Prioritizing reef resilience through spatial planning following a mass coral bleaching event

Following the recent 2014–2017 global coral bleaching event, managers are seeking interventions to promote long-term resilience beyond monitoring coral decline. Here, we applied a spatial approach to investigate one potential intervention, mapping areas where local management could build coral reef resilience using herbivore management. Although herbivore management is a top recommendation in resilience-based management, site-specific attributes are thought to affect its success, and thus strategizing placement and design of these areas are crucial. Using Marxan, we mapped and prioritized potential Herbivore Management Areas (HMAs), where herbivores are protected but other types of fishing are allowed, in the main Hawaiian Islands. Through four scenarios, we found multiple hotspots along the west coast of Hawai‘i Island and around the islands of Moloka‘i, Lana‘i, Maui, and Kaho‘olawe where HMAs may have the best chance for success based on habitat, ecologically critical areas, life history, and social considerations. We further analyzed top results and found that a subset of characteristics including habitat types, biomass of herbivore functional groups, and temperature variability were significantly different from surrounding areas and thus contain potential drivers for selection. This unique approach can serve as an example for coral reef management in Hawai‘i, on other Pacific Islands, and beyond, as it provides practical guidance on how to apply a resilience-building tool at a local level, incorporating site-specific biological and socioeconomic considerations

Estimating blue carbon sequestration under coastal management scenarios

Restoring and protecting "blue carbon" ecosystems - mangrove forests, tidal marshes, and seagrass meadows - are actions considered for increasing global carbon sequestration. To improve understanding of which management actions produce the greatest gains in sequestration, we used a spatially explicit model to compare carbon sequestration and its economic value over a broad spatial scale (2500 km of coastline in southeastern Australia) for four management scenarios: (1) Managed Retreat, (2) Managed Retreat Plus Levee Removal, (3) Erosion of High Risk Areas, (4) Erosion of Moderate to High Risk Areas. We found that carbon sequestration from avoiding erosion-related emissions (abatement) would far exceed sequestration from coastal restoration. If erosion were limited only to the areas with highest erosion risk, sequestration in the non-eroded area exceeded emissions by 4.2 million Mg CO<sub>2</sub> by 2100. However, losing blue carbon ecosystems in both moderate and high erosion risk areas would result in net emissions of 23.0 million Mg CO<sub>2</sub> by 2100. The removal of levees combined with managed retreat was the strategy that sequestered the most carbon. Across all time points, removal of levees increased sequestration by only an additional 1 to 3% compared to managed retreat alone. Compared to the baseline erosion scenario, the managed retreat scenario increased sequestration by 7.40 million Mg CO<sub>2</sub> by 2030, 8.69 million Mg CO<sub>2</sub> by 2050, and 16.6 million Mg CO<sub>2</sub> by 2100. Associated economic value followed the same patterns, with large potential value loss from erosion greater than potential gains from conserving or restoring ecosystems. This study quantifies the potential benefits of managed retreat and preventing erosion in existing blue carbon ecosystems to help meet climate change mitigation goals by reducing carbon emissions