Seawater carbonate chemistry and competition between the scleractinian corals Galaxea fascicularis and Acropora hyacinthus

Ocean acidification is expected to affect coral reefs in multiple ways, in part, by depressing the calcification of scleractinian corals. To evaluate how coral communities will respond to ocean acidification, research into the effects on ecological processes determining community structure is now needed. The present study focused on corals utilizing soft tissues (i.e., mesenterial filaments) as agonistic mechanism, and evaluated their ability to compete for space under ocean acidification. Using aquarium-reared specimens in Monaco, single polyps of Galaxea fascicularis were paired with branch tips of Acropora hyacinthus to stimulate competitive interactions, which were evaluated through the production and use of mesenterial filaments in causing tissue damage under ambient (600 µatm) and elevated pCO2 (1200 µatm). At 1200 µatm pCO2, and when paired with A. hyacinthus, the extrusion of mesenterial filaments from G. fascicularis occurred 2 days earlier than under ambient pCO2, although ultimately the mesenterial filaments caused the same amount of tissue necrosis on A. hyacinthus under both pCO2 regimes after 7 days. This outcome supports the hypothesis that some kinds of competitive mechanisms utilized by scleractinian corals (i.e., mesenterial filaments) will be unaffected by short exposure to pCO2 as high as 1200 ?atm.海洋酸化预计将以多种途径影响珊瑚礁，其中部分机制为抑制石珊瑚（scleractinian corals）的钙化作用。为明确珊瑚群落对海洋酸化的响应模式，当前亟需开展针对调控群落结构的生态过程所受影响的相关研究。本研究聚焦于以软组织（即肠系膜丝（mesenterial filaments））作为拮抗机制（agonistic mechanism）的珊瑚类群，评估其在海洋酸化环境下的空间竞争能力。实验采用摩纳哥实验室培育的样本，将Galaxea fascicularis的单个水螅体与Acropora hyacinthus的枝梢进行配对以诱导竞争互作，并通过观测两种二氧化碳分压（pCO₂）环境下（本底对照组为600 µatm，高CO₂组为1200 µatm）肠系膜丝的产生与作用导致的组织损伤情况，对该竞争互作进行评估。在1200 µatm的二氧化碳分压环境下，当与Acropora hyacinthus配对时，Galaxea fascicularis的肠系膜丝伸出时间较本底二氧化碳分压环境提前2天；尽管如此，在培养7天后，两种二氧化碳分压条件下肠系膜丝对Acropora hyacinthus造成的组织坏死程度并无显著差异。该实验结果支持以下假说：石珊瑚（scleractinian corals）所利用的部分竞争机制（即肠系膜丝（mesenterial filaments）），在短期暴露于最高达1200 µatm的二氧化碳分压环境时，不会受到显著影响。