Coral bleaching occurs when coral polyps expel algae that live inside their tissues. Normally, coral polyps live in an endosymbiotic relationship with this algae crucial for the health of the coral and the reef. The algae provides up to 90 percent of the coral's energy. Bleached corals continue to live but begin to starve after bleaching. Some corals recover.
Above-average sea water temperatures caused by global warming is the leading cause of coral bleaching. According to the United Nations Environment Programme, between 2014 and 2016 the longest recorded global bleaching events killed coral on an unprecedented scale. In 2016, bleaching of coral on the Great Barrier Reef killed between 29 and 50 percent of the reef's coral. In 2017, the bleaching extended into the central region of the reef. The average interval between bleaching events has halved between 1980 and 2016.
The corals that form the great reef ecosystems of tropical seas depend upon a symbiotic relationship with algae-like single-celled flagellate protozoa called zooxanthellae that live within their tissues and give the coral its coloration. The zooxanthellae provide the coral with nutrients through photosynthesis, a crucial factor in the clear and nutrient-poor tropical waters. In exchange, the coral provide the zooxanthellae with the carbon dioxide and ammonium needed for photosynthesis. Negative environmental conditions thwart the coral's ability to provide for the zooxanthellae's needs. To ensure short-term survival, the coral-polyp then expels the zooxanthellae. This leads to a lighter or completely white appearance, hence the term "bleached". As the zooxanthellae provide up to 90 percent of the coral's energy needs through products of photosynthesis, after expelling, the coral may begin to starve.
Coral can survive short-term disturbances, but if the conditions that lead to the expulsion of the zooxanthellae persist, the coral's chances of survival diminish. In order to recover from bleaching, the zooxanthellae have to re-enter the tissues of the coral polyps and restart photosynthesis to sustain the coral as a whole and the ecosystem that depends on it. If the coral polyps die of starvation after bleaching, they will decay. The hard coral species will then leave behind their calcium carbonate skeletons, which will be taken over by algae, effectively blocking coral re-growth. Eventually, the coral skeletons will erode, causing the reef structure to collapse.
Coral bleaching may be caused by a number of factors. While localized triggers lead to localized bleaching, the large scale coral bleaching events of the recent years have been triggered by global warming. Under increased carbon dioxide concentration expected in the 21st century, corals are expected to becoming increasingly rare on reef systems. Coral reefs located in warm, shallow water with low water flow have been more affected than reefs located in areas with higher water flow.
Elevated sea water temperatures are the main cause of mass bleaching events. Sixty major episodes of coral bleaching have occurred between 1979 and 1990, with the associated coral mortality affecting reefs in every part of the world. In 2016, the longest coral bleaching event was recorded. The longest and most destructive coral bleaching event was because of the El Niño that occurred from 2014–2017. During this time, over 70 percent of the coral reefs around the world have become damaged.
Factors that influence the outcome of a bleaching event include stress-resistance which reduces bleaching, tolerance to the absence of zooxanthellae, and how quickly new coral grows to replace the dead. Due to the patchy nature of bleaching, local climatic conditions such as shade or a stream of cooler water can reduce bleaching incidence. Coral and zooxanthellae health and genetics also influence bleaching.
Large coral colonies such as Porites are able to withstand extreme temperature shocks, while fragile branching corals such Acropora are far more susceptible to stress following a temperature change. Corals consistently exposed to low stress levels may be more resistant to bleaching.
Scientists believe that the oldest known bleaching was that of the Late Devonian (Frasnian/Famennian), also triggered by the rise of sea surface temperatures. It resulted in the demise of the largest coral reefs in the Earth's history.
According to Clive Wilkinson of Global Coral Reef Monitoring Network of Townsville Australia ,in 1998 the mass bleaching event occurred the indian ocean region worst affected by it due to rising of temperature of sea by 2℃ to normal temperature level coupled by strong El nino event in 1997-1998.
In the 2012–2040 period, coral reefs are expected to experience more frequent bleaching events. The Intergovernmental Panel on Climate Change (IPCC) sees this as the greatest threat to the world's reef systems. Coral reefs worldwide were lost by 19 percent, and 60 percent of the remaining reefs are at immediate risk of being lost. There are a few ways to tell the impacts of coral bleaching on reefs. First by the coral cover, the more coral that is covering the ground the less of an impact bleaching had. Second, coral abundance, which is the number of different living species on the coral reef. With the increase of coral bleaching events worldwide, In 2017, the National Geographic proposed "In the past three years, 25 reefs—which comprise three-fourths of the world’s reef systems— experienced severe bleaching events in what scientists concluded was the worst-ever sequence of bleachings to date." 
