After years of fishing-related damage and coral bleaching, researchers and technicians are working to restore the once-thriving coral reefs at Dongsha Atoll.
White sand is a typical feature of some of the world’s most renowned beaches, but when visitors take a closer look at the white sand of Dongsha Island, they find that it consists of not only seashell fragments, but also bits of shattered coral. One does not have to go far to find the source of the coral, as the island’s central lagoon has many reefs, while Y-shaped, weathered pieces of Staghorn coral lie scattered along the beach.
Dongsha Atoll is a circular coral reef in the South China Sea lying about 450 kilometers southwest of Kaohsiung City, southern Taiwan. In 2007, the atoll was incorporated into Dongsha Marine National Park and came under the supervision of the Marine National Park Headquarters (MNPH), which was founded in October of the same year. With a land area of 1.74 square kilometers, Dongsha Island is the biggest island in the atoll, rising from the water at its western side. The lagoon within the atoll contains many scattered living coral colonies, small islands, shallow reefs and dead coral reefs.
According to researchers, the behavior of Dongsha’s coral can be a bit atypical. “Coral communities usually establish themselves on solid bases, such as continental shelves or shelves around islands,” says Chen Hui-ru, a technician working at the Dongsha Service Station, which officially opened in July 2010. “But the reefs at Dongsha grow on the sandy bottom of the lagoon. And the really special thing is that some patch reefs even grow on sea grass beds.”
Sea grass attaches itself to the sandy bottom of the atoll via rhizomes and roots, effectively decreasing the impact of wave and wind erosion and forming a relatively solid base for Dongsha’s coral to grow on, Chen says. Once the coral organism dies, the stony skeleton it leaves behind provides a nursery for other coral strains to grow on. As a result, thousands of the patch reefs grow on grass beds in the lagoon, assuming various branching, dome-shaped and leaf-shaped forms. Sea grass beds cover an area of about 12 square kilometers inside Dongsha’s lagoon and are home to patch reefs ranging from a few centimeters to several meters in height or width, depending on the species. Inhabitants of the patch reefs include fish, crabs, prawns, worms, algae, sponges and other invertebrates.
Dongsha Service Station researchers examine coral inside the lagoon. (Photo courtesy of Marine National Park Headquarters)
The coverage of living coral on the reefs varies significantly between sites located inside and outside the atoll. Outside, seawater circulates freely and the estimated live coral coverage reaches 80 percent. Waves originating in the Luzon Strait in the western Pacific propagate westward and help circulate water outside the atoll, Chen says. “The waves bring cold water to the outer part of the atoll and help cool it down,” she explains.
Coral colonies inside the atoll, however, sometimes suffer from limited water circulation, which results in hotter temperatures. Dai Chang-feng, a professor in the Institute of Oceanography at National Taiwan University (NTU), points out that coral reefs grow best at temperatures between 20 degrees and 29 degrees Celsius. The seawater in Dongsha’s lagoon, however, typically heats up to more than 30 degrees Celsius during the summer.
Aside from its 295 coral species, Dongsha Atoll is home to 614 fish species and 210 kinds of plants, says Song Zi-yang, deputy commander of the Coast Guard Administration’s Dongsha Command. The atoll also provides a stopover point for as many as 230 species of birds during their seasonal migrations through East Asia, he says.
In 1994, around 20 oceanographers and marine biologists were invited by the Council of Agriculture to investigate the living environment and health of Dongsha’s coral. Dai, one of the academics who made the trip, recalls that the ecosystem of the area was very healthy then, with at least 137 species of coral and more than 1,000 fish species. “It was like a coral forest,” he recalls.
The atoll’s biodiversity and rich marine resources, however, made it a popular fishing ground in the past, attracting fleets of fishing boats from countries along the South China Sea. While the area’s ecosystem suffered from the high number of boats operating in the area, the damage was compounded by the employment of unsustainable fishing methods such as the use of dynamite and cyanide, according to the Coast Guard.
