Rising carbon dioxide levels in the world's oceans due to climate change, combined with rising sea temperatures, could accelerate coral bleaching, destroying some reefs before 2050, says a new Australian study.
The study says earlier research may have significantly understated the likely damage to the world's reefs caused by man-made change to the Earth's atmosphere.
"Previous predictions of coral bleaching have been far too conservative, because they didn't factor in the effect of acidification on the bleaching process and how the two interact," said Ove Hoegh-Guldberg from the ARC Centre of Excellence for Coral Reef Studies and Queensland University.
The Australian scientists erected 30 large aquaria in the waters off Heron Island on the Great Barrier Reef to study the combined effects of ocean warming, acidification due to rising CO2, and sunlight on a large range of reef organisms.
Using CO2 and temperatures predicted for the middle and end of the century, the scientists found ocean acidification from CO2, which reduces coral calcification, had the potential to worsen the impact of bleaching and the death of reef-building organisms.
The study found that coralline algae, which glue the reef together and help coral larvae settle successfully, were highly sensitive to increased CO2.
"These may die on reefs such as those in the southern Great Barrier Reef before year 2050," study leader Ken Anthony said in a statement released yesterday.
Some coral species were able to cope with higher levels of ocean acidification by enhancing their rates of photosynthesis, but if CO2 levels became too high "the coral-algal system crashes and the corals die," said the study.
"The implications of this finding are massive as it means that our current bleaching models, which are based on temperature only, severely underestimate the amount of coral bleaching we will see in the future," said Mr Anthony.
"These results highlight the urgency of reducing CO2 emissions globally. Without political will and commitment to abatement, entire reef systems such as the Great Barrier Reef will be severely threatened in coming decades".