The Great Barrier Reef along the coast of Australia experienced bleaching events in 1980, 1982, 1992, 1994, 1998, 2002, 2006, 2016 and 2017. Some locations suffered severe damage, with up to 90% mortality. The most widespread and intense events occurred in the summers of 1998 and 2002, with 42% and 54% respectively of reefs bleached to some extent, and 18% strongly bleached. However coral losses on the reef between 1995 and 2009 were largely offset by growth of new corals. An overall analysis of coral loss found that coral populations on the Great Barrier Reef had declined by 50.7% from 1985 to 2012, but with only about 10% of that decline attributable to bleaching, and the remaining 90% caused about equally by tropical cyclones and by predation by crown-of-thorns starfishes. A global mass coral bleaching has been occurring since 2014 because of the highest recorded temperatures plaguing oceans. These temperatures have caused the most severe and widespread coral bleaching ever recorded in the Great Barrier reef. The most severe bleaching in 2016 occurred near Port Douglas. In late November 2016 surveys of 62 reefs showed that long term heat stress from climate change caused a 29% loss of shallow water coral. The highest coral death and reef habitat loss was inshore and mid-shelf reefs around Cape Grenville and Princess Charlotte Bay. The IPCC's moderate warming scenarios (B1 to A1T, 2 °C by 2100, IPCC, 2007, Table SPM.3, p. 13) forecast that corals on the Great Barrier Reef are very likely to regularly experience summer temperatures high enough to induce bleaching.
Major bleaching occurred in Hawaiian coral reefs in 1996 and in 2002. In 2014, biologists from the University of Queensland observed the first mass bleaching event, and attributed it to The Blob. In 2014 and 2015, a survey in Hanauma Bay Nature Preserve on Oahu found 47% of the corals suffering from coral bleaching and close to 10% of the corals dying. In 2014 and 2015, 56% of the coral reefs of the big island were affected by coral bleaching events. During the same period, 44% of the corals on west Maui were effected. On January 24, 2019, scientists with The Nature Conservancy found that the reefs had begun to stabilize nearly 4 years after the last bleaching event.
Eight severe and two moderate bleaching events occurred between 1960 and 2016 in the coral community in Jarvis Island, with the 2015-16 bleaching displaying the unprecedented severity in the record.
Coral reef provinces have been permanently damaged by warm sea temperatures, most severely 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 massive 1997–98 bleaching event.
In 2017 there was a study done on two islands in Indonesia to see how their coral cover was. One of the places was Melinjo Islands and the other was Saktu Islands. In Saktu Island the lifeform conditions were categorized as bad, with an average coral cover of 22.3%. In Melinjo Islands the lifeform conditions were categorized as bad, with an average coral cover of 22.2%.
The first recorded mass bleaching event that took place in the Belize Barrier Reef was in 1998, where sea level temperatures reached up to 31.5 °C (88.7 °F) from 10 August to 14 October. For a few days, Hurricane Mitch brought in stormy weather on 27 October but only reduced temperatures by 1 degree or less. During this time period, mass bleaching in the fore-reef and lagoon occurred. While some fore reef colonies suffered some damage, coral mortality in the lagoon was catastrophic.
The most prevalent coral in the reefs Belize in 1998 was the lettuce coral, Agaricia tenuifolia. On 22 and 23 October, surveys were conducted at two sites and the findings were devastating. Virtually all the living coral was bleached white and their skeletons indicated that they had died recently. At the lagoon floor, complete bleaching was evident among A. tenuifolia. Furthermore, surveys done in 1999 and 2000 showed a near total mortality of A. tenuifolia at all depths. Similar patterns occurred in other coral species as well. Measurements on water turbidity suggest that these mortalities were attributed to rising water temperatures rather than solar radiation.
Hard coral cover on reefs in the Caribbean have declined by an estimated 80%, from an average of 50% cover in the 1970s to only about 10% cover in the early 2000s. A 2013 study to follow up on a mass bleaching event in Tobago from 2010 showed that after only 1 year, the majority of the dominant species declined by about 62% while coral abundance declined by about 50%. However, between 2011 and 2013, coral cover increased for 10 of the 26 dominant species but declined for 5 other populations.
