Abstract：
The concentration of chlorophyll-a (Chl-a) in seawater reflects phytoplankton growth and water eutrophication, which are usually assessed for evaluation of primary productivity and carbon source/sink of coral reefs. However, the precise delineation of Chl-a concentration in coral reefs remains a challenge when ocean satellites with low spatial resolution are utilized. In this study, a remote sensing inversion model for Chl-a was developed in fringing reefs (R2 = 0.76, RMSE =0.41 μg/L, MRE = 14 %) and atolls (R2 = 0.79, RMSE =0.02 μg/L, MRE = 8 %), utilizing reflectance data from the sensitive band of the Landsat-8 Operational Land Imagers (OLI) with a spatial resolution of 30 m. The aforementioned model was utilized to invert high-resolution distribution maps of Chl-a concentration in six major coral reef regions of the South China Sea from 2013 to 2022 and subsequently used to analyze the variations in Chl-a concentration and its influencing factors. The results indicate a Chl-a concentration gradient among coral reefs Daya Bay, Weizhou Island, Luhuitou, Xuwen, Huangyan Island, and Xisha Island in that order. The Chl-a concentration in coral reefs exhibited an overall increasing trend, with significant seasonal fluctuations, characterized by higher concentrations during winter and spring and lower concentrations during summer and autumn. The concentration of Chl-a in coral reefs was positively correlated with the average wind speed.
摘要：
海水中叶绿素a（Chl-a）的浓度反映了浮游植物的生长和水体富营养化，通常对其进行评估，以评估珊瑚礁的初级生产力和碳源/汇。然而,当利用低空间分辨率的海洋卫星时，精确划定珊瑚礁中Chl-a浓度仍然是一个挑战。在这项研究中,在边缘礁中建立了Chl-a的遥感反演模型（R2=0.76，RMSE=0.41μg/L，MRE=14%)和环礁(R2=0.79，RMSE=0.02μg/L，MRE=8%)，利用空间分辨率为30m的Landsat-8作战陆地成像仪（OLI）敏感波段的反射率数据。利用上述模型反演了2013年至2022年南海六个主要珊瑚礁地区Chl-a浓度的高分辨率分布图，随后用于分析Chl-a浓度的变化及其影响因素。结果表明，大亚湾珊瑚礁之间存在Chl-a浓度梯度，渭洲岛,鹿怀头,徐闻,黄岩岛,和西沙岛的顺序。珊瑚礁中Chl-a浓度总体呈上升趋势，有明显的季节性波动，其特征是冬季和春季浓度较高，夏季和秋季浓度较低。珊瑚礁中Chl-a的浓度与平均风速呈正相关。
