Monitoring shallow coral reef exposure to environmental stressors using satellite earth observation: the reef environmental stress exposure toolbox (RESET)

Abstract

Coral reefs are significantly threatened by multiple environmental stressors associated with climate change. While there is growing recognition of the importance of interacting stressors on coral reefs, so far this has been primarily limited to in situ studies. Satellite remote sensing has potential for investigating coral reef exposure to multiple environmental stressors at a global scale over multiple years; however, current satellite monitoring is primarily focused on thermal stress. Here we collate nine environmental variables (cloud cover, current, depth, salinity, wind, and four sea surface temperature-based metrics) from readily available satellite datasets using the Google Earth Engine geospatial processing platform. Using ecological and health-based thresholds obtained from the literature, we developed, using fuzzy logic (discontinuous functions), a Reef Environmental Stress Exposure Toolbox (RESET) for monitoring environmental stress exposure at multiple scales. Stress exposure scores for 3157 reefs were generated and mapped globally across 12 coral reef ecosystem regions. RESET was also applied to three case-study reefs, previously well monitored for stress and disturbance using other methods. PCA analysis indicated that depth, current, sea surface temperature (SST) and SST anomaly accounted for the greatest contribution to the variance in environmental stress exposure in these three regions. Depth, degree heating weeks, and SST anomaly were identified as the potential drivers of inter-and intra-region variation in environmental stress exposure. Individual variables were then integrated into a multi-metric index of combined stress exposure which corroborated temporal and spatial differences due to known disturbance events. RESET provides a open access, easily interpretable set of tools and associated indices for monitoring environmental stress exposure on coral reefs, designed to inform conservation and management decisions. As such RESET has broad potential to assist in the monitoring of our increasingly imperilled coral ecosystems, in particular, those that are remote or inaccessible.

A GEE toolkit for water quality monitoring from 2002 to 2022 in support of SDG 14 and coral health in marine protected areas in Belize

“…The areas with higher coral stress index values were areas that were near large towns and cities with fishing pressure accounting for the majority of variation. Most recently, a Google Earth Engine based tool used a combination of stressors and reducers to find strong correlations between their stress exposure score and El Niño bleaching events for corals in the Red Sea, Chagos Archipelago, and Gilbert Islands (Williamson et al, 2022). While this tool extensively uses SST in their score along with other factors like wind, they do not include water clarity as the toolkit presented here.…”

“…In the literature, Degree Heating Weeks (DHW) is often used for assessing heat stress on coral. The NOAA Coral Reef Watch DHW product is widely used (Eakin et al, 2010;Baumann et al, 2019;De et al, 2021a;Johnson et al, 2022), but some studies have utilized Aqua MODIS SST to calculate DHW as well (Wouthuyzen et al, 2018;Williamson et al, 2022).…”