Global warming, ocean acidification and pollution: most of the world’s coral reefs are suffering immensely. But there are many projects worldwide to help the stressed cnidarians.
“Very carefully,” says Tran Van Chuong, placing a small brown coral with delicate white tips in the hands of a tourist. Wearing a diving suit, he kneels with her in front of a white metal frame in the shallow water near the Vietnamese holiday resort of Nha Trang. A fragment of the species Acropora muricata is attached to each link – very carefully. The holidaymaker carefully places them in position, then Chuong gently attaches the fragile cnidarians with cable ties. “Corals are extremely sensitive,” he knows.
Tourists are often denounced as coral killers: a careless kick with a diving fin or a light touch is enough to destroy hundreds of years of growth. It is rather the exception that holidaymakers contribute to saving the endangered marine animals. A project launched last year by the Hotel Villa Le Corail Gran Meliá in collaboration with a team of experts from the company Avatar is trying to do just that: combine environmentally conscious tourism and constructive marine protection.
As in other dream locations around the world, many corals in Nha Trang have bleached or died in recent years – partly due to warming as a result of climate change. When the water temperature is too high, the stressed cnidarians shed the algae that give them their color, which has led to almost half a dozen mass bleachings in the Australian Great Barrier Reef – the largest reef in the world – within eight years.
Coral-eating starfish
In Nha Trang, which is located directly on the South China Sea, where a cool current mitigates the effects of ocean warming, most of the corals fell victim to a violent typhoon in 2017. Marine pollution, overfishing and a monster called the crown-of-thorns starfish have also taken a heavy toll on them.
The often red-colored starfish prefer to feed on hard corals and are native to almost all tropical waters of the Indo-Pacific. Divers regularly collect the animals, which are equipped with poisonous spines, in the bay in front of the hotel. “It’s a bit like weeding in the sea – and important because they play a major role in the death of coral reefs,” explains Hoang Do, marine expert at Avatar.
The company uses two different methods to grow new corals: firstly, frames that tourists can place in the sea, either in the bay or off a nearby island. Secondly, strings to which fragments of particularly resilient and fast-growing coral species are attached at a depth of several metres. An underwater breeding station or, if you like, a kind of coral nursery.
What exactly are corals?
Corals are invertebrate, colony-forming marine animals that consist of small polyps and do not move. They secrete calcium carbonate at their base and use it to form reefs that grow into enormous structures over the course of many years. They live on these layers of calcium carbonate in symbiosis with tiny algae, which give them their bright colors and provide them with food.
“Although coral reefs cover less than 0.2 percent of the earth’s surface, a quarter of known marine species depend on them,” explains the environmental organization WWF. They offer protection to ocean dwellers and serve as breeding and rearing grounds.
There are two main types of coral: soft corals and stony corals, also known as hard corals. In general, the flower animals can grow between 1 and 20 centimeters per year, with staghorn corals growing the fastest. In addition to the extremely resistant Acropora muricata, Avatar in Nha Trang also works with other stony coral species such as the cream-colored Porites rus with its many thin branches, the bush-forming Pocillopora damicornis and the Acropora hyacinthus, also known as table coral.
If the fragments are strong enough, they are “transplanted” onto artificial concrete reefs. While snorkeling, vacationers can see not only the breeding station and several already prepared but still bare concrete reefs, but also the result of the hard work. Several artificial reefs are already covered with coral, among which tropical fish frolic.
Success in the shortest time
“Tourists are always completely stunned when we tell them that we only planted these corals in early 2023,” says Hoang Do. A Frenchman nods in agreement as he takes off his fins and snorkel on the beach: “It’s really amazing. I never thought it would be possible to create a new reef in such a short time.”
A small plaque with the tourist’s name and exact coordinates has been attached to the rack just placed in the sea with dozens of Acropora muricata fragments – which are now also starting their growth process. The Hotel Villa Le Corail will regularly inform him about the progress of “his” corals – a special service for all those who are actively involved in the construction of the new reef.
There are countless approaches worldwide to help coral reefs in distress. Corals are not only raised in the sea, but also in aquariums and farms on land. In addition to artificial reefs, there are attempts to save damaged reefs by planting new corals. Scientists are also breeding coral hybrids that can cope better with warmer water temperatures. The search is on for a type of super coral that can withstand climate change.
Given the devastating state of most reefs, the efforts may seem like a drop in the ocean – or rather, ocean. But they show that rescue is possible – even if so far on a smaller scale. A selection of other projects:
Underwater museum in the Pacific and Caribbean
Art can also help to raise awareness of ocean problems. Since 2006, Briton Jason deCaires Taylor has placed hundreds of sculptures made of environmentally friendly materials on the seabed in the Caribbean and the Pacific, which over time develop into artificial coral reefs.
“The sculptures create a habitat for marine life while illustrating the fragility of humans and their relationship with the marine world,” Taylor’s website states. The installations attract tourists to the artificial coral reefs and thus also contribute to the recovery of the natural reefs.
The artist and former diving instructor built the world’s largest underwater museum with life-sized sculptures off Cancún in Mexico. For example, a man sits underwater on a sofa in front of the television. Algae and corals turn the works of art into living figures that are constantly changing.
“Midwifery” from the aquarium laboratory
The four-meter-high coral reef in the California Academy of Sciences natural history museum in San Francisco is one of the largest indoor reefs in the world. But behind the colorful backdrop of brightly colored fish, research is also being conducted: As part of the “Hope for Reefs” initiative, the aquarium has been working since 2016 on the artificial breeding of corals, which are then released into the sea. The scientists say it is the first facility in the USA to be able to get corals to spawn simultaneously in an aquarium facility. This is because the process is difficult to replicate in the laboratory.
To do this, researchers collected corals around the Pacific state of Palau and created conditions in the laboratory that were as similar as possible to those found in the corals. The circumstances have to be exactly right to encourage the cnidarians to reproduce sexually – from temperature to light and currents to the lunar cycle.
Corals only spawn once a year, whether in the sea or under artificial conditions. They then release small packets of eggs and sperm that float to the water’s surface. This spectacular underwater snowstorm is called “coral spawning.”
Employees catch the small bundles with nets and mix eggs and sperm from different colonies to crossbreed them. At the end of 2023, the laboratory welcomed thousands of baby corals in a short time window. Through breeding, the researchers want to obtain embryos and larvae that can survive even under stress factors – such as rising temperatures.
Microfragmentation in the Bahamas
After completing their studies, two Americans founded a commercial coral farm on land in the Caribbean island state of the Bahamas a good five years ago: Coral Vita. They use the technique of microfragmentation to grow corals particularly quickly – up to 50 times faster than in nature, they say.
Corals from local reefs, cut into small pieces, are grown in water tanks in Freeport on the island of Grand Bahama, to then be re-implanted into reefs. The grown corals are expected to mature in months rather than decades and also become more resilient to warmer and more acidic sea water.
The farm in Freeport can be visited, corals can be “adopted”, and donations are matched by the Mexican beer brand Corona. Coral Vita was one of the first recipients of the Earthshot Prize in 2021, established by the British heir to the throne, Prince William.