Autonomous robotic systems for coral reef monitoring: Review and open research issues

Coral reefs, vital ecosystems for marine life, face extinction threats from natural and human-induced factors. Conventional conservation methods struggle to provide the necessary scale and frequency of monitoring data. This review explores the potential of Autonomous Underwater Vehicles (AUVs) for comprehensive coral reef monitoring, which enables systematic, high-resolution, and non-invasive assessments over extensive and remote reef areas. The review examines conventional monitoring methods, identifying their strengths and limitations. AUVs are then introduced as a powerful tool for enhanced conservation efforts. Recent advances in robotic coral reef monitoring are discussed, highlighting imaging, acoustic, and environmental sensing technologies integrated with onboard intelligence, with a particular focus on visual modalities. It compares robotic approaches to conventional methods, highlighting improvements in data quality, safety, and efficiency. Key applications such as species identification, disease detection, 3D mapping of reef structures, and early detection of coral bleaching are discussed. Challenges related to navigation, ecological impacts, and standardization are identified as critical areas for future research. The review concludes by summarizing key findings, highlighting ongoing challenges, and proposing future research directions to further enhance the role of AUVs in safeguarding these vital ecosystems. Our synthesis suggests that integrating advanced vision-based methods with multi-modal sensing, data-driven machine learning, and autonomous decision-making frameworks can significantly enhance the precision and scalability of coral reef health assessments, thereby facilitating more robust conservation strategies.