Coral in the south Red Sea does not bleach despite summer water temperatures up to 34 °C (93 °F). Coral bleaching in the Red Sea is more common in the northern section of the reefs, the southern part of the reef has been plagued by coral eating starfish, dynamite fishing and human impacts on the environment. In 1988 there was a massive bleaching event that affected the reefs in Saudi Arabia and in Sudan, the southern reefs were more resilient and affected them very little. Previously it was thought that the North suffers more from coral bleaching but they show a fast turnover of coral and the southern reef was thought to not suffer from bleaching as harshly, they show more consistency. However, new research shows where the south reef should be bigger and healthier than the north it was not. This is believed to be because of major disturbances in recent history from bleaching events, and coral eating starfish. In 2010, coral bleaching occurred in Saudi Arabia and Sudan, where the temperature rose 10 to 11 degrees. Certain taxa experienced 80% to 100% of their colonies bleaching, while some showed on average 20% of that taxa bleaching.
According to Brian Skoloff of The Christian Science Monitor, "If the reefs vanished, experts say, hunger, poverty and political instability could ensue." Since countless sea life depend on the reefs for shelter and protection from predators, the extinction of the reefs would ultimately create a domino effect that would trickle down to the many human societies that depend on those fish for food and livelihood. There has been a 44% decline over the last 20 years in the Florida Keys, and up to 80% in the Caribbean alone.
Coral reefs provide various ecosystem services, one of which is being a natural fishery, as many frequently consumed commercial fish spawn or live out their juvenile lives in coral reefs around the tropics. Thus, reefs are a popular fishing site and are an important source of income for fishers, especially small, local fisheries. As coral reef habitat decreases due to bleaching, reef associated fish populations also decrease, which affects fishing opportunities. A model from one study by Speers et al. calculated direct losses to fisheries from decreased coral cover to be around $49 – $69 billion, if human societies continue to emit high levels of greenhouse gases. But, these losses could be reduced for a consumer surplus benefit of about $14 – $20 billion, if societies chose to emit a lower level of greenhouse gases instead. These economic losses also have important political implications, as they fall disproportionately on developing countries where the reefs are located, namely in Southeast Asia and around the Indian Ocean. It would cost more for countries in these areas to respond to coral reef loss as they would need to turn to different sources of income and food, in addition to losing other ecosystem services such as ecotourism. A study completed by Chen et al. suggested that the commercial value of reefs decreases by almost 4% every time coral cover decreases by 1% because of losses in ecotourism and other potential outdoor recreational activities.
Coral reefs also act as a protective barrier for coastlines by reducing wave impact, which lowers the damage from storms, erosions, and flooding. Countries that lose this natural protection will lose more money because of the increased susceptibility of storms. This indirect cost, combined with the lost revenue in tourism, will result in enormous economic effects.
The US National Oceanic and Atmospheric Administration (NOAA) monitors for bleaching "hot spots", areas where sea surface temperature rises 1 °C or more above the long-term monthly average. The "hot spots" are the location in which thermal stress is measured and with the development of Degree Heating Week (DHW), the coral reef's thermal stress is monitored. Global coral bleaching is being detected earlier due to the satellite remote sensing the rise of sea temperatures. It is necessary to monitor the high temperatures because coral bleaching events are affecting coral reef reproduction and normal growth capacity, as well as it weakening corals, eventually leading to their mortality. This system detected the worldwide 1998 bleaching event, that corresponded to the 1997–98 El Niño event. Currently, 190 reef sites around the globe are monitored by the NOAA, and send alerts to research scientists and reef managers via NOAA Coral Reef Watch (CRW) website. By monitoring the warming of sea temperatures, the early warnings of coral bleaching, alerts reef managers to prepare and draw awareness to future bleaching events. The first mass global bleaching events were recorded in 1998 and 2010, which was when the El Niño caused the oceans temperatures to rise and worsened the corals living conditions. The 2014–2017 El Niño was recorded to be the longest and most damaging to the corals, which harmed over 70% of our coral reefs. Over two thirds of the Great Barrier Reef have been reported to be bleached or dead. the people didn't lie
Increasing ocean acidification due to rises in carbon dioxide levels exacerbates the bleaching effects of thermal stress. Acidification affects the corals' ability to create calcareous skeletons, essential to their survival. This is because ocean acidification decreases the amount of carbonate ion in the water, making it more difficult for corals to absorb the calcium carbonate they need for the skeleton. As a result, the resilience of reefs goes down, while it becomes easier for them to erode and dissolve. In addition, the increase in CO2 allows herbivore overfishing and nutrification to change coral-dominated ecosystems to algal-dominated ecosystems. A recent study from the Atkinson Center for a Sustainable Future found that with the combination of acidification and temperature rises, the levels of CO2 could become too high for coral to survive in as little as 50 years.
