If the current level of carbon dioxide emissions is not reduced, essential reef-building corals would suffer and may die off by 2100, according to a study.
Researchers from Griffith University, in collaboration with experts in reef and chemical ecology, predicted that algae would compete with corals for space on reefs, eventually winning the battle in an environment with increased carbon dioxide. They discovered that the algae's predicted success was due to an increase in the potency of chemical compounds that poison corals.
Co-author Professor Mark Hay, from the Georgia Institute of Technology, said, "What we've discovered is that some algae produce more potent chemicals that suppress or kill corals more rapidly. This can occur rapidly, in a matter of only weeks.”
“If the algae overtake the coral, we have a problem which contributes to reef degradation, on top of what we already know with coral bleaching, crown-of-thorn starfish outbreaks, cyclones or any other disturbance,” he added.
Associate Professor Guillermo Diaz-Pulido, of Griffith's School of Environment, said, “This is a major step forward in understanding how seaweeds can harm corals and has important implications for comprehending the consequences of increased carbon dioxide emissions on the health of the Great Barrier Reef.”
The research took place at Heron Island, a coral cay at the reef's southern end. One of the seaweeds used in the study was a common brown alga species found in reefs around the world, and it caused the most damage.
“That's a problem because if these algae take advantage of elevated CO2 in seawater, that's even more a matter of concern. The scale of the problem is so big [that] removing a bunch of seaweed from the reef isn't going to do much because it just regrows and regenerates, so I think the way to address this really is to reduce the levels of CO2 in the atmosphere,” said Associate Professor Diaz-Pulido.