Coral Bleaching. Ann-Tin Cheng, ID# Cathy Wu, ID#

Transcription

1 Coral Bleaching Ann-Tin Cheng, ID# Cathy Wu, ID#

2 1. Elevated/ Decreased Sea Water Temperature Causes Solar Irradiance Subaerial Exposure 4. Sedimentation 5. Fresh Water Dilution 6. Inorganic Nutrients Xenobiotics Epizootics 9. Reduced Salinity

3 Elevated/ Decreased Sea Water Temperature Coral species live within a relatively narrow temperature margin, and anomalously low and high sea temperatures can induce coral bleaching. Bleaching events occur during sudden temperature drops accompanying intense upwelling episodes, (-3 degrees C to 5 degrees C for 5-10 days), seasonal cold-air outbreaks. Bleaching is much more frequently reported from elevated se water temperature. A small positive anomaly of 1-2 degrees C for 5-10 weeks during the summer season will usually induce bleaching. Bleaching during the summer months, during seasonal temperature and irradiance maxima often occurs disproportionately in shallow-living corals and on the exposed summits of colonies. Solar radiation has been suspected to play a role in coral bleaching. Both photosyntheticaly active radiation (PAR, nm) and ultraviolet radiation (UVR, nm) have been implicated in bleaching. Bleaching during the winter months may be a natural phenomenon for high-latitude coral reefs. However, climnate change may also lead to local decreases in temperature or to greater variability in seasonal conditions. This could possibily result in two consecutive bleaching events within one year of the same reef. Cold water bleaching is therefore an additional component to be considered among the climate change projections for coral reefs at some locations. Solar Irradiance Bleaching during the summer months, during seasonal temperature and irradiance maxima often occurs disproportionately in shallow-living corals and on the exposed summits of colonies. Solar radiation has been suspected to play a role in coral bleaching. Both photosyntheticaly active radiation (PAR, nm) and ultraviolet radiation (UVR, nm) have been implicated in bleaching. Subaerial Exposure Sudden exposure of reef flat corals to the atmosphere during events such as extreme low tides, ENSO-related sea level drops or tectonic uplift can potentially induce bleaching. The consequent exposure to high or low temperatures, increased solar radiation, desiccation, and sea water dilution by heavy rains could all play a role in zooxanthellae loss, but could also very well lead to coral death. Causes Sedimentation Relatively few instances of coral bleaching have been linked solely to sediment. It is possible, but has not been demonstrated, that sediment loading could make zooxanthellate species more likely to bleach. Fresh Water Dilution Rapid dilution of reef waters from storm-generated precipitation and runoff has been demonstrated to cause coral reef bleaching. Generally, such bleaching events are rare and confined to relatively small, nearshore areas. Inorganic Nutrients Rather than causing coral reef bleaching, an increase in ambient elemental nutrient concentrations (e.g. ammonia and nitrate) actually increases zooxanthellae densities 2-3 times. Although eutrophication is not directly involved in zooxanthellae loss, it could cause secondary adverse affects such as lowering of coral resistance and greater susceptibility to diseases. Xenobiotics Zooxanthellae loss occurs during exposure of coral to elevated concentrations of various chemical contaminants, such as Cu, herbicides and oil. Because high concentrations of xenobiotics are required to induce zooxanthellae loss, bleaching from such sources is usually extremely localized and / or transitory. Epizootics Pathogen induced bleaching is different from other sorts of bleaching. Most coral diseases cause patchy or whole colony death and sloughing of soft tissues, resulting in a white skeleton (not to be confused with bleached corals). A few pathogens have been identified the cause translucent white tissues, a protozoan. Reduced Salinity This is a much more localised bleaching than the effects of extensive sea temperature anomalies in the major tropical oceans. references: Brown, B.. Coral bleaching: causes and consequences. Coral Reefs Feb 2009 Dodge, Richard. Low temperatures cause coral bleaching. Coral Reefs 2329 July Feb 2009

4 Reef-base data of worldwide bleaching records (as of March 2008)

5 Mass coral moralities in coral reef ecosystems have been reported in all major reef provinces since the 1870s. The frequency and scale of bleaching disturbances has increased dramatically since the late 70 s. This is possibly due to more observers and a greater interest in reporting in recent years. More than 60 coral reef bleaching events out of 105 mass coral moralities were reported between , compared with only three bleaching events among 63 mass coral moralities recorded during the preceding 103 years. Nearly all of the world s major coral reef regions (Caribbean/ western Atlantic, eastern Pacific, central and western Pacific, Indian Ocean, Arabian Gulf, Red Sea) experienced some degree of coral bleaching and mortality during the 1980s. Prior to the 1980s, most mass coral moralities were related to non-thermal disturbances such as storms, aerial exposures during extreme low tides, and Acanthaster outbreaks. Coral bleaching accompanied some of the mortality events prior to the 1980s during periods of elevated sea water temperature, but these disturbances were geographically isolated and restricted to particular reefs zones. In contrast, many of the coral bleaching events observed in the 1980s occurred over large geographic regions and at all depths. Most of the coral reef bleaching events of the 1980s occurred during years of large-scale ENSO activity. In 1998, the worst coral bleaching in 700 years struck the Great Barrier Reef, followed by an even worse bleaching only 4 years later. Massive areas of corals were affected all over the world. In Australia alone, the 2002 bleaching saw nearly 60 per cent of the reef suffer bleaching and, in the worst areas, 90% of the coral was bleached. Aerial surveys of more than 640 reefs found that nearly 55% of the reef area in the Great Barrier Reef Marine Park showed some degree of bleaching as a result of heat-stress. Not all reefs bleached as severely as others and the impacts of bleaching were not evenly distributed throughout the Great Barrier Reef. The coral bleaching event in 2002 event was considered worse than the 1998 event because more reef area was affected. The most severe bleaching occurred on reefs closest to shore in both bleaching events, but the 2002 event affected a greater area of reefs further offshore. references: Baker, Andre, Peter Glynn & Bernhard Riegl. Climate change and coral reef bleaching: An ecological assessment of longterm impacts, recovery trends and future outlook. Estuarine, Coastal and Shelf Science Feb

