Physical degradation or destruction of habitats may be caused by a variety of natural causes including cyclones, hurricanes, typhoons, volcanism, earthquakes and tsunamis. These factors can cause significant physical damage to the structure of habitat, thus altering biological diversity and ecosystem function.
Global climate change and periodic climatic events are a significant threat to habitats on the global scale, particularly to coral reefs. The increase in sea-surface temperature associated with the major El Niño and La Niña climate switches in 1997-1998 resulted in extensive coral bleaching and mortality over large portions of the Indian Ocean and Southeast and East Asia. Some of the changes caused by periodic climate events are not necessarily permanent. However, direct human-induced stresses to habitats often exacerbate the effects these events or limit the recovery capability of marine and coastal ecosystems.
Direct human activities posing threats to marine and coastal habitats are relatively well documented. Each of these activities may independently threaten ecosystem structure and function. However, more significant impacts are often the result of compounded effects of multiple activities. These direct threats include:
· Destructive fishing practices
· Mining
Underlying these direct threats are often societal components contributing to the destructive activities. Some of these driving factors may be incomplete knowledge, lack of conviction, inadequate laws or regulatory regimes, lack of economic alternatives, high population growth, lack of effective management or limited human or financial resources. In considering appropriate response measures to address destructive human activities, it is important to identify and address the underlying causes as well as the proximate threats.
Global climate change stands to alter sea-surface temperature, sea levels, oceanic currents and patterns of marine productivity. Coral reefs are particularly sensitive to climatic influences, exhibiting the phenomenon known as coral bleaching when stressed by higher sea temperatures and other factors. Coral bleaching, or the exposure of the underlying white skeleton of reef-building corals, results when coral polyps eject the microscopic algae, or zooxanthellae, living within their tissues. Reef-building corals are highly dependent on a symbiotic relationship with zooxanthellae and frequently demise after ejecting these algae.
This reaction of corals has been observed for many years, but reports of coral bleaching have been increasing greatly recently. Various types of stress, including temperature extremes, pollution and exposure to air, can cause bleaching; but recent increases in temperature-related stress due to climate change are suspected in the rise in regional bleaching events. Recent reports have shown that bleaching events related to extreme periodic climatic events remain the primary threat to coral reefs on the global scale. The increase in sea-surface temperature associated with the major El Niño and La Niña climate switches in 1997-1998 resulted in extensive coral bleaching and mortality over large portions of the Indian Ocean and Southeast and East Asia. On some reefs, there were mortality levels greater than 90% leaving some reefs almost bare of corals and with early indication of major shifts in the population structures.
The critical feature of recent coral-bleaching events is that areas have been struck indiscriminately, irrespective of the existing health of reef. Impacts have been felt both on pristine remote reefs, and on reefs already under significant human-induced stress. Although some changes caused by bleaching events are not necessarily permanent, additional stresses, such as those created by pollution and physical degradation, exacerbate the effects of these events and limit the recovery capability of coral reef ecosystems.
Source: CBD Report of the Expert Consultation on Coral Bleaching UNEP/CBD/SBSSTA/5/INF/11
Global Coral Reef Monitoring Network
UNEP World Conservation Monitoring Centre/Biodiversity and Climate Change
World Resources International/Reefs at Risk
UNEP World Conservation Monitoring Centre/World Atlas of Coral Reefs
Assessments to late 2000 now indicate that 27% of the world's reefs have been effectively lost, with the largest single cause being the massive climate-related coral bleaching event of 1998. While there is a good chance that many of the 16% of damaged reefs will recover over time, some predict that half will never adequately recover. The latest global predictions suggest that a further 14% of the world's coral reefs will be lost by 2010, and another 18% in the 20 years following, without reductions in the current human-induced stresses on reef ecosystems from growing coastal populations and economies. This means that 59% of the world's reefs are under immediate threat of loss within several decades.
Arabian/Persian Gulf region: The near-shore reefs of the Arabian/Persian Gulf were severely damaged by severe coral bleaching in 1996 and 1998, while offshore reefs were less affected. Major coral bleaching occurred in late 2000 in the northern Gulf, while Red Sea reefs remain predominantly healthy with few localized anthropogenic stresses. Rapid growth in tourism and shipping present the potential for growing physical degradation and destruction in the region.
South Asia: Most coral reefs in the region were severely affected by the extreme climate events of 1998, most significantly in the Maldives, Sri Lanka and parts of western India. These losses have added to the major human-induced damage off the mainland of India and Sri Lanka particularly from coral mining, over-fishing and land-based pollution.
