Coral bleaching

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Coral bleaching occurs when coral polyps expel algae living in their tissues. Normally, coral polyps living in endosymbiotic relationships with algae are important for coral and coral health. Algae provide up to 90% of the energy of the reef. Lightened corals continue to live but begin to starve after bleaching. Some corals recovered.

The above average sea-level temperatures caused by global warming are the main causes of coral bleaching. According to the United Nations Environment Program, between 2014 and 2016, the longest recorded global bleaching event has killed corals on an unprecedented scale. In 2016, coral bleaching at the Great Barrier Reef killed between 29 and 50 percent of coral reefs. In 2017, bleaching extends into the reef center region. The average interval between whitening events has been halved between 1980 and 2016.

Video Coral bleaching

Cause

The coral reefs that form large tropical coral reef ecosystems depend on symbiotic relationships with protozoa flagell protozoa with algae winged called zooxanthellae that live within their tissues and colorize the reef. Zooxanthellae provides corals with nutrients through photosynthesis, an important factor in clear and nutrient-poor tropical waters. Instead, corals provide zooxanthellae with the carbon dioxide and ammonium needed for photosynthesis. Negative environmental conditions thwart the ability of corals to meet the needs of zooxanthellae. To ensure short-term survival, coral polyps then repel zooxanthellae. This leads to a brighter or wholly white appearance, hence the term "bleached". Because zooxanthellae provides up to 90% of coral energy needs through photosynthesis products, after removing, corals may begin to starve.

Corals can withstand short-term disturbances, but if conditions leading to the expulsion of zooxanthellae persist, chances of survival reefs diminish. To recover from bleaching, the zooxanthellae must reenter the coral polyp network and restart photosynthesis to maintain the overall reef and the ecosystems that depend on it. If coral polyps die of starvation after bleaching, they will rot. Hard coral species will then abandon their calcium carbonate framework, which will be taken over by algae, which effectively inhibit reef growth. Finally, the coral framework will erode, causing the coral structure to collapse.

Maps Coral bleaching

Triggers

Coral bleaching can be caused by a number of factors. While local triggers lead to local bleaching, large-scale coral bleaching events in recent years have been fueled by rising sea surface temperatures. Coral reefs located in warm shallow waters with low water flow are more affected than reefs located in areas with higher water flow.

List of triggers

• increase in water temperature (most often due to global warming), or decrease in water temperature
• oxygen starvation caused by increased levels of zooplankton as a result of overfishing
• increase solar radiation (photosynthesis and ultraviolet radiation)
• increased sedimentation (due to mudflow)
• bacterial infection
• salinity change
• herbicide
• is retroactively and exposed
• cyanide fishing
• sea level elevation due to global warming (Watson)
• mineral dust from African dust storms caused by drought
• pollutants such as oxybenzone, butylparaben, octyl methoxycinnamate, or enzacamene: four common non-biodegradable sunscreens and can cleanse skin
• Ocean acidification due to elevated CO ₂ levels caused by air pollution
• Exposed to Oil or other chemical spills

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Bulk bleaching event

High sea water temperatures are the main cause of mass bleaching. Sixty major episodes of coral bleaching occurred between 1979 and 1990, with coral-related mortality affecting coral reefs in every part of the world. In 2016, the longest coral bleaching event was recorded. The longest and most destructive coral bleaching event is due to El Nià ± o occurring from 2014-2017. During this time, more than 70% of coral reefs around the world have become damaged.

Factors that affect the outcome of bleaching events include stress-reducing stresses, tolerance for the absence of zooxanthellae, and how quickly new corals grow to replace the dead. Due to the uneven nature of bleaching, local climatic conditions such as shadows or cooler water flow may reduce the incidence of bleaching. Corals and health of zooxanthellae and genetics also affect bleaching.

Large coral colonies such as Porites are able to withstand extreme temperature shocks, while fragile branched corals like Acropora are much more susceptible to stress after temperature changes. Corals that are consistently exposed to low stress levels may be more resistant to bleaching.

Scientists believe that the oldest known bleaching is that of the Devonian End (Frasnian/Famennian), also triggered by rising sea surface temperatures. This resulted in the death of the largest coral reef in Earth's history.

