当周围海洋变得更加酸化时，珊瑚礁会发生什么？答案可能不仅限于珊瑚生长变慢。珊瑚礁上一些最微小的生物也能在维系礁体结构方面发挥重要作用，它们数量的变化可能改变生态系统随时间的演变。
What happens to a coral reef when the ocean around it becomes more acidic? The answer may not be limited to slower-growing corals. Some of the smallest organisms on a reef can also play an important role in holding its structure together, and changes in their abundance could alter how the ecosystem develops over time.
据美国地质调查局称，在夏威夷进行的一项为期10个月的对照实验中，研究人员让珊瑚礁群落暴露在升高的二氧化碳水平下，旨在模拟本世纪晚些时候预期出现的条件。在酸化水箱中，壳状珊瑚藻覆盖了仅4%的可用表面，而对照水箱中这一比例为25%。这一差异代表覆盖率相对减少了86%。海洋酸化改变了什么该实验在位于欧胡岛卡内奥赫湾的夏威夷海洋生物学研究所椰子岛的持续流通中宇宙装置中进行，使用来自卡内奥赫湾的未过滤海水。
According to the U.S. Geological Survey, a 10-month controlled experiment in Hawaii exposed reef communities to elevated carbon dioxide levels designed to represent conditions expected later this century. In the acidified tanks, crustose coralline algae covered just 4% of the available surface, compared with 25% in control tanks. The difference represented an 86% relative reduction in coverage. What ocean acidification changesThe experiment was conducted in continuous-flow mesocosms at the Hawaii Institute of Marine Biology on Coconut Island, using unfiltered seawater from Kāneʻohe Bay on Oahu.
水箱置于室外全日照环境下，使其经历与附近珊瑚礁相似的日间和季节性温度及海水化学变化。研究人员提高了处理水箱中二氧化碳的分压（pCO₂）。在正午时分，酸化中宇宙装置中的二氧化碳水平比对照水箱平均高出约365微个大气压，围绕该平均值有相当大的变异。该处理旨在模拟本世纪预期出现的升高条件。
The tanks were kept outdoors in full sunlight, allowing them to experience daily and seasonal changes in temperature and seawater chemistry similar to those on the nearby reef. Researchers increased the partial pressure of carbon dioxide, or pCO₂, in treatment tanks. At midday, CO₂ levels in the acidified mesocosms exceeded those in the control tanks by an average of about 365 microatmospheres, with considerable variation around that average. The treatment was intended to simulate elevated conditions expected during this century.
海洋酸化是由海洋吸收二氧化碳引起的。额外的二氧化碳引发化学反应，导致氢离子增加、碳酸根离子减少。由于碳酸根离子构成碳酸钙骨架的基础，钙化生物在酸性条件下更难构建其外壳和骨架。这凸显了壳状珊瑚藻的重要性。这些藻类质地坚硬且呈壳状，能在珊瑚礁上形成碳酸钙结构。造礁藻类急剧减少实验水箱之间的对比十分明显。
Ocean acidification is caused by the ocean’s absorption of carbon dioxide. The extra carbon dioxide initiates chemical reactions leading to an increase in hydrogen ions and a decrease in the amount of carbonate ions. Since carbonate ions form the foundation of calcium carbonate skeletons, calcifying organisms have a harder time building their shells and skeletons under acidic conditions. This highlights the significance of crustose coralline algae. The algae are hard and encrusting, and they form calcium carbonate structures on reefs.A sharp decline in reef-building algaeThe contrast between the experimental tanks was striking.
10个月结束时，壳状珊瑚藻在对照中型生态系统中的覆盖率约为25%，而在暴露于高浓度二氧化碳的水箱中仅约为4%。研究人员计算出，这相当于86%的相对减少。这种影响不仅限于覆盖水箱表面的藻类。在对照条件下，由珊瑚藻形成的游离结构——红藻石，以每年约0.6克浮重的速度生长。而在高浓度二氧化碳条件下，它们反而每年损失约0.9克。
At the end of the 10 months, crustose coralline algae had developed around 25% cover in the control mesocosms but only about 4% in those exposed to elevated CO₂. The researchers calculated this as an 86% relative reduction. The effect was not limited to the algae covering the tank surfaces. Rhodoliths, free-living structures made from coralline algae, grew in the control conditions at a rate of about 0.6 grams of buoyant weight per year. Under elevated CO₂, they instead lost about 0.9 grams per year.
