There are six regional coral reef regions — Atlantic, Australia, Indian Ocean, Middle East, Pacific, and Southeast Asia.

Reef areas are not distributed evenly across the globe: some regions have more reef area than others. The largest reef areas are found in Southeast Asia (69,637 sq km or 28% of the global reef area) and the Pacific (65,972 sq km or 26% of global reef area) and the smallest reef areas are found in the Middle East (14,399 sq km or 6% of global reef area) and the Atlantic Ocean (25,849 sq km or 10% of global reef area).

There is no discernable pattern for the population that lives within 30 km of reefs relative to the size of the reef system — i.e., larger reef systems do not necessarily have a large population living near them. While Southeast Asia, which has the largest reef area (69,637 sq km or 28% of the global reef area) also has the largest population within 30 km (138,156,000), the regions with the next two largest reef areas have the smallest populations among all the regional reef systems. The Pacific with the second largest reef area (65,972 sq km or 26% of global reef area) has a population of only 7,487,000; while Australia with the third largest reef area (42,315 sq km) has an even smaller population of 3,509,000.

In general there is a direct relationship between size of population within 30 km of reefs and coral reefs areas under significant risk from integrated local threats. As population size increases, the threat to reefs increases. Thus, Australia has the smallest population (3,509,000 people live within 30 km of reefs) and the least reef area under risk from integrated local threats (14% of its total reef area) while Southeast Asia has the largest population (138,156,000 people live within 30 km of reefs) and the most reef area under medium or higher level of risk from integrated local threats (94% of its total reef area). The only exception to this pattern is for the Atlantic and Indian Ocean reef systems. Though the Atlantic has a smaller coastal population than the Indian Ocean (about 22,611,00 people less), more of its reef (about 9% more) is at risk from local threats risk.

Thermal stress refers to coral reefs being exposed to water temperatures warm enough to cause coral bleaching. Based on data between 1998 and 2007, every coral reef region has experienced some thermal stress, with the most severe thermal stress in the Atlantic (56% of reef area) and Indian Ocean (50% of reef area) and the least in Southeast Asia (27% of reef area) and Australia (33% of reef area). This suggests that there is no correlation between thermal stress and population within 30 km of reefs as the reef systems with the largest (Southeast Asia) and smallest (Australia) populations both have the lowest levels of thermal stress.

Local threats, on the other hand, do show a correlation between the level of threat and the size of the population within 30 km of reefs. The reason for this difference is likely the causes of thermal stress versus integrated local threats. Local threats are activities that can be correlated to local human actions and hence to local population size: more people can mean more fishing, more pollution, or more development and thus more impact on local reef systems. Thermal stress is the result of both natural variations in ocean surface waters as well as global human activities that contribute to global warming (not necessarily local actions).

As global warming increases, it would be expected that the incidences of thermal stress (and hence coral bleaching) will likely increase in the future. As with thermal stress, acidification arises from global human activities that are changing the Earth’s atmosphere. As carbon dioxide in the atmosphere increases more is absorbed by the oceans, acidifying them and affecting the ability of organisms like corals to build and maintain a calcium skeleton. Acidification will also be an additional source of stress that will compound the problem of coral bleaching.

While local threats such as overfishing and destructive fishing, marine pollution, coastal development, and land-based pollution are activities that can be controlled, they are not easily stopped. Those who inhabit coastal areas often have livelihoods directly tied to coral reefs, and the larger the coastal population, the larger the impact. Marine Protected Areas are one way to reverse some of these effects, and under the right circumstances, MPAs can reverse the effects of many of these local threats. But given that thermal stress and ocean acidification do not have direct controllable paths it will be much harder to protect reefs from such global changes.

The reefs in Australia with the least area under threat (only 14% of its total reef area) and the most area in MPAs (75% of its total reef area) seem to currently be most secure. The region with the reefs that are least secure is the Middle East. This region has the smallest reefs (6% of global reefs — a problem because there are fewer to lose before all are lost), which are heavily stressed (65% stressed from local threats and 36% to thermal stress), and only 12% of its total reef area is in MPAs.