In the height of summer in August, the sky is blue, the sun shines directly into the clear sea, and the water temperature exceeds 30 °C.
Li Yuanchao surfaced, climbed on the boat, squinted his eyes in the harsh sunlight, pulled open his wetsuit, and wiped away the sweat and sea water mixed on his face. After a short break, he put the gas cylinder on his back again, picked up the net pocket and the long clip, and dived into the water.
Li Yuanchao is an associate researcher at the Hainan Academy of Oceanography and Fisheries Sciences, and one of the tasks of his team is to monitor and protect the marine environment and restore it. One of the purposes of his trip to the Paracel Islands in the South China Sea was to catch 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.
Coral reefs are one of the most diverse ecosystems on Earth and are known as undersea rainforests, covering less than two-thousandths of the seafloor but providing a living environment for nearly 30% of marine species.
According to public information, the South China Sea has 2.57% of the world's coral reef resources, ranking eighth in the world. In 2018, the long-spined starfish erupted in the Sansha waters of the South China Sea, seriously threatening the health and ecological balance of the islands and reefs.
The fishing process is simple and arduous. Li Yuanchao and his colleagues dived about 15 meters underwater and found long-spined starfish — some of them lying on the coral and eating wildly, others hiding in the crevices of the reef to rest. Fishermen carefully pick them up, put them in the net pockets, and look for the next target.
A bottle of compressed air can support underwater breathing for 40-60 minutes, and Li Yuanchao repeats the action of "clamping and bagging" until the air is about to run out, or the "captured" starfish is too heavy to carry, they will float to the surface and pour the booty on the ship.
Eight people, spent more than a dozen hours, caught more than 3,000 long-spined starfish in a 10-hectare area, but Li Yuanchao said that the catch was not large. In the first half of this year, Sansha City launched a round of large-scale centralized clean-up of long-spined starfish, with more than 60,000 fished.
While "hunting" long-spined starfish, researchers are also cultivating new coral reefs, and in this contest with starfish and time, they are full of confidence in the future of coral reefs in the South China Sea.
In West Sand Pan Islet, the clean-up crew is cleaning up the long-spined starfish with clips and net pockets. Courtesy of respondents
Outbreak of coral "killers"
"Ugly", this is the first reaction of Li Xiubao, a professor at the State Key Laboratory of Marine Resource Utilization in the South China Sea at Hainan University, mentioning the long-spined starfish.
The long-spined starfish is shaped like a wheel, stretching out 8-21 tentacles from the center to the surroundings, covered with thorns of different lengths, and the relatively soft abdomen clings to the submarine reef or coral, looking like a flattened hedgehog from a distance. An adult long-spined starfish generally has a spoke diameter of 20-30 cm, and the largest can even reach 70 cm.
"Long-spined starfish have a lethal effect on coral reefs", Li Xiubao told the Beijing News reporter, long-spined starfish usually climb to the coral and eat the surface of the coral. Corals that are eaten often die from the loss of polyps, or even die directly, leaving only a piece of "white bone" - bleached coral.
Corals found in the Paracels have been eaten to bleach by long-spined starfish. Courtesy of respondents
In a healthy coral reef ecosystem, there is a dynamic equilibrium between the long-spined starfish and other seafloor organisms. Long-spined starfish are tasked with cleaning up "sick" corals and maintaining the healthy growth of coral reefs.
Li Xiubao introduced that in the normal coral reef ecosystem, the distribution density of long-spined starfish is about 2-3 per hectare. In areas where coral coverage is about 30 per cent, coral growth barely offsets the nibbling of 15 spiny starfish per hectare.
And the long-spined starfish also has natural enemies. The long-spined starfish has numerous predators in the floating wave larval stage, such as some plankton-feeding fish. Subsequently, the larvae of the long-spined starfish will attach to the seafloor, and some large invertebrates can still be scraped. As the individuals of long-spined starfish grow larger, a small number of carnivorous fish, including groupers and phylloscopes, can prey on them. After the adult long-spined starfish, only a very small number of marine creatures such as Dafa snails are left.
Dafa snails eat long-spined starfish, and long-spined starfish eat corals. In this food chain, once the number of a species fluctuates significantly, the equilibrium will be completely broken.
