High Resolution Remote Sensing Monitoring and Analysis of Coral Reef Degradation Caused by Outbreaks of Biological Natural Enemies: A Case Study of the Taiping Island in the South China Sea

Abstract

The global proliferation of natural predators, including Terpios hoshinota sponge and crown-of-thorns starfish, poses a significant threat to the ecological vitality of coral reefs. However, coral reef research currently lacks comprehensive quantitative studies on the ramifications of predator outbreaks in various coral reef landform types. To bridge this knowledge gap, this study utilized a dataset comprising 26 Sentinel-2 remote sensing images spanning the years 2016 to 2022, both pre- and post-two distinct episodes of natural predator outbreaks involving the Terpios hoshinota sponge and crown-of-thorns starfish, within the vicinity of Taiping Island. High-resolution GF-2 (PMS) remote-sensing images and satellite data were used to augment the analysis. Based on data obtained from the Google Earth platform of the Geographic Information System for remote sensing imagery, we conducted an experiment involving the classification of coral reef landform types in Taiping Island in the South China Sea. During the Support Vector Machine (SVM) classification experiments, we performed a meticulous examination of the image interpretation outcomes, making comparisons and rectifications in consultation with domain experts. Classification was performed by analyzing remote sensing images, and the identified landform types included areas characterized by dense coral sedimentation, sparse coral sedimentation, coral clusters, sand flats, and shallow reef front slopes. Subsequent analyses focused on discerning distinctive characteristics and tracing their evolutionary patterns. The findings reveal that (1) this study effectively integrates expert interpretation knowledge and an SVM classification algorithm to classify the various landform types present in Taiping Island's coral reef ecosystem. Remarkably, the classification achieved an unprecedented level of accuracy, with an overall accuracy rate of 96.46% and a kappa coefficient of 0.94. (2) The analysis showed that during the two natural predator outbreaks, the coral reef landforms on Taiping Island, which included dense coral reef areas, dense coral sedimentation areas, and sparse coral sedimentation areas, displayed significant decreases in their respective areas. The outbreak of Terpios hoshinota sponge had the most profound impact on the dense coral sedimentation area, resulting in a 72.92% decrease in the total area. Meanwhile, the outbreak of crown-of-thorns starfish had the most significant effect on the coral cluster area, causing a 59.17% reduction in total area. (3) Over the period spanning from 2016 to 2022, the degradation rate of the coral reefs on Taiping Island exceeded the recovery rate. Notably, the highest degradation rate (23.88%) occurred between March-June 2017. Conversely, the highest rate of recovery (18.03%) was observed from June-September 2017. We analyzed the dynamic characteristics of coral reef landform types, including changes in type distribution, areal extent, degradation rate, and recovery rate. Furthermore, we assessed the influence of natural disturbances on the degradation of coral reef ecosystems, thereby providing valuable insights for conservation and scientific inquiries pertaining to coral reef ecological resources in the waters surrounding Taiping Island. This effort is underpinned by a solid theoretical foundation. The Chinese and English literature cited in this article have contributed significantly to various facets, including coral reef monitoring methodologies, construction of coral reef classification systems, and assessment of coral reef ecosystem health.

Keywords

• coral reef
• terpios hoshinota sponge
• crown-of-thorns starfish
• high-resolution remote sensing
• taiping island