, culture experiment
In this study, sea urchins were raised under the following five carbon dioxide partial pressures (pCO2, µatm): (i) 2000, (ii) 1000, (iii) 700, (iv) 350 (controlled setting), (v) 250. The conditions from (i) to (iii) were adjusted by addition of CO2 and that of (v) was adjusted chemically. For the culture experiment, 5 to 7 sea urchins were placed in individual bottles at each setting. The shell length and the body weight were measured monthly, and one spine from individual sea urchin was also collected at this time. Oxygen and carbon isotope ratios (δ18O, δ13C) contained in the spines of M. nudus were measured with a stable isotope ratio mass spectrometer (IsoPrime). The Mg/Ca ratio contained in the spines of both sea urchins, the shell and the lantern (chewing part) of S. intermedius were measured with an inductivity coupled plasma optical emission spectrometer (Agilent 720). The observation of the surface structure of both sea urchins was performed by a scanning electron microscope (JEOL, JSM-5500G).
As the result of culture experiments, the shell length and the body weight decreased with increasing pCO2. The spine Mg/Ca ratios of both sea urchins showed positive relations against pCO2. Since it has been reported that calcites with higher Mg contents have higher solubility, spines of sea urchins would become vulnerable under the projected OA conditions. The SEM observations of surface structures of spines showed that spines reared under higher pCO2 conditions were disordered compared to those reared at controlled setting. For the results of δ18O and δ13C measurements on the spines of M. nudus, variation of δ13C showed a clear negative correlation without temperature effect. On the other hand, δ18O in the spines showed a seasonal change which is probably related to variation of seawater temperature during the rearing period with negligible effects from differences of pCO2. Therefore, δ18O and δ13C in the spines of M. nudus would have potential for environmental proxies of water temperature and seawater pCO2, respectively.