A large majority of the population in the region resides along the coasts and one quarter of the world’s 75 largest cities are situated near, or on, the region’s coastlines (ESCAP, 1995a). Growth rates of coastal populations are generally higher than the national average as a result of migration to coastal urban areas and industrial centres. Most of these large cities and industrial areas are located in highly productive, low lying estuarine areas. The coastal characteristics of selected Asia-Pacific countries are shown in Figure 1.16. (see Figure 1.16)

The marine resources of the region are economically important to most countries. Forty seven per cent of world fisheries production occurs in this region, of which marine and freshwater fisheries account for 76 per cent and 24 per cent respectively (FAO/RAPA, 1994). This region is also the centre of global mariculture (87 per cent of total world production) (FAO/RAPA, 1994), which has major consequences for coastal habitats and coastal water quality. For insular and archipelagic states, marine resources are the key source of external earnings for development, and marine-based tourism is playing an increasingly important role in the economy of such countries. Most countries in the region rely almost exclusively on fisheries products for dietary protein. Figures 17A–17D show trends in the marine fish catch in all of the four sub-regions. (see Figures 1.17a, 1.17b, 1.17c, 1.17d) It is evident from the trends that in almost all of the sub-regions the marine fish catch is steadily increasing. A major cause for concern throughout the region is over-fishing and the use of destructive fishing techniques, particularly in the highly diverse coral reef systems. Most fish stocks throughout the region are currently being fully harvested, while some are being exploited at unsustainable levels. 

Coastal and marine water pollution in this region is mainly due to direct discharges from rivers, surface run-off and drainage from port areas, domestic and industrial effluent discharges through outfalls and various contaminants from ships. Rivers in this region are generally heavily contaminated with municipal sewage, industrial effluent and sediments. Asian rivers account for nearly 50 per cent of the total sediment load (13.5 billion tonnes per year) transported by the world’s rivers (UNEP, 1992). Unfortunately, most of the coastal cities in this region discharge their domestic and industrial wastes directly into the sea without any treatment. 

As much as 70 per cent of the waste effluent discharged into the Pacific Ocean has no prior treatment (Fuavo, 1990). Over 40 per cent of marine pollution in the region is derived from land-based activities (via riverine discharge) and maritime transport contributes a further 12 per cent (Weber, 1993). The Government of Korea estimates that over 80 per cent of pollutants in the Yellow Sea and South Sea of the Korean peninsula come from inland activities (domestic and industrial) via the four largest Korean rivers (Government of Korea, 1994). 
 

The major sources of heavy metal contamination are industrial effluents and the dumping of land-based solid waste into the sea. In India, for example, exceptionally high concentrations of lead (820 micrograms per litre) and cadmium (336 micrograms per litre) have been observed in Thane creeks on the Bombay Coast and the mercury concentration was 778 micrograms per litre. Sediment along the creeks and off-shore stations was also reported to contain significant concentrations of lead (Government of India, 1993). In Pakistan, heavy metal contamination has been detected in water and sediment from the coastal area within the mouth of the Indus River (Tariq et al., 1993). Moreover, there is increasing evidence that these toxic substances are getting into the food chain. 

Marine pollution also arises from sea-based activities, including marine transportation and offshore mineral exploration and production activities. Accidental oil spills are frequently reported in this region. In the Straits of Malacca alone, 490 shipping accidents were reported between 1988 and 1992, resulting in a considerable amount of oil spillage at sea (Straits Times, 1993). Beach tar is also considered a severe problem along the west coast of India, with total deposits of up to 1,000 tonnes a year (GESAMP, 1991). In the port of Chittagong in Bangladesh, it is estimated that about 6,000 tonnes of crude oil are spilled a year and crude oil residue and wastewater effluent from land-based refineries amount to about 50,000 tonnes per year (Khan, 1993). Approximately 5 million tonnes of oil enter the Arabian Sea each year and the Bay of Bengal receives some 400,000 tonnes from similar sources (ESCAP, 1995a). Oil pollution from shipping and offshore oil rigs is also a concern in the East Asian seas. The highest hydrocarbon concentrations occur in the South China Sea off the southern part of Viet Nam and the Straits of Malacca, both of which are major shipping areas. 

