Crown Of Thorns Starfish On Coral Reefs
Pitch: This article is written to inform the reader of the issues pose by crown of thorns starfish on coral reefs. The target audience is the general public who may view coral reefs as a tourist destination. There is a need to warn about crown of thorns as research shows that it causes more destruction to corals reefs than bleaching or other disturbances. More details on how these starfish population boomed are given in the article, revealing both natural and anthropogenic factors. The article however ends on a positive note since this threat can be managed through direct intervention to reduce the crown of thorns population. The first photo graph is chosen to show how the crown of thorns outbreak looks like in a coral reef. The second photo
…show more content…
is to show the current management methods of injection to cull the crown of thorns to control the outbreaks. (147words)
Crown of Thorns: Coral Reefs’ Silent Killer
Dive into the pristine sea water and be prepared to immense yourself in one of the most beautiful places on Earth, the coral reefs. Coral reefs are one of the most diverse and vibrant ecosystem that support thousands of marine organisms, many of which are economically important for human consumption and livelihood. However the underwater paradise is increasingly threatened and the once colourful seascape that was buzzing with life is now bleached or in the ruins. There are various stresses that threaten the coral reefs such as overfishing, pollution and climate change, etc., and one of the direct destruction of corals is the outbreak of crown of thorns.
The crown of thorns, as its name suggests, is a type of starfish that is covered with numerous venomous spines. This species is a native species in coral reefs of the Indo-Pacific and can be found from the tropics to the subtropics. It is bluish to reddish-brown in colour with around 13 to 16 limbs and grows to half a metre in diameter. Some large ones may even grow up to 80cm!
Source: http://theconversation.com/how-scaring-starfish-could-help-to-save-the-great-barrier-reef-36759
By nature, crown of thorns are corallivores unlike other starfishes and mainly feast on the coral’s soft tissues inside the carbonate reef skeleton.
The feeding is through eversion, whereby the gastric sacs (stomach) is pushed out of its mouth to surround the corals before releasing enzymes that digest the coral tissues into a liquid slush for consumption. A single crown of thorns can feed up to the size of a dinner plate in 1 night which is equivalent to 10m2 in a year!
Under normal conditions, the crown of thorn population is small and maintains coral species biodiversity by consuming the fast-growing species. However in the recent decades, population density of crown of thorns are getting unsustainable, resulting in the localized extinction of corals where outbreaks of crown of thorns occurred. An outbreak is defined as more than 30 adults in one hectare of reefs or when the rate of coral consumption is more than the rate of coral …show more content…
growth.
One of the best example is the Great Barrier Reef in Australia whereby outbreaks are greatly increasing in frequency, from 1 in 80 years to 1 in 15 years. The Australian Institute of Marine Science has documented four outbreaks in the past 50 years and suggests that crown of thorns are responsible for more than 42% of the decrease in coral cover in the Great Barrier Reef, more so than the effect of bleaching (10%). This greatly affects the tourism industry as almost one in every three coral reefs in the Great Barrier Reef has experienced the crown of thorn outbreaks, leaving them vulnerable to other environmental disturbances such as cyclones.
So why are the outbreaks happening? Let’s take a look at some of the factors that encourage the detrimental outbreaks of crown of thorns. Firstly, crown of thorns has one of the highest fertility rates among all the marine invertebrates with approximately 70% fertilisation rate. In addition, an adult female can release more than 65 million eggs per spawning season, producing millions of larvae that reach sexual maturity in just two years! The biology of the crown of thorns gives it a great advantage when it comes to reproduction, resulting in greater stress on the coral reefs.
Secondly, although crown of thorns is naturally part of the coral reef ecosystem, its recent surge in population numbers may have an anthropogenic cause. Research published in the Journal of the International Society for Reef Studies in 2010 has found a strong link between phytoplankton (algae) availability and the frequency of outbreaks. Data from the last 30 years from the Great Barrier Reef shown that the outbreaks coincide with major flooding events that allow sewage and agricultural runoff to reach the Great Barrier Reef lagoon.
The increase in nutrients (nitrogen and phosphorus) in runoffs into the ocean leads to eutrophication which encourages algae growth, forming algae blooms. The crown of thorns greatly benefit from the abundance of algae as they are the source of food for the crown of thorns larvae, increasing the larvae survival rate. Experiments has shown that doubling the number of algae leads to a 10 fold increase in growth and survival of the larvae!
Lastly, overfishing of crown of thorns’ natural predators are giving the starfish a greater chance of survival. While the crown of thorns are packed with intimidating-looking venomous spines, natural predators exist such as the triton shells, trigger fish, pufferfish and painted shrimps. These marine animals are not affected by the venom and keep the crown of thorns numbers in check. However the population of these predator species are in the decline from overharvesting and less are available to control the population of crown of thorns.
