Case study coral bleaching in the indian ocean in 19971998 between 50 and 90 percent of corals in shallow waters of the indian ocean were bleached and died. Coral bleaching causes, effects, concerns and measures continue reading what causes coral. It may result from increases in seawater temperature, particularly when associated with elevated levels of solar irradiance e. Average coral cover in the northern section of the reef is now at its lowest point on record, and coral cover in the central section of the reef declined from 22 percent in 2016 to 14 percent in 2018, largely due to the 2017 bleaching event. When ocean temperatures rise beyond a certain threshold, the algaes photosynthetic machinery may be damaged and produce harmful reactive oxygen molecules. Bleaching results from the loss of the corals intracellular endosymbionts symbiodinium, also known as zooxanthellae through either expulsion or loss of algal pigmentation. Coral bleaching occurs when heat stress causes the coral to release its brightly coloured algae, leaving it completely white. Nov 11, 2008 ocean acidification represents a key threat to coral reefs by reducing the calcification rate of framework builders. Coral reef bleaching marine biology learning center. Bleaching slows coral growth and can make them susceptible to disease. Nasa recently developed some very sensitive instruments to study coral reefs from an airplane flying above the ocean. Climate change causes ocean acidification and a rise of both the water temperature and level. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext. Bleached corals continue to live but begin to starve after.
Ecological causes of coral bleaching as coral reef bleaching is a general response to stress, it can be induced by a variety of factors, alone or in combination. Sunscreens cause coral bleaching by promoting viral infections. The intent of this task is to provide evidence of a students ability to engage in argument from evidence while evaluating the possible cause of coral bleaching based on the data provided. The coral reefs are distributed in the tropical regions and cover less than one percent of the earths surface, but provide habitat for many species in the marine realm. Most coral reefs have experienced heat stress sufficient to cause frequent mass coral. Coral species live within a relatively narrow temperature margin, and anomalously low and high sea temperatures corals are absent on the west coast of tropical temperate continents because of the cold currents can induce coral bleaching. These events have produced widespread coral mortality and significant ecological, social and economic impacts to coral reefs and the communities that depend on them. Noaa coris a reef managers guide to coral bleaching. Australian government issues emergency response level and warns that bleaching may be. Ocean acidification causes bleaching and productivity loss in coral reef builders k. In addition, acidification is likely to affect the relationship between corals and their symbiotic dinoflagellates and the productivity of this association.
Note the extreme bleaching in this diploria at the grotto, san salvador, bahamas coral reef bleaching. Coral bleaching is an element of the programme, and a work plan on the physical degradation and destruction of coral reefs is in progress. What is coral bleaching and what causes it fight for our reef. Climate change is the biggest threat to our great barrier reef. Temperatureinduced bleaching that affects the condition and diversity of coral reef ecosystems is expected to simultaneously affect reef fish.
Scientists have already observed that when the water around coral reefs becomes warmer than the typical or average temperature, coral bleaching occurs. Pdf the coral reefs are distributed in the tropical regions and cover less than one percent of the earths surface, but provide habitat for many. However, when corals are immoderately stressed, this causes them to expel more zooxanthellae than necessary, and therefore loss of color results from the expulsion of too many zooxanthellae, andor the concentration of photosynthetic pigments in these organisms are diminished. Mar 07, 2020 are you ready for insta 75 days revision plan upsc prelims 2020. Mass coral bleaching causes biotic homogenization of reef. The broad scale of recent mass coral bleaching and mortality, however, appears to be a relatively recent thing. Coral bleaching was observed only a few times before 1980.
Coral bleaching occurs when coral polyps expel algae that live inside their tissues. Coral bleaching is not strictly a disease but is in impairment in the overall health of the coral. Attributing cause and effect has not been straightforward, with an apparent lack of correlation between coral reef bleaching and sea surface temperature. Change in ocean temperature increased ocean temperature caused by climate change is the leading cause of coral bleaching. Ocean acidification causes bleaching and productivity loss in coral. There are no scientific records of mass coral bleaching and mortality before the early 1980s. The following stressors have been implicated in coral reef bleaching events. The primary cause of mass coral bleaching is increased sea temperatures 9,18,23,53. Coral reef bleaching and ideal conditions for coral growth. The primary cause of mass coral bleaching is increased sea temperatures9, 18, 23, 53. Additions were last made on wednesday, may 7, 2014. Most people have seen images of brightly colored fishes and other reefdwelling organisms, yet many do not understand why these systems are personally important. Coral bleaching is a stress reaction of the coral animals that happens when they expel their symbiotic algae, zooxanthellae, which is their main food and energy source.