Infectious bacteria of the species Vibrio shiloi are the bleaching agent of Oculina patagonica in the Mediterranean Sea, causing this effect by attacking the zooxanthellae. V. shiloi is infectious only during warm periods. Elevated temperature increases the virulence of V. shiloi, which then become able to adhere to a beta-galactoside-containing receptor in the surface mucus of the host coral. V. shiloi then penetrates the coral's epidermis, multiplies, and produces both heat-stable and heat-sensitive toxins, which affect zooxanthellae by inhibiting photosynthesis and causing lysis.
During the summer of 2003, coral reefs in the Mediterranean Sea appeared to gain resistance to the pathogen, and further infection was not observed. The main hypothesis for the emerged resistance is the presence of symbiotic communities of protective bacteria living in the corals. The bacterial species capable of lysing V. shiloi had not been identified as of 2011.
In 2010, researchers at Penn State discovered corals that were thriving while using an unusual species of symbiotic algae in the warm waters of the Andaman Sea in the Indian Ocean. Normal zooxanthellae cannot withstand temperatures as high as was there, so this finding was 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 temperature, and can live within the reefs. In 2010, researchers from Stanford University also found corals around the Samoan Islands that experience a drastic temperature increase for about four hours a day during low tide. The corals do not bleach or die regardless of the high heat increase. Studies showed that the corals off the coast of Ofu Island near America Samoa have become trained to withstand the high temperatures. Researchers are now asking a new question: can we condition corals, that are not from this area, in this manner and slowly introduce them to higher temperatures for short periods of time and make them more resilient against rising ocean temperatures.
After corals experience a bleaching event to increased temperature stress some reefs are able to return to their original, pre-bleaching state. Reefs either recover from bleaching, where they are recolonized by zooxanthellae, or they experience a regime shift, where previously flourishing coral reefs are taken over by thick layers of macroalgae. This inhibits further coral growth because the algae produces antifouling compounds to deter settlement and competes with corals for space and light. As a result, macroalgae forms stable communities that make it difficult for corals to grow again. Reefs will then be more susceptible to other issues, such as declining water quality and removal of herbivore fish, because coral growth is weaker. Discovering what causes reefs to be resilient or recover from bleaching events is of primary importance because it helps inform conservation efforts and protect coral more effectively.
Corals have shown to be resilient to short-term disturbances. Recovery has been shown in after storm disturbance and crown of thorns starfish invasions. Fish species tend to fare better following reef disturbance than coral species as corals show limited recovery and reef fish assemblages have shown little change as a result of short-term disturbances. In contrast, fish assemblages in reefs that experience bleaching exhibit potentially damaging changes. One study by Bellwood et al. notes that while species richness, diversity, and abundance did not change, fish assemblages contained more generalist species and less coral dependent species. Responses to coral bleaching are diverse between reef fish species, based on what resources are affected. Rising sea temperature and coral bleaching do not directly impact adult fish mortality, but there are many indirect consequences of both. Coral-associated fish populations tend to be in decline due to habitat loss; however, some herbivorous fish populations have seen a drastic increase due to the increase of algae colonization on dead coral. Studies note that better methods are needed to measure the effects of disturbance on the resilience of corals.
Until recently, the factors mediating the recovery of coral reefs from bleaching were not well studied. Research by Graham et al. (2005) studied 21 reefs around Seychelles in the Indo-Pacific in order to document the long-term effects of coral bleaching. After the loss of more than 90% of corals due to bleaching in 1998 around 50% of the reefs recovered and roughly 40% of the reefs experienced regime shifts to macroalgae dominated compositions. After an assessment of factors influencing the probability of recovery, the study identified five major factors: density of juvenile corals, initial structural complexity, water depth, biomass of herbivorous fishes, and nutrient conditions on the reef. Overall, resilience was seen most in coral reef systems that were structurally complex and in deeper water.