In May last year, the Coral Reef Branch of the Pacific Society of China discovered an outbreak of long-spined starfish in the waters off Panshi Island during an ecological survey. Liu Sheng, a researcher at the branch, told the Beijing News that when he and 4 divers went down to the southwest-south side of Panshiyu Island, they found a large number of long-spined starfish.
This year, he passed panshiyu again on the way to the scientific expedition. Since the typhoon has just passed, the wind and waves are still large, and the long-spined starfish are mostly concentrated in the reef disk with smaller winds and waves. On Panshi Island, the long-spined starfish are concentrated on the northeast side of the sheltered northeast.
Li Xiubao said that on the reef disk with the worst outbreak, the distribution density of long-spined starfish once reached 700 per hectare. "I've seen a coral about 30 centimeters tall with 5-6 long spiny starfish lying on it, with tentacles all stacked on top of each other, and I couldn't see the coral itself at all."
Once the ecological balance is upset, more creatures will be affected in addition to the reef itself. The continuous growth of coral reefs provides food and shelter for many marine life such as tropical fish and molluscs, and the gnawed coral reefs naturally lose this shelter.
Some people say that the long-spined starfish is like a locust in the sea, spreading very quickly. Li Xiubao said that they move faster than other starfish, and a long-spined starfish can eat about 250 cm2 of live coral every day.
Last August, researchers found a long-spined starfish in the Paracels, which was nibbling on corals. Courtesy of respondents
Human activity accelerates starfish eruptions
The outbreak of long-spined starfish in the South China Sea is the second time since observations have been recorded.
Around 2006, researchers monitored an outbreak of long-spined starfish in the waters off Ganquan Island on the west side of the Paracel Islands. Subsequently, outbreaks were observed in the Xuande Islands on the eastern side.
According to the 2009 Hainan Marine Environment Quality Bulletin, the coral reef ecosystem in Xisha showed a trend of degradation in that year, and the number and types of live corals in reef building were significantly reduced, which was a sub-healthy state. The coverage of live reefer corals fell from over 50 per cent in 2006 to less than 10 per cent that year.
Since then, the destruction of coral reefs by long-spined starfish has continued, with the average of living coral cover in the Paracels in 2014 being only 4.1 percent. It wasn't until 2018 that the number slowly recovered to an average of 8.58 percent.
There have been similar situations abroad. As early as the 1960s, a coral island in Australia's Great Barrier Reef had erupted with long-spined starfish, and since then there have been four outbreaks, the outbreak has continued to expand, the most recent of which was in 2010.
The local coral reefs have also been severely damaged. A 2012 study by the Australian Institute of Oceanography showed that more than half of the coral layers of the Great Barrier Reef have disappeared in the past 27 years, while the eruption of long-spined starfish has been associated with the disappearance of 42% of the great barrier reef coral layers.
It is generally believed that climate change brings acidification of the seawater, which slows the growth rate of corals and does not offset the rate of nibbling on the long-spined starfish.
In addition, the eutrophication of seawater and the reduction in the number of natural enemies caused by human activities are also considered to be contributing factors.
The influx of domestic sewage has gradually trophicated the coral reef seas that are originally poor in nutrients, and the plankton has grown in large quantities, which has greatly improved the "diet" of juvenile long-spined starfish and improved the survival rate of juveniles.
In China, the snail is heavily caught because of its large shell and beautiful pattern, and then sold as an ornament, while the spotted scaly pufferfish can be eaten or pet-reared.
Huang Hui, head of the coral biology and coral reef ecology discipline group at the South China Sea Institute of Oceanography of the Chinese Academy of Sciences, once said that global climate change is the main cause of coral reef degradation worldwide, specific to the waters around China, human activities are the main cause of degradation.
Li Haifeng, chairman of the Sanya Association for Science and Technology, has said that land-based sewage discharge, illegal fishing activities, the large number of predators such as long-spined starfish and over-capacity tourism activities are the main threats to coral reef ecosystems.
Statistics from the Australian Institute of Oceanography show that the long-spined starfish has an outbreak every average of every 17 years, and this outbreak cycle is shortening with the intervention of human activities.
Tens of thousands of starfish were "seized"
More than a decade ago, after the paracel Islands first monitored the outbreak of long-spined starfish, neither researchers nor local governments paid enough attention.
