American Oceans

Crown of Thorns Starfish

Crown of Thorns Starfish (COTS) is a species of sea star that is widely known for its destructive impact on coral reefs.

a crown of thorns starfish underwater

COTS are named for their long spines that are sharp and venomous, which can cause severe pain and injury to humans who come into contact with them.

They are native to the Indo-Pacific region, but have spread to other areas through human activities.

COTS feed on coral polyps, and their population outbreaks can cause significant damage to coral reefs.

The outbreaks are believed to be caused by a combination of factors, including natural population cycles, predation release, and human activities such as overfishing and nutrient pollution.

The impact of COTS outbreaks on coral reefs can be devastating, as they can lead to a decline in the biodiversity of marine life and the loss of important ecosystem services.

Overview of Crown of Thorns Starfish

a massive crown of thorns starfish in the ocean

The Crown of Thorns Starfish (COTS) is a species of starfish belonging to the family Acanthasteridae.

It is a marine invertebrate that is widely distributed throughout the Indo-Pacific region, including the Great Barrier Reef. The scientific name for this species is Acanthaster planci.

COTS is a large starfish that can grow up to 50 centimeters in diameter. It has a distinctive appearance with long, sharp spines that protrude from its body and a crown-like arrangement of arms.

The color of the starfish varies from green to brown to purple.

COTS is a predator that feeds on coral polyps. It has a powerful stomach that can digest even the hard calcium carbonate skeletons of coral.

This makes COTS a significant threat to coral reefs, which are already under pressure from climate change and other human activities.

The life cycle of COTS involves a free-swimming larval stage that lasts for several weeks. During this time, the larvae feed on plankton before settling on the ocean floor and metamorphosing into juvenile starfish.

The juvenile starfish then grow into adults, which can live for up to 10 years.

COTS outbreaks have been recorded throughout the Indo-Pacific region since the 1960s. These outbreaks can have a devastating impact on coral reefs, causing widespread coral mortality and altering the structure of reef communities.

The causes of these outbreaks are not fully understood, but they are thought to be influenced by a range of factors, including nutrient availability, water temperature, and predation pressure.

Efforts to control COTS outbreaks have focused on removing the starfish from affected reefs. This can be done manually or using chemical treatments.

However, these methods can be expensive and labor-intensive, and they may have unintended ecological consequences.

Researchers are currently exploring alternative methods for controlling COTS outbreaks, including the use of biological control agents and the development of coral reef resilience strategies.

Physical Characteristics

a crown of thorns starfish on a coral reef

The Crown-of-Thorns Starfish (COTS) is a large, spiny echinoderm that can grow up to 50 cm in diameter.

Its body is covered in long, sharp spines that are used for protection against predators. The COTS has up to 21 arms that radiate out from its central disc, which is covered in small, tube-like feet that it uses for locomotion.

The spines of the COTS are typically purple in color, although they can also be brown or green. The arms of the starfish are covered in a thorny texture that is used for gripping onto surfaces.

The COTS also has a unique feeding mechanism that involves extruding its stomach out of its mouth and onto the surface of coral, where it releases digestive enzymes to break down the coral tissue.

The diameter of the COTS can vary depending on its age and the availability of food in its environment. Younger starfish tend to be smaller in size, while older individuals can grow to be quite large.

The COTS is known for its ability to reproduce rapidly, with females capable of producing up to 65 million eggs per year.

Habitat and Distribution

The crown-of-thorns starfish is a predatory species that feeds on coral polyps, posing a significant threat to coral reefs in many parts of the world.

These starfish are found in a range of habitats, including coral reefs, rocky areas, and seagrass beds.

The distribution of the crown-of-thorns starfish is primarily limited to the Indo-Pacific region, including the Great Barrier Reef, Hawaii, and the Indian Ocean.

In these areas, the starfish can be found in shallow waters of obliquely exposed fore reef habitats.

The distribution and abundance of settlement-stage crown-of-thorns starfish in these areas are still not well understood, and further research is needed to gain a better understanding of their habitat associations.

The crown-of-thorns starfish can have a significant impact on the surrounding ecosystem, as they can consume large amounts of coral, leading to a decline in coral cover.

The density and biomass of selected species of herbivorous fish on crown-of-thorns starfish are hypothesized to be important factors in the observed distribution of these starfish.

Climate change can also impact the distribution of the crown-of-thorns starfish, as it can alter the distribution of their prey and affect the suitability of their habitat.

A case study examining the potential habitat of the starfish found that the distribution of the corallivore crown-of-thorns starfish could be impacted by climate change.

In a shallow coral reef habitat, the eggs and sperm of the crown-of-thorns starfish can disperse over small distances.

Basic advection models can predict the distribution of eggs and sperm of crown-of-thorns starfish in the field, which can be used to predict the potential impact of these starfish on coral reefs.

Diet and Predation

crown of thorns starfish hurting coral reef

Crown-of-thorns starfish (COTS) are corallivores, which means they feed on coral polyps.