The ecological roles and functional groups of species also play a role in the recovery of regime shifting potential in reef systems. Coral reefs are affected by bioeroding, scraping, and grazing fish species. Bioeroding species remove dead corals, scraping species remove algae and sediment to further future growth, grazing species remove algae. The presence of each type of species can influence the ability for normal levels of coral recruitment which is an important part of coral recovery. Lowered numbers of grazing species after coral bleaching in the Caribbean has been likened to sea-urchin-dominated systems which do not undergo regime shifts to fleshy macroalgae dominated conditions.
There is always the possibility of unobservable changes, or cryptic losses or resilience, in a coral community's ability to perform ecological processes. These cryptic losses can result in unforeseen regime changes or ecological flips. More detailed methods for determining the health of coral reefs that take into account long-term changes to the coral ecosystems and better-informed conservation policies are necessary to protect coral reefs in the years to come.
Research is being done to help slow down the mortality rate of corals. Worldwide projects are being completed to help replenish and restore our coral reefs. The population of corals is rapidly declining, so scientists are doing experiments in coral growth and research tanks to help replenish the population of corals. These research tanks mimic the coral reefs natural environment in the ocean. They are growing corals in these tanks to use for their experiments, so no more corals are being harmed or taken from the ocean. They are also transplanting the successfully grown corals from the research tanks and putting them into the areas of the ocean where the reefs are dying out. An experiment is being done in some coral growth and research tanks by Ruth Gates and Madelaine Van Oppen. They are trying to make "super corals" that can withstand some of the environmental factors that the corals are currently dying from. Van Oppen is also working on developing a type of algae that will have a symbiotic relationship with corals and can withstand water temperature fluctuations for long periods of time. This project may be helping to replenish our reefs, but the growing process of corals in research tanks is very time consuming. It can take at least 10 years for the corals to fully grow and mature enough to where they will be able to breed.
Coral reefs provide shelter to an estimated quarter of all ocean species.  Experts estimate that coral reef services are worth up to $1.2 million per hectare which translates to an average of $172 billion per year. The benefits of coral reefs include providing physical structures such as coastal shoreline protection, biotic services within and between ecosystems, biogeochemical services such as maintaining nitrogen levels in the ocean, climate records, and recreational and commercial (tourism) services. Coral reefs are one of the best marine ecosystems to use to as a food source. The coral reefs are also the perfect habitat for rare and economically important species of tropical fish, as they provide the perfect area for fish to breed and create nurseries in. If the populations of the fish and corals in the reef are high, then we can use the area as a place to gather food and things with medicinal properties, which also helps create jobs for people who can collect these specimens. The reefs also have some cultural importance in specific regions around the world.
In 2010, the Convention on Biological Diversity's (CBD) Strategic Plan for Biodiversity 2011–2020 created twenty distinct targets for sustainable development for post-2015. Target 10 indicates the goal of minimizing "anthropogenic pressures on coral reefs". Two programs were looked at, one that reduces coral reef loss by 50% that has a capital cost of $684 million and a recurrent cost of $81 million. The other program reduces coral reef loss by 80 percent and has a capital cost of $1,036 million with recurring costs of $130 million. CBD acknowledges that they may be underestimating the costs and resources needed to achieve this target due to lack of relevant data but nonetheless, the cost-benefit analysis shows that the benefits outweigh the costs by a great enough amount for both programs (Benefit Cost Ratio of 95.3 and 98.5) that "there is ample scope to increase outlays on coral protection and still achieve a benefit to cost ratio that is well over one".
When coral experiences abnormal conditions, it releases an algae called zooxanthellae. The loss of the colorful algae causes the coral to turn white.
