Reefs at Risk
3. People and corals
Millions of people in developing countries depend on reefs for food and part of their livelihood.
It's hard to say precisely how large an area of the seas is covered by coral reefs. One commonly quoted estimate is 600,000 km2for reefs from the surface down to 30m. More important than their total area, however, is their role in global and local environmental processes and their contribution to human welfare. Millions of people in developing countries depend on reefs, at least in part, for their livelihood. Reefs provide an important source of food for the inhabitants of countries as populous as Indonesia, Jamaica, Kenya and the Philippines.
Coral reefs are not just passive parts of the environment. They form natural breakwaters, creating sheltered lagoons and protected coastlines. They protect mangroves - the nursery for many commercially important marine species - against wave damage, while the coastal mangrove systems act in turn as a barrier against sediments and nutrient loading that could create problems for the reefs.
The economy of atoll nations such as the Maldives is based on marine resources, mainly those of coral reefs. Atoll islands account for most of Kiribati, the Marshall Islands, Tokelau, Tuvalu, and French Polynesia. The Pacific is home to some 2.5 million people living on islands that are either exclusively built by coral or surrounded by significant coral reefs. Another 300,000 people live on coral islands in the Indian Ocean, and many more in the Caribbean.
Coral reefs provide 10-12% of the harvest of finfish and shellfish in tropical countries. Apart from snapper and grouper, jacks, grunts, parrotfish, goatfish and siganids are favourite catches. It has been estimated that coral reefs may account for 20-25% of the fish catch of developing countries. Up to 90% of the animal protein consumed on many Pacific islands comes from marine sources. In the South Pacific, reef and lagoon fish can make up 29% of the commercialised local fishery as well as supplying subsistence food.
Tourism and recreational use of reefs on a large-scale are recent developments, but the use of coral for building has been a central part of some island cultures for nearly 2500 years (see Coral, Maldives and the sea-level rise).
Preparing coral rock for construction on Fadiffolu Atoll, Maldives. Coral mining has been part of the island culture for nearly 2500 years.
Photo: WWF / Jack S. Grove
Coral, Maldives and the sea-level rise
People in the Maldives have been mining coral for over 2400 years. Before the 12th century, when Buddhism was the dominant religion, statues were carved from the slow-growing, massive Porites coral and temples constructed in part from the material. Porites was also used for steps in sacred baths and other special purposes such as decoration, while coral rock was used in boundary walls of monasteries.
In the mid-1650s Porites became widely used for building: mosques, wells and public baths were made of coral, sometimes even coffins where the water-table was high. The Friday Mosque, Hukuru Miskiy, built in 1656, is a 26x14m construction using nothing but Porites : its blocks, carvings and decorations are locked together without mortar.
Demand for coral as building material increased many times as a result of the construction boom resulting from the development of tourism in the early 1970s. Mined reefs show little or no sign of recovery even after 30 years. In some mined reefs, coral cover was reduced to less than 1%, resulting in a very low diversity and small numbers of fish. Severe erosion is found on almost all the islands that have a history of coral or sand mining.
Because the islands of the Maldives are no more than 2m above the mean sea-level and some 80% of the land is less than lm in height, global changes predicted to occur over the next 50 years threaten this country's survival. It has been estimated to cost over US$1.3 billion to create even minimal sea defences for about 50 of the 200 inhabited islands. Authorities have now banned the use, of coral in building tourist facilities and public buildings, and are making imported cement and aggregate more attractive for construction by reducing import duty. They recognise that the natural protection provided by the reef is of greater long-term value than the benefit from short-term unsustainable mining of the reef.
Mariculture and its problems
Faced with a decline in commercially attractive coral reef species, some countries have tried on-site mariculture to build up their export stock. Four countries at least are trying to farm the giant clam Tridacna on their reefs, following the local extinction of these shellfish on many Pacific islands and throughout large areas of Asia.
Clams are easily collected because they are found in clear, shallow waters. They are also relatively easy to breed in hatcheries. Since their tissues contain symbiotic algae like those in corals, they grow rapidly when exposed to steady light on shallow reef flats.
Commercial hatcheries have been established in the Solomon Islands, Micronesia, Samoa, and both northern and southern Philippines. The aim is to produce enough juvenile clams to establish village industries both for local consumption and export.
People depending on coral reefs may be forced to turn from rapidly declining natural resources to mariculture as a source of seafood. The potential effects of climate change, however, will have to be factored into their projects. They will need to consider the chances of storm damage and their distance from potential land-based effects. For example, clams seem vulnerable to bleaching in the same way as corals, putting their survival at risk under warmer conditions. To avoid this problem, growers may need to locate the clams in deeper water where light and temperatures will be more stable. This, however, may reduce the clam's growth rate markedly, and produce smaller returns to the clam farmer.
A fishing canoe in Western Samoa. The sea provides 90% of the animal protein consumed on many Pacific Islands.
Photo: J.W. Thorsell
March 30, 2010