It has already led to increased levels of coral bleaching around the world, which are predicted to increase in frequency and severity in the coming decades. The mining and burning of coal releases carbon pollution into the air, which is heating our planet and warming our oceans. If we continue to pollute the air and the ocean with carbon emissions at our high rate, coral reefs around the world will face a catastrophic future in coming decades — in our lifetime.
The stunning colours in corals come from a marine algae called zooxanthellae, which live inside their tissues. This algae provides the corals with an easy food supply thanks to photosynthesis, which gives the corals energy, allowing them to grow and reproduce.
When corals get stressed, from things such as heat or pollution, they react by expelling this algae, leaving a ghostly, transparent skeleton behind.
Some corals can feed themselves, but without the zooxanthellae most corals starve. In some instances corals can recover from bleaching. If conditions return to normal, and stay that way corals can regain their algae, return to their bright colours and survive. However prolonged warmer temperatures and other stressors, like poor water quality, can leave the living coral in a weakened state.
It can struggle to regrow, reproduce and resist disease — so is very vulnerable to coral diseases and mortality. It can take decades for coral reefs to fully recover from a bleaching event, so it is vital that these events do not occur frequently. If we continue burning fossil fuels at our current rate, severe bleaching events are likely to hit reefs annually by the middle of the century.
We need your observations to tell us whether their predictions are accurate, how to make better use of these predictions , and to help improve them. Red areas indicate highest risk of bleaching. This means that corals are already bleaching, or might bleach in the next few months. Your observations will help us see how broad the effects of this event become.
They are known as colonial organisms, which means many individuals live and grow while connected to one another. Each individual coral is made of a polyp — a clear, tube-shaped structure attached to a reef at one end and open at the other.
The open end has a mouth that is surrounded by a ring of tentacles. Hard corals extract calcium from seawater to make limestone outer skeletons, which form coral reefs. Soft corals tend to be feathery in appearance such as sea fans and sea feathers.
This algae, called zooxanthellae pronounced zo-UH-zan-thuh-lay , helps corals by removing waste and using it to produce food in a process known as photosynthesis. When corals are stressed, they expel the zooxanthellae that live inside their tissues.
Without the algae to provide colour, corals appear transparent and reveal their white skeletons. Bleaching occurs when corals are under stress. A primary cause of coral bleaching on the Great Barrier Reef during summer is heat stress from raised water temperatures and increased UV radiation.
Deprived of zooxanthellae and therefore their food source, corals begin to starve. If raised water temperatures persist for long periods eight weeks or more corals begin to die. Yes, corals can recover from bleaching over time, but only if temperatures drop and conditions return to normal. Coral bleaching is a stress response and individual coral colonies suffer from a degree of bleaching in any given summer. Bleached coral at Australia's Great Barrier Reef appear bone white compared to remaining healthy coral, which are golden brown and purple.
The scientists summarized the event in stark terms:. More than half of affected reef areas were impacted at least twice. This global event has punctuated the recent acceleration of mass bleaching. Occurring at an average rate of once every 25—30 years in the s, mass bleaching now returns about every six years and is expected to further accelerate….
Severe bleaching is now occurring more quickly than reefs can recover, with severe downstream consequences to ecosystems and people. Eakin, C. Unprecedented three years of global coral bleaching —
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