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An adult crown-of-thorns starfish
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Eating habits of baby predator starfish revealed

21 July 2020
Juvenile crown-of-thorns starfish will eat almost anything to survive
The creatures' varied diet complicates scientists' ability to age them. This makes plans for the management of this invasive species more difficult.
A juvenile crown-of-thorns starfish on Amphiroa – a type of pink algae.

A juvenile crown-of-thorns starfish on Amphiroa – a type of pink algae. The yellow and white patches on the algae are feeding scars.

Adult crown-of-thorns starfish pose one of the greatest threats to the Great Barrier Reef due to their coral diet. Marine life, including fish, crabs, seahorses, and turtles, depend on coral as a food source, as well as for shelter. No coral means no smaller creatures. This has a domino effect, ultimately decimating the food chain and ecosystem. Learning more about this starfish is crucial for efforts to save the Reef.

New research from Dione Deaker, a PhD student at the University of Sydney's Marine Studies Institute, and her adviser Professor Maria Byrne, along with colleagues at the National Marine Science Centre, Coffs Harbour, adds another piece to the crown-of-thorns puzzle. The research team has already shown that baby starfish can survive on algae for up to six and a half years instead of switching to a coral diet at four months of age, per their typical growth pattern. Now, they have discovered that juveniles can eat a range of algae, not just the algae they are thought to prefer; crustose coralline algae. They can even subsist on biofilm – microorganisms that cover the sea floor, including bacteria and protists – to avoid starvation.

The diet flexibility of juvenile crown-of-thorns starfish complicates our ability to age this species and, therefore, our ability to predict devastating outbreaks of adults on reefs

“The diet flexibility of juvenile crown-of-thorns starfish complicates our ability to age this species and, therefore, our ability to predict devastating outbreaks of adults on reefs,” Ms Deaker said.

“There is potential for reserves of juveniles to accumulate on the reef and produce outbreaks when favourable feeding conditions arise.

“There is no doubt that these starfish are extremely opportunistic and resilient when their preferred food source is limited. We now demonstrate that this resilience also applies to the youngest juveniles.”

The researchers came to their conclusions, published in influential journal PLOS ONE, after feeding newly settled juveniles either crustose coralline algae, a different kind of algae (Amphiroa) or biofilm in a controlled environment, and then monitoring their growth.

Small juvenile crown-of-thorns starfish are just millimetres in diameter. Once they switch to a coral diet, they can grow to up to a metre wide.

Declaration

This study was supported by funding from the Australian Government’s National Environmental Science Program Tropical Water Quality Hub. The Australian Marine Tourist Operators Association provided adult crown of thorns starfish.

Hero image: An adult crown-of-thorns starfish. Credit: National Park of American Samoa.

Loren Smith

Assistant Media Adviser (Humanities & Science)

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