An improved method for thermal stress detection of coral bleaching in the South China Sea
LIU Bailu1(), GUAN Lei1,2()
1. College of Marine Technology/Faculty of Information Science and Engineering/Sanya Oceanographic Institution, Ocean University of China, Qingdao/Sanya, 266100/572024, China 2. Laboratory for Regional Oceanography and Numerical Modeling, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China
In recent years, coral bleaching events have frequently occurred globally due to global warming and other factors. However, the Coral Reef Watch (CRW) program established by the National Oceanic and Atmospheric Administration (NOAA) has underestimated the actual situation of coral bleaching in the South China Sea. Based on 180 cases of coral bleaching in the South China Sea and its surrounding waters since 1985, this paper obtains the optimum threshold combination by calculating the false negative rate (FNR), the false positive rate (FPR), and the accuracy (ACC) of different threshold combinations, thus improving the detection accuracy of coral bleaching events in the South China Sea. The results are as follows: (1) The FNR of the bleaching detecting results obtained using the NOAA threshold was 70.70%, indicating the long-term underestimation of the coral bleaching; (2) With the optimized critical threshold (CT) and alert threshold (AT), the ACC was improved from 58.13% to 73.90%, meanwhile the FNR and FPR were both less than 30%. As revealed by the coral bleaching event in the Nansha Islands in June 2007, the optimized thermal stress index can be used to effectively detect the event and mark the bleaching alarm level in time compared to the past underestimation. Therefore, the improved method for thermal threshold detection can improve the monitoring level of coral bleaching and are conducive to the management and protection of coral reefs in the South China Sea.
Bailu LIU,Lei GUAN. An improved method for thermal stress detection of coral bleaching in the South China Sea[J]. Remote Sensing for Natural Resources,
2021, 33(4): 136-142.
Fig.1 Sketch map of main coral reefs in the study area[17]
级别
定义
对珊瑚礁的影响
无压力
Hotspot≤0
—
观察
0<Hotspot<CT
—
白化警告
Hotspot≥CT,DHW<AT
可能发生白化
白化警报
Hotspot≥CT,DHW≥AT
极易发生白化
Tab.1 Coral bleaching thermal stress levels
Fig.2 FNR and FPR with different threshold combinations
Fig.3 ACC with different threshold combinations
Fig.4 DHW in the South China Sea
Fig.5 Maximum bleaching area level in seven days from June 19, 2007 to June 25, 2007 [16]
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