They use their sharp spines to climb onto coral colonies and then extrude their stomach over the coral surface to digest the coral polyps.

COTS can consume up to six square meters of coral reef per year, which can lead to significant damage to coral reefs and the marine ecosystem.

Despite their destructive feeding habits, COTS are an important part of the marine food chain. They are preyed upon by a variety of predators, including the giant triton (Charonia tritonis) and several species of fish.

A study found that the regulation of COTS populations by fish predators is dependent on the number of predators present.

The study predicted that a threshold density of fish predators is required to control COTS populations.

COTS larvae are planktonic and are also consumed by a variety of filter feeders and planktivorous fish.

As they grow, COTS shift their diet from planktonic organisms to coral polyps. A recent study found that juvenile COTS undergo ontogenetic dietary shifts, where they consume smaller-sized coral polyps when they are small and then shift to larger-sized coral polyps as they grow.

COTS are able to digest coral polyps using digestive enzymes that break down the calcium carbonate skeleton of the coral.

This ability allows them to extract nutrients from the coral polyps that would otherwise be unavailable to other predators.

Despite their specialized digestive system, COTS can still fall prey to predators that are able to overcome their spines and consume them.

Reproduction and Life Cycle

a crown of thorns starfish

The crown-of-thorns starfish (Acanthaster planci) is a sexual species with separate sexes, meaning that individuals are either male or female.

The reproductive cycle of the crown-of-thorns starfish is not well understood, but it is known that they spawn gametes (eggs and sperm) into the water column during the breeding season.

Fertilization occurs externally, and the resulting larvae are planktonic and undergo a pelagic stage before settling on the ocean floor.

The larval stage of the crown-of-thorns starfish is critical for its survival, as most larvae do not survive to adulthood due to predation and environmental factors.

Once settled, the larvae metamorphose into juvenile crown-of-thorns starfish, which grow rapidly and feed voraciously on coral polyps.

The crown-of-thorns starfish is known for its ability to regrow lost arms, which allows it to recover from predation and other injuries.

Outbreaks and Impact on Coral Reefs

a crown of thorns on a coral reef

The Crown of Thorns Starfish (COTS) is a predator that feeds on coral polyps and is known to cause significant damage to coral reefs during outbreaks.

These outbreaks can have devastating impacts on coral communities, leading to the degradation of entire ecosystems.

Outbreaks of COTS were first identified as a significant threat to coral reefs in the 1960s and have since become one of the leading causes of coral reef decline.

COTS populations can reach outbreak proportions, with thousands of individuals per hectare, and can consume large amounts of coral over a short period of time.

COTS outbreaks can have cascading effects on reef fish and benthic communities, leading to mass mortality of corals and the decline of fish populations.

Additionally, COTS outbreaks can exacerbate the impacts of other stressors on coral reefs, such as coral bleaching.

Coral bleaching occurs when corals expel the symbiotic algae that provide them with energy, leaving them vulnerable to disease and death.

COTS outbreaks can further damage coral reefs that have already been weakened by bleaching events.

Branching corals are particularly susceptible to COTS predation, as they are easier for the starfish to access and consume.

Plagues of COTS can result in the loss of entire coral colonies and can have long-lasting impacts on coral reef ecosystems.

The Great Barrier Reef has experienced several COTS outbreaks in recent decades, with surveys indicating that many reefs have recently experienced or are currently experiencing outbreaks.

The distribution of these outbreaks is concentrated within the central third of the Great Barrier Reef.

Efforts to manage COTS outbreaks include culling programs and the development of biological control methods.

However, the effectiveness of these methods is limited, and the prevention of outbreaks through improved management of other stressors on coral reefs remains the most promising approach.

Conservation and Control Measures

harmful crown of thorns starfish laying on a reef

Crown of thorns starfish (COTS) are a significant threat to coral reefs around the world. Reef managers, traditional owners, scientific experts, and trained divers are all working together to implement conservation and control measures to mitigate the impact of COTS outbreaks.

One of the most effective conservation measures is the establishment of marine protected areas (MPAs) and conservation park zones.

Research has shown that sites with greater protection had lower COTS densities than sites zoned for habitat protection at the start of manual control [1].

This highlights the importance of long-term planning for reef management, and the need to consider the effectiveness of different management strategies.

Control programs for the protection of small areas of reef from aggregations of COTS have met with mixed success in the past.

Targeted COTS control programs, which involve the removal of COTS from high-value areas, have been shown to be effective in reducing COTS populations [2].

However, the success of these programs depends on factors such as the size and location of the outbreak, the availability of trained divers, and the use of appropriate removal methods.

The Pacific triton (Charonia tritonis) is a natural predator of COTS and has been used as a biological control method.

However, the effectiveness of this method is limited by the availability of tritons and their ability to control COTS populations [3].


Role of Human Activities and Climate Change

crown of thorns sea star laying in the sand

The crown-of-thorns starfish (Acanthaster spp.) is a major predator of coral reefs in the Indo-Pacific region.

