Image Credit: David Burdick

Increasing CO2 levels to grow coral-eating starfish populations

  • BY Angela Heathcote |
  • June 07, 2017

Scientists say increasing CO2 levels, which acidifies ocean waters, will exacerbate the population of crown-of-thorns starfish—one of the biggest threats to the Great Barrier Reef.

OCEAN ACIDIFICATION, CAUSED by increased CO2 levels, will provide a boost to the juveniles of the coral-eating crown-of-thorns starfish (COTS) populations.

Researchers say that climate change may exacerbate outbreaks of the COTS, which is one of the leading causes of coral death on the Great Barrier Reef.

Head researcher Symon Dworjanyn, from Southern Cross University, was surprised to find that the increase in growth of the COTS was an indirect effect of higher CO2 levels.

“In experiments that stimulate how the pH and the ocean might change over the next 70 to 100 years we found that the sea stars grew quicker. Intriguingly, what was making them grow quick wasn’t the changes in pH but because the food they were eating, which was becoming more palatable and easier to eat,” Symon told Australian Geographic.

Symon says this is because the seaweed usually defends itself with hard calcium carbonate in its tissue, but higher acidity inhibits this, making the algae less protected against herbivores and more edible and nutritious for infantile COTS.

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

“We use the guidelines from the Intergovernmental Panel on Climate Change that predict how water conditions will change. Then we put the critters in our simulator to see how they were affected by those different conditions and see how they’re affected by these conditions,” Symon said, adding that the research clearly indicates that humans need to reduce the level of CO2 in the atmosphere.

As for short-term solutions, earlier this year it was reported that vinegar injections are lethal to the COTS, making it easier for small and remote operators to make a difference on their local reefs. “Vinegar is so much easier to access for communities in the Indo-Pacific, where access to ox bile (the previously used control method) was not feasible, for them vinegar is not an alternative, it’s the only option,” said Lisa Boström-Einarsson, a marine biologist at James Cook University.

As for how to prevent further damage to the Great Barrier Reef, Symon says that a multi-dimensional approach is necessary.

“It’s all about reef resilience. We know that there is a whole suite of factors affecting the resilience of coral reefs. You can’t just fix one thing. For example, we have to release less nitrogen onto reefs, we have desperately need to reduce the amount of CO2 we put in the atmosphere and we also have to protect reefs so they can have healthy predator populations.”

This research was published in the journal Royal Society