Along with direct loss of area, a variety of other factors are significantly altering coastal ecosystems around the world. Some of the major pressures are population growth, pollution, overharvesting and destructive fishing practices, and the looming threat of climate change.

Globally, the number of people living within 100 km of the coast increased from roughly 2 billion in 1990 to 2.2 billion in 1995-39 percent of the world's population. However, the number of people whose activities affect coastal ecosystems is much larger than the actual coastal population because rivers deliver pollutants from inland watersheds and populations to estuaries and surrounding coastal waters. As coastal and inland populations continue to grow, their impacts-in terms of pollutant loads and the development and conversion of coastal habitats-can be expected to grow as well.

An increasing number of pollutants affect the world's coasts and oceans. Most pollution of coastal waters comes from the land, but atmospheric sources and marine-based sources such as oil leaks and spills from vessels also play a role. Nutrient pollution, especially nitrates and phosphates, has increased dramatically this century. Greater use of fertilizers, growth in quantities of domestic and industrial sewage, and increased aquaculture, which releases considerable amounts of waste directly into the water, are all contributing factors (GESAMP 1990:96).

In terms of food production, forty-five years of increasing fishing pressure have left many major fish stocks depleted or in decline. The scale of the global fishing enterprise has grown rapidly and exploitation of fish stocks has followed a predictable pattern, progressing from region to region across the world's oceans. As each area in turn reaches its maximum production level, it then begins to decline (Grainger and Garcia 1996:8, 42-44). Overexploitation of fish, shellfish, seaweeds, and other marine organisms not only diminishes production of the harvested species but can profoundly alter species composition and the biological structure of coastal ecosystems.

Global climate change may compound other pressures on coastal ecosystems through the additional effects of warmer ocean temperatures, altered ocean circulation patterns, changing storm frequency, and rising sea levels. Changing concentrations of CO2 in ocean waters may also affect marine productivity or even change the rate of coral calcification (Kleypas et al. 1999). Rising sea level, associated with climate change, is likely to affect virtually all of the world's coasts. During the past century, sea level has risen at a rate of 1.0-2.5 mm per year (IPCC 1996:296). Rising sea levels will also increase the impact of storm surges. This, in turn, could accelerate erosion and associated habitat loss, increase salinity in estuaries and freshwater aquifers, alter tidal ranges, change sediment and nutrient transport, and increase coastal flooding.

Because of the current pressures on coastal ecosystems, and the immense value of the goods and services derived from them, there is an increasing need to evaluate tradeoffs between different activities that may be proposed for a particular coastal area. However, to integrate this evaluation into the decisionmaking process, better information on the location, extent, and change in coastal habitats is urgently needed. Information regarding the interaction between ocean, land, and atmosphere is also a key to understanding the functions of the coastal zone but so far most of the information is anecdotal or fragmentary. One factor contributing to this lack of information is the partitioning of disciplines into separate entities. Terrestrial ecology, wetland ecology, and marine ecology are, for example, distinct fields among the biological sciences. The separation between these and the physical, chemical, and social sciences is even greater, making it difficult to conduct a more integrated analysis.

The problems affecting the coastal zone are cross-sectoral and complex. Collaboration among climatologists, ecologists, ocean chemists, toxicologists, soil scientists, statisticians, coastal engineers, economists, and practitioners of monitoring and information technology will be needed to develop the information base and linkages necessary to fully assess the condition of the world's coastal environments.