Eastern Africa: Significant levels of sediment runoff, nutrient pollution and over-exploitation of reef resources from growing populations remain the largest threats to coral reefs in the region. There was a massive coral-bleaching event and subsequent coral mortality with the El Niño climate switch of 1998, with some areas losing up to 80% of live corals, particularly parts of Kenya and Tanzania.
Southern Indian Ocean: The reefs of the northern part of the region suffered damage during 1998 as a result of the El Niño event, with losses of 80 to 90% of the corals in parts of the Comoros and of the Seychelles. Coral reefs of Madagascar continue to be under very high human-induced threats.
Southern Asia: Some reefs in the region were damaged by the 1998 bleaching event, but the region is the center of a live fish trade worth over US $1 billion per year, with virtually all reefs being physically damaged or destroyed by destructive cyanide and blast fishing methods.
East Asia: The reefs of southern Japan and Taiwan were severely affected by coral bleaching and mortality during the 1998 La Niña climate switch in the region. There are many reports of coral losses of 30 to 60% with some losses as high as 80 to 90%. Some localized extinctions of prominent corals have been reported.
Australia and Papua New Guinea: Australian coral reefs continue to have the lowest levels of human-induced impacts of any continental reefs. In general, they are considered to be in good to excellent condition, although problems with sediment and nutrient run-off from land-based sources have been identified on the Great Barrier Reef. Increasing pressure from professional and recreational fishing is now being experienced and a population explosion of crown-of-thorns starfish is currently attacking offshore reefs. Most of the reefs of Papua New Guinea are in generally very good condition, except for localized areas of damage from excessive logging and increasing levels of exploitation on near shore reefs.
Micronesia: Coral reefs of Micronesia remain predominantly in good to excellent condition, although some damage from coastal development activities on the high islands and over-fishing around centers of population has been experienced. Most of the region has escaped damage from the 1997-1998 bleaching event; however, there were significant losses of coral around Palau.
Southwest Pacific: While this region escaped major bleaching in 1997-1998, it was damaged by relatively severe coral bleaching between February and April 2000 with extensive mortality in some parts of Fiji and the Solomon Islands. Human impacts on these reefs are steadily increasing but still concentrated at a few sites per country, mainly around the capital cities and in lagoons. Most reefs in the region remain in healthy condition, with some local over-fishing for subsistence and small-scale commercial activities.
Southeast Pacific: Most of the coral reefs in this region remain healthy, with few human-induced threats, concentrated around population centers and within enclosed lagoons. Considerable shoreline modification on these islands for tourism developments has resulted in damage to the near shore reefs, but the outer reefs facing the ocean show no real impacts. Fishing pressures are increasing in the region and there are increasing conflicts between fishers and tourist operators.
North-east (American) Pacific: Strong population and economic growth in the Hawaiian Islands is resulting in considerable local damage to reefs around the major population centers and tourist operations, while all coral reefs are experiencing increased fishing pressure. Collecting for the aquarium trade has caused major depletion of some species. In contrast, the scattered islands are under minimal human-induced threats and none experienced climate related bleaching in 1998.
The American Caribbean: The region is experiencing significant problems with over-fishing and physical damage to coastal nursery areas of mangrove forests and seagrass beds. The primary threats to coral reefs off Florida are pollution from agriculture and growing tourism and recreational fishing industries.
Northern Caribbean and Western Atlantic: Primary threats to coral reefs in Jamaica, Haiti and the Dominican Republic are over-fishing and pollution, while over-exploitation is less significant in Cuba, Bahamas, Turks and Caicos Islands. Reefs in Bermuda and Cayman Islands are healthy, resulting largely from the demands of the tourism industry. White-band disease has caused a reduction of Acropora spp. Reefs close to land still show low cover (e.g., coral cover in northern Jamaica dropped from 52% in the 1970s to 3% in the early 1990s, but is gradually recovering (currently 10-15%). Bleaching in 1998 was severe in places, but there was little or no mortality. Much of the tourism development based of the coral reefs is poorly planned and results in sediment run-off and nutrient pollution damaging the reefs.
Central America: Though most of the region escaped the Caribbean bleaching events in 1995 and 1998 and the intense Hurricane Mitch, also in 1998, coral reefs from the Mexican Yucatan to Nicaragua were heavily impacted, with losses in coral cover of 15 to 20% across the region with some losses as high as 75% in parts of Belize. Throughout large parts of the region there are intense fishing pressures (Honduras and Nicaragua, and Veracruz and Campeche in Mexico), and major damage to reefs from sediment runoff because of poor land-use.
