Recently, Nature's photo team selected the most powerful technological images from September, focusing on the shocking scenes of climate change and environmental pollution.
Among them, a coral "sunscreen photo" is believed to have attracted the attention of many people. It turns out that corals can't stand the sun to protect themselves from the sun?
The intense sunlight has exposed corals to a potentially deadly bleaching crisis, and some of them produce brightly colored fluorescent pigments on their own, which is their last-ditch effort to prevent overheating. These proteins act like chemical sunscreens, absorbing and reflecting sunlight components that can harm coral symbiotic algae.
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In order to "protect themselves", it seems that the corals that are frequently affected by disasters are getting stronger and stronger.
The data shows that over the past 20 years, Great Barrier Reef corals have experienced 4 severe mass bleaching events:
In 2006, severe coral bleaching struck the world's largest coral reef, the Great Barrier Reef in southern Australia, and Nature magazine also investigated the disaster and issued an "autopsy report". Amber staghorn corals and flattened, fan-shaped plate corals – suffered the worst casualties. Destruction has spread throughout the ecosystem.
In the summers of 2016 and 2017, marine heat waves caused 60 per cent of Australia's Great Barrier Reef corals to undergo two large-scale bleachings, a phenomenon that left researchers feeling "ecological grief".
By mid-2018, the survey said that more than half of the corals in the Great Barrier Reef had "died", and the coral "bones" after complete bleaching were dead in the seawater, and the scene was painfully silenced.
How did this disaster happen so quickly? In fact, the rise in sea temperature can easily do this. At the end of 2015, the Pacific ocean was mired in one of the largest El Niño events of all time. El Niño is an umbrella term for a range of global weather symptoms that typically raise global temperatures and alter precipitation patterns. El Niño-like conditions have hit the Great Barrier Reef thousands of times, but the events of 2016 have witnessed a continued surge in global ocean temperatures. About 50% of all corals killed in the 2016 bleaching incident died in the fall and winter. In the past two years, the high temperature and hot weather, I believe many people have already seen it strangely.
The "knock-on effect" of coral reef deaths
If coral reefs continue to die, global coastlines will be hit hard.
According to the National Oceanic and Atmospheric Administration, coral reefs are a natural protection of the coastline, absorbing 97 percent of the wave energy to prevent erosion and potential property damage due to currents and storms.
They are also home to 25% of all marine life and are tropical rainforests that protect marine biodiversity. The degradation of coral reefs that were originally rich in species has also led to the compression of habitats for organisms such as fish and seabirds.
But research published in the journal Natural Climate Change shows that 74 percent of the world's corals will be bleached by 2045. Biologist Ove Hoegh-Guldberg also said that by 2050, global warming is expected to wipe out 90% of the remaining corals. Several scientists have published articles in the British journal Nature that if warming continues at the current rate, the world's coral reefs could all disappear by 2070. These numbers are undoubtedly terrible!
What causes coral bleaching? How do they affect?
Thirty years ago, large-scale coral bleaching was rare, but in recent years it has become more and more common. This suggests that the natural environment has been depleted by humans. What are the reasons behind this shocking scene?
Studies in recent years have shown that corals may be bleached in two ways:
1) The number of symbiotic algae contained in the coral tissue per unit area is reduced;
2) Each symbiotic algae contains a reduced amount of pigment; and different species of corals may be bleached by different mechanisms.
Currently, most corals are mainly bleached due to a decrease in the number of zooxanthellae, and only a few corals are bleached due to the loss of photosynthetic pigments.
Scientists say the ocean's increasing acidity and rising sea temperatures, combined with tens of millions of divers, tourists and wildlife enthusiasts who visit the reef, have devastated the reef.
The direct external causes of coral bleaching manifest themselves in four forms: 1) increased ocean temperatures; 2) pollution caused by the deposition of chemicals caused by lightning and human remnants (such as sunscreen); 3) overexposure in the sun; and 4) shallow shoals that hinder growth.
Such destruction would also be a disaster for tropical marine fish and marine life that depend on coral reefs for their livelihoods and forage. As ocean temperatures continue to rise, corals rely less on seaweed and are therefore more susceptible to bleaching.
It can be seen that the impact of the increase in sea temperature is the most intuitive. To this end, scientists have also conducted experiments to confirm the associative changes it brings. They observed all 3,863 constituent reefs of the Great Barrier Reef via satellite and then investigated them themselves, and Hughes' team also came up with new guidelines to predict when the entire reef would fade.
They found that even small changes in heat that seemed to us could make corals very fragile. Within a few weeks of a 2°C increase in temperature, most of the local corals will be lightly bleached. At an elevation of 4 °C, corals in the area will begin to bleach and die. Hughes said local reef temperatures rise to 6°C and would suffer a "catastrophic death" comparable to 2016.
