What’s going on at the core of the Coral Triangle? Results from over 10 years of Reef Check and CoralWatch community-based monitoring

Coral reefs' health is declining worldwide, increasingly threatened by multiple stressors. These include local disturbances, which act synergically with thermal-stress events associated with climate change, triggering regional and global scale bleaching events. Preventing further decline and maintaining the resilience of these habitats requires implementing appropriate and timely ecosystem-based management actions and adaptive management policies, which rely on targeted, long-term, and integrated monitoring programs. Since 2011, two community-based monitoring protocols have been applied annually to collect data and provide baseline knowledge at six study sites at 6 and 12 m depth in Bangka and Gangga Archipelago, North Sulawesi, Indonesia, involving more than a hundred people, including students, researchers, and tourists: i) Reef Check Tropical protocol, based on the abundance of easily recognizable reef indicator organisms and substrates, able to reflect the condition of the ecosystem; and ii) CoralWatch protocol, which quantifies coral bleaching using a reference colour card, discriminating bleaching events from normal coral colour variation. Study sites well reflected the range of coral reefs’ health status in the area, which over the years remained generally good. However, some sites showed signs of coral diseases, excess Diadema sea urchins and local impacts, such as destructive artisanal fishing and overexploitation. However, they never showed major bleaching events until 2023, when a local bleaching event occurred at two sites on Gangga Island, affecting around 30% of the coral population at both depths. The integration of these two protocols and the involvement of volunteers, students, and researchers from local and foreign universities and stakeholders (i.e., resorts) have proved effective in providing scientifically sound data and increasing public awareness. This report may represent a good example of how monitoring remote areas that are not specifically protected can be faced. However, conservation actions must be strengthened, and attention maintained high at the Coral Triangle core.