Ocean acidification is perceived to be a major threat for many calcifying organisms, including scleractinian corals. Here, we investigate (1) whether past exposure to low pH environments associated with CO₂ vents could increase corals tolerance to low pH and (2) whether zooxanthellate corals are more tolerant to low pH than azooxanthellate corals. To test these hypotheses, two Mediterranean colonial corals Cladocora caespitosa (zooxanthellate) and Astroides calycularis (azooxanthellate) were collected from CO₂ vents and reference sites and incubated in the laboratory under present day (pH on the total scale, pH_T 8.07) and low pH conditions (pH_T 7.70). Rates of net calcification, dark respiration, and photosynthesis were monitored during a 6-month experiment. Monthly net calcification was assessed every 27–35 d using the buoyant weight technique, whereas light and dark net calcification was estimated using the alkalinity anomaly technique during 1-h incubations. Neither species showed any change in net calcification rates, respiration, and photosynthesis regardless of their environmental history, pH treatment, and trophic strategy. Our results indicate that C. caespitosa and As. calycularis could tolerate future ocean acidification conditions for at least 6 months. These results will aid in predicting species' future responses to ocean acidification, and thus improve the management and conservation of Mediterranean corals.

中文翻译：

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无论之前是否接触过天然二氧化碳排放口，两种温带珊瑚都能耐受低 pH 值

海洋酸化被认为是许多钙化生物的主要威胁，包括石珊瑚。在这里，我们调查（1）过去暴露于与 CO ₂喷口相关的低 pH 值环境是否会增加珊瑚对低 pH 值的耐受性，以及（2）虫黄藻珊瑚是否比偶氮黄藻珊瑚更能耐受低 pH 值。为了验证这些假设，从 CO ₂喷口和参考地点收集了两种地中海殖民地珊瑚Cladocora caespitosa（虫黄藻）和Astroides calycularis（azooxanthellate），并在实验室中在当今（总规模的 pH 值，pH _T 8.07）和低pH 条件 (pH _T7.70）。在为期 6 个月的实验中监测净钙化、暗呼吸和光合作用的速率。使用浮重技术每 27-35 天评估每月净钙化，而在 1 小时孵化期间使用碱度异常技术评估明暗净钙化。无论它们的环境历史、pH 处理和营养策略如何，这两个物种的净钙化率、呼吸作用和光合作用均未出现任何变化。我们的结果表明C. caespitosa和As。calycularis可以忍受未来海洋酸化条件至少 6 个月。这些结果将有助于预测物种未来对海洋酸化的反应，从而改善地中海珊瑚的管理和保护。