Microborers Represent New Threat To Earth’s Coral Reefs
March 18, 2013

A New Threat To Earth’s Coral Reefs: Microborers

Brett Smith for redOrbit.com - Your Universe Online

Previous studies have shown that warming oceans and ocean acidification threaten to destroy the ocean´s coral reefs. Now, a new study from Australian researchers published in the journal Global Change Biology suggests that yet another threat could decimate these delicate ecosystems.

“Our research shows that when seawater is both acidic and warm — which is predicted to happen under future climate scenarios — coral reefs could be made more fragile by microborers, such as algae, blue-green algae and fungi that inhabit reefs and bore tiny holes in it that undermine the strength of the coral skeleton,” said co-author Catalina Reyes of The University of Queensland.

“So fish, turtles, sharks, lobsters and other reef organisms may lose their homes, threatening reef biodiversity and the livelihoods of tens of millions of people,” she added.

Corals use calcium carbonate in the water to build the exoskeletons that compose the reef structure. As the reef grows, older dead parts are washed away by waves, fish and tiny plants that live inside the reef itself.

“There is a fine balance between accumulating and losing carbonate, and healthy reefs are the ones that gain more than they lose,” Reyes said. “Anything that disrupts this balance puts coral reefs in danger.”

To determine to impact of these tiny plants, or microborers, the researchers exposed different types of coral skeletons to two different future climate scenarios in a laboratory setting.

“The first scenario was ℠business as usual´ where nothing is done by humanity to decrease CO2 emissions,” Reyes said. “In this case, the rate of erosion by the microborers of the coral skeletons almost doubled compared to the present day.”

She said that the second scenario — which involved elevated CO2 levels, but less than the first scenario — experienced a rate of erosion of about 35 percent.

“So if we look into the future, not only do corals have less material with which to build their reefs, but the old, dead parts that support them are eroded much faster,” said co-author Sophie Dove, from the University of Queensland. “If we think of the reef as a scaffold, it´s now being taken apart faster than it can re-build, which means that it´s at a higher risk of collapsing.”

“We found that microborers were more abundant under both predicted scenarios, so it is possible that acidic and warm seawater will stimulate their growth, leading to coral skeletons dissolving faster,” Reyes said.

Reyes noted that the most abundant type of algae in the study, Ostreobium, is also the world´s most common photosynthetic microborer. The algae lives in 85 percent of the world´s corals and is remarkable for thriving in low light conditions. This ability allows it to penetrate deep into coral skeletons.

In their conclusion, the authors noted that the magnitude of algae erosion on the coral reefs could depend on the structural integrity of coral skeletons.

“Even if there are ℠super corals´ that do well in an acidic ocean, this study shows that we mustn´t underestimate how much climate change can affect other important reef processes,” Dove concluded.