Data from: Nutrient pollution disrupts key ecosystem functions on coral reefs

There is a long history of examining the impacts of nutrient pollution and pH on coral reefs. However, little is known about how these two stressors interact and influence coral reef ecosystem functioning. Using a six-week nutrient addition experiment, we measured the impact of elevated nitrate (NO3) and phosphate (PO43) on net community calcification (NCC) and net community production (NCP) rates of individual taxa and combined reef communities. Our study had four major outcomes: 1) NCC rates declined in response to nutrient addition in all substrate types; 2) the mixed community switched from net calcification to net dissolution under medium and high nutrient conditions; 3) nutrients augmented pH variability through modified photosynthesis and respiration rates; and 4) nutrients disrupted the relationship between NCC and aragonite saturation state documented in ambient conditions. These results indicate that the negative effect of NO3 and PO43 addition on reef calcification is likely both a direct physiological response to nutrients and also an indirect response to a shifting pH environment from altered NCP rates. Here, we show that nutrient pollution could make reefs more vulnerable to global changes associated with ocean acidification and accelerate the predicted shift from net accretion to net erosion.

长期以来，学界围绕营养盐污染与酸碱度（pH）对珊瑚礁的影响展开了持续研究。然而，关于这两类胁迫因子如何相互作用并影响珊瑚礁生态系统功能，目前仍缺乏深入认知。
本研究通过为期六周的营养盐添加实验，测定了浓度升高的硝酸盐（NO₃⁻）与磷酸盐（PO₄³⁻）对单个珊瑚类群以及复合珊瑚礁群落的净群落钙化率（Net Community Calcification，NCC）与净群落生产力（Net Community Production，NCP）的影响。本研究得到四项核心结论：
1) 所有基质类型下的净群落钙化率均随营养盐添加出现下降；
2) 中等与高营养盐浓度条件下，混合群落从净钙化状态转变为净溶解状态；
3) 营养盐通过改变光合作用与呼吸作用速率，加剧了酸碱度变异性；
4) 营养盐破坏了自然环境中已观测到的净群落钙化率与文石饱和状态之间的关联。
研究结果表明，硝酸盐与磷酸盐添加对珊瑚礁钙化的负面影响，既可能源于生物对营养盐的直接生理响应，也可能源于净群落生产力改变引发的酸碱度环境变化所带来的间接响应。本研究显示，营养盐污染可能会使珊瑚礁更易受海洋酸化相关全球变化的影响，并加速学界预测的珊瑚礁从净沉积向净侵蚀的转变。