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Impact

In the period 2012-2040, coral reefs are expected to experience more bleaching events. The Intergovernmental Panel on Climate Change (IPCC) sees this as the biggest threat to the world's coral reef system. Coral reefs around the world are gone by 19%, and 60% of the remaining coral reefs are at risk of disappearing. There are several ways to know the impact of coral bleaching on coral reefs. First by coral cover, the more corals that cover the soil the less the impact of bleaching it has. Second, the abundance of coral, which is the number of different living species on the coral reefs. (Shidqi et al 2017)

Pacific Ocean

Great Barrier Reef

The Great Barrier Reef along the Australian coast experienced a bleaching event in 1980, 1982, 1992, 1994, 1998, 2002, 2006, 2016 and 2017. Some locations suffered severe damage, with mortality rates up to 90%. The most widespread and intense events occurred in the summer of 1998 and 2002, with 42% and 54% of coral reefs turned white each, and 18% very white. But the loss of corals on the reefs between 1995 and 2009 was largely offset by the growth of new corals. The overall reef loss analysis found that the reef population on the Great Barrier Reef had decreased 50.7% from 1985 to 2012, but only about 10% of the decline was due to bleaching, and the remaining 90% was due to tropical cyclones and by predation by star crowns sea. Global bulk coral bleaching has occurred since 2014 due to the highest temperatures recorded in the oceans. This temperature has caused the most severe and widespread coral bleaching ever recorded on the Great Barrier Reef. The most severe bleaching in 2016 occurred near Port Douglas. At the end of November 2016 a survey of 62 reefs indicated that long-term heat stress from climate change led to a 29% loss of shallow reefs. The highest coral mortality and loss of reef habitat are on the beaches and reefs around Cape Grenville and Princess Charlotte Bay. The IPCC moderate heating scenario (B1 to A1T, 2 Â ° C in 2100, IPCC, 2007, Table SPM.3, p.1 13) estimates that reefs in the Great Barrier Reef are highly likely to regularly experience high thermal temperatures to induce bleaching.

Hawaii

Great bleaching took place on the coral reefs of Hawaii in 1996 and in 2002. In 2014, biologists from the University of Queensland observed the first mass bleaching event, and linked it to The Blob. In 2014 and 2015, a survey at the Hanauma Bay Nature Preserve in Oahu found 47% of coral reef bleaching and nearly 10% dead corals.

Japanese

According to a Japanese government report of 2017, nearly 75% of Japan's largest coral reefs in Okinawa have died from bleaching.

Indian Ocean

The province of coral reefs has been permanently damaged by the warmest temperatures of the ocean, the most severe in the Indian Ocean. Up to 90% of coral cover has been lost in the Maldives, Sri Lanka, Kenya and Tanzania and in the Seychelles during the 1997-98 massive bleaching event. Maldives

More than 60% of reefs in the Maldives have been bleached by 2016.

Thai

Thailand suffered severe bulk bleaching in 2010 affecting 70% of corals in the Andaman Sea. Between 30% and 95% of the dead white corals.

Indonesia

In 2017 there are studies conducted on two islands in Indonesia to see how their corals are closing. One of them is Melinjo Island and the other is Pulau Saktu. On Pulau Saktu lifeform conditions were categorized as bad, with average coral covering 22.3%. In the Melinjo Islands lifeform conditions were categorized as bad, with average coral covering 22.2%. (Shidqi et al 2017)

Atlantic Ocean

United States

In South Florida, a 2016 large coral survey from Key Biscayne to Fort Lauderdale found that about 66% of corals died or reduced to less than half of their living tissue.

Belize

The first recorded massive bleaching event to occur in Belize Barrier Reef was in 1998, where sea-surface temperatures reached up to 31.5 ° C (88.7 ° F) from 10 August to 14 October. For several days, Hurricane Mitch brought a stormy weather on October 27 but only reduced the temperature to 1 degree or less. During this period, mass bleaching in front of reefs and lagoons occurred. While some coral colonies previously were damaged, coral mortality in the lagoon was a major disaster.

The most common coral in Belize reef in 1998 was the lettuce coral, Agaricia tenuifolia. On 22 and 23 October, the survey was conducted in two locations and the findings were devastating. Almost all live corals are whitened white and their skeletons show that they have died recently. On the floor of the lagoon, complete bleaching is seen among Agaricia tenuifolia. Furthermore, surveys conducted in 1999 and 2000 show almost total agaricia mortality in tenuifolia at all depths. A similar pattern occurs in other reef species as well. Measurements in the turbidity of water show that this death is associated with an increase in water temperature rather than solar radiation.

Caribbean

Hard coral cover on coral reefs in the Caribbean has declined by about 80%, from an average 50% cover in the 1970s to only about 10% in the early 2000s. A 2013 study to follow up on a mass bleaching event in Tobago from 2010 showed that after just 1 year, the majority of dominant species decreased by about 62% while coral abundance decreased by about 50%. However, between 2011 and 2013, coral cover increased for 10 of the 26 dominant species but decreased for 5 other populations.

