The Pacific Ocean is a vast region and includes four distinct sub regions: Australia, Melanesia, Micronesia and Polynesia, incorporating the eastern shores of Australia and stretching towards the coastline of the Americas. There are more coral reefs here than in any other part of the world: over forty percent of the global total, including the most extensive areas of barrier reefs and coral atolls. It was by looking at this region that Darwin developed many of his ideas on the development of reefs. 

Tropical storms or cyclones are a regular disturbance in areas away from the equator, and become more numerous in the western parts of the Pacific. The general westward flow of the surface waters, which are heated as they flow, sets up a number of gradients, including an important pressure gradient. Occasionally this system undergoes reversal in a process known as El Nino Southern Oscillation (an "El Nino event").  Such processes are typified by warm water upwellings across the region and even around the globe. The impacts of such events on coral reefs can be considerable, as witnessed by the mass bleaching events of recent years.

In terms of biodiversity this is a very important, although still little studied, region. In the far west it encompasses the edges of the Indonesian-Philippine center of coral diversity, and there is evidence to suggest that biodiversity on reefs in Papua New Guinea may be at least as high as in these countries. Moving east across the region there is a clear gradient of diminishing diversity which appears to be reflected in all of the major groups of coral organisms, as well as in mangroves and seagrasses. There are some forty-five mangrove species recorded from Australia and Papua New Guinea, but only three from Samoa, with none occuring east of Samoa. Knowledge of reefs in this region is still extremely limited. Australia's Great Barrier Reef has been extensively studied, but its vast size means that, even here, many reefs are only occasionally visited by scientists. French Polynesia is another relatively well studied area, but it has been estimated that only about half of the reef systems have been visited by scientists, and there is published material on less than a quarter of them.

In the Reefs at Risk anaylsis this region was assessed as being one of the least threatened in the world. Population densities are generally low, and there are large areas of coral reefs which are far from any human populations. Despite this, human reliance on the coral reefs of the region is considerable. For many of the small island nations they are a critical source of food, as well as offering protection from storms. Many areas, and some entire nations, are comprised solely of small cays, entirely the product of reef development, and only a few meters above sea level at their highest points.

Western-style development is limited in many countries, and wide areas of reef still fall under some form of customary marine tenure. Traditional systems for controlling local fishing often include relatively complex and effective management routines. Enviromental problems do occur in some areas. There is evidence of target species over fishing in many countries, and populations of clams and trochus have collapsed in several nations, even before export fisheries for these species had begun. Modern fishing methods have allowed access to more remote reefs, and more thorough harvesting. As traditional systems break down, some areas have seen considerable overexploitation, and also destructive fishing. These problems do not affect wide areas, but are important, particularly because they are focussed close to high population densities and they are clearly diminishing the potential of the reefs as a renewable source of food.

Pollution and sedimentation are generally not widespread, but are clearly a concern in localized areas, especially where there is urban development. On the high islands sediment runoff and pollution from agriculture and mining can be a problem.

Extracted from The World Atlas of Coral Reefs, by Mark D. Spalding, Corinna Ravilious and Edmund P. Green, published by the University of California Press . For more complete and in-depth coverage of the topics presented in this webpage, I recommend highly purchasing a copy of this beautifully illustrated book. Just click on the University of California Press link above to do so.