Studying the impact of sea surface temperature (SST) changes and El Niño phenomenon on coral reefs bleaching around Kish Island in the northern Persian Gulf: A remote sensing approach

Coral reefs are among the most biodiverse marine ecosystems but are increasingly threatened by environmental stressors, particularly coral bleaching caused by rising Sea Surface Temperature (SST). Monitoring SST changes is therefore critical for coral conservation. This study investigates thermal anomalies around Kish Island in the northern Persian Gulf using the Degree Heating Weeks (DHW) index, which quantifies cumulative thermal stress on corals. SST and DHW data from 1982 to 2022 were obtained from the National Oceanic and Atmospheric Administration (NOAA). Trends were analyzed using the Mann-Kendall test and Sen's slope estimator, while the Pierce Skill Score was employed to estimate the DHW threshold indicating coral bleaching risk. The relationship between the El Niño phenomenon and DHW was also assessed. Spatial and temporal SST changes were examined using MODIS Aqua satellite data processed via the Google Earth Engine. Results show maximum SST and DHW values of 35.17 °C and 13.6°C-weeks in August–September 2017, respectively, with DHW exhibiting an upward trend of 0.025°C-weeks per year. The DHW threshold was estimated at 5.3°C-weeks. Spatial analyses suggest increasing thermal stress along the southern and northern coasts of the Persian Gulf, particularly near Kish Island. Finally, El Niño events corresponded with elevated DHW values, highlighting their influence on coral bleaching. These findings underscore the importance of long-term monitoring to mitigate climate-induced threats to coral ecosystems.