These distinctions are not just academic. The International Union for Conservation of Nature (IUCN), a global organization declaring species "endangered" or "threatened," is currently establishing a similar scale rating for ecosystems. The head of the alliance hopes that individual ecosystems will soon be listed as "endangered", as is the case with the protection of giant pandas and mountain gorillas.
Such a move is not an exaggeration at all. A recent study by Nature Climate Change found that if the world warms by an average of 2°C, ocean temperatures will continue to exceed 2016 levels even in non-El Niño years. In another study released in January, scientists surveyed observations of 100 coral reefs around the world over 35 years. They found that mass bleaching events were already five times more frequent than in the early 1980s.
Other studies have shown that the time between bleaching periods is now reduced, usually less than 10 years, after which they die directly because they do not recover. The study notes that in the case of 100 coral reefs located in the tropics, bleaching occurred on average every 25 years in the 1980s and every 6 years around 2010. Climate models predict that by 2035, coral bleaching will occur on average every five years, and if global warming does not change substantially, coral bleaching will occur annually after 2044.
The researchers caution that as the effects of climate change continue to escalate, the future of coral reefs is fraught with uncertainty.
Can coral bleaching still be restored?
Due to changes in the surrounding environment, corals will have poor growth, commonly known as bleaching (Coral Bleaching), which is not the same as coral death, if the growth environment is well changed, coral bleaching is not irreversible, but can be restored to alleviate.
When gazing at their hard, rough exterior, it's easy to forget that corals are animals. In fact, coral bleaching is the loss of symbiotic algae in the body, the loss of the original color, showing the color of the coral itself white and transparent bones.
So we see that the colorful colors of corals are actually the color of symbiotic algae - zooxanthellae, the two are interdependent, zooxanthellae photosynthesis during the day to provide energy for corals, and at night corals prey on zooxanthellae to provide food, without zooxanthellae corals are easy to be "starved" alive.
Corals are very demanding on the growing environment, which is why there are fewer coral distribution areas, and global warming (or sharp decline in sea temperature in some years), pollution of the marine environment, and overfishing of marine life can affect coral growth. Even in some areas, the environment itself is more likely to lead to coral bleaching – in the case of the Great Barrier Reef, the adult coral lifespan of the central and northern reef groups is more affected by factors such as global warming.
Coral bleaching in a short period of time, it itself is still a certain tolerance, after the environment tends to stabilize or can be restored (it takes years or even decades), but long-term bleaching, it is difficult to survive.
A new study has found that while bleaching threatens Great Barrier Reef corals, corals that can "survive" bleaching become tougher and better able to withstand environmental pressures.
What are the means to cure its "albinism"?
Coral bleaching is so severe, and the factors behind it are so complex. So, what other means can we use to cure its "albinism"?
- Reduce carbon emissions, marine disturbance and pollution
There is no doubt that reducing greenhouse gas emissions and reducing human interference and pollution of the oceans is the most fundamental way to save corals.
- Sunscreen is prohibited
A florida senator wants to ban certain sunscreens altogether because they could be harmful to marine life. In 2018, Hawaii passed a new bill that prohibits people from using sunscreen that harms coral reefs to protect Hawaii's reefs and tourism. The new ban could take effect in 2021.
- "Annihilate" the long-spined starfish
Long-spined starfish, also known as spiny-crowned starfish, known as "coral killers", prefer to eat corals and can cause a large number of live coral deaths. And the long-spined starfish is like a locust in the sea, spreading very quickly. In the past two years, Australian authorities have successfully eliminated more than 250,000 crown of thorn starfish through the "poison needle" method.
- Transplant corals from the seabed for reconstruction
Australian scientists have sown the seabed on the Great Barrier Reef and transplanted corals to rebuild coral formations. Corals lay only about 48 to 72 hours of spawning, and their breeding season has begun a few days ago, so how to scientifically "sow" has become a big problem. Nowadays, many projects will use diving robots for launch.
- 3D printed coral camp
Studies have shown that some fish are happy to shuttle through 3D printed reefs, just like in real-world coral reefs. 3D printed corals made from biodegradable materials are expected to mitigate coral degradation and will not have harmful effects on reef fish or breeding coral species. Test facilities for 3D printed corals are now in operation in the Mediterranean, Caribbean, Persian Gulf and Australia.
- Protect the mangroves on the shore first
Scientists at the U.S. Geological Survey have pointed to another way to save coral reefs: save mangroves first. Mangrove forests have intricate roots that protect the coast from sea erosion and serve as a refuge for corals.
- Build "Super Coral"
People are trying to save corals with breeding techniques. The scientists placed "pregnant" corals in aquariums that simulated climate warming, respectively, and then assessed whether epigenetic traits were passed on to the next generation. If so, these generations of molecules could contribute to the birth of "super corals," which are more powerful in the face of climate change than corals in nature.