Seawater carbonate chemistry and calcification response of a tropical scleractinian coral to seasonal upwelling conditions

Natural processes such as upwelling of deeper-water masses change the physical-chemical conditions of the water column creating localized ocean acidification events that can have an impact on the natural communities. This study was performed in a coral reef system of an archetypical bay within the Tayrona National Natural Park (PNNT) (Colombia), and aimed to quantify net calcification rates of a foundational coral species within a temporal context (6 months) taking into account the dynamics of seasonal upwelling that influence the study area. Net calcification rates of coral fragments were obtained in situ by the alkalinity anomaly technique in short-term incubations (~2.5 h). We found a significant effect of the upwelling on net calcification rates (Gnet) (p < 0.05) with an 42% increase in CaCO3 accretion compared to non-upwelling season. We found an increase in total alkalinity (AT) and dissolved inorganic carbon (DIC) with decreased aragonite saturation (Ωara) for the upwelling months, indicating an influence of the Subtropical Under Water mass (SAW) in the PNNT coral community. Significant negative correlations between net calcification with temperature and Ωara, which indicates a positive response of M. auretenra with the upwelling conditions, thus, acting as “enhancer” of resilience for coral calcification.

深层水体上涌等自然过程会改变水柱的物理化学条件，形成局部海洋酸化事件，进而影响自然群落。本研究于哥伦比亚Tayrona国家自然公园（PNNT）内一个典型海湾的珊瑚礁系统中开展，旨在结合影响研究区域的季节性上涌动态，量化6个月时间尺度下某一基础珊瑚物种的净钙化率。通过碱度异常技术（alkalinity anomaly technique）对珊瑚碎片进行原位短期培养（约2.5小时），获取其净钙化率数据。结果表明，上涌对净钙化率（Gnet）具有显著影响（p < 0.05），与非上涌季节相比，碳酸钙沉积量增加42%。上涌月份的总碱度（AT）和溶解无机碳（DIC）升高，文石饱和度（Ωara）降低，这提示亚热带深层水团（Subtropical Underwater mass, SAW）对PNNT珊瑚群落存在影响。净钙化率与温度及Ωara呈显著负相关，说明M. auretenra对上涌条件表现出积极响应，从而充当珊瑚钙化韧性的“增强因子”。