El Niño Incident
To make matters worse, a massive bleaching incident occurred in 1998, when El Niño caused water temperatures to rise. As a result, the coverage rate of living coral on Dongsha’s reefs dropped to an alarming 10 percent from the original figure of roughly 80 percent, technician Chen Hui-ru says. The El Niño effect was particularly hard on the coral species inside the atoll that are sensitive to temperature changes. When he returned to Dongsha for further research in 2001, Dai says that the atoll “looked like a huge coral cemetery.”
Technician Chen Hui-ru, center top, explains the impact of the massive bleaching event on Dongsha’s reefs to foreign media. (Photo by Chen Chun-lin)
“Ten years ago, El Niño’s large-scale warming effect bleached out a lot of coral reefs around the world, together with many of Dongsha’s reefs,” says Wu Jui-hsien, another researcher at the Dongsha Service Station. “But because heat accumulates and stays high inside the atoll, the coral reefs there haven’t recovered as well as other places around the world.”
Whether caused by overfishing or El Niño, damage to Dongsha’s coral has had a wider effect on the surrounding ecosystem, as currents flowing past the atoll make it a way station for marine organisms traveling between the South China Sea and the Taiwan Strait. With its large reefs and sea grass beds, Dongsha serves as a prime spawning ground for fish as they travel with the currents, Wu says. Dai notes that when the coral reefs at Dongsha are damaged, marine species that migrate through the area have difficulty in obtaining food, with carryon effects on up the food chain.
In 1999, the responsibility for protecting Dongsha passed from the Ministry of National Defense to the Coast Guard, while the Kaohsiung City Government took over general administration of the area in 2000. To protect Dongsha’s ecosystem, in 2002 the city government prohibited fishing within a 12-nautical-mile (22-kilometer) radius of the atoll. A higher standard of conservation was imposed in 2007 when the marine park was established, as its mission is to protect the area’s marine and terrestrial resources, promote international scientific research and establish a venue for ecotourism, according to the MNPH.
The Coast Guard is responsible for enforcing environmental regulations in the waters around the atoll. In addition to regular patrols through the area, in 2005 the Coast Guard began dispatching cruisers to expel fishing boats entering the 12-nautical-mile exclusion zone. Although it did not provide a figure for Dongsha alone, the Coast Guard reported that in 2009 it expelled 671 fishing boats that had illegally entered the waters around Dongsha and the Nansha Islands, which also lie in the South China Sea and are known in English as the Spratly Islands. “The Coast Guard carries out scheduled and unscheduled patrols to protect the environment and fisheries around Dongsha Atoll,” Deputy Commander Song Zi-yang says, and even goes as far as removing resupply platforms illegally erected by fishermen in the waters around the atoll.
Night Market at Sea
Wu praises the Coast Guard’s recent efforts, saying that when researchers arrived at Dongsha Island as little as two years ago, they could see many fishing boats anchored just off the island. “When night fell, there were so many boats that their lights looked like a night market on the sea,” he describes. “But now they patrol more often and it’s apparent that the number of fishing boats in the area has decreased.”
While the Coast Guard is working to prevent further fishing-related damage at Dongsha, the park administration is turning its attention toward restoration of the damaged coral. The first stage of that effort—conducting research to determine the extent of the damage and which reefs are salvageable—is occurring now, NTU’s Dai says. Along with the national park’s technicians, the Taiwanese Coral Reef Society (TCRS) and a group of students from National Sun Yat-sen University in Kaohsiung are also carrying out short-term research on Dongsha’s reefs. Much of the underwater research Dongsha technicians perform is accomplished by scuba diving. “Sometimes we even jump into the sea right from the runway of Dongsha Airport when we start our work,” Dongsha technician Chen Hui-ru says.
A student researcher from National Sun Yat-sen University tests the health of coral samples. (Photo by Chen Chun-lin)
The research often focuses on the diverse species of coral that create patch reefs in the area. As each species reacts to environmental stressors differently, researchers have discovered that survey locations around the atoll vary widely in their percentage of live coral coverage. “So we can’t provide an overall number for the coral coverage of the whole atoll,” Chen says. “But our recent studies do show that the reefs in the atoll aren’t suffering further damage now.”