The increased use of agro-chemicals in this region also contributed to marine pollution. Fertilizer consumption in the Asia and the Pacific region rose 74 per cent, from 33.3 million tonnes to 57.8 million tonnes, over the period 1982–92 (ESCAP, 1995a). The use of pesticides to enhance agricultural productivity appears to be increasing, especially in the developing countries in the region. For example, in South Asia, India alone uses 55,000 metric tonnes of pesticides a year (herbicides, insecticides and fungicides), of which 25 per cent are thought to end up in the sea (WRI/UNEP/UNEP, 1990). An estimated 1,800 tonnes of pesticides enter the Bay of Bengal each year (Holmgren, 1994). The increased use of pesticides in some areas has resulted in contamination of shell and finfish. 

There is a substantial loss of coastal habitats in South-East Asia as mangroves are used for the construction of shrimp ponds and for paddy rice cultivation. These activities affect, indirectly, commercial demersal fisheries that rely on the mangroves as nursery areas. Thailand and the Philippines are typical examples, where some 208,218 hectares and 200,000 hectares (during 1961–93), respectively, were cleared (GESAMP, 1993). Identical problems resulting from shrimp culture have occurred in Bangladesh, India and Sri Lanka. One example of this destructive sequence of events is the Chakaria Sundarbans in eastern Bangladesh, which have been almost completely cleared for aquaculture (ESCAP, 1995a). 

Coastal construction, particularly for tourist facilities and inland mining, and poor land-use practices have resulted in increased sediment loads in coastal waters in countries such as Fiji, Malaysia, Indonesia and Thailand. The increased sediment has adverse impacts on sensitive coral reef systems, but in Thailand there has been a significant improvement in the condition of the reefs as a result of the efforts of non-governmental organizations (NGOs) and local people (OEPP, 1996). 

Tourism, tourism encroachment and recreational activities can themselves be a threat to marine and coastal environments. The construction activities which accompany most tourism developments, such as hotels, beach clubs and marinas, have a range of direct and indirect impacts on coral reefs through infilling, dredging and the resuspension of contaminated silts. Furthermore, pressure from large numbers of visitors can lead to continuing impacts, such as physical damage to reefs from trampling, boat abrasion and the removal of coral ecosystem for "souvenirs"; discharge of untreated or partially treated sewage; operational leaks and discharges of hydrocarbons; and waste dumping. 

The occurrences of "red tides" caused by blooms of particular plankton species have become an environmental problem of major concern in the coastal areas of the region. In addition to depleting oxygen levels such that mass deaths of aquatic organisms occur, the red tides also cause paralytic shellfish poisoning (PSP) with serious risks to the health of people consuming affected shellfish. An outbreak of red tides in the Philippines in 1990 caused economic losses for the fish and shellfish industries (ESCAP, 1995a). The frequency of red tides in Tolo Harbour, Hong Kong ranged from two in 1977 to nine in 1994. The People’s Republic of China is also experiencing increasing occurrences of red tides in its coastal waters, with a total of 19 incidents in 1993 (ESCAP, 1995a). 

Coastal erosion, resulting from increased land subsidence from groundwater extraction, sediment starvation as a consequence of inland dam and irrigation barrage construction, and off-shore mining of sand are notable problems in some localities in the region. The high volume of maritime traffic and increasing numbers of international tourist arrivals pose additional threats to the marine and coastal environments of the region. 

Although the consequences of marine environmental pollution are becoming increasingly evident, the level of pollution in most coastal waters is still manageable. The countries of the Asia-Pacific region have joined various international and regional agreements to resolve the problem. Over the past five years, the situation in the coastal zone has improved in a few localities in the region. This has been helped along by extensive use of remote sensing in the region as part of a pilot project to obtain data on suspended sediments in the water column, topography, bathymetry, sea state, water colour, chlorophyll-a, sea-surface temperature, fisheries, oil slicks, and submerged and emergent vegetation, including mangroves and seagrass.