作者还警告称，这种幅度的变化可能会影响珊瑚礁生长并保持结构稳定的能力。实验还发现，在酸化条件下，珊瑚钙化率下降了15%至20%，而在一项实验中，线性延伸率下降了14%。这些发现与另一项发表在《自然·地球科学》上的夏威夷中型生态系统研究结果一致，该研究发现高浓度二氧化碳强烈抑制了壳状珊瑚藻的定着和生长。
Authors also warned that changes of this magnitude could affect the ability of coral reefs to grow and remain structurally stable. The experiment also found that coral calcification declined by 15% to 20% under acidified conditions, while linear extension fell by 14% in one experiment. These findings were consistent with a separate Hawaiian mesocosm study published in Nature Geoscience, which found that elevated CO₂ strongly inhibited the recruitment and growth of crustose coralline algae.
这些发现共同表明，海洋酸化可能同时影响造礁过程以及争夺珊瑚礁表面生存空间的生物平衡。为何微小藻类关乎整个珊瑚礁珊瑚藻的重要性不仅在于它们占据的空间大小。与软体藻类不同，这些生物将碳酸钙融入其结构中。因此，它们能促进珊瑚礁物质的累积和稳定。其数量的减少可能引发连锁反应。如果暴露表面上生长的珊瑚藻减少，可供某些珊瑚幼虫定着的区域可能就会变少。
Together, the findings suggest that ocean acidification could affect both reef-building processes and the balance of organisms competing for space on reef surfaces. Why a small algae matters to an entire reefThe importance of coralline algae goes beyond the amount of space they occupy. Unlike soft-bodied algae, these organisms incorporate calcium carbonate into their structures. They can therefore contribute to the accumulation and stabilization of reef material. A reduction in their abundance could create a ripple effect. If fewer coralline algae grows on exposed surfaces, fewer areas may be available for some coral larvae to settle.
与此同时，钙化速度减慢意味着添加到礁体结构中的碳酸盐减少。这并不意味着所有珊瑚礁对未来海洋变化都会做出相同反应。珊瑚礁在物种、水化学成分、温度以及当地生态系统的其他特征方面可能存在差异。由于该实验是在中生态系统中进行的，而非在整个珊瑚礁上进行，因此不能将其解读为对全球珊瑚礁的精确预测。
At the same time, slower calcification means less carbonate is being added to the reef framework. It does not mean that all reefs will react the same way to future ocean changes. Reefs can vary in their species, water chemical composition, temperatures, and other features of the local ecosystem. Because the experiment was done in mesocosms rather than on an entire reef, it cannot be read as a precise forecast for reefs worldwide.
然而，该实验确实显示了该系统的脆弱性。更高浓度的二氧化碳不仅影响水质，还影响了有助于构建礁体结构的生物体的发育。随着海洋继续吸收更多人类产生的二氧化碳，珊瑚礁周围的化学环境正随着气候一同发生变化。夏威夷的水槽让人们得以一窥这种转变可能意味着什么：不仅是珊瑚难以构建其骨骼，还有一些帮助珊瑚礁构建和维系自身的生物体正在逐渐衰弱。
However, the experiment did show the system’s vulnerability. Higher concentrations of CO₂ affected not just the water but also the development of organisms that help build reef structure. As oceans continue to absorb more human-produced carbon dioxide, the chemistry surrounding coral reefs is changing alongside the climate. The Hawaii tanks offered a glimpse of what that shift could mean: not just corals struggling to build their skeletons, but the gradual weakening of some of the organisms that help reefs build and hold themselves together.