Six decades of global coral bleaching monitoring: A review of methods and call for enhanced standardization and coordination

Andrea Rivera-Sosa ^1* Aarón Israel Muñiz-Castillo ² Ben Charo ¹ Gregory P. Asner ³ Chris M Roelfsema ⁴ Simon D. Donner ⁵ Brianna D. Bambic ⁶ Ana Gabriela Bonelli ⁷ Morgan Pomeroy ^8,9 Derek Manzello ⁹ Paulina Martin ³ Helen Fox ¹

• ¹ Conservation Science, Coral Reef Alliance, San Francisco, United States
• ² Healthy Reefs for Healthy People, Puerto Morelos, Mexico
• ³ Center for Global Discovery and Conservation Science, Arizona State University, Hilo, Hawaii, United States
• ⁴ Marine Ecosystems Monitoring, The School Of The Environment, University of Queensland, Queensland, Australia
• ⁵ Department of Geography and Institute for Resources, Environment and Sustainability, University of British Columbia, Vancouver, Canada
• ⁶ Resource & Ecosystem Management, Idaho, United States
• ⁷ Département de biologie, chimie et géographie, Université du Québec à Rimouski, Rimouski, Quebec, Canada
• ⁸ Global Science and Technology, Inc., Greenbelt, Maryland, United States
• ⁹ U.S. National Oceanic and Atmospheric Administration, National Environmental Satellite Data and Information Service, Center for Satellite Applications and Research, Coral Reef Watch, Maryland, United States

Coral bleaching poses a severe threat to the health and survival of global coral reef ecosystems, with recent events surpassing historical heat stress records. To address this crisis, improved longterm monitoring, communication, and coordination are urgently required to enhance conservation, management, and policy responses. This study reviews global coral bleaching survey methodologies and datasets spanning 1963 to 2022, identifying key challenges in methodological standardization, including database duplication and inconsistencies in naming and reporting bleaching metrics. These issues hinder comparative analyses and contribute to discrepancies in global bleaching impact assessments. We developed a typology of twenty-nine coral bleaching methods used across various scales, encompassing remote sensing tools, underwater surveys, and specimen collection. Analysis of 77,370 observations from three major datasets revealed that 9.36% of entries lacked methodological descriptions. Among recorded methods, belt transects (42%), line and point intercept transects (33%), and random surveys (17%) were the most widely applied. Practitioner surveys underscored the dominance of in situ transect and visual methods, highlighting the growing adoption of photo quadrats-an emerging yet underrepresented technique in existing datasets. To enhance global coral bleaching assessments, we propose a standardized framework that ensures open access and accessible data that aligns with decision-makers' needs for efficient data aggregation and interoperability to better understand temporal and spatial bleaching events. A globally coordinated coalition should unify protocols, improve data-sharing capabilities, and empower regional networks through targeted training, incentives, and open communication channels. Strengthening field capacity in coral taxonomy and standardized survey methodologies, alongside integrating advanced tools, will improve data quality and comparability. Additionally, creating precise geolocated datasets will bridge on-the-ground observations with advanced remote sensing systems, refining the accuracy of satellite-based early warning tools. Establishing interoperable online platforms will further streamline data integration and accessibility, providing a robust foundation to support global responses to coral bleaching and foster impactful conservation initiatives.