These three factors indeed forms a recipe for disaster as the outbreaks threaten the survival of corals, leaving them with little time to recover from the attacks of crown of thorns. Yet the threat that crown of thorn poses to coral reefs is more manageable than other major disturbances to the coral reef ecosystem such as global warming or ocean acidification. Direct intervention to remove or reduce this notorious starfish can be done to save the corals from the destructive outbreaks.
In the Great Barrier Reef, the Australian government has been funding management program to manually remove crown of thorns since the 1980s. This is done by divers employed by the Association of Marine Park Tourism Operators injecting a toxic chemical solution (sodium bisulphate) into the crown of thorns to cull them without removing them from the ecosystem. While the method worked, it required several dosage to take effect which was not cost-effective.
Source: http://www.arkive.org/crown-of-thorns-starfish/acanthaster-planci/image-G100843.html
In 2012, researchers had successfully developed a new solution using bile salt and this method requires only one injection shot to take effect, giving a 2.5 times more efficiency than before. The injection method is part of the 3 step control programme that involves surveillance to detect crown of thorns outbreaks and assess coral health and the monitoring of the effectiveness of the programme by collecting data of crown of thorns population and assess the change in coral cover in the long term.
Interestingly, new research are being done to make use of chemical cues to deter crown of thorns from the coral reefs.
In an experiment done by the Australian Institute of Marine Science, the crown of thorns reacts violently in waters which once held its predator, the giant triton shell. The giant triton shell is a large gastropod that feeds on crown of thorns but due to its low metabolism, it can only consume one crown of thorn per week. A chemical released by the giant triton seems to be causing fear and panic in the crown of thorns which is deaf and nearly blind, relying on its keen sense of smell to navigate. If the chemical can be made known and produced, it can be placed on coral reefs especially those with great ecological and economic importance to protect the coral against these vicious coral
killers.
Other methods involves the removal of the crown of thorns from the coral reefs and culling them through sun drying or placing them in freshwater to kill them through suffocation, but are met with controversies due to the inhumane handling. As a traveller yourself, if you happen to see an outbreak crown of thorns during your snorkel or diving trip, you can inform the relevant authorities to report the situation and perhaps save the coral reefs and the vast range of organisms that depend on it.
Ultimately, the outbreaks of crown of thorns are dependent on the water quality management near the coast. With better management to reduce agricultural or nutrient-rich runoff into the ocean, there will be less chance of algae blooms that benefit the starfish larvae and lower chance of future outbreaks of these silent killers to degrade our breath-taking coral reefs.
is to show the current management methods of injection to cull the crown of thorns to control the outbreaks. (147words)
Crown of Thorns: Coral Reefs’ Silent Killer
Dive into the pristine sea water and be prepared to immense yourself in one of the most beautiful places on Earth, the coral reefs. Coral reefs are one of the most diverse and vibrant ecosystem that support thousands of marine organisms, many of which are economically important for human consumption and livelihood. However the underwater paradise is increasingly threatened and the once colourful seascape that was buzzing with life is now bleached or in the ruins. There are various stresses that threaten the coral reefs such as overfishing, pollution and climate change, etc., and one of the direct destruction of corals is the outbreak of crown of thorns.
The crown of thorns, as its name suggests, is a type of starfish that is covered with numerous venomous spines. This species is a native species in coral reefs of the Indo-Pacific and can be found from the tropics to the subtropics. It is bluish to reddish-brown in colour with around 13 to 16 limbs and grows to half a metre in diameter. Some large ones may even grow up to 80cm!
Source: http://theconversation.com/how-scaring-starfish-could-help-to-save-the-great-barrier-reef-36759
By nature, crown of thorns are corallivores unlike other starfishes and mainly feast on the coral’s soft tissues inside the carbonate reef skeleton.
The feeding is through eversion, whereby the gastric sacs (stomach) is pushed out of its mouth to surround the corals before releasing enzymes that digest the coral tissues into a liquid slush for consumption. A single crown of thorns can feed up to the size of a dinner plate in 1 night which is equivalent to 10m2 in a year!
Under normal conditions, the crown of thorn population is small and maintains coral species biodiversity by consuming the fast-growing species. However in the recent decades, population density of crown of thorns are getting unsustainable, resulting in the localized extinction of corals where outbreaks of crown of thorns occurred. An outbreak is defined as more than 30 adults in one hectare of reefs or when the rate of coral consumption is more than the rate of coral …show more content…
growth.