"It wasn't until around 2009 that I suddenly found that the corals were almost all eaten." Liu Sheng said.
Therefore, after receiving a briefing from the Coral Reef Branch of the China Pacific Society last year, the Sansha Municipal Government quickly joined forces with a number of agencies to form a clean-up team, organized experts to conduct research, and began to clean up on a small scale.
In the first half of this year, in the waters of Panshiyu Island, where the outbreak of long-spined starfish was severe, Sansha City launched a round of large-scale centralized clean-up of long-spined starfish. This is also the first time that China has carried out large-scale clean-up of long-spined starfish.
It is estimated that the number of long-spined starfish in the area is about 60,000 to 100,000, and if left unchecked, in one to two years, long-spined starfish can eat all the coral reefs in the sea.
In addition to marine researchers, local fishermen were involved in the cleanup. The three fishermen who undertook the task of clearing the waters of Panshiyu Island were all from Tanmen Town, Qionghai City, Hainan Province, and they had been fishing in the South China Sea for generations, with rich experience at sea and excellent water quality.
The three members of the "Einsatzgruppen" set sail in an ordinary fishing boat and worked at sea for 20 consecutive days without positioning, detection equipment, or even a mobile phone signal, diving and fishing. Excluding the time between land and Panshi Island, the three fishermen cleared more than 45,000 long-spined starfish in seven days.
The cleaning tools are clips and net pockets, and although the method is not complicated, it is not easy to clean up. The long-spined starfish is lying out at night and likes to hide in rock crevices during the day to "sleep", which makes the cleaning work more difficult.
In addition, due to safety and diving equipment limitations, the clearance crew generally travels to a depth of less than 20 meters below sea level, but deeper waters may also hide a large number of long-spined starfish. "After the superficial arrest, I often crawl out of other places," Liu Sheng told the Beijing News reporter.
At the same time, it is a dangerous job, the long-spined starfish is called "devil starfish", and each of its spines contains neurotoxins, and once it is stabbed, the skin will be red and swollen, and the pain will be unbearable.
"In the process of fishing, we must do a good job of personal protection." Li Yuanchao introduced that people involved in the clean-up need to have excellent diving skills, and they should also wear gloves and wear thicker wetsuits during the fishing process.
Due to the excessive number of long-spined starfish cleared, these captured "coral killers" will be loaded into cold storage, transported back to Haikou, dried and landfilled as dry garbage.
Dried long-spined starfish are transported to land for landfill. Courtesy of respondents
This treatment is done to prevent the carcasses of long-spined starfish from contaminating the soil and fresh water of nearby islands, Liu explains.
In response to the Beijing News reporter's question about whether the long-spined starfish can be sold as food, he said that some cleaning personnel have tried to eat a little long-spined starfish, "It is difficult to eat, and it hurts after eating." The reporter learned that the edible starfish sold on the market is generally a five-pointed star-shaped spiny sea disc car.
Researchers have tried to "turn the harvested long-spined starfish into treasure", such as trying to extract the active ingredient from the long-spined starfish into medicine; trying to dry and crush it thoroughly, mixing it with other materials and making recycled plastic; or using it to feed artificially farmed Dafa snails. So far, however, these attempts have not been successful, and drying in landfills is still the best way to deal with long-spined starfish.
Cost and monitoring challenges
Cleaning methods that rely entirely on artificial fishing are costly.
Li Xiubao calculated an account for the Beijing News reporter, the cost of renting a fishing boat is about 20,000-30,000 yuan / day, the cost of hiring diving operators is about 1500 yuan / day, if you go to the far sea for cleaning, the time spent on the way back and forth alone will be 4-6 days.
In addition, uncertainties such as weather cannot be completed on schedule, and subsequent processing processes such as cold chain transportation will require additional costs. "The current clean-up effort is almost cost-effective," said one person involved in the clean-up.
In Australia, which also faces outbreaks of long-spined starfish, the researchers took a different approach by injecting a cultured bacterium into the body of long-spined starfish, causing it to die of infection. Between 2014 and 2016, more than 200,000 long-spined starfish were wiped out. The researchers have even developed a robot that carries an injection needle and specializes in hunting long-spined starfish.
