Table 1. Reefs at risk analysis method
TABLE 1. REEFS AT RISK ANALYSIS METHOD
Threat Analysis Approach Limitations
Coastal Development
  • Threats to reefs evaluated based on distance from cities, ports, airports, and dive tourism centers. Cities and ports stratified by size.
  • Coastal population density (2000), coastal population growth (1990–2000), and annual tourism growth combined into indicator of "population pressure" treated as an additional stressor.
  • Thresholds selected for each stressor based on guidance from project collaborators and observations of local damage from coastal development (including sewage discharge). Stressors aggregated into single map layer.
  • Management effectiveness included as mitigating factor for threats to reefs inside marine protected areas (MPAs).
  • Provides a good indicator of relative threat across the region, but is likely to miss some site-specific threats.
  • Data sets used are the best available, but limitations regarding accuracy and completeness are inevitable.
  • In particular, rapid growth of tourism sector makes it difficult to capture the most recent developments.
Sediment and Pollution from Inland Sources
  • Watershed-based analysis links land-based sources of threat with point of discharge to the sea.
  • Analysis of sediment and pollution threat to coral reefs implemented for more than 3,000 watersheds discharging to the Caribbean.
  • Relative erosion rates estimated across the landscape, based on slope, land cover type, precipitation (during the month of maximum rainfall), and soil type.[a]
  • Erosion rates summarized by watershed (adjusting for watershed size) to estimate resulting sediment delivery at river mouths.
  • Sediment plume dispersion estimated using a function in which sediment diminishes as distance from the river mouth increases. Estimated sediment plumes calibrated against observed sediment impacts on selected coral reefs.[b]
  • Nutrient delivery to coastal waters probably underestimated due to lack of spatial data on crop cultivation and fertilizer application and resulting use of a proxy (sediment delivery) for indirect estimation.[c]
  • Sediment and nutrient delivery from flat agricultural lands probably underestimated because slope is a very influential variable in estimating relative erosion rates.
Marine-Based Sources of Threat
  • Threats to coral reefs from marine-based sources evaluated based on distance to ports, stratified by size; intensity of cruise ship visitation; and distance to oil and gas infrastructure, processing, and pipelines.
  • Estimates focus on ships in or near port. Threat associated with marine travel lanes probably underestimated due to lack of sufficiently detailed database on Caribbean shipping lanes.
Overfishing
  • Threats to coral reefs evaluated based on coastal population density and shelf area (up to 30 m depth) within 30 km of reef. Analysis calibrated using survey observations of coral reef fish abundance.
  • Management effectiveness included as mitigating factor for threats to reefs inside marine protected areas (MPAs).
  • Destructive fishing practices not evaluated, as these are rare in the Caribbean region.
  • Local overfishing pressure captured in proxy indicator (based on human population per unit of coastal shelf area), due to lack of spatially-specific data on numbers of fishers, landing sites, fishing method/effort, or fish catch from reef fisheries.
  • Indicator reflects fishing within 30 km of shore. Impacts of larger-scale commercial fishing pressure, illegal fishing, or movement of fleets not included in analysis.
NOTES:
a. "Relative Erosion Potential" was estimated at WRI using a simplified version of the Revised Universal Soil Loss Equation, United States Department of Agriculture (USDA) Agricultural Research Service (Washington, DC: USDA, 1989).
b. Data from Reef Check surveys and expert opinion from the Reefs at Risk workshop were used to calibrate the estimate of threat from inland sources. Data on percent live coral cover and algal cover from Atlantic and Gulf Rapid Reef Assessment (AGRRA) surveys were used to evaluate results.
c. Although phosphorus is often attached to soil particles, nitrogen is highly soluble and moves more independently of soil particles.