Coral polyps have a fluid-filled internal compartment, the gastrovascular cavity (GVC). Respiration and photosynthesis cause large daily excursions in GVC oxygen concentration (O2) and pH, but few studies have examined how this correlates with calcification rates. We hypothesized that GVC chemistry can mediate and ameliorate the effects of decreasing seawater pH (pHSW) on coral calcification. Microelectrodes were used to monitor O2 and pH within the GVC of Montastraea cavernosa and Duncanopsammia axifuga (pH only) in both the light and the dark, and three pHSW levels (8.2, 7.9, and 7.6). At pHSW 8.2, GVC O2 ranged from ca. 0 to over 400% saturation in the dark and light, respectively, with transitions from low to high (and vice versa) within minutes of turning the light on or off. For all three pHSW treatments and both species, pHGVC was always significantly above and below pHSW in the light and dark, respectively. For M. cavernosa in the light, pHGVC reached levels of pH 8.4–8.7 with no difference among pHSW treatments tested; in the dark, pHGVC dropped below pHSW and even below pH 7.0 in some trials at pHSW 7.6. For D. axifuga in both the light and the dark, pHGVC decreased linearly as pHSW decreased. Calcification rates were measured in the light concurrent with measurements of GVC O2 and pHGVC. For both species, calcification rates were similar at pHSW 8.2 and 7.9 but were significantly lower at pHSW 7.6. Thus, for both species, calcification was protected from seawater acidification by intrinsic coral physiology at pHSW 7.9 but not 7.6. Calcification was not correlated with pHGVC for M. cavernosa but was for D. axifuga. These results highlight the diverse responses of corals to changes in pHSW, their varying abilities to control pHGVC, and consequently their susceptibility to ocean acidification.

中文翻译：

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浅色和深色孵化期间珊瑚血管腔 pH 值对海水 pH 值降低的反应表明物种对海洋酸化对钙化影响的特异性反应

珊瑚息肉有一个充满液体的内部隔室，即胃血管腔 (GVC)。呼吸和光合作用导致 GVC 氧浓度 (O2) 和 pH 值每日大幅波动，但很少有研究探讨这与钙化率之间的关系。我们假设 GVC 化学可以调节和改善降低海水 pH 值 (pHSW) 对珊瑚钙化的影响。微电极用于在明暗和三个 pHSW 水平（8.2、7.9 和 7.6）下监测海绵状山蛾和 Duncanopsammia axifuga（仅 pH 值）的 GVC 内的 O2 和 pH 值。在 pHSW 8.2 时，GVC O2 的范围从大约 在黑暗和光明中分别为 0 到 400% 以上的饱和度，在打开或关闭灯的几分钟内从低到高（反之亦然）过渡。对于所有三种 pHSW 处理和两种物种，pHGVC 总是分别在明暗条件下显着高于和低于 pHSW。对于光照下的海绵状海绵体，pHGVC 达到了 8.4-8.7 的水平，测试的 pHSW 处理之间没有差异；在黑暗中，pHGVC 在 pHSW 7.6 的某些试验中降至 pHSW 以下，甚至低于 pH 7.0。对于 D. axifuga 在明亮和黑暗中，pHGVC 随着 pHSW 的降低而线性降低。在测量 GVC O2 和 pHGVC 的同时，在光照下测量钙化率。对于这两种物种，钙化率在 pHSW 8.2 和 7.9 时相似，但在 pHSW 7.6 时明显较低。因此，对于这两个物种，在 pHSW 7.9 但不是 7.6 的情况下，内在珊瑚生理学可以保护钙化免受海水酸化。钙化与海绵状海绵体的 pHGVC 无关，但与 D. axifuga 相关。