Crown of Thorns Starfish

Updated: Aug 23, 2021

The crown of thorns starfish (Acanthaster planci) are marine invertebrates that mainly feed on coral and algae. Invertebrates are spineless creatures that don’t have any backbone. Some examples are sea stars, insects, earthworms, and lobsters. The crown of thorns starfish is naturally found in coral reefs throughout the Indian and Pacific oceans.

Since the crown of thorns starfish consumes corals, sea sponges, and numerous algae, it’s important for marine biologists to check and maintain their growing population. If their population is not maintained, these creatures can consume numerous surrounding coral reefs, harming not only the ecosystem but human lives. Luckily there are some predators that help marine biologists keep these starfish in check, including giant triton snail, humphead wrasse, starry pufferfish, and titian triggerfish.

Due to numerous human activities such as overfishing, pollution, climate change, and underwater explorations, these creatures are pressured to reproduce to ensure their species survives. In normal conditions, the crown of thorns starfish population helps maintain a healthy coral reef and ecosystem by eating faster-growing corals and allowing new coral species to flourish, enhancing the coral reef's diversity. However, if these creatures aren't maintained due to numerous human activities, these creatures can be serious threats.


As the name implies, crown of thorns starfish are regular starfish covered in numerous long poisonous spines. Their color ranges from purplish-blue to reddish-gray to green. Their general size is around 25-35 cm in diameter and their spines are around 2 inches long attached to 7-23 arms. Despite their appearance, the crown of thorns starfish are surprisingly agile. Despite having poisonous spikes, there are certain predators that are immune to their venom, including the giant triton snail, the humphead wrasse, starry pufferfish, and titan triggerfish.

Why are they misunderstood?

As previously stated, the crown of thorns starfish are extremely helpful in maintaining healthy coral reefs and other sea life. When the crown of thorns starfish populations are at healthy levels, they help keep fast-growing corals in check and allow new smaller corals to flourish. However, if their population grows out of control there won't be any coral reefs left. Without any coral reefs, many surrounding fish species that utilize the coral reefs for food and shelter would be open to numerous predators, drastically decreasing their populations.

In the 1970s on the northern Great Barrier Reef, a COTS outbreak occurred that lasted eight years. This outbreak peaked with about 1,000 starfish per hectare, leaving 150 reefs devoid of coral, and 500 reefs damaged.

Although these outbreaks occurred for thousands of years, there have been more frequent and severe outbreaks due to the world’s current climate. Another major issue that was not addressed previously could be runoff, where toxic chemicals wash from sewers or land into the ocean. This pumps more nutrients into the water that causes a bloom in plankton, which provides more food or the crown of thorns starfish, allowing more of them to reproduce. Since a single crown of thorns starfish can produce around 108 eggs, once these eggs become fully grown adults they can consume the entire coral reef. If you want to learn more about more crown of thorns starfish outbreaks like previously stated here is the link:



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