Apr 8, 2024
The Anambas Islands, nestled in the South China Sea, boast some of the world's most breathtaking coral reefs. These reefs are not only vital for the local ecosystem but also serve as a source of
livelihood for the communities that rely on fishing and tourism. However, an insidious threat has
been looming over this underwater paradise - the Crown of Thorns starfish (CoTS). In this blog, we
explore what the CoTS is, why it poses a significant risk to the Anambas Islands; and coral reefs, and what can be done to mitigate this threat.
The Crown of Thorns starfish (Acanthaster Planci) is a marine invertebrate that has become
infamous for its detrimental impact on coral reefs around the world. Named for its spiky
appearance, this creature is native to Indo-Pacific waters. While they play a natural role in reef
ecosystems by controlling fast-growing corals, their populations can explode due to various
environmental factors, leading to destructive consequences. Outbreaks of CoTS are generally
considered to be populations that exceed 15 individual starfish per hectare.
The Anambas Islands; coral reefs, with their rich biodiversity and vibrant ecosystems, face a serious
threat from the unchecked proliferation of the CoTS. Here are some reasons why this situation is
alarming:
- Overpopulation: In recent years, the Anambas Islands have witnessed an alarming surge in
CoTS populations. This surge can be attributed to factors such as nutrient runoff from
agriculture, overfishing of their natural predators, and climate change-induced changes in
ocean conditions.
- Rapid Coral Consumption: Adult CoTS can consume large amounts of coral tissue, leaving
behind bleached, dead coral skeletons. A single CoTS can devour up to 6 square meters of
living coral per year, making them incredibly destructive to reef ecosystems.
- Disruption of Ecosystem Balance: Healthy coral reefs are crucial for the overall balance of
marine ecosystems. They provide shelter, food, and breeding grounds for numerous species
of fish and other marine life. The decline of coral reefs can lead to a cascading effect on the
entire ecosystem, affecting both local wildlife and the communities that depend on them.
- Impact on Local Livelihoods: The fishing and tourism industries in the Anambas Islands are
heavily reliant on the health of the coral reefs. The degradation of these reefs due to CoTS
infestations can lead to economic hardship for the communities that depend on these
industries.
Efforts to combat the CoTS threat in the Anambas Islands require a multi-faceted approach:
- Population Control: Implementing targeted culling efforts to reduce the number of adult
CoTS can help curb their destructive impact on coral reefs. This must be done carefully and
with the involvement of trained professionals to minimize collateral damage.
- Monitoring and Early Detection: Regular surveys and monitoring of reef health can help
detect CoTS outbreaks early, allowing for prompt intervention.
- Promoting Sustainable Practices: Implementing sustainable fishing and agricultural practices
can help reduce the nutrient runoff that fuels CoTS population explosions. Additionally,
regulating fishing practices that target CoTS predators can help restore natural population
balances.
- Raising Awareness: Educating local communities, fishermen, and tourists about the
importance of coral reefs and the threats they face can foster a sense of stewardship and
encourage responsible behaviour.
As part of the Anambas Islands, Bawah Reserve is not isolated from the threat of CoTS outbreaks.
Over the past 12 months, we have noticed an increasing number of CoTS individuals on our reefs,
especially in exceptionally vibrant areas with lots of branching and tabulating coral colonies.
It is easy to spot CoTS activity even if you cannot find the starfish itself. Feeding patterns are
noticeable when small areas of coral look totally bleached and completely dead, but other areas of
the coral are very colourful and alive.
This is much different from other coral afflictions, such as disease (where coral death tends to
spread out uniformly from the original infection), or temperature-induced bleaching (where all the
coral colony bleaches at the same time). However, CoTS do have the ability to release a chemical
that will attract other CoTS in the area to come and feed on the same coral. In these cases, coral
death can look similar to other causes of coral death as there are so many individuals feeding on the
same coral. Tabulate coral species are often victims to many CoTS feeding on them at one time.
It is also sometimes possible to see a ‘trail’ across different corals where the CoTS has partially fed off
of one coral and then moved on to the next coral.
To reduce the populations of CoTS on our reefs we frequently dive in affected areas to
survey the population of individuals on the reefs, and if it is determined that there is an outbreak we
will do multiple dives to the affected area. During these dives, we will pick up the CoTS by using BBQ
tongs to pick up the starfish and then depositing it in a rice bag.
Once out of the water, we count the number of starfish as we take them out of the bag and bury
them in the forest, where they will decompose over time and feed the foliage that grows above
them.
In 2023 we removed a total of 892 CoTS from our reefs throughout 31 dives.
The Crown of Thorns starfish poses a significant threat to the coral reefs of Bawah Reserve and the
Anambas Islands as a whole, endangering both the delicate marine ecosystems and the livelihoods
of the communities that depend on them. By implementing a comprehensive strategy that includes
population control, monitoring, sustainable practices, and education, we can work towards
preserving the natural beauty and ecological richness of these precious reefs for generations to
come.
We must act now, united in our commitment to protect these underwater
wonders.
Fancy a trip to Bawah Reserve?
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