Coastal Zone and Marine Pollution

The coastal zone is defined as the interface between the land and sea where the land and sea influence each other. Its landward and seaward boundaries are not fixed. If the water depth is extended to 200 meters (m), the waters cover an area of about 7% (26 × 106 square kilometers [km2]) of the surface of the global ocean. This area accounts for at least 15% of oceanic primary production, 80% of organic matter burial, 90% of sedimentary mineralization, 75% to 90% of the oceanic sink of suspended river load, and about 50% of the deposition of calcium carbonate. In addition, 90% of the world fish catch and its overall economic value and at least 40% of the value of the world's ecosystem services and natural capital are in this area. Fisheries provide livelihoods to about 40 million people worldwide, and 80% of them are in Asia; the three top fisheries producers are China, Peru, and the United States.

About 40% of the world's people live within 100 km of the coastline, or 7.6% of Earth's total land area. Each year, roughly 50 million more people move into this narrow fringe of coastal land worldwide. By 2050, with the world's population projected to be around 9 billion, some 60% will be living within 60 km of the sea. From another perspective, the contiguous coastal area less than 10 m above sea level covers 2% of the world's land area but contains 10% of the world's population and 13% of the world's urban population. This low-lying zone has 21% of the world's cities, with populations over 5 million; in Asia, 32% of the population lives in such coastal cities.

Population growth has a direct bearing on the extent and magnitude of physical alterations of coastal areas and their consequent destruction. The most damaging actions are changes in land use, including draining wetlands and mangroves for agriculture or settlements; building structures such as ports, seawalls, dams, aquaculture installations, and tourist facilities; and overuse of resources, including overfishing, water use, and sand and gravel extraction.

Several examples of the types of physical alterations currently occurring in coastal environments give an idea of the magnitude of the problem. Of the world's wetlands, 50% have been lost over the past century, and the percentage is higher for mangroves. Already 34% of the world's coral reefs are lost or seriously damaged, and another 20% are threatened in the next 20 to 40 years. The destruction of habitats varies from region to region, but all show deterioration of some kind.

Climate-induced changes in sea level are likely to increase the risk of inundation in many low-lying parts of the coastal zone. Hotspots of coastal [Page 501]vulnerability are the populated deltas, especially the megadeltas of Asia; low-lying urban areas; and atolls, where the stresses on natural systems coincide with low human adaptive capacity and high exposure. Regionally, South Asia, southeast and East Asia, Africa, and small islands are the most vulnerable. Of growing concern is the impact of increasing atmospheric carbon dioxide concentrations and the resultant acidification of the sea. Acidification is expected to disrupt calcium carbonate formation, affect the oxygen metabolism of animals, and influence the availability of nutrients.

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