In order to conserve the healthy coral reefs of the Southern Four Islands of Penghu, the Marine National Park Headquarters (hereinafter referred to as the Headquarters) brought together 22 divers from the Penghu Marine Biology Research Center of the Fisheries Research Institute, the Agriculture and Fisheries Bureau of the Penghu County Government, the Fire Bureau, and the Penghu Zooxanthellae Association, among other units. With support from the Penghu County Government vessel Pengxing, a crown-of-thorns starfish removal operation was launched. The Headquarters stated that today (June 26), a total of 142 crown-of-thorns starfish were removed from the waters of Xiji Islet, effectively reducing their population density in the area.
The Headquarters further indicated that during yesterday’s comprehensive coral reef survey in the waters of Xiji Islet, coral cover was found to reach approximately 50%. As for other indicator species, although fish species richness and abundance were relatively low, other invertebrate indicator species—such as giant clams, sea urchins, and sea cucumbers—met international standards for healthy coral reefs in both quantity and density.
The survey also recorded a density of 280 crown-of-thorns starfish per hectare in the waters of Xiji Islet. Known as “coral killers,” such a high density poses a serious threat to local coral reefs. Therefore, today’s targeted removal action was carried out. During two dives, 142 crown-of-thorns starfish were removed, demonstrating highly efficient removal results.
The Headquarters noted that manual removal is an effective way to reduce crown-of-thorns starfish population density. However, given the high density in the waters of Xiji Islet, continuous monitoring and repeated removal efforts will be necessary to effectively mitigate damage to coral reefs. In the future, “Comprehensive Coral Reef Checkups” will continue to document ecological changes in the coral reefs of the Southern Four Islands of Penghu, alongside long-term monitoring of crown-of-thorns starfish densities to maintain reef health.
Healthy Coral Reef Reference Guide (per 100 m² reference values)
| Coral Cover |
> 50% |
| Butterflyfish |
> 5 individuals |
| Sweetlips |
> 1 individual |
| Snappers |
4 individuals |
| Groupers |
0.5 individuals |
| Cherry Shrimp |
1 individual |
| Diadema Sea Urchin |
2–3 individuals |
| Edible Sea Cucumber |
0.5–1 individual |
| Crown-of-Thorns Starfish |
< 0.2 individuals |
| Giant Clam |
> 0.1 individuals |
| Triton’s Trumpet |
> 0.1 individuals |
| Lobster |
> 0.1 individuals |
The health status of a coral reef should be evaluated comprehensively using the above indicators. If some of the indicator values meet the standards, the reef may be considered healthy.
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| Figure 1. Personnel removing crown-of-thorns starfish (Provided by the Headquarters) |
Figure 2. Survey personnel conducting a comprehensive coral reef check in the waters of Xiji Islet, showing good coral cover (Provided by the Headquarters) |
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| Figure 3. Researchers measuring body length and arm count of crown-of-thorns starfish (Provided by the Headquarters) |