Acanthastrea brevis is a vulnerable species of stony coral found in reef habitats at depths of 1–20 m. It is threatened by habitat loss and crown-of-thorns starfish predation. It is particularly susceptible to coral bleaching and ocean acidification.Acropora abrotanoides
Acropora abrotanoides is a species of acroporid coral found in Indo-Pacific waters from the Red Sea and the Gulf of Aden east to the East China Sea, Japan, the central Pacific Ocean and Australia. It is found in shallow coral reefs that are exposed to the action of strong waves, at depths up to 15 m. It is vulnerable to coral bleaching, disease and crown-of-thorns starfish. It is resistant to predation as it has well-developed radial corallite lips.Alveopora allingi
Alveopora allingi is a species of stony coral that is found in the Red Sea, the Gulf of Aden, the southwest and northern Indian Ocean, the central Indo-Pacific, Australia, Southeast Asia, Japan, the East China Sea and the oceanic west and central Pacific Ocean. It has also been found in Palau and the Mariana Islands. It is susceptible to coral bleaching and is rated by the International Union for Conservation of Nature as a "vulnerable species".Alveopora fenestrata
Alveopora fenestrata is a species of stony coral that is found in the Red Sea, the Gulf of Aden, the southwest and northern Indian Ocean, the central Indo-Pacific, Australia, Southeast Asia and the oceanic west Pacific Ocean. It can be found in shallow coral reefs, to a depth of 30 metres (100 ft). It is particularly susceptible to coral bleaching.Alveopora spongiosa
Alveopora spongiosa is a species of stony coral that is found in the Red Sea, the Gulf of Aden, the southwest and northern Indian Ocean, the central Indo-Pacific, Australia, Southeast Asia Japan, the East China Sea and the oceanic west and central Pacific Ocean. It can be found on protected upper coral reef slopes, generally from depth of 9–20 m, but can grow at depths of up to 50 m. It is moderately susceptible to coral bleaching, and is harvested for the aquarium trade.Alveopora verrilliana
Alveopora verrilliana is a species of stony coral that is found in the Red Sea, the Gulf of Aden, the northern Indian Ocean, the central Indo-Pacific, Australia, Southeast Asia, Japan, the East China Sea, the oceanic west and central Pacific Ocean and the Johnston Atoll. It can also be found in Palau and the southern Mariana Islands. It grows on shallow coral reefs to a depth of 30 metres (100 ft). It is particularly susceptible to coral bleaching and is harvested for the aquarium trade.Anacropora puertogalerae
Anacropora puertogalerae is a species of briar coral that can be found in the central Indo-Pacific, Japan, the East China Sea, eastern Australia, the oceanic west Pacific Ocean, the Philippines and the Maldives. It is also found in the Andaman Islands, Rodrigues, Fiji and Vanuatu. It occurs in shallow reefs, from depths of 5–20 m. It is very fragile, and is particularly susceptible to coral bleaching, disease and habitat loss.Anacropora spinosa
Anacropora spinosa is a species of briar coral that can be found in the central Indo-Pacific, Southeast Asia, the Solomon Islands, Japan, the East China Sea and the oceanic west Pacific Ocean. It is also found in Rodrigues and the Andaman Islands. It occurs in shallow reefs, from depths of 5–15 m. It is particularly susceptible to coral bleaching, disease and reduction of coral reef habitats.Belize Barrier Reef
The Belize Barrier Reef is a series of coral reefs straddling the coast of Belize, roughly 300 meters (980 ft) offshore in the north and 40 kilometers (25 mi) in the south within the country limits. The Belize Barrier Reef is a 300-kilometer (190 mi) long section of the 900-kilometer (560 mi) Mesoamerican Barrier Reef System, which is continuous from Cancún on the north-eastern tip of the Yucatán Peninsula through the Riviera Maya and up to Honduras, making it as of 2019 the World's largest coral reef system in the world. (Australia's Great Barrier Reef is now ranked second only because of the coral bleaching that has occurred.) It is Belize's top tourist destination, popular for scuba diving and snorkeling and attracting almost half of its 260,000 visitors. It is also vital to the country's fishing industry.Charles Darwin described it as "the most remarkable reef in the West Indies" in 1842.
