Why in news
The U.S. National Oceanic and Atmospheric Administration (NOAA) announced last month that the world's coral reefs were in the throes of a fourth mass bleaching event, as climate change combined with an El Nino climate pattern has pushed ocean temperatures to record highs.
Now, the agency reports some 60.5% of the world's reef area has been affected and that number is still rising.
Coral Bleaching
Coral bleaching is the process when corals become white due to loss of symbiotic algae and photosynthetic pigments.
This loss of pigment can be caused by various stressors, such as changes in temperature, light, or nutrients.
Causes
Coral bleaching occurs when water temperatures rise more than one degree Celsius (33.8 degrees Fahrenheit)
As the world’s oceans continue to warm, coral bleaching is becoming more frequent and severe
In a bid to survive, the coral expels microscopic algae, known as zooxanthellae, which it needs to live.
If high temperatures persist, the coral eventually evicts most of the zooxanthellae, turns white, and dies.
As the planet continues to warm, bleaching is forecast to reduce global coral cover by 95% if temperatures warm by about two degrees
Consequences
Coral bleaching matters because once these corals die, reefs rarely come back.
With few corals surviving, they struggle to reproduce, and entire reef ecosystems, on which people and wildlife depend, deteriorate.
Changes in coral communities 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.
Declines in genetic and species diversity may occur when corals die because of bleaching
Degraded coral reefs are less able to provide the ecosystem services on which local human communities depend.
For example, degraded reefs are less productive and may not be able to sustain accretion rates necessary to ensure reefs continue to provide shoreline protection services.
Reefs damaged by coral bleaching can quickly lose many of the features that underpin the aesthetic appeal that is fundamental to reef tourism
Coral bleaching events that lead to significant coral mortality can drive large shifts in fish communities.
This can translate into reduced catches for fishers targeting reef fish species, which in turn leads to impacts on food supply and associated economic activities
Cultural values of many tropical island communities (e.g., religious sites and traditional uses of marine resources) depend upon healthy coral reef ecosystems and can be adversely affected by coral bleaching.
National Oceanic and Atmospheric Administration (NOAA)
The National Oceanic and Atmospheric Administration is a scientific and regulatory agency within the Washington, D.C.–based United States Department of Commerce, headquartered in Silver Spring, Maryland.
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