Conservation of corals against the risk of development of crown-of-thorns starfish

21/06/2022

The crown-of-thorns starfish (Acanthaster planci) is a large starfish with a diameter of up to 0.5m. Unlike other starfish, their most preferred feeding habit is on living coral polyps, soft tissues of reef-forming corals and other coral groups. The populations of thorny starfish can grow rapidly with exponential growth leading to the destruction of coral reef structures and altering the ecological balance in the reef. During the explosive growth phase, the spiny starfish not only eats live coral, but also suppresses the replenishment of coral larvae. This prevents the growth of coral populations, hindering the natural resilience of the reef. This is an environmental problem that coral reef scientists around the world and Vietnam are focusing on solving to save coral reefs.

External morphology of the crown-of-thorns starfish Acanthaster planci

Outbreak development of thorny starfish at Nam Yet Island coral reef, Truong Sa Archipelago (Photo: Institute of Marine Environment and Resources)

In Vietnam, the crown-of-thorns starfish are commonly found in coral reefs from the South Central back inward to offshore islands such as Truong Sa, Con Dao and Phu Quoc. They reproduce quickly and created outbreaks on coral reefs in Nha Trang Bay Marine Reserve in 2010, and continue to exist and destroy coral reefs in this area until now (Nguyen Van Quan et al., 2020). In the coastal areas of Nam Yet Island, Truong Sa Archipelago, the crown-of-thorns starfish has grown and developed to such a high degree that its density can seriously threaten the existence of coral reefs in this offshore island area (Nguyen Dang Ngai et al., 2010).

In order to provide a way to handle this problem, the Institute of Marine Environment and Resources, Vietnam Academy of Science and Technology has researched and proposed a number of measures to limit the development of crown-of-thorns starfish, specifically:Chemical measures to limit the growth of crown-of-thorns starfish are believed to be effective and have been used in many areas of the world. As in Guam, divers use poison to inject adult crown-of-thorns starfish directly. The limitation of this method is that many chemicals are used to inject the crown-of-thorns starfish, in which toxic heavy metals such as copper sulphate work most effectively, which can pollute the marine environment. Some other poisons are also used to replace copper sulphate, but they are not very effective, easily damage the injection device and cause direct toxicity to the user. Currently, bisulphate salt is being selected as the best chemical to poison starfish because it can decompose in seawater.

The initial conventional physical method used was by divers using knives or sharp objects to cut the thorny starfish into debris just above the reef's surface. This is a quick and easy solution to apply on a large scale, but the limitation is that the debris on the body of the spiny starfish can be regenerated and grown into a new body at an exponential rate of growth compared with the original populations.

Using divers to collect thorny starfish and bury them on the shore is more feasible because it can involve a large number of volunteers and people living around the reef. However, the limitation of this option is that volunteers need to be well trained to avoid injury from starfish spines. In the years 2010 - 2011, the Management Board of the Protected Areas of Nha Trang Bay and Cu Lao Cham of Vietnam launched campaigns to eradicate thorny starfish with encouraging initial results.

Using divers to collect crown-of-thorns starfish at Nha Trang Bay Marine Reserve (Photo by Khanh Hoa Newspaper)

In addition, environmental management measures at the source are also applied. Some studies have shown that the increase of nutrients in the aquatic environment is related to the transport of nutrients from the continent to the sea, especially waste from coastal aquaculture activities. Shoreline is the underlying cause of large-scale outbreaks of crown-of-thorns starfish as it is an important source of nutrients for the larvae of the spiny starfish in the floating stage. However, due to the scope of macro-planning, it is necessary to have a strong impact on coastal development policy.

Chroniaare natural enemies of crown-of-thorns starfish (Photo: Australian Institute of Marine Science)

“Bò da” fish has the ability to destroy adult crown-of-thorns starfish, but it is a delicacy of seafood restaurants (Photo Institute of Marine Environment and Resources)

On the basis of the fact that there are a number of groups of organisms in the reef that are natural enemies of starfish, such as charonia, rock crab, “Bò da” fish, etc., technical measures such as fishing bans or restrictions can be used to create the conditions for wild populations to recover. From there, it will help to regulate the growth of starfish in the reef at a more appropriate level in the direction of ensuring ecological balance in the reef.

See more information about the article at Marine Environment Magazine:
https://sti.vista.gov.vn/file_DuLieu/dataTLKHCN//CVv359/2015/CVv359S82015048.pdf

Translated by Phuong Ha
Link to Vietnamese version

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