In addition to its barrier reef, it also boasts three distinct Caribbean atolls: Turneffe Atoll, Glover's Reef and Lighthouse Reef. Lighthouse Reef is the most easterly diving area in Belize, it is home to the Great Blue Hole, made famous by Jacques Cousteau in 1970; Turneffe Atoll lies directly to the east of Belize City and is the nearest of the atolls to the capital. These different reefs provide diverse scuba diving opportunities that include walls, pinnacles and reef flats that are located throughout an enormous area of sea.Census of Coral Reefs
The Census of Coral Reefs (CReefs) is a field project of the Census of Marine Life that surveys the biodiversity of coral reef ecosystems internationally. The project works to study what species live in coral reef ecosystems, to develop standardized protocols for studying coral reef ecosystems, and to increase access to and exchange of information about coral reefs scattered throughout the globe. The CReefs project uses the implementation of autonomous reef-monitoring structures (ARMS) to study the species that inhabit coral reefs. These structures are placed on the sea floor in areas where coral reefs exist, where they are left for one year. At the end of the year, the ARMvS is pulled to the surface, along with the species which have inhabited it, for analysis. Coral reefs are thought to be the most organically different of all marine ecosystems. Major declines in key reef ecosystems suggest a decline in reef population throughout the world due to environmental stresses. The vulnerability of coral reef ecosystems is expected to increase significantly in response to climate change. The reefs are also being threatened by induced coral bleaching, ocean acidification, sea-level rise, and changing storm tracks. Reef biodiversity could be in danger of being lost before it is even documented, and researchers will be left with a limited and poor understanding of these complex ecosystems.
In an attempt to enhance global understanding of reef biodiversity, the goals of the CReefs Census of Coral Reef Ecosystems were to conduct a diverse global census of coral reef ecosystems. And increase access to and exchange of coral reef data throughout the world. Because coral reefs are the most diverse and among the most threatened of all marine ecosystems, there is great justification to learn more about them.Environmental issues with coral reefs
Human impact on coral reefs is significant. Coral reefs are dying around the world. Damaging activities include coral mining, pollution (organic and non-organic), overfishing, blast fishing, the digging of canals and access into islands and bays. Other dangers include disease, destructive fishing practices and warming oceans. Factors that affect coral reefs include the ocean's role as a carbon dioxide sink, atmospheric changes, ultraviolet light, ocean acidification, viruses, impacts of dust storms carrying agents to far-flung reefs, pollutants, algal blooms and others. Reefs are threatened well beyond coastal areas. Climate change, such as warming temperatures, causes coral bleaching, which if severe kills the coral.
In 2008, a worldwide study estimated that 19% of the existing area of coral reefs has already been lost, and that a further 17% is likely to be lost over the subsequent 10–20 years. Only 46% of the world's reefs could be currently regarded as in good health and about 60% of the world's reefs may be at risk due to destructive, human-related activities. The threat to the health of reefs is particularly strong in Southeast Asia, where 80% of reefs are endangered. By the 2030s, 90% of reefs are expected to be at risk from both human activities and climate change; by 2050, it is predicted that all coral reefs will be in danger.Goniastrea stelligera
Goniastrea stelligera, commonly known as knob coral, is a species of stony coral in the family Merulinidae. It occurs in shallow water on the coast of East Africa and in the Indo-Pacific region. This is a common species of coral but it seems to be decreasing in abundance. The main threat it faces is from the destruction of its coral reef habitat, and it is also moderately susceptible to coral bleaching, so the International Union for Conservation of Nature has rated its conservation status as being "near threatened".Great Barrier Reef
The Great Barrier Reef is the world's largest coral reef system composed of over 2,900 individual reefs and 900 islands stretching for over 2,300 kilometres (1,400 mi) over an area of approximately 344,400 square kilometres (133,000 sq mi). The reef is located in the Coral Sea, off the coast of Queensland, Australia. The Great Barrier Reef can be seen from outer space and is the world's biggest single structure made by living organisms. This reef structure is composed of and built by billions of tiny organisms, known as coral polyps. It supports a wide diversity of life and was selected as a World Heritage Site in 1981. CNN labelled it one of the seven natural wonders of the world. The Queensland National Trust named it a state icon of Queensland.A large part of the reef is protected by the Great Barrier Reef Marine Park, which helps to limit the impact of human use, such as fishing and tourism. Other environmental pressures on the reef and its ecosystem include runoff, climate change accompanied by mass coral bleaching, dumping of dredging sludge and cyclic population outbreaks of the crown-of-thorns starfish. According to a study published in October 2012 by the