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7 Coral reefs generate billions of dollars in fishing and tourism. Tourism is the fastest growing industry in the world, and coral reef tourism generates billions in areas such as Florida and Australia, which would greatly affect these areas. Coral reefs protect coasts from strong currents and waves by providing a barrier that slows water down before it reaches the shore. The costs of repairing damage from water currents are great and definitely increase with the destruction of coral reefs. Globally, reefs generate about $30 billion annually in fishing, tourism, and protection to coasts from storm surges. Coral are very important in controlling how much carbon dioxide is in the ocean water. Coral polyps turn carbon dioxide in the water into a limestone shell. without coral, the amount of carbon dioxide in the water would rise dramatically, and the acidity of the world s oceans would increase and threaten the future of our coral reef ecosystems. Coral reefs provide protection and shelter for many different species of fish. In terms of biodiversity, coral reefs are often compared with tropical rain forests. Coral reefs shelter and nourish up to 9 million species (a third of all known marine life forms) including 4000 kinds of fish. Examples of animals that rely on coral reefs include parrotfish, butterflyfish, sponges, shrimp, starfish, sea urchins, sea turtles, and many others. SOURCES

8 What is being done? 1. by governments MPAs Biosphere reserves Marine parks and world heritage sites Coral restoration methods 2. by people Adjust personal habits to be more conscious of reefs Actively go out to help coral reefs

9 1. 2. By governments Implementation of Marine Protected Areas (MPAs). they are a lot like national parks and wildlife refuges, in that potentially damaging extraction activies are prohibited. objectives are both social and biological, including restoration of coral reefs, aesthetic maintenance, increased and protected biodiversity, and economic benefits. Biosphere reserves are other protected areas that may protect reefs Marine parks and world heritage sites can provide protection for coral reefs. Low voltage electrical currents applied throuhg seawater crystallizes dissolved minerals onto steel structures In large restoration projects, depending on type of coral, placement of propogated hermatype coral through the use of metal pins are used. Also to restore large sections of broken coral reef, concrete has also been used. Special structures such as reef balls can be placed to provide corals a ground base to grow on. By citizens People who live near reefs are being encouraged to- Conserve water, use ecological or organic fertilizers, help reduce pollution, dispose of trash properly, support reef-friendly businesses, dont touch reefs, practice safe/responsible diving and snorkeling Volunteer for coral reef cleanup, contact government representatives SOURCES

10 Other The most prominent reasons are sea water temperature change and solar radiation. The most severe coral bleaching areas are: Caribbean/ western Atlantic and western Pacific. Coral reefs impact: fishing, tourism, carbon dioxide levels in the ocean, and the surrounding ocean biosphere Both the government and everyday citizens are encouraged to do their part in protecting coral reefs

11 Coral reefs are important for many different reasons. Apart from protecting the shoreline from the damaging effects of the ocean, they provide habitats and shelter for many organisms and are the source of nitrogen and other nutrients essential for the food chain. If a global warming trend impacts on shallow tropical and subtropical seas, we may expect an increase in the frequency, severity and scale of coral reef bleaching. Coral mortality could exceed 95% regionally with species extirpation and extinctions. A conservative temperature increase of 1-2 degrees C would cause regions between degrees N to experience sustained warming that falls within the lethal limits of most reef-building coral species. In conjunction with sea temperature rise would be a sea level rise, and it has been suggested that sea level rise would suppress coral growth or kill many corals through drowning or lower light levels. Some coral populations and their endosymbiotic zooxanthellae may be able to adapt to the extreme conditions predicted during global climate change. Refuges in benign habitats, such as deep, sunlit reef substrates, oceanic shoals and relatively high latitude locations, might exist, but widespread coral mortality and reef decline would be expected in shallow reef zones in most low latitude. Even if significant sea warming and elevated irradiance levels do not occur, coral reef degradation from anthropogenic pollution and overexploitation will still continue, a result of unrelenting human population growth. Coral reefs impact the fishing and tourism industries, as well as provide protection to coastal regions from storm surges. Furthermore, they are important in controlling the ocean s carbon dioxide levels and are home and shelter to a large part of the ocean biosphere that they are a part of. There are several ways people are trying to help damage to coral reefs. One way is through government programs to protect and restore the reefs, and another way is by encouraging everyday citizens who live near the reefs to adjust their daily habits to benefit the reefs, as well as speak out and voice their support for protecting the reefs.