The Eastern Antilles: Within the region, primary island threats are currently over-exploitation, sedimentation and nutrient pollution to near-shore coral reefs. Coral cover on some islands has dropped recently due to the passage of hurricanes and coral bleaching, with St. Lucia experiencing a decline from 50% to 25% at a depth of 3 metres and from 35% to 17% at 10 metres.
South America: Coral reefs in the region experienced significant declines in the 1980s and early 1990s due to both natural and human-induced stresses. Repeated coral bleaching episodes have resulted in cumulative mortalities, while human-induced threats from increased sediment and nutrient pollution on the near shore reefs have resulted from deforestation, poor agricultural practices and diversion of rivers. Offshore reefs are being increasingly over-exploited for fisheries, coral rock and sand, resulting in distinct declines of coral cover and fish populations.
Based on: Wilkinson, C. ed. Status of Coral Reefs of the World: 2000. Australian Institute of Marine Science. Cape Ferguson: Australia
Marine and coastal ecosystems and the biological diversity that comprise them provide significant physical, economical, social and cultural benefits to humankind. Some of the direct benefits include sources of food and medicine. However, human overexploitation of many of ocean living resources has placed these very ecosystems under severe threat.
Widespread over-harvesting of many target species is well documented, and has resulted in severe stock collapses. The removal of breeding age individuals has a significant and direct impact on the sustainability of populations; and traditional single-species management approaches have largely failed for many fisheries. With reduced numbers of these target species, fishing pressure often increases as fishers search previously untouched and remote areas, or develop more aggressive fishing methods. Additionally, bycatch, or the incidental catch of non-targeted species, is discarded at sea. This provides a supplemental food source for scavengers and opportunistic predators, including fish, crabs seabirds and raptors, and may in turn impact populations of competitors or prey and influence community structure.
Increasing evidence indicates that removal of these top predators, or human-induced perturbations such as bycatch, can have significant cascading effects across the marine food web. Ultimately, this can affect a habitat's ability to sustain the community. For example, in the Caribbean, decades of over-fishing have led, in many places, to very low levels of grazing fish species. Because of this, herbivorous sea urchins have played an increasingly important role in keeping down algal growth. In the 1980s, huge numbers of these urchins succumbed to disease. Without grazing fish or urchin populations, and spurred on in many areas by organic pollution, algae quickly dominated the reefs, inhibiting coral settlement and sometimes overgrowing living corals. Thus, ecosystem function was transformed so that the habitat no longer supports the same assemblage of species. Long-term, such cascading effects could greatly inhibit future human use of marine and coastal living resources.
Approximately 66% of the human population, or close to four billion people, now live within 80 kilometres of the coast. This figure isexpected to increase to 75% by 2020. Such a dense coastal population and the attraction of the coast as a travel destination exert increasing direct and indirect pressures on marine and coastal ecosystems through extensive coastal development.
Direct physical alteration and destruction of native habitats occur in coastal regions through dredging for shipping channels and harbours, the filling of shallow habitats for coastal building, and contamination of water sources.
Indirectly, poorly planned urban, industrial and port developments contribute to the destructive effects of land-based sources of pollution to the marine environment through contaminated sediment. Watersheds cleared of their forests and other vegetation covers are vulnerable to erosion and flooding. During high water periods, silt and pollutants within these basins are carried far beyond normal, impacting a greater number and extent of coastal habitats.
Trawling for target species in many marine and coastal habitats directly damages those habitats and disrupts both ecosystem structure and function. Because these methods are generally non-selective, large numbers of non-target animals, along with undersized target species, may be swept up in nets; as well as benthic species being killed directly by trawl doors or drag chains. Additionally, abandoned fishing gear or "ghost fishing" poses a significant threat in some regions. As not all fishing methods are destructive, this is less of a widespread threat to habitats than overexploitation.
Blast fishing on coral reefs inherently destroys stony corals and kills fish and invertebrates in a large surrounding area. The resulting changes may lead to a decrease in biological diversity through a reduction in livable niches or through changes in ecosystem dynamics. A recent cost-benefit analysis calculated the economic cost to society for one blast fishery to be four times higher than the potential total net benefits offered to the region by tourism and coastal protection.
Fishing with cyanide or other poisons to stun and capture live aquarium and food fish for the restaurant retail business and the aquarium trade kills larvae of many coral-reef organisms and may add to the bleaching of corals. Several studies now show that habitat destruction through poison fishing is not as large as earlier anticipated. Estimates of the reef-degrading capacity of the cyanide fishery for food fish on Indonesia's coral reefs suggest a loss of live coral cover of .047 to .06 percentage points per year. This is significantly less than the threats noted for blast fishing (3.75% per year) or coral-bleaching events.