The resulting change in the composition of coral reefs may be irreversible. One factor that scientists study is the effects of warm water on corals. This book provides comprehensive information on the causes and consequences of coral bleaching for coral reef ecosystems, from the genes and microbes involved in the bleaching response, to individual coral colonies and whole reef systems. This increasing worldwide phenomenon is associated with temperature anomalies, high irradiance, pollution, and bacterial diseases. This panoramic image reveals coral bleaching at lizard island on the great barrier reef in march 2016.
Bare coral skeleton is left behind allowing for the colonization of algae. Warmer water temperatures can result in coral bleaching. It is estimated that half of the worlds coral reefs have been lost due to coral bleaching over the last 30 years, with ongoing underwater heatwaves caused by. The bleaching may lead the coral reef to death slowly, it also shows that the algae and phytoplankton inside the coral reef is died and cant distribute food for coral. Feb 05, 2020 mass coral bleaching events have increased in frequency and severity over the past two decades associated with anomalously high sea surface temperatures. Ocean acidification causes bleaching and productivity loss in. By now you have learned about the process of coral bleaching, and why it is such a concern to scientists. The most common cause of coral bleaching is sustained heat stress, which is occurring more frequently as our climate changes and oceans become warmer. It is therefore difficult to unequivocally identify the causes for bleaching events. Coral bleaching is a stress response caused by the breakdown of the symbiotic relationship between the coral and the algae zooxanthellae that live inside its tissues. Corals and reefs for pdf international coral reef initiative. Gorgeous, delicate coral reefs are home to millions of fish and fundamental to our own survival. Largescale coral bleaching events are driven by extreme sea temperatures and are intensified by sunlight stress associated with calm, clear. Coral bleaching on an individual colony scale has occurred in the past and is a natural process.
If the bleaching event lasts for more than a couple of weeks, the corals will starve to death. Ocean acidification and coral bleaching earth journalism. In most cases bleaching has been attributed to elevated temperature, but other instances involving high solar irradiance, and sometimes disease, have also been documented. Get ready for upsc civil services preliminary exam 2020 with insights insta 75 days revision plan. Other stressors that cause bleaching include freshwater inundation which results in low salinity, poor water quality from sediment or. When water is too warm, corals will expel the algae zooxanthellae living in their tissues causing the coral to turn completely white. Coral bleaching is a global crisis, caused by increased ocean temperatures driven by carbon pollution. At a local scale,many stressors including disease, sedimentation, cyanide fishing, pollutants and changes in salinity may cause corals to bleach. Coral bleaching is a generalized stress response of corals and can be caused by a number of biotic and abiotic factors which are given below. We show that these socalled proximal causes are not the ones that have acted over long time periods or that have caused the most intense degradation of reefs and associated ecosystems. Hoeghguldberg centre for marine studies and arc centre of excellence for coral reef studies, the university of queensland, st lucia 4072 queensland, australia. Corals can survive a bleaching event, but they are under more stress and are subject to mortality. Stressed coral bleached coral without the algae, the coral loses its major source of food, turns white or very pale, and is more susceptible to disease.
It has been over 10 years since the phenomenon of extensive coral bleaching was first described. The algae provides up to 90 percent of the coral s energy. Overall, the book is a useful addition to the library of reef ecology researchers and students. Ocean acidification represents a key threat to coral reefs by reducing the. Coral reefs zooxanthellae symbiosis bleaching background coral reefs are one of the most biologically productive ecosystems on earth. This does not necessarily mean the coral is dead corals can survive bleaching. This band of pathogens spreads across the surface of a coral at a rate of a few millimeters per day, digesting the coral as it progresses. Scientists are working to understand the different factors, both natural and. What causes coral bleaching at the great barrier reef. Coral reefs factsheet corals are the organism most vulnerable to warming ocean temperatures. Those are some from many causes of coral bleaching and so when the temperature and ph change it will let the bleaching occur. Even the slightest warming of ocean waters can cause corals to eject their symbiotic algae, resulting in coral bleaching. Jan 16, 2016 ecological causes of coral bleaching temperature. What is the temperature threshold for coral bleaching events.
1345 405 1377 1065 1260 1399 870 1553 1016 1386 414 626 452 1621 1263 1537 1323 780 303 1070 398 550 1075 1400 378 1179 1412 672 1464 534