Reefs At Risk Revisited Technical Notes

Reefs at Risk Revisited brings together data on the world’s coral reefs in a global analysis designed to quantify threats and to map where reefs are at greatest risk of degradation or loss. We incorporated more than 50 data sources into the analysis—including data on bathymetry (ocean depth), land cover, population distribution and growth rate, observations of coral bleaching, and location of human infrastructure. These data were consolidated within a geographic information system (GIS), and then used to model several broad categories of threat from human activities, climate change, and ocean acidification. In the absence of complete global information on reef condition, this analysis represents a pragmatic hybrid of monitoring observations and modeled predictions of reef condition. Human pressures on coral reefs are categorized throughout the report as either “local” or “global” in origin.  

These categories are used to distinguish between threats that involve human activities near reefs that have a direct and relatively localized impact, versus threats that affect the reef environment indirectly through the cumulative impact of human activities on the global climate and ocean chemistry.  

Local threats addressed in this analysis are:

• Coastal development
• Watershed‐based pollution
• Marine‐based pollution and damage
• Overfishing and destructive fishing.

Global threats addressed are:  

• Thermal stress (warming sea temperatures, which can induce coral bleaching)
• Ocean acidification (driven by increased CO2, which can reduce coral growth rates).

This is the first Reefs at Risk project to incorporate data on these global‐level threats.  These data allow us not only to estimate current and imminent reef condition, but also to project trends well into the future.   For the global‐level threats, we did not develop new models, but rather incorporated existing data from partner organizations on past thermal stress, future thermal stress, and ocean acidification. These data have enabled us to consider impacts to date and the potential future effects of ocean warming and acidification on reefs to 2030 and 2050 using climate projection scenarios.   

The Reefs at Risk Revisited project delivers results as maps showing the distribution of local and climate‐ related threats to coral reefs.  These threats are also consolidated into a single integrated index, which represents their combined impact on mapped reef locations.  The analysis draws on a newly compiled global reef map—the most comprehensive and detailed rendition of global coral reef locations created to date—that we compiled into a 500‐m resolution grid for modeling.