A newly settled crown of thorns starfish
A newly settled crown of thorns starfish

’Cockroach of the ocean’ less picky than first thought

RIDDING your house of cockroaches can be hard enough, so just imagine trying do the same across three hundred thousand odd square kilometres of reef.

The team at Southern Cross University's National Marine Science Centre have been conducting research into the dreaded crown of thorns star fish - destroyer of reefs the world over.

That research has found the juvenile sea animals, beginning life just a few millimetres in diameter, have a much wider diet than first thought, complicating their ability to predict outbreaks.

"Juvenile COTS appear to be the 'cockroach' of the oceans - highly resilient and able to survive for months on food that we initially thought they would not eat," said NMSC lead researcher Dr Benjamin Mos.

"Learning about the strengths and weaknesses of this lifestage may help us find new ways to manage population outbreaks that devastate coral reefs in Australia and the Indo-Pacific."

Earlier this year the research team showed 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, as is their typical growth pattern.

Now, they have discovered that juveniles can eat a range of algae, not just the algae they were thought to prefer, crustose coralline algae. They can even subsist on biofilm - microorganisms that cover almost all surfaces in the ocean - to avoid starvation.

The new research was conducted in conjunction with the University of Sydney and is published on Tuesday in PLOS ONE.

Crown of Thorns Starfish at the Great Barrier Reef.
Crown of Thorns Starfish at the Great Barrier Reef.

Because it is so hard to study the juvenile COTS in the wild, the NMSC have been raising the animals in captivity - in state-of-the-art seawater systems that adjust conditions to match those found on coral reefs.

The technology has meant the NMSC is one of the few across the world able to conduct this type of research.

Diet flexibility and growth of the early herbivorous juveniles has implications for its boom-bust population dynamics as they must grow-up on a vegetarian diet until they are large enough to eat coral.

The adults can grow up to a metre in size.

When many juveniles make it through their herbivorous stage, population outbreaks may occur with devastating impacts on coral reefs as corals are literally eaten away.

"Outbreaks of COTS are a diabolical problem for coral reefs," said NMSC professor Symon Dworjanyn.

"Despite decades of focused research on COTS we are still uncovering surprising information about this sneaky species. The ability for the young starfish to eat such a broad range of foods shocked us."

The new findings highlight the need to consider the longevity and dietary flexibility of juveniles when modelling population dynamics, locating juveniles in the wild, and designing strategies to effectively manage the COTS problem.

The study was supported by the Australian Government's National Environmental Science Program Ecosystem Functioning Project.

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