Global imperatives for coastal management
The above quote clearly illustrates the international importance of coastal and marine management. This is one of the major program areas dealt with in Chapter 17 of Agenda 21 (UNCED 1992), which is essentially the United Nations' blueprint for sustainable development (see page 207 for definition and discussion). At the United Nations Conference on Environment and Development (UNCED), often referred to as the 'Earth Summit', held in Rio de Janiero in 1992, there was a recognition that the world was beginning to live beyond its ecological means and that rapid action was necessary to avert future disaster (UNCED 1992). In this global context, the coast is particularly important for three reasons.
First, most of the world's population lives around the coast. There have been various estimates for just how many people live around the coast, and these estimates will differ depending on what definitions of 'the coast' are used. Agenda 21 (17.3) stated that in 1992 more than half of the world's population lived within 60 km of the coast, and that by the year 2020 this proportion could rise to two thirds. Hinrichsen (1998) quotes a figure of 3.2 billion people living within 200 km of the coast, on about 10% of the Earth's land area, and two thirds of the world's population already living within 400 km of the coast. Estimates of current world population are around 6.2 billion people (US Census Bureau 2000). Global population concentrations in coastal areas have been illustrated graphically through the population density maps of the Global Demography Project (Tobler et al. 1995). These maps also clearly depict regional differences; for example, major concentrations around the coasts of the Indian and Asian subcontinents, but a sparsely populated Australian coast. The majority of the world's largest cities are located on the coast, and in some areas they have expanded into what have been termed coastal megacities (cities with a population of over 10 million people). There are now more than 20 of these, and many are in Southeast Asia.
Second, humans are highly dependent on coastal resources. Although the coastal ocean accounts for only 8% of the global ocean surface and less than 0.5% of its volume, it accounts for about 14% of its production; up to 50% of its denitrification; up to 80% of global organic matter burial; 90% of global sedimentary mineralisation; 75 to 90% of the global sink of suspended river load and associated elements/pollutants; in excess of 50% of present-day global carbonate deposition; and approximately 90% of the world's fish catch (Pernetta & Milliman 1995, p 16). Given the importance of the coastal zone for humans, it is interesting to consider what value it has, in broad terms. A recent study attempted to estimate the contribution of various ecosystems to the total economic value of the planet (Costanza et al. 1997). Here, it was estimated that the coastal biome contributed a total global flow value of ecosystem services amounting to $US12 x el2 per year out of the total global flow value of $US33 el2 per year. If Costanza et al.'s tidal marsh and mangrove category is also included in the coastal figure, this increases the coastal value to $US14 el2 per year, or more than 40% of the total global flow value (Costanza et al. 1997).
Third, the coast is being subjected to increasing development-related impacts as a consequence of the combined effect of increasing population pressure together with the high dependency on coastal resources. In 1995, the World Resources Institute published the results of a study which concluded that half of the world's coastal ecosystems are already suffering from severe development-related impacts (WRI 1995). This study used cities, major ports, road density and pipeline density as key development indicators in addition to population density data. It is this increasing global pressure on coastal ecosystem resource use which has provided the imperative for developing better approaches to managing the world's coastal zone.
In addition, special attention to management is needed because the coast is naturally dynamic at a variety of time scales, important changes are not only brought about by human use, but also by natural forces. For example, coastal wetlands are lost through local relative sea level change as well as through reclamation and development. Coasts are eroded by wave action, as well as by human activities such as harbour construction. Sand dunes are destabilised by storms or fires, as well as by vehicle impact. A common problem in coastal management is how to separate rapid natural change from human-induced change.