Characterizing the spatial distribution of coral reefs in the South-Central Coast region of Viet Nam using Planetscope imagery.

Khanh V Nguyen,Thuong V Tran,Thien M Hoang,Ruth Reef,Vinh C Duong,Kinh T Kieu,Cho-Ying Huang

doi:10.7717/peerj.12413

Abstract

This study aims to understand the spatial distribution of coral reefs in the central region of Viet Nam. We classified live coral cover in Son Tra Peninsula (ST) and Cu Lao Cham Island (CLC) in the South-Central Coast Region of Viet Nam using the Maximum Likelihood Classifier on 3 m Planetscope imagery. Confusion matrices and the accuracy of the classifier were assessed using field data (1,543 and 1,560 photographs in ST and CLC, respectively). The results showed that the reef’s width ranged from 30 to 300 m across the study site, and we were able to detect live coral cover across a depth gradient of 2 to 6 m below the sea surface. The overall accuracies of the classifier (the Kappa coefficient) were 76.78% (0.76) and 78.08% (0.78) for ST and CLC, respectively. We found that 60.25% of coral reefs in ST were unhealthy and the live coral cover was less than 50%, while 25.75% and 11.46% of those in CLC were in good and excellent conditions, respectively. This study demonstrates the feasibility of utilizing Planetscope imagery to monitor shallow coral reefs of small islands at a high spatial resolution of 3 m. The results of this study provide valuable information for coral reef protection and conservation.

Highlights

Coral reefs make up only 0.1% of the global ocean substrate, yet they are one of the most biodiverse marine ecosystems and they play a key role in providing a range of ecosystem services (Hoegh-Guldberg, Pendleton & Kaup, 2019; Obura et al, 2019; Pawlik & McMurray, 2020)
Long term monitoring programs of coral health in the SE Asia region are important for managing this global biodiversity hotspot which is facing a range of impacts (Tun et al, 2008), Characterize coral reef cover and health over large spatial and temporal scales is critical for the effective management and protection of coral reef resources (McCarthy et al, 2017; Zhou et al, 2018)
The study areas (i.e., Son Tra Peninsula (ST) (108◦13 58.1 E–16◦08 54.4 N and 108◦20 22.4 E–16◦05 16.2 N) and Cu Lao Cham Island (CLC) (108◦24 42.8 E–15◦58 57.7 N and 108◦33 04.2 E–15◦ 53 58.4 N)) are nature reserve areas located in the South-Central coast region of Viet Nam (Nguyen, Luong & Ho, 2015; Nguyen, Huynh & Zhang, 2015; Hoang et al, 2019) (Fig. 1)

Summary

Introduction

Coral reefs make up only 0.1% of the global ocean substrate, yet they are one of the most biodiverse marine ecosystems and they play a key role in providing a range of ecosystem services (Hoegh-Guldberg, Pendleton & Kaup, 2019; Obura et al, 2019; Pawlik & McMurray, 2020). Coral cover in the SE Asia region has declined and is being threatened by both local and global stressors such as marine pollution and runoff, direct destruction, overexploitation of key species, outbreaks of coral predators, and climate change (Zhou et al, 2018; Hoegh-Guldberg, Pendleton & Kaup, 2019; Carriger, Yee & Fisher, 2021). Long term monitoring programs of coral health in the SE Asia region are important for managing this global biodiversity hotspot which is facing a range of impacts (Tun et al, 2008), Characterize coral reef cover and health over large spatial and temporal scales is critical for the effective management and protection of coral reef resources (McCarthy et al, 2017; Zhou et al, 2018). The use of remote sensing to monitor reefs over large temporal and spatial scales will be necessary to provide standardized data for reef health across the SE Asian region over this period of rapid change and population growth

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Discussion

Conclusion