Coral microborers starving as CO2 and temperature rise

By May 3, 2013Ocean News

We have talked many times about the threats a coral reef has to face, like ocean acidification or global warming. But they don’t affect just the coral itself! A healthy coral has a balance between growth of new parts and erosion of the older ones, which is done by waves, fishes and photosynthetic microborers. Well, these microborers seem to be more effective in warm and acidic oceans.

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The microborers can be algae, blue-green algae or fungi, and they make little holes in the coral skeleton, “eating” the carbonate part, the skeleton. Which is less consistent due to acidification, because it reduces the amount of carbonate in the water. To see exactly what the effects can be of the warm and acidic environment combination, researchers from ARC Centre of Excellence for Coral Reef Studies (CoECRS) and The University of Queensland (UQ) designed an experiment with three different scenarios: one with present-day conditions as a control, and another two with the predicted conditions for the end of the century, with medium and high predictions. Other coral samples were kept in the dark. They used two kinds of reef-building corals. Porites cylindricaand Isopora cuneata.

Looking at their results, they concluded that microborers were essential in the skeleton dissolution, as the samples in the dark didn’t decalcify. On the high futuristic scenario, the conditions were made thinking that humans won’t do anything to decrease CO2 emissions. And the rate of erosion by the microborers was almost the double compared to the control!

In P. cylindrica the rate was 89% higher than the control, per month! And in I. cuneata it was 46% higher. They also associated enhanced skeletal dissolution with increased endolithic biomass and respiration under high CO2 temperature conditions.

The principal microborer identified is the green algae Ostreobium spp, which inhabits 85% of the world’s corals. That means that maybe these results could be applicable to many corals species.

Everyday we discover new awful threats to the coral reefs, so do you think its time to take this studies more seriously?

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