Seawater carbonate chemistry and calcification and productivity of sporadic coral reef

Estimates of coral reef ecosystem calcification (Gnet) and productivity (Pnet) provide insight into coral community health and functionality in response to short- and long-term stressors such as ocean warming and acidification. Here, we investigate spatial variability in calcification and organic production at One Tree Island (OTI) and compare our new observations to sporadic metabolic rates reported over the previous 50 years on the same reef flat. Gnet and Pnet estimates at the nearshore site were 50% and 166% lower than an offshore site with a shift in organic production from net productive to net respiratory. Contrary to expectations, calcification rates in 2017 (145.7 +- 20.2 mmol/m**2/d) were comparable to the 1970s estimate (125.0 +- 12.5 mmol/m**2/d) and 400% greater than similar observations in 2014. Our results indicate only weak associations between Gnet and aragonite (Omega ar). A local increase in coral cover from 18% in 2014 to 31% in 2017 was the likely driver of increased calcification. A steeper TA–DIC slope in 2017 demonstrates a greater control of calcification on seawater carbonate chemistry than prior years. Overall, these results highlight the importance of site selection and replication when comparing metabolic datasets, and demonstrate major short-term variability in metabolic rates. The predictive capabilities of ecosystem metabolism studies may be constrained by using the available short-term datasets to represent long-term calcification trends.珊瑚礁生态系统钙化速率（Gnet）与有机生产力（Pnet）的估算值，可为理解珊瑚群落应对海洋变暖、酸化等短期及长期胁迫因子的健康状态与功能机制提供重要参考。本研究针对奥斯特雷岛（One Tree Island, OTI）海域的钙化与有机生产空间变异特征展开调查，并将新观测数据与该礁坪过去50年间零星报道的代谢速率记录进行对比。近岸站位的Gnet与Pnet估算值分别较远岸站位低50%与166%，且有机生产模式从净生产转向净呼吸。与预期相悖的是，2017年的钙化速率（145.7 ± 20.2 mmol/m²/d）与1970年代的估算值（125.0 ± 12.5 mmol/m²/d）相当，却较2014年的同类观测结果高出400%。本研究结果显示，Gnet与文石饱和参数（Omega_ar）仅存在微弱的相关性。该海域珊瑚覆盖率从2014年的18%升至2017年的31%，这或是钙化速率提升的潜在驱动因素。2017年更陡的总碱度（TA）-溶解无机碳（DIC）斜率表明，相较于往年，当年的钙化过程对海水碳酸盐化学的调控作用更强。综上，本研究结果凸显了在对比代谢数据集时，站位选择与重复采样的重要性，并证实了代谢速率存在显著的短期变异特征。若仅采用现有短期数据集来表征长期钙化趋势，则可能会限制生态系统代谢研究的预测能力。