Predicting extreme tide events to inform shallow reef community restoration and management in Guam

This study builds on previous research and management efforts to develop a comprehensive region-wide management and restoration approach for sensitive and critical fish habitat on shallow reef flats. These habitats have precipitously declined over recent years from annual coral mass mortality events. Ocean warming-induced bleaching and ENSO-related extreme low-stand tidal events (particularly in 2015) have decimated staghorn Acropora and caused significant mortality in other dominant genera and species, including the ESA-listed species A. globiceps. A management plan for remaining populations involves investigating the environmental attributes contributing to survival at sites with remaining populations, analyzing biotic factors contributing to resilience and recovery, and restoration using ocean nursery culture and reestablishment. To support these initiatives, this project has applied a novel approach to a high-tide flooding model, using existing data from the Guam Apra Harbor station tide gauge to develop a spatially explicit model to predict the frequency of low-stand events. These data were calibrated to ground-truthed tidal measurements from 18 sites around Guam that have seen significant recent coral mortality from extreme low tide events or were strategically selected to give geographic representation around the island. Assessment surveys at these sites were undertaken to evaluate mortality, providing an additional longitudinal reference point for the sites that were already within monitoring programs. This information will help guide the selection of restoration sites, and identify both sites at future risk and those with greater refuge from low-stand events that could benefit from increased management. We also see a future application of the results of this study in forecasting of such events in Guam, CNMI, and American Samoa that have also experienced recent mass mortality. Grant no. NA14NES4320003