Impact of the 2023 ENSO Event on the Benthic Community of the San Luciano Shipwreck Reef

Shipwrecks and artificial reefs play a critical role in restoring marine biodiversity in degraded ecosystems. This study assesses the ecological impacts of the 2023 ENSO event and chronic anthropogenic pressures on the San Luciano Shipwreck Reef (central Mexican Pacific), based on comparative monitoring during 2017–2018 and 2023. Using standardized indicators from the Global Coral Reef Monitoring Network and the biological condition gradient (BCG), we evaluated benthic communities, structural features, and physiological stress markers. Biodiversity was highest at the wreck's ends, where structural complexity increased due to metal degradation. In 2023, over 90% of coral colonies showed bleaching and mortality, accompanied by bioeroder proliferation and invasive species such as Carijoa riisei. Coral cover declined by over 85%, and biomarkers such as the Chl a/PC ratio and zooxanthellae density confirmed elevated stress levels. These changes placed the reef at level V of the BCG. The deterioration observed is strongly linked to the combined influence of ENSO-related anomalies and persistent port-related impacts, such as nutrient loading, turbidity, and invasive species transport. Findings underscore the vulnerability of artificial reefs to cumulative stressors and support the inclusion of shipwrecks as valuable sentinel sites in reef monitoring and conservation planning.