However, will allowing a large number of long-spined starfish corpses to rot in the sea have an impact on the already fragile coral reef ecology? Mr. Li said the impact of this approach remains to be seen. In his view, artificial fishing, despite its huge costs, is still the most effective and thorough way to clean up at this stage.
In addition, how to find the flashpoint of the long-spined starfish in the first place is not only a scientific problem, but also a certain element of luck.
The use of robotics and remote sensing techniques has been proposed, however, due to differences in seabed landforms and disturbances from currents, these technologies have limited effectiveness in ocean monitoring. Manual cruises are still the best way to obtain real information under the sea, but the existing number and frequency are far from timely monitoring.
Several experts who have participated in the south China Sea natural resources survey said they found the long-spined starfish flashpoint either by accident during the cruise or through reports from diving enthusiasts and fishermen. But divers and fishermen, with limited expertise, sometimes "turn a blind eye" even when they spot something.
In Liu Sheng's view, the top priority is to establish an effective multiple monitoring system, "we can consider through mechanism innovation, fishermen who are familiar with the surrounding sea conditions into the monitoring system, train them, and become mobile monitoring points." ”
The artificial parade process is arduous, "the temperature in the Sansha area is high, and the ultraviolet radiation is relatively strong, even if you wear a diving suit, you have the risk of sunburn." Liu Sheng mentioned that they have become accustomed to tanning. In order to prevent the dissolution of sunscreen from causing harm to corals, researchers can only use physical sunscreen in daily sewage - wrapping themselves tightly.
On the way back from Panshi Island, the clean-up crew dried the long-spined starfish caught on the boat. Courtesy of respondents
Bring corals back to life
Faced with the devastation left by the long-spined starfish, researchers are trying to plant new corals.
Corals reproduce in two ways, sexually and asexually. The former is the cultivation of coral fertilized eggs into coral larvae in an artificial environment and then released back into the ocean; the latter is similar to tree grafting, cutting healthy corals into finger-sized broken branches, which are briefly bred and attached to pre-selected reefs.
Li Xiubao said that although the coral reefs cultivated through sexual reproduction are well adapted, the cultivation speed is slow and the cost is high. Currently, asexual reproduction is more often used in coral reef restoration.
Just as large, leafy trees can provide a home for birds, complex corals can provide shelter for fish. Therefore, when researchers "graft" corals, in addition to mainly selecting common species in the local area, they will also tend to choose branch corals with complex structures, which is usually more conducive to the restoration of coral reef ecology.
Laying a good foundation to build a house, when encountering areas that cannot be repaired, researchers will place several tons of bionic reefs and plant corals on this basis.
The staff used ropes to hoist the bionic reef and put them into a predetermined position more than ten meters underwater, and under the impact of the current, the ropes sometimes swung sharply, or even entangled together. Once entangled, the diver has to cut the rope to get out.
At present, Huang Hui's team has successfully planted about 100,000 square meters of coral in the South China Sea, and by the end of 2016, the survival rate of coral broken branches is about 75%. The nursery created in the coral reef restoration demonstration area can cultivate 40,000 coral branches at the same time.
After the reef is built, the researchers will stock some marine life, "the underwater world is not silent, the marine life will also make different sounds, these sounds will attract the creatures back." Liu Sheng said.
When the returning fish stay in the "Deluxe Sea View Room" in the coral reef, they will also help to do some cleaning work and nibble on the algae that covers the surface of the coral. When the "house" is cleaned, the fertilized eggs of corals wandering around in the sea can "move in" at any time, and then revitalize the whole coral.
"Natural restoration is the mainstay, supplemented by artificial restoration" is the thinking of most coral reef restoration teams. Studies have shown that nature can initiate an automatic restoration program as long as 15% of the coral reef ecology in a certain area is restored and the biological movement roads are kept open.
But despite nature's amazing resilience, it will take time for the nascent reef to grow. In this race against time, the researchers hope to gain more opportunities for the recovery of coral reefs through artificial intervention.
In Li Xiubao's view, overfishing is the main reason for the weakening of the control of natural enemies of long-spined starfish. People's consumption concepts need to be correctly guided, and the consumption of Dafa snails and other reef fish and invertebrates should be reduced.
"Be confident in the future. Those reefs I've seen before, I want to see again. Huang Hui said.
Beijing News reporter Han Qinke
Edited by Wang Jingyi Proofreader Jia Ning