Destruction of coral reefs can be induced by a variety of factors, alone or in combination. However, unprecedented global warming and climate change combined with growing local pressures have resulted in the destruction of coral reefs to a large extent.Impact of global warming on the coral life system is discussed below.
Impact of global warming on the coral life system:
- The impacts from coral bleaching are becoming global in scale, and are increasing in frequency and intensity.
- Mass coral bleaching generally happen, when temperatures around coral reefs exceed 1 degree Celsius above an area’s historical norm for four or more weeks. Sea surface temperature increases have been strongly associated with El Nino weather patterns.
- However, light intensity, (during doldrums, i.e. flat calm conditions), also plays a critical role in triggering the bleaching response.
- If temperatures climb to more than 2 0 C for similar or longer periods, coral mortalities following bleaching increase. Rising sea levels
- since 1961 show that the average temperature of the global ocean has increased even at depths of 3000m (IPCC report), and that the ocean has been absorbing more than 80% of the heat added to the climate system.
- Such warming causes sea level rise and creates problems for low-lying nations and islands. Ocean acidification
- Bleached corals are likely to experience reduced growth rates, decreased reproductive capacity, increased susceptibility to diseases and elevated mortality rates.
- Ocean acidification, or increased CO2 levels has reduced calcification rates in reef-building and reefassociated organisms, causing their skeletons to become weaker and growth to be impaired.
- Sea level rise may lead to increases in sedimentation for reefs located near land-based sources of sediment. Sedimentation runoff can lead to the smothering of coral.
- Changes in storm patterns, due to climate change, may lead to stronger and more frequent storms that can cause the destruction of coral reefs.
- Changes in coral ecosystem also affect the species that depend on them, such as the fish and invertebrates that rely on live coral for food, shelter, or recruitment habitat.
- Changes in precipitation result in increased runoff of freshwater, sediment, and land-based pollutants contribute to algal blooms and cause murky water conditions that reduce light.
- it refers to a change in ocean chemistry in response to the uptake of carbon dioxide from the atmosphere. The amount of carbon dioxide in the atmosphere is in equilibrium with that in seawater, so when atmospheric concentrations increase, so do oceanic concentrations.
- Carbon dioxide entering seawater reacts to form carbonic acid, causing an increase in acidity. •Each year, the ocean absorbs about one-quarter of the carbon dioxide emitted from the burning of fossil fuels (oil, coal, and natural gas).
- Since the Industrial Revolution, ocean acidity has increased by about 30%, a rate that is more than 10 times what has previously occurred for millions of years. Further, ocean acidity levels are expected to increase by an additional 40% above present levels by the end of this century.
- It is also expected that there will be a gradual decrease in the quantity of marine plants such as phytoplankton in warmer waters, effectively reducing the amount of nutrients available to animals further along the food chain.
- In addition, the collapse of coral life system due to global warming can have direct impacts on tourism, aquaculture, and pharmaceutical industries as well as reduce the overall resilience of coastal communities
- As temperature rises, mass coral bleaching events occurs leading to more frequent infectious disease outbreaks
- Ocean acidification: carbon dioxide absorbed into the ocean from the atmosphere has already begun to reduce calcification rates in coral reef-building and reef-associated organisms by altering seawater chemistry through decrease in pH.
- Due to global warming there are increasing changes to the frequency and intensity of tropical storms, which adversely affect coral reef.
- Rapid dilution of reef waters from storm-generated precipitation and runoff has been demonstrated to cause coral reef bleaching.
- Global warming and rise of El Nino Southern Oscillation (ENSO) events lead to increase in bleaching. Coral bleaching events occur during sudden temperature drops accompanying intense upwelling episodes.
Instances of coral bleaching:
- According to UNESCO, the coral reefs in all 29 reef-containing World Heritage sites would cease to exist by the end of this century if we continue to emit greenhouse gases under a business-as-usual scenario. (Clive Wilkinson report).
- 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 coral bleaching and mortality.
- The bleaching of the Great Barrier Reef in 2016 and 2017, for instance, killed around 50% of its corals.
- Coral reefs harbour the highest biodiversity of any ecosystem globally and directly support over 500 million people worldwide, mostly in poor countries
- However, according to UNESCO, the coral reefs in all 29 reef-containing World Heritage sites would cease to exist by the end of this century,
- if we continue to emit greenhouse gases. Limiting global average temperature to well below 2°C above pre-industrial levels in line with the Paris Agreement provides the only chance for the survival of coral reefs globally.
As Coral reefs harbour the highest biodiversity and support over 500 million people worldwide, mostly in poor countries. Its bleaching would also have adverse effect on them. Alliances and organizations like Global Coral Reef Monitoring Network, International Coral Reef Initiative (ICRI), are involved in preventing damage to healthy reefs and restoring damaged ones through assessment, conservation and restoration programs world-wide involving local communities should push forward for conserving the corals.
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