More areas

Reefs in the Southern Red Sea are not white even though the water temperature in summer reaches 34 ° C (93 ° F). Red coral bleaching in the Red Sea is more common in the northern part of coral reefs, the southern part of coral reefs has been plagued by starfish eating, dynamite fishing and human impact on the environment. In 1988 there was a massive bleaching event affecting coral reefs in Saudi Arabia and in Sudan, the southern reefs were tougher and had very little influence on them. Earlier it was estimated that North Korea suffered more because of coral bleaching but they showed fast coral reefs and southern reefs considered not to suffer from rough bleaching, they showed more consistency. However, new research shows where the southern coral should be bigger and healthier than the northern part is not. It is believed to be due to major disruptions in recent history of bleaching events, and corals eating starfish. In 2010, coral bleaching occurred in Saudi Arabia and Sudan, where temperatures rose 10 to 11 degrees. Certain taxa experience 80% to 100% of the bleaching of the colony, while others show an average of 20% of the taxa bleaching.

Economic and political impact

According to Brian Skoloff from the Christian Science Monitor, if the reefs disappear, experts say starvation, poverty and political instability can happen. Because countless marine life depends on the reef for protection and protection from predators, the extinction of reefs will eventually create a domino effect that will trickle into many human societies that depend on the fish for food and livelihoods. There has been a 44% decline over the last 20 years in Florida Keys, and up to 80% in the Caribbean alone.

Coral reefs provide a variety of ecosystem services, one of which is natural fisheries, as many commercial fish often lay their eggs or live their teenagers on coral reefs around the tropics. Thus, coral reefs are popular fishing sites and are an important source of income for fishermen, especially small local fisheries. As coral habitat habitat declines due to bleaching, the associated reef fish populations are also reduced, affecting fishing opportunities. A model from one study by Speers et al. calculated direct losses to fisheries from a coral cover decrease to about $ 49- $ 69 billion, if human societies continue to emit high levels of greenhouse gases. But, these losses can be reduced to a consumer surplus benefit of about $ 14- $ 20 billion, if people choose to emit lower levels of greenhouse gases instead. These economic losses also have important political implications, as they fall disproportionately in the developing countries where coral reefs are located, namely in Southeast Asia and around the Indian Ocean. It would be more costly for countries in the region to respond to the loss of coral reefs as they have to switch to different sources of income and food, in addition to losing the services of other ecosystems such as ecotourism. A study completed by Chen et al. suggests that the commercial value of reefs is reduced by almost 4% each time coral cover is reduced by 1% due to losses in ecotourism and other outdoor recreational activities.

Coral reefs also act as a protective barrier for shorelines by reducing the impact of waves, which decreases damage from storms, erosion, and flooding. Countries that lose this natural protection will lose more money due to increased storm vulnerability. These indirect costs, combined with lost incomes in tourism, will generate enormous economic effects.

Monitor reef sea surface temperature

The US National Oceanic and Atmospheric Administration Monitor (NOAA) monitors bleaching "hot spots", areas where sea-surface temperatures rise 1 Ã,  ° C or more above the long-term monthly average. The "hot spot" is the location where thermal stress is measured and with the development of Degree of Heating Degree (DHW), thermal stress of coral reefs is monitored. Global coral bleaching is detected early due to remote satellite sensing to sea temperature rise. It is necessary to monitor high temperatures because coral bleaching events affect coral reef reproduction and normal growth capacity, as well as weaken the corals, leading eventually to their death. This system detected worldwide bleaching events in 1998, which was associated with the El Nià ± o 1997-98 event. Currently, 190 coral reef sites around the world are monitored by NOAA, and send alerts to reef research scientists and managers via the NOAA Coral Reef Watch (CRW) website. By monitoring warming of sea temperatures, early warning of coral bleaching, inform coral reef managers to prepare and draw awareness of future bleaching events. The first mass global bleaching event was recorded in 1998 and 2010, which, when El Nià ± o caused the temperature of the ocean to rise and worsen the coral reef conditions. El NiÃÆ'  ± o 2014-2017 is listed as the longest and most destructive coral, which destroys more than 70% of our coral reefs. More than two thirds of the Great Barrier Reef is reported to have bleached or died.

