Diverse coral communities in naturally acidified waters of a Western Pacific reef

Anthropogenic carbon dioxide emissions are acidifying the oceans, reducing the concentration of carbonate ions ([CO32-) that calcifying organisms need to build and cement coral reefs. To date, studies of a handful of naturally acidified reef systems reveal depauperate communities, sometimes with reduced coral cover and calcification rates, consistent with results of laboratory-based studies. Here we report the existence of highly diverse, coral-dominated reef communities under chronically low pH and aragonite saturation state (Omega ar). Biological and hydrographic processes change the chemistry of the seawater moving across the barrier reefs and into Palau's Rock Island bays, where levels of acidification approach those projected for the western tropical Pacific open ocean by 2100. Nevertheless, coral diversity, cover, and calcification rates are maintained across this natural acidification gradient. Identifying the combination of biological and environmental factors that enable these communities to persist could provide important insights into the future of coral reefs under anthropogenic acidification.

人为二氧化碳排放正在引发海洋酸化，降低了钙化生物用以构建和胶结珊瑚礁的碳酸根离子（[CO₃²⁻]）浓度。迄今为止，针对少量自然酸化珊瑚礁系统的研究显示其群落物种贫乏，部分区域的珊瑚盖度与钙化速率有所下降，这与实验室研究的结果相一致。本研究报道了在长期低pH与文石饱和状态（Omega ar）条件下，存在高度多样、以珊瑚为主导的礁群群落。生物与水文过程改变了穿越堡礁并流入帕劳岩岛海湾的海水化学性质，该区域的酸化程度接近2100年热带西太平洋开阔海域的预测酸化水平。尽管如此，沿该自然酸化梯度的珊瑚多样性、盖度与钙化速率均得以维持。厘清支撑这些群落存续的生物与环境因子组合，可为理解人为酸化背景下珊瑚礁的未来走向提供重要科学见解。