Publications > Our Precious Coasts > What is Marine Polluti ...

Our Precious Coasts

What is Marine Pollution and How Does it Affect Marine Life

Figure 5. Coral reefs at risk from human activities. Extreme climatic events, population growth and coastal fisheries account for major causes of coral reef decline – excessive domestic and agricultural waste pouring into ocean waters, poor land-use practices that increase sedimentation of rivers and then of reefs, and over-exploitation of reef resources, often in combination with practices such as harvesting with dynamite and poison, all degrade reefs. These factors, however, also make it far harder for coral reefs to recover from bleaching events.
Marine pollution includes a range of threats including from land-based sources, oil spills, untreated sewage, heavy siltation, eutrophication (nutrient enrichment), invasive species, persistent organic pollutants (POP’s), heavy metals from mine tailings and other sources, acidification, radioactive substances, marine litter, overfishing and destruction of coastal and marine habitats (McCook 1999, Nyström et al. 2000, Bellwood et al. 2004). Overall, good progress has been made on reducing Persistent organic pollutants (POP’s), with the exception of the Arctic. Oil discharges and spills to the Seas has been reduced by 63% compared to the mid-1980’ies, and tanker accidents have gone down by 75%, from tanker operations by 90% and from industrial discharges by some 90%, partly as a result of the shift to double-hulled tankers (UNEP, 2006; Brown et al., 2006). Some progress on reducing emissions of heavy metals is reported in some regions, while increased emissions are happening in others. Electronic waste and mine tailings are included amongst the sources of heavy metal pollution in Southeast Asia. Sedimentation has decreased in some areas due to reduced river flows as a result of terrestrial overuse for agricultural irrigation, while increasing in other regions as a result of coastal development and deforestation along rivers, water sheds and costal areas, and clearing of mangroves (Burke et al., 2002; McCulloch et al., 2003; Brown et al., 2006; UNEP, 2004, 2006).

A major threat beyond overexploitation of fisheries and physical destruction of marine coastal habitats by dredging, is undoubtedly the strong increase in coastal development and discharge of untreated sewage into the near-shore waters, resulting in enormous amounts of nutrients spreading into the sea and coastal zones (Burke et al., 2002; Wilkinson, 2002; Brown et al., 2006; UNEP, 2006). This, together with changes in salinity, melting sea ice, increased sea temperatures and future changes in sea currents may severely affect marine life and their ability to recover from extreme climatic events. 

Figure 6. Threats to the World’s coral reefs. Major observed threats to the world’s coral reefs include extreme climate events, unsustainable  tourism practices, poison fishing for ornamental fish, overexploitation by fisheries, sedimentation, coral harvesting, dynamite fishing and pollution (not in order of priority). This graphic explains which activities or conditions are affecting various coral reefs throughout the world. The graphic ‘Major Threats to Reefs’ shows the percentage of reefs that are threatened by overexploitation, coastal development, inland pollution and marine pollution, and the degree to which they are under threat. The graphic ‘Destroyed Coral Reefs’ shows the percentage of coral reefs that have been destroyed in the world’s major regions.

Around 60% of the wastewater discharged into the Caspian Sea is untreated, in Latin America and the Caribbean the figure is close to 80%, and in large parts of Africa and the Indo-Pacific the proportion is as high as 80-90% (UNEP, 2006). An estimated US$ 56 billion is needed annually to address this enormous wastewater problem. However, the costs to coral reefs, tourism and losses in fisheries and human health risks may be far more expensive. It is also the area where least progress is being made globally.

Together with agricultural run-off to the Sea or into major rivers and eventually into the ocean, Nitrogen (mainly nitrate and ammonium) exports to the marine environment are projected to increase at least 14% globally by 2030 (UNEP, 2006). In Southeast Asia more than 600,000 tons of Nitrogen are discharged annually from the major rivers. These numbers may become further exacerbated as coastal populations are depicted to increase from 77 people/km2 to 115 people per km2 in 2025. In Southeast Asia, the numbers are much higher and the situation more severe. Wetlands and mangroves are also declining rapidly, typically by 50-90% in most regions in the past 4 decades (UNEP, 2006). All of the above, together with changes in salinity, melting sea ice, increased sea temperatures and future changes in sea currents may severely affect marine life and its ability to recover from extreme climatic events. Also, it will severely exacerbate the effects of extreme weather and the productivity of coastal ecosystems to supply livelihoods and basic food to impoverished. Hence, the poor management of sewage not only presents a dire threat to health and ecosystems services, it may increase poverty, malnutrition and security for over a billion people (UNEP 2006)

In these two Landsat images shrimp farms appear as bluish purple squares located near the streams. Between the earlier image acquired in January, 1990 and the later image acquired approximately 11 years later there is an explosion in shrimp farming throughout the estuary.

These Landsat satellite images from 1974 and 2005 show the gradual spread of development and the loss of mangrove forest that has resulted. By 1975, many areas of mangrove had already been converted to agriculture. As thirty years pass, the agricultural areas expanded and more mangroves were converted to farms. At the same time, these images show the agricultural areas being converted to industrial and urban land use. Elsewhere along the Malaysian coastline, mangroves are rapidly being converted to commercial shrimp farms. Forestry Department statistics show that peninsular Malaysia had 85,800 hectares (214,500 acres) of mangrove swamp forests in 2003, down from 86,497 hectares just one year earlier.

Figure 7. These mangroves, in the Trang River Estuary in Thailand, are under threat from upstream discharge of wastewater, industrial facilities and unsustainable aqua culture practices – particularly commercial shrimp farming. From 1975 to 1993, it is estimated that about half of Thailand’s mangroves along its 2,560 kilometer coastline have been lost. The larger area of the Had Chao Mai Marine National Park, the Ta Libong Island Non-Hunting Area and the Trang River Estuaries has been designated a Ramsar Wetland Site and supports over 200 bird species including many “Critically Endangered”, “Endangered”, “Vulnerable” and “Threatened” species according to the IUCN Red List (IUCN, 2006).   Figure 8. Coastal population and shoreline degradation. This graphic shows that the coastal areas with the greatest population densities are also those with the most shoreline degradation or alteration. The graphic shows the proportion of the population that lives within 100 km of the coast, for each of the world’s nations. It also shows the locations of selected coastal cities with a population of more than one million people.

Figure 9. With a population over 1.4 million (and approximately twice that number in the greater metropolitan area), Kuala Lumpur is the largest city in Malaysia and is growing rapidly. Its sprawl is now encroaching on the mangrove forests at the coastline (approximately 35 kilometers to the west of the city centre).    Figure 10. Threats to coral reefs in Eastern Africa. Human land use along coasts and in major river basins can threaten coral reefs through toxic material inputs to coastal ecosystems. This graphic shows the areas of low, medium and high estimated threats to coral reefs on Africa’s eastern coast.