While it is a natural part of coral reef ecosystems, it can cause significant damage when populations become too large.

The causes of outbreaks of crown-of-thorns starfish are complex and multifactorial, but human activities and climate change are believed to play a significant role.

Human activities such as overfishing and runoff from coastal development can lead to an increase in nutrients in the water, which can promote the growth of phytoplankton.

This, in turn, can lead to an increase in the population of zooplankton, which is a food source for the crown-of-thorns starfish. Therefore, human activities that increase nutrient levels in the water can indirectly contribute to the outbreak of crown-of-thorns starfish.

Climate change is also believed to play a role in the outbreak of crown-of-thorns starfish. Rising sea temperatures can lead to coral bleaching, which can reduce the availability of food for the starfish.

This, in turn, can cause the starfish to switch to feeding on healthy coral, leading to an outbreak.

Additionally, climate change can alter ocean currents and weather patterns, which can affect the dispersal and recruitment of the starfish.

Efforts to manage outbreaks of crown-of-thorns starfish should take into account the role of human activities and climate change.

While it may not be possible to control all the factors that contribute to outbreaks, reducing human impacts on coral reefs can help to mitigate the effects of outbreaks.

Additionally, efforts to reduce greenhouse gas emissions can help to slow the pace of climate change, which may help to reduce the frequency and severity of outbreaks of crown-of-thorns starfish.

Research and Studies

crown of thorns starfish in a coral reef

Crown of thorns starfish (COTS) have been the subject of numerous research studies over the years.

The species is known for its destructive impact on coral reefs, and researchers have been studying ways to mitigate this impact.

One area of research has focused on understanding the reproductive output of COTS. Studies have shown that female COTS with larger gonads tend to have higher reproductive output, indicating a positive correlation between size and reproductive output [1].

Another area of research has focused on the genome of COTS. A study published in 2017 analyzed the neuropeptidome of COTS and identified 37 neuropeptides, providing insights into the molecular mechanisms underlying the behavior and physiology of COTS [3].

The study also identified several neuropeptides that are involved in the regulation of feeding behavior, which could be targeted in the development of control measures for COTS.

Studies have also been conducted on the mitochondria and nucleus of COTS. A study published in 2016 analyzed the mitochondrial genome of COTS and identified several genetic markers that could be used to distinguish between different populations of COTS [1].

The study also highlighted the need for further research on the population genetics of COTS, which could help inform conservation efforts.

Research on COTS has also contributed to our understanding of species diversity and resilience.

A study published in 2008 identified four different species of COTS, which were previously thought to be a single species [4]. This discovery has important implications for conservation efforts, as different species may have different ecological roles and responses to environmental stressors.

Additionally, research has shown that some coral reefs are more resilient to COTS outbreaks than others, highlighting the importance of understanding the factors that contribute to reef resilience [2].


  1. Relationships between size and reproductive output in the crown-of-thorns starfish
  2. Thirty years of research on crown-of-thorns starfish (1986–2016): scientific advances and emerging opportunities
  3. The neuropeptidome of the Crown-of-Thorns Starfish, Acanthaster planci
  4. A threat to coral reefs multiplied? Four species of crown-of-thorns starfish

Frequently Asked Questions

What are the negative effects of crown-of-thorns starfish on coral reefs?

Crown-of-thorns starfish (CoTS) are known to cause significant damage to coral reefs. They feed on coral tissue, leaving behind white scars on the coral surface.

This can lead to coral death, which in turn can have a cascading effect on the entire reef ecosystem. CoTS outbreaks can also reduce the diversity of coral species on a reef and alter the balance of the ecosystem.

How large can crown-of-thorns starfish grow?

Crown-of-thorns starfish can grow up to 50 centimeters in diameter. They have a large number of arms, ranging from 7 to 23, and are covered in long, sharp spines.

What is the classification of crown-of-thorns starfish?

Crown-of-thorns starfish belong to the phylum Echinodermata, class Asteroidea, and genus Acanthaster. There are several species of CoTS, including Acanthaster planci, which is the most well-known and widespread.

What are some interesting facts about crown-of-thorns starfish?

Crown-of-thorns starfish get their name from the long, sharp spines that cover their body and resemble a crown of thorns.

They are also known for their ability to regenerate lost arms. CoTS are found in tropical and subtropical waters around the world, and can live for up to 10 years.

Why are crown-of-thorns starfish considered a threat to coral reefs?

Crown-of-thorns starfish are considered a threat to coral reefs because of their ability to cause significant damage to coral colonies.

CoTS outbreaks can occur naturally, but human activities such as overfishing and nutrient pollution can contribute to their frequency and severity.

Is it advisable to remove crown-of-thorns starfish from coral reefs?

The removal of crown-of-thorns starfish from coral reefs can be a controversial topic. While removing CoTS can help reduce their impact on coral colonies, it can also be a difficult and expensive process.

Additionally, removing CoTS can disrupt the natural balance of the ecosystem and may not be a sustainable long-term solution.

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