The future of the Great Barrier Reef looks increasingly precarious. Researchers in Australia have identified a new threat -- not bleaching, but encroaching algae.

Through a series of experiments and observations, researchers were able to measure the effects of rising CO2 levels on algae behavior. Their findings -- detailed in the journal Scientific Reports -- suggest algae, like a weed, will continue to outcompete and overtake coral as CO2 levels rise.

"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," Guillermo Diaz-Pulido, a professor of environmental sciences at Griffith University, said in a news release.

As CO2 levels rise, algae's chemical weapons become more potent. The poisons weaken coral and aid the algae's territorial conquest.

"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," explained Mark Hay, from the Georgia Institute of Technology. "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."

If CO2 emissions continue unabated, researchers believe the Great Barrier Reef could become entirely overrun -- killed off -- by algae by the end of the century. What's more, scientists found the most potent algae is a common brown algae species found across the globe.

"That's a problem because if these algae take advantage of elevated CO2 in seawater that's even more a matter of concern," Diaz-Pulido said. "The scale of the problem is so big 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."