The destructive coral-eating starfish, which feeds on pink ‘coralline’ algae in its infancy, were found to grow quicker in the high-CO2 ocean conditions predicted to occur before 2100.

Marine researchers Pamela Kamya and Associate Professor Symon Dworjanyn were surprised to find ocean acidification caused the algal food to become easier to eat and more nutritious for the juvenile starfish.

The research paper ‘Indirect effects of ocean acidification drive feeding and growth of juvenile crown-of-thorns starfish, Acanthaster planci’ is published today (June 7) in the Proceedings of the Royal Society B: Biological Sciences journal.

Professor Dworjanyn from the University’s National Marine Science Centre in Coffs Harbour worked with Ms Kamya, who is a PhD student from Papua New Guinea.

“Crown-of-thorns Starfish populations boom periodically and can cause great damage to coral reefs.  By some assessments, on the Great Barrier Reef they cause more damage than ocean warming or cyclones,” Professor Dworjanyn said.

“This species is causing destruction to coral reefs right through the Indo-Pacific, from Japan to Indonesia, so we were interested in how these starfish would fare in future ocean conditions.

“This study shows that this starfish may become even more of a threat as a result of climate change.”

Professor Dworjanyn explained oceans are becoming more acidic as they absorb increasing concentrations of atmospheric carbon dioxide (CO2).

The scientists used a computer-controlled, marine climate change simulator which automatically injected CO2 to simulate ocean conditions predicted in the future.

“Surprisingly, the indirect effects of ocean acidification cause the starfish to grow faster as their algae food becomes more palatable and easier to eat,” Professor Dworjanyn said.

“This happens because the seaweed usually defends itself with hard calcium carbonate in its tissue, but higher acidity inhibits this, making the algae less defended against herbivores and more edible and nutritious for baby starfish.

“We were studying the crown-of-thorns starfish at a size just before they start munching on coral, which is important because we are still unsure what triggers outbreaks of adults.”

Professor Dworjanyn said this was another reason humans need to reduce the amount of CO2 in the atmosphere.

“Coral reefs are already affected directly by climate change, indirect effects such as this may speed their decline and we need to take action,” he said.

Pamela Kamya said research into the crown-of-thorns starfish would help marine scientists understand and manage its impacts and protect these pristine coral reefs in Papua New Guinea, Australia and throughout the region.

“Coral reefs in Papua New Guinea provide livelihoods for thousands of coastal communities, so understanding how threats like this starfish will proceed is important for the future of these people,” Pamela said.

The study was funded by an Australian Research Council grant, an Australian Development Scholarship award from AusAID, and a WWF Russell E Train Fellowship award.