One of the best example is the Great Barrier Reef in Australia whereby outbreaks are greatly increasing in frequency, from 1 in 80 years to 1 in 15 years. The Australian Institute of Marine Science has documented four outbreaks in the past 50 years and suggests that crown of thorns are responsible for more than 42% of the decrease in coral cover in the Great Barrier Reef, more so than the effect of bleaching (10%). This greatly affects the tourism industry as almost one in every three coral reefs in the Great Barrier Reef has experienced the crown of thorn outbreaks, leaving them vulnerable to other environmental disturbances such as cyclones.
So why are the outbreaks happening? Let’s take a look at some of the factors that encourage the detrimental outbreaks of crown of thorns. Firstly, crown of thorns has one of the highest fertility rates among all the marine invertebrates with approximately 70% fertilisation rate. In addition, an adult female can release more than 65 million eggs per spawning season, producing millions of larvae that reach sexual maturity in just two years! The biology of the crown of thorns gives it a great advantage when it comes to reproduction, resulting in greater stress on the coral reefs.
Secondly, although crown of thorns is naturally part of the coral reef ecosystem, its recent surge in population numbers may have an anthropogenic cause. Research published in the Journal of the International Society for Reef Studies in 2010 has found a strong link between phytoplankton (algae) availability and the frequency of outbreaks. Data from the last 30 years from the Great Barrier Reef shown that the outbreaks coincide with major flooding events that allow sewage and agricultural runoff to reach the Great Barrier Reef lagoon.
The increase in nutrients (nitrogen and phosphorus) in runoffs into the ocean leads to eutrophication which encourages algae growth, forming algae blooms. The crown of thorns greatly benefit from the abundance of algae as they are the source of food for the crown of thorns larvae, increasing the larvae survival rate. Experiments has shown that doubling the number of algae leads to a 10 fold increase in growth and survival of the larvae!
Lastly, overfishing of crown of thorns’ natural predators are giving the starfish a greater chance of survival. While the crown of thorns are packed with intimidating-looking venomous spines, natural predators exist such as the triton shells, trigger fish, pufferfish and painted shrimps. These marine animals are not affected by the venom and keep the crown of thorns numbers in check. However the population of these predator species are in the decline from overharvesting and less are available to control the population of crown of thorns.
These three factors indeed forms a recipe for disaster as the outbreaks threaten the survival of corals, leaving them with little time to recover from the attacks of crown of thorns. Yet the threat that crown of thorn poses to coral reefs is more manageable than other major disturbances to the coral reef ecosystem such as global warming or ocean acidification. Direct intervention to remove or reduce this notorious starfish can be done to save the corals from the destructive outbreaks.
In the Great Barrier Reef, the Australian government has been funding management program to manually remove crown of thorns since the 1980s. This is done by divers employed by the Association of Marine Park Tourism Operators injecting a toxic chemical solution (sodium bisulphate) into the crown of thorns to cull them without removing them from the ecosystem. While the method worked, it required several dosage to take effect which was not cost-effective.
Source: http://www.arkive.org/crown-of-thorns-starfish/acanthaster-planci/image-G100843.html
In 2012, researchers had successfully developed a new solution using bile salt and this method requires only one injection shot to take effect, giving a 2.5 times more efficiency than before. The injection method is part of the 3 step control programme that involves surveillance to detect crown of thorns outbreaks and assess coral health and the monitoring of the effectiveness of the programme by collecting data of crown of thorns population and assess the change in coral cover in the long term.
Interestingly, new research are being done to make use of chemical cues to deter crown of thorns from the coral reefs.
In an experiment done by the Australian Institute of Marine Science, the crown of thorns reacts violently in waters which once held its predator, the giant triton shell. The giant triton shell is a large gastropod that feeds on crown of thorns but due to its low metabolism, it can only consume one crown of thorn per week. A chemical released by the giant triton seems to be causing fear and panic in the crown of thorns which is deaf and nearly blind, relying on its keen sense of smell to navigate. If the chemical can be made known and produced, it can be placed on coral reefs especially those with great ecological and economic importance to protect the coral against these vicious coral
killers.
Other methods involves the removal of the crown of thorns from the coral reefs and culling them through sun drying or placing them in freshwater to kill them through suffocation, but are met with controversies due to the inhumane handling. As a traveller yourself, if you happen to see an outbreak crown of thorns during your snorkel or diving trip, you can inform the relevant authorities to report the situation and perhaps save the coral reefs and the vast range of organisms that depend on it.
Ultimately, the outbreaks of crown of thorns are dependent on the water quality management near the coast. With better management to reduce agricultural or nutrient-rich runoff into the ocean, there will be less chance of algae blooms that benefit the starfish larvae and lower chance of future outbreaks of these silent killers to degrade our breath-taking coral reefs.