- The Crown-of-thorns starfish is responsible for depletion of 40 percent of the coral cover on the Great Barrier Reef over the last 30 years
- Currently the Crown-of-thorns starfish can only be controlled by the labor intensive use of an expensive lethal injection, administered by divers
- Researchers have discovered a chemical compound produced by the giant Triton snail, that repels the starfish and could help protect the Great Barrier Reef
The Crown-of-thorns starfish (Acanthaster planci) is responsible for depletion of 40 percent of the coral cover on the Great Barrier Reef over the last 30 years, and currently can only be controlled by the labor intensive use of an expensive lethal injection, administered by divers. Now researchers have discovered a chemical compound produced by the giant Triton snail (Charoniatritonis), that repels the starfish and could help protect the Great Barrier Reef.
The discovery was made by researchers at the University of the Sunshine Coast (USC), and the Australian Institute of Marine Science (AIMS). Dr. Scott Cummins, a molecular and cellular biologist, an Australian Council Future Fellow, and lead scientist at USC, hopes to isolate the repellent chemical molecule, synthesize it and dispense it to manipulate starfish movements for eradication and to protect coral.
The giant Triton, one of the world’s largest marine snails, is common throughout the tropical Indo-Pacific and is a chief predator of the Crown-of-thorns starfish. Dr Mike Hall, Principal Research Scientist at AIMS, intends to develop novel control techniques by understanding the vulnerability of the Crown-of-thorns starfish.
Researchers found that the snails excrete a specialized scent hormone that when detected by the starfish, causes them to move away from the scent,which could keep the Crown-of-thorns from destroying coral. The discovery offers a promising breakthrough for continued protection of the Great Barrier Reef.
Dr. Cummins has been working with his team to find a way to control the starfish by understanding the various molecular communication processes used by aquatic animals. The multidisciplinary study spanned genomics, proteomics (the study of proteins), cell biology, and behavioral methods and focused on chemical communication between starfish, abalone, sea cucumbers, oysters, sea slugs, and snails.
In an email interview with Mongabay, Dr. Cummins discusses recent discoveries and future research plans:
Mongabay: What is the objective of your research project?
Dr. Scott Cummins: We’d like to determine the olfactory molecules, including pheromones that Crown-of-thorns starfish use to communicate with each other, and with other species. The majority of animals use their sense of smell, rather than sight, to communicate especially in aquatic environments where it is often dark. If we can identify key odors that the starfish use, we can start to manipulate their behavior.
Mongabay: Is the Crown-of-thorns starfish invasive in Australia?
Dr. Scott Cummins: Although many people think that the Crown-of-thorns starfish is invasive to Australia, this is incorrect. For a long time they’ve been a natural predator to the coral, and since they prefer to eat the fast growing coral, they have helped the slower growing corals to survive. But due to recent circumstances (e.g. human impact, increased water temperature, loss of their predator [the giant Triton snail]), there’s been an increase in [starfish]populations that are detrimental to the reef.
Mongabay: What factors are responsible for these rising populations in Australian waters?
Dr. Scott Cummins: There is no single factor that people can label as the primary contributor for the population increase. However, an increase in man-made land runoff chemicals have raised the nutrient levels in the reef on which the starfish larvae possibly feed, thus increasing their ability to survive. Another factor is the appearance of pockets of reef with unusual conditions, such as higher temperatures, that support better survival of [starfish] larvae. The depletion of the adult starfish’s natural predator– the giant Triton snail–on the reef, could also be contributing to population outbreaks.
Mongabay: It’s reported that Crown-of-thorns starfish contributed to a decline of 40 percent of the Great Barrier Reef corals over the last 30 years. Is this due to increased competition for food,some sort of parasitic infection, or other causes?
Dr. Scott Cummins: My view would favor competition for resources. More animals imply that there is a greater need for food resources. I’m not familiar with the parasite, although I do know of a bacterial disease, called sea star wasting disease, which has impacted the North American starfish populations. To my knowledge, this has not been reported in the Crown-of-thorns starfish.
Mongabay: How will the hormone under investigation be utilized to control starfish?
Dr. Scott Cummins: The giant Triton snail appears to release an odor that is detected by the starfish. Technically, this odor from the Triton is termed a kairomone (a pheromone works only within animals of the same species). A kairomone odor benefits animals detecting the odor, and in this case it’s the starfish that benefits since it can run away [from the giant Triton snail]. Use of the kairomone as a slow release system could stop starfish from entering coral reef regions. It may also trigger the movement of starfish into open areas, facilitating the more rapid injection of a poison currently used by divers to kill them.
Mongabay: Are there plans to revive the declining giant Triton snail populations?
Dr. Scott Cummins: Our investigation of the giant Triton snail has enabled better understanding of their behavior patterns and identified key hormones that control reproduction. This information could be important towards facilitating efficient culture of this animal, and then placing them back into the reef.
Mongabay: How does the proliferation of Crown-of-thorns starfish impact people?
Dr. Scott Cummins: The Crown-of-thorns starfish does impact an ecosystem, particularly coral reefs, which support numerous aquatic animals that are not found elsewhere. People visit the reefs to observe their amazing biodiversity, which in turn supports a massive tourism industry. This equates to a sustainable economy and jobs.
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In future, Dr. Cummins and his team hope to gain insights into the biology of starfish at the DNA level, and also study factors involved in their interaction with the environment. They hypothesize that the giant Triton snail, and its repellant scent, will play an important role as a control organism. Though the chemically synthesized scent will not kill the starfish, it can “disperse aggregations [of the starfish] during breeding season to significantly reduce numbers,” said Dr. Cummins. Alternatively, the scientists also plan to use the scent to “scare the starfishes away from particular parts of the reef, and even make them move to areas that are more accessible for divers to poison and remove them in the traditional way.”
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