Chemical change of the oceans

Increasing ocean acidification due to rising carbon dioxide levels exacerbates the effects of thermal stress bleaching. Acidity affects the ability of corals to create calcareous skeletons, essential for their survival. This is because ocean acidification reduces the amount of carbonate ions in the water, making it harder for the reef to absorb the calcium carbonate they need for the skeleton. As a result, coral resistance decreases, while it becomes easier for them to erode and dissolve. Additionally, an increase in CO ₂ allows fish herbivores and excessive nutrification to transform coral-dominated ecosystems into alga-dominated ecosystems. A recent study from the Atkinson Center for the Sustainable Future found that with a combination of acidification and temperature rise, the CO ₂ level could be too high for corals to survive in just 50 years.

Infectious diseases

The infectious bacteria of the species Vibrio shiloi are the Oculina patagonica bleaching agents in the Mediterranean Sea, causing this effect by attacking zooxanthellae. V. shiloi is only transmitted during warm periods. Increased temperature increases virulence V. shiloi , which then becomes able to adhere to receptors containing beta-galactoside on the surface of mucus from host corals. V. shiloi then penetrates the coral epidermis, multiplies, and produces heat-sensitive and heat-sensitive toxins, which affect zooxanthellae by inhibiting photosynthesis and causing lysis.

During the summer of 2003, coral reefs in the Mediterranean Sea seemed to gain resistance to pathogens, and further infections were not observed. The main hypothesis for the emerging resistance is the existence of a symbiotic community of protective bacteria living on corals. The lyophilic bacteria species V. shiloi have not been identified in 2011.

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Coral adaptation

In 2010, researchers at Penn State discovered the growing corals while using an unusual symbiotic alga species in the warm waters of the Andaman Sea in the Indian Ocean. Normal Zooxanthellae can not withstand the high temperatures there, so this finding is unexpected. This gives researchers hope that with rising temperatures due to global warming, coral reefs will develop tolerance for different species of symbiotic algae that are resistant to high temperatures, and can live on the reef. In 2010, researchers from Stanford University also found reefs around the Samoan Islands that experienced drastic temperature increases for about four hours a day during low tide. The corals do not bleach or die irrespective of the elevated heat. Studies show that corals off the coast of Ofu Island near American Samoa have been trained to withstand high temperatures. Researchers are now asking a new question: can we condition reefs, which are not from this region, in this way and slowly introduce them to higher temperatures for short periods of time and make them more resistant to rising ocean temperatures.

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Recovery and change of macroalgal regime

After the corals experience a bleaching event to increase the temperature, some reefs can return to their original state, prior to bleaching. The corals are well recovered from bleaching, where they are colonized by zooxanthellae, or they experience regenerative shifts, where previously coral reefs evolved were taken over by thick layers of macroalgae. This inhibits further coral growth because algae produce antifouling compounds to prevent settlements and compete with corals for space and light. As a result, the macroalgae form a stable community that makes corals difficult to grow again. Coral will then be more susceptible to other problems, such as decreasing water quality and removal of herbivorous fish, as coral growth is weaker. Finding what causes corals to be resilient or recovered from bleaching events is of utmost importance as it helps inform conservation efforts and protect corals more effectively.

Corals proved to be resistant to short-term disturbances. Recovery has been shown after the storm disorder and the crown of thorns of starfish invasion. Fish species tend to be better off following reef disturbances than coral species because corals exhibit limited recovery and coral fish collection has shown little change as a result of short-term disturbance. In contrast, fish batches on bleached reefs exhibit potentially damaging changes. One study by Bellwood et al . notes that while species richness, diversity, and abundance are unchanged, fish stocks contain more common species and species less dependent on corals. Responses to coral bleaching vary among reef fish species, based on which resources are affected. Rising sea temperatures and coral bleaching do not have a direct impact on adult mortality, but there are many indirect consequences of both. Coral-associated fish populations tend to decrease due to habitat loss; However, some herbivorous fish populations have increased dramatically due to increased colonization of algae on dead corals. The study notes that better methods are needed to measure the effects of disturbances on coral resistance.

To date, the factors that mediate coral reef recovery from bleaching have not been well studied. Research by Graham et al. (2005) studied 21 coral reefs around the Seychelles in the Indo-Pacific to document the long-term effects of coral bleaching. After losing more than 90% of corals due to bleaching in 1998 about 50% of coral reefs recovered and about 40% of the reefs shifted regimes to predominantly macroalgae compositions. Following assessment of factors affecting the likelihood of recovery, the study identified five major factors: adolescent coral density, initial structural complexity, water depth, herbivorous fish biomass, and nutritional conditions on the reef. Overall, resistance is seen most in coral reef systems that are structurally complex and deeper in water.