Proceedings of the National Academy of Sciences, the reef has lost more than half its coral cover since 1985.The Great Barrier Reef has long been known to and used by the Aboriginal Australian and Torres Strait Islander peoples, and is an important part of local groups' cultures and spirituality. The reef is a very popular destination for tourists, especially in the Whitsunday Islands and Cairns regions. Tourism is an important economic activity for the region, generating over AUD$3 billion per year. In November 2014, Google launched Google Underwater Street View in 3D of the Great Barrier Reef.A March 2016 report stated that coral bleaching was more widespread than previously thought, seriously affecting the northern parts of the reef as a result of warming ocean temperatures. In October 2016, Outside published an obituary for the reef; the article was criticized for being premature and hindering efforts to bolster the resilience of the reef. In March 2017, the journal Nature published a paper showing that huge sections of an 800-kilometre (500 mi) stretch in the northern part of the reef had died in the course of 2016 due to high water temperatures, an event that the authors put down to the effects of global climate change. The percentage of baby corals being born on the Great Barrier Reef dropped drastically in 2018 and scientists are describing it as the early stage of a "huge natural selection event unfolding". The reason behind low birth of new corals is that many of the mature breeding adults died in the bleaching events of 2016-17, and thus could not produce offspring. The types of corals that reproduced changed too, which points towards the fact that there will be long-term reorganisation of the reef ecosystem if the trend continues.Lobophyllia ishigakiensis
Lobophyllia ishigakiensis is a species of coral found in Indo-Pacific waters. It is widespread but uncommon throughout its range. It has a narrow depth range, and is susceptible to coral bleaching and disease. It is also threatened by the global loss of coral reef habitats.Micromussa regularis
Micromussa regularis is a species of coral found in Indo-Pacific waters from Australia to the western Pacific Ocean. It is usually uncommon throughout its range, but can be more common locally. It has a narrow depth range, and so is susceptible to coral bleaching and disease. It is also threatened by the global decline in coral reef habitats.Resilience of coral reefs
The resilience of coral reefs is the biological ability of coral reefs to recover from natural disturbances such as storms and bleaching episodes. Resilience refers to the ability of biological or social systems to overcome pressures and stresses by maintaining key functions through resisting or adapting to change. Reef resistance measures how well coral reefs tolerate changes in ocean chemistry, sea level, and sea surface temperature. Reef resistance and resilience are important factors in coral reef recovery from the effects of ocean acidification. Natural reef resilience can be used as a recovery model for coral reefs and an opportunity for management in marine protected areas (MPAs).Scott and Seringapatam Reefs
Scott and Seringapatam Reefs is a group of atoll-like reefs in the Timor Sea more than 300 kilometres (190 mi) northwest of Cape Leveque, Western Australia, on the edge of the continental shelf. There are three or four separate reef structures, depending on whether Scott Reef Central is counted separately.
The group is just one of a number of reef formations off the northwest coast of Australia and belongs to Western Australia. Further to the northeast are Ashmore and Cartier Islands, and to the southwest are the Rowley Shoals.UV filter
UV filters are individual compounds or mixtures that block or absorb ultraviolet (UV) light. Two major applications of UV filters are in sunscreens, where they protect the skin from sunburn and other damage, and in photography, where they reduce the level of ultraviolet light that strikes the recording medium. When exposed to UV light, these filters can undergo transformations into other chemicals that are less protective and possibly toxic. As a result, there are practical concerns about the choice of chemical to use beyond just which has the desired filtering properties.White pox disease
White pox disease (also "acroporid serratiosis" and "patchy necrosis"), first noted in 1996 on coral reefs near the Florida keys, is a coral disease affecting Elkhorn coral (Acropora palmata) throughout the Caribbean. It causes irregular white patches or blotches on the coral that result from the loss of coral tissue. These patches distinguish white pox disease from white band disease which produces a distinctive white band where the coral skeleton has been denuded. The blotches caused by this disease are also clearly differentiated from
coral bleaching and scars caused by coral-eating snails. It is very contagious, spreading to nearby coral.At the locations where white pox disease has been observed, it is estimated to have reduced the living tissue in elkhorn corals by 50–80%. In the Florida Keys National Marine Sanctuary (FKNMS), the losses of living coral are estimated to average around 88%. Elkhorn coral was formerly the dominant shallow water reef-building coral throughout the Caribbean but now is listed as a threatened, due in part to disease. Elkhorn coral is the first species of coral to be listed as threatened in the United States, Also due in part to this disease.