The response of photosynthetic organisms to rising CO₂ levels is a key topic in ocean acidification research. Most of the work in this field has focused on physiological responses in laboratory conditions which lack ecological realism. Studies using seeps as natural analogues for ocean acidification have demonstrated shifts in algal community composition, but the effect of CO₂ on carbon fixation and export remains unclear. Here, we deployed artificial substrata in a warm-temperate region of Japan to collect algal communities using a CO₂ seep off Shikine Island. Diatoms became dominant on settlement substrata in areas with elevated CO₂ levels, whereas macroalgae dominated at present-day levels of CO₂ (reference site). This was supported by pigment composition; fucoxanthin content, characteristic of diatoms, was higher at the high CO₂ site, while more Chlorophyll b, which is characteristic of Chlorophyta, was found in the reference site. Algal communities that recruited in water with high levels of CO₂ had elevated rates of photosynthesis. Algal biomass was similar on all settlement panels, regardless of CO₂ concentration. Much of the carbon that was fixed by algae in the high CO₂ conditions was exported, likely due to detachment from the substratum. Diatoms that dominated under high CO₂ conditions are more easily transported away as they have no holdfast, whereas newly settled macroalgae became firmly attached at present-day levels of CO₂. These results show that ocean acidification may fundamentally alter coastal carbon cycling, increasing photosynthesis and carbon export from coastal ecosystems in warm-temperate biogeographic regions due to a shift in community composition from perennial to ephemeral algae.

光合生物对CO ₂含量升高的反应是海洋酸化研究的关键主题。该领域的大部分工作都集中在缺乏生态现实性的实验室条件下的生理反应上。使用渗水作为海洋酸化的天然类似物的研究表明藻类群落组成发生了变化，但CO ₂对碳固定和出口的影响尚不清楚。在这里，我们在日本的一个温带地区部署了人工基质，以利用Shikine岛附近的CO ₂渗漏来收集藻类群落。硅藻地区成为了附着基主导与高浓度CO ₂的水平，而海藻的CO的现今水平为主₂（参考站点）。这由颜料组合物支持；在高CO ₂位点，硅藻的岩藻黄质含量较高，而在参考位点发现叶绿素b（叶绿素的特征）更多。在高CO ₂水平的水中募集的藻类群落的光合作用速率升高。不论CO ₂浓度如何，所有沉降面板上的藻类生物量均相似。在高CO ₂条件下，藻类固定的大部分碳都被出口了，这很可能是由于与基质的分离。在高CO ₂下占主导地位的硅藻由于没有持久性，因此更容易被带走，而新沉淀的大型藻类已牢固地附着在当今的CO ₂水平上。这些结果表明，由于群落组成从多年生藻类转变为短暂藻类，海洋酸化可能从根本上改变沿海碳循环，增加光合作用和增加来自温带生物地理区域沿海生态系统的碳出口。