The role of ecology and functional groups of species also play a role in restoring the potential for regime shifts in coral reef systems. Coral reefs are influenced by bioeroding, scraping, and grazing species. The bioeroding species removes dead corals, scavenging species removing algae and sediments for further future growth, grazing species removing algae. The presence of any species may affect the ability to normal levels of coral recruitment which are an essential part of coral recovery. Lowering the number of grazing species after coral bleaching in the Caribbean has been likened to a system dominated by sea-hedgehogs that have not shifted the regime to a meat-dominated macroalgae.

There is always the possibility of changes that can not be observed, or a vague loss or resilience, in the ability of the coral community to perform ecological processes. Losing these secrets can lead to unexpected regime changes or ecological changes. More detailed methods to determine the health of coral reefs that take account of long-term changes to coral ecosystems and better conservation policies are needed to protect coral reefs in the coming years.

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Rebuilding coral reef

Research is underway to help slow coral mortality. The Worldwide Project is being completed to help fill and restore our coral reefs. Coral populations are rapidly declining, allowing scientists to experiment in coral growth and research tanks to help populate corals. These research tanks mimic the natural environment of coral reefs in the oceans. They plant corals in this tank to use as their experiments, so no more corals are damaged or taken from the ocean. They also transplanted successful corals from a research tank and place them in a sea area where coral reefs are dying. Experiments are underway at several coral growth tanks and research by Ruth Gates and Madelaine Van Oppen. They are trying to create a "super reef" that can withstand some of the environmental factors that are currently being killed by corals. Van Oppen is also working on developing a kind of alga that will have a symbiotic relationship with the reef and can withstand water temperature fluctuations for long periods of time. This project might help refuel our coral reefs, but the coral growth process in the research tank is very time consuming. It takes at least 10 years for corals to fully grow and mature enough where they will be able to multiply.

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Economic value of coral reef

Coral reefs provide goods and services to about a quarter of all marine species. Experts estimate that coral reef services cost up to $ 1.2 million per hectare, which averages $ 172 billion annually. The benefits of coral reefs include the provision of physical structures such as coastal shoreline protection, biotic services within and between ecosystems, biogeochemical services such as maintaining nitrogen levels in the oceans, climate records, and recreational and commercial services (tourism). Coral reefs are one of the best marine ecosystems to use as food sources. Coral reefs are also a perfect habitat for rare and economically important tropical fish species, as they provide the perfect area for fish to breed and make nurseries in. If fish and coral populations on the reef are high, then we can use the area as a place to collect food and items with medicinal properties, which also help create jobs for people who can collect these specimens. Coral reefs also have some cultural interest in certain areas around the world.

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Cost benefit analysis to reduce coral loss

In 2010, the Convention on Biodiversity Strategic Plan (CBD) 2011-2020 created twenty different targets for sustainable development for post-2015. Target 10 indicates the goal of minimizing "anthropogenic stress on coral reefs". Two programs are seen, one that reduces the loss of coral reefs by 50% which has a capital cost of $ 684 million and a recurring fee of $ 81 million. Another program reduces coral losses by 80% and has a capital cost of $ 1,036 million with recurrent costs of $ 130 million. The CBD recognizes that they may underestimate the costs and resources required to achieve these targets due to the lack of relevant data but nevertheless, the cost-benefit analysis shows that benefits outweigh the costs by a sufficiently large amount for both programs (Benefit Cost Ratio of 95.3 and 98.5) that "there is vast space to increase spending on coral protection and still achieve a benefit-to-cost ratio of more than one".

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See also

• Climate change
• Coral reef
• Ove Hoegh-Guldberg (biologist)

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Note

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References

• Watson ME (2011). "Coral reefs". At Allin CW. Encyclopedia of environmental issues . 1 . Pasadena, Calif.: Salem Press. pp.Ã, 317-318. ISBN: 978-1-58765-735-1.

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External links

• Great Barrier Reef Marine Authorization Park Information about bleaching.
• ReefBase: a global information system on coral reefs.
• More details on coral bleaching, causes and effects.
• Tourist Impressions
• The relationship between overfishing and mass coral bleaching
• Discussions on overfishing and coral bleaching
• Social & amp; Economic Cost of Coral Bleaching from the "NOAA Socioeconomics" website initiative
• Microdocs: Coral bleaching
• Coral Bleaching at Maro Reef, September 2004

Source of the article : Wikipedia