Scientists have found the invasive crown-of-thorns starfish, which decimates coral populations, is feasting on blue-green algae bacteria known as sea sawdust.
Blue-green algae floats on the ocean's surface in large rafts like sawdust and can stretch for hundreds or thousands of kilometres.
Research suggests it can form and thrive as a result of human activities like fertiliser use, sewage treatment and stormwater runoff into the ocean.
But one of the algae bacteria types - trichodesmium - can also form naturally by creating its own fertiliser from nitrogen in the atmosphere.
Previously, scientists thought nothing consumed the algae because of its toxicity and poor nutritional content.
But new research reveals crown-of-thorns starfish are indulging in the bacteria.
The discovery was made by tracing atoms from the algae to crown-of-thorns starfish larvae which showed the species digests nitrogen from the bacteria.
Given previous research findings that human activities lead to an increase in algae blooms, scientists are concerned this is contributing to the higher numbers of starfish.
"The outbreaks of crown-of-thorn starfish are, we believe, related to human activity" the University of Queensland researcher told AAP.
"We are noticing that trichodesmium (algae bacteria) is blooming more frequently and given we've found the crown-of-thrown starfish larvae can feed on it, there may be a relationship between the two."
Dr Benjamin Mos said understanding how crown-of-thorns starfish thrive on the algae could reveal solutions to curbing the population rises.
Preventing fertiliser runoff and sewage from farms into the ocean is likely one of the key prevention methods, he suggested.
Professor Symon Dworjanyn said more research was needed on the connection between more algae blooms and larger starfish populations.
"We don't yet know if sea sawdust blooms result in more adult crown-of-thorns on coral reefs, so this research needs more work," the Southern Cross University researcher said.
If researchers crack the puzzle, it may lead to a solution to providing coral reefs a break from the invasive species.
The research was published in Science Advances.
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