Over the past two years, Dongsha researchers have been studying reefs close to the main island and sometimes in the center of the lagoon. The single-engine boat the technicians are currently using is too small to withstand the waves further out in the open sea, Wu says, although the station plans to purchase a double-engine boat to extend the reach of research activities.
A shortage of personnel is the chief factor slowing research and restoration efforts at the atoll, technicians say. The TCRS members and university students are only able to stay for short periods, and the Dongsha Service Station has just nine full-time staffers, not all of whom work on the island at the same time. “Usually, only four or five stay on the island,” Wu Jui-hsien of the Dongsha Service Station says. “And sometimes last year there were just two or three.” Chen Hui-ru adds that Dongsha’s technicians specialize in different fields, and that only she, Wu and Kao Ji-bang focus on coral research and restoration. Along with coral research, all crew members also have other tasks that fill their working hours, including performing weekly patrols, recording ecological phenomena occurring on the island, restoring native plants and removing alien species in cooperation with the Coast Guard.
Performing research while scuba diving can be dangerous, particularly in a place as remote as Dongsha, as the Coast Guard is well aware. “If we have an accident, it’d be difficult for them to rescue us in time,” Wu says, explaining why the Coast Guard has a strict rule that all research that involves scuba diving must be reported at least one day in advance so that rescue transportation can be made available.
Long-Distance Larvae
The atoll’s remoteness also means that currents bring relatively few coral larvae from other islands, which adds to the difficulty of restoring Dongsha’s reefs. Larvae spawn at Nansha and at the Paracel Islands, but the former lies about 1,190 kilometers to the southwest of Dongsha and the latter about 450 kilometers in the same direction. “It’s difficult for coral larvae from other islands to travel such a long distance to develop into a single baby coral polyp at Dongsha,” Dai says.
Staghorn Coral at Dongsha. Coral provides shelter for many animals in this complex habitat, including various species of colorful coral reef fish. (Photo courtesy of Marine National Park Headquarters)
Giving the dearth of larvae arriving from other areas, Dai believes that transplanting coral is the most viable option for restoring Dongsha’s reefs. Moreover, transplantation has been used successfully to promote the growth of new coral on damaged reefs around the world, the professor says. “In the ocean, it’s impossible to ‘plant’ the larvae and ‘grow’ a coral forest anywhere you like,” Wu Jui-hsien says. “What we can do is transplant some healthy coral to the damaged areas, but the success of the work depends on the coral’s vitality and ability to reproduce.”
Coral grows at a slow pace, and the growth occurs at different rates for different species, Chen Hui-ru points out. “Most wounded corals recover slowly,” she says. The species Porites lobata, for example, grows just 1 to 2 centimeters per year, she says, while Acropora coral, one of main reef-building corals, is a fast-growing exception, with branch tips extending as much as 10 centimeters in a year. Dongsha Service Station technicians mainly harvest healthy Acropora coral growing in the shallow water to the north of the island for transplantation, as the genus is capable of withstanding the high temperatures at the restoration site in the central lagoon. To reduce damage, the station tries to harvest and transplant the bare minimum of coral necessary for testing the effectiveness of the method.
Restoring Elkhorn coral, a species of Acropora, can be as simple as picking up broken Elkhorn fragments and attaching them to barren reefs, Wu explains. “If the transplanted coral survives, it can reproduce on its own in the future,” he says. Not every species of Acropora withstands the transplantation process equally well, however. Some species that secrete mucus when their branches are broken off have a particularly low survival rate, while seaweed must be cleared from the transplantation site to ensure the survival of others, Wu says.
Chen and Wu acknowledge that in the wider perspective, the problem of coral bleaching is huge and their efforts are small. Although restoring the coral reefs at the atoll to pre-1998 levels continues to be an uphill battle, the Dongsha technicians remain resolute about developing viable methods for transplanting coral, boosting the number of coral species in the area, improving their habitat and monitoring the impact warming seawater has on them. There are plenty of challenges, but they see the goal—that of a beautiful atoll with a healthy coral forest—as well worth the effort.
Write to Vicky Huang at powery18@mail.gio.gov.tw