Seawater carbon chemistry and calcification,carbonic anhydrase activity of cold-water coral Lophelia pertusa

Ocean acidification, the decrease in seawater pH due to the absorption of atmospheric CO2, profoundly threatens the survival of a large number of marine species. Cold-water corals are considered to be among the most vulnerable organisms to ocean acidification because they are already exposed to relatively low pH and corresponding low calcium carbonate saturation states (Omega). Lophelia pertusa is a globally distributed cold-water scleractinian coral that provides critical three-dimensional habitat for many ecologically and economically significant species. In this study, four different genotypes of L. pertusa were exposed to three pH treatments (pH=7.60, 7.75, and 7.90) over a short (two-week) experimental period, and six genotypes were exposed to two pH treatments (pH=7.60, and 7.90) over a long (six-month) experimental period. Their physiological response was measured as net calcification rate and the activity of carbonic anhydrase, a key enzyme in the calcification pathway. In the short-term experiment, net calcification rates did not significantly change with pH, although they were highly variable in the low pH treatment, including some genotypes that maintained positive net calcification in undersaturated conditions. In the six-month experiment, average net calcification was significantly reduced at low pH, with corals exhibiting net dissolution of skeleton. However, one of the same genotypes that maintained positive net calcification (+0.04% day-1) under the low pH treatment in the short-term experiment also maintained positive net calcification longer than the other genotypes in the long-term experiment, although none of the corals maintained positive calcification for the entire 6 months. Average carbonic anhydrase activity was not affected by pH, although some genotypes exhibited small, insignificant, increases in activity after the sixth month. Our results suggest that while net calcification in L. pertusa is adversely affected by ocean acidification in the long term, it is possible that some genotypes may prove to be more resilient than others, particularly to short perturbations of the carbonate system. These results provide evidence that populations of L. pertusa in the Gulf of Mexico may contain the genetic variability necessary to support an adaptive response to future ocean acidification.

海洋酸化（Ocean Acidification）指因吸收大气二氧化碳（CO₂）而导致的海水pH值降低现象，该过程严重威胁大量海洋物种的生存。冷水珊瑚（Cold-water Corals）被视为对海洋酸化最为敏感的生物类群之一，因其本身已处于相对较低的pH环境与对应的低碳酸钙饱和状态（Omega）。歧根珊瑚（Lophelia pertusa）是一种全球分布的冷水石珊瑚，为诸多具有重要生态与经济价值的物种提供了关键的三维栖息生境。本研究中，4株不同基因型的歧根珊瑚在短期（2周）实验周期内接受了3组pH处理（pH=7.60、7.75与7.90）；另有6株基因型的歧根珊瑚在长期（6个月）实验周期内接受了2组pH处理（pH=7.60与7.90）。本研究以净钙化速率与碳酸酐酶（Carbonic Anhydrase，钙化通路中的关键酶）的活性作为其生理响应的检测指标。在短期实验中，净钙化速率未随pH值发生显著变化，但在低pH处理组中其变异程度极高，部分基因型在碳酸钙不饱和环境下仍维持了正净钙化速率。在为期6个月的长期实验中，低pH处理组的平均净钙化速率显著降低，珊瑚出现了骨骼净溶解现象。然而，在短期实验中于低pH处理组维持正净钙化速率（+0.04%·d⁻¹）的基因型中，有一株在长期实验中维持正净钙化速率的时长显著长于其他基因型，尽管所有珊瑚均未在完整6个月的实验周期内维持正钙化状态。平均碳酸酐酶活性未受pH值影响，但在实验第6个月后，部分基因型的酶活性出现了小幅且无统计学显著性的上升。本研究结果表明，尽管歧根珊瑚的净钙化速率在长期尺度上会受到海洋酸化的负面影响，但部分基因型可能相较于其他基因型具备更强的耐受能力，尤其在碳酸盐系统短期扰动的情况下。上述结果证实，墨西哥湾的歧根珊瑚种群可能携带足够的遗传变异，以支持其对未来海洋酸化产生适应性响应。