Extractive mining and seafloor drilling can directly or indirectly threaten marine and coastal habitats through degradation and destruction.
Coral mining for lime production is a source of income and subsistence in many developing countries. The lime is processed into plaster or mixed with cement to reduce costs for local construction. However, the associated damage to the environment is significant, not only through physical destruction of coral reefs, thereby damaging its coastal protection function and reducing biological diversity, but also because secondary forests may be logged for fuel wood to process the lime.
Located downstream from land, the sea inevitably becomes the ultimate sink of human-generated pollutants via runoff or through direct dumping. This host of pollutants includes sewage, persistent organic pollutants (POPs), radioactive substances, heavy metals, excess nutrients (fertilizers, nitrogenous compounds, etc), halogenated hydrocarbons (pesticide, PCBs, dioxins, etc), liter, or simply excessive amounts of sediment. Each of these pollutants independently, or in combination contributes to the degradation or destruction of marine habitats.
Many of these pollutants pose direct human-health risks. Heavy metals, such as arsenic, cadmium, chromium, copper, nickel, lead and mercury, concentrate in the tissues of many marine species, becoming highly contaminated in the process. Persistent organic pollutants and hydrocarbons are commonly found in land-based runoff and ultimately accumulate in harvested species.
Currently, the most widespread threat of land-based pollutants to marine and coastal habitats is posed by a combination of municipal sewage, solid waste, fertilizers, urban run-off and other nitrogenous compounds. Human activities now add at least as much fixed nitrogen to terrestrial ecosystems as do all natural sources combined and the oceans receive this nitrogenous pollution from both coastal runoff and atmospheric deposition. The nutrients cause an over-production of algae in coastal regions. When the algae die, an over-production of micro bacteria occurs, including some highly toxic species. As these bacteria decompose the algal remains, they consume much of the oxygen dissolved in the water, causing mass mortality of fish and invertebrates. In coastal marine habitats, areas affected by anthropogenic eutrophication are particularly widespread, persistent and increasing.
UNEP Global Programme on Land-based Activities
Oil and chemical spills and the deliberate discharge of oily ballast water by ships pose a potential, but poorly documented, threat to marine and coastal habitats. This threat, though important, is thought to be less significant than land-based sources of pollution.
Oil or chemical spills can smother habitats and associated organisms. Studies of the impact of oil discharges into the Arabian Gulf during the Iran-Iraq and Gulf Wars indicate that spills are associated with short-term declines in many fish and other species. In 1986, a major spill off the mouth of the Panama Canal was linked to significant losses in diversity of corals and losses to the extent of coral cover in affected areas.
The discharge of ballast water from ships may pose a more significant threat to some marine habitats as a primary vector in the transport of invasive alien species, rather than as a result of the direct threat created by its chemical contents.
International Maritime Organization
Although tourism in coastal areas and the recreational use of marine habitats may be the best sustainable alternative to more consumptive and destructive activities in many areas, it may also contribute to the physical degradation and destruction of those habitats. Therefore, a precautionary approach should be used in any development of tourism and recreation use.
Physical damage to marine and coastal habitats can be caused during coastal development for tourist activities, or caused by ship or boat grounding, anchor damage, souvenir-collecting or physical contact from divers and swimmers.
Aside from the ecological threats that these activities pose to marine habitats, they additionally threaten the socio-economic values associated with the goods and services provided by these habitats.
World Tourism Organization/Sustainable Development of Tourism
Marine and brackish water aquaculture, or mariculture, offers possibilities for sustainable protein-rich food production and for economic development in local communities. Worldwide, mariculture is growing at the rate of about five to seven percent annually. Currently, the main types of organisms being produced through mariculture include seaweeds, mussels, oysters, shrimps, prawns, salmon and other species of fish.
However, mariculture on an industrial scale may pose several threats to marine and coastal biological diversity and their associated habitats. For example, in some regions, conversion of coastal mangrove habitat for mariculture production of shrimp is the primary habitat threat. Mariculture may pose additional threats through excess nutrients and antibiotics in mariculture wastes, accidental releases of exotic species or genotypes, transmission of diseases to wild stocks, and displacement of local and indigenous species.
In consideration of these threats and the difficulties of complete containment, mariculture should be responsibly conducted using a precautionary approach. Such an approach should include: assessments and an appropriate monitoring programme; preference should be given to the use of local species; development of technology to ensure a more complete containment should be encouraged.