Acid ocean poses global reef threat

Southern Cross University Professor Bradley Eyre and colleagues from the US have found that the sands which provide material for the building and maintenance of coral reefs will begin to dissolve due to increasing ocean acidity.

Their paper, published in Science today, shows the rate at which coral reef sediments dissolve is ten times more sensitive to ocean acidification than the rate at which corals grow. Corals are expected to grow more slowly due to ocean acidification and this new study shows dissolving sands could greatly exacerbate reef loss associated with this reduction in coral growth.

“Coral reef sediments around the world will trend towards dissolving when seawater reaches a tipping point in acidity – which is likely to occur well before the end of the century,” said Professor Eyre from the University’s Centre for Coastal Biogeochemistry.

“This will potentially impact coral reef ecosystems – not to mention tourism, fisheries and the many other human activities that occur around reefs.

“It is vital that we put pressure on governments globally to act in concert to lower CO₂ emissions as this is the only way we can stop the oceans acidifying and dissolving our reefs.”

Professor Eyre said the oceans have absorbed around one third of the carbon dioxide emitted to the atmosphere and have become increasingly acidic as a result.

The researchers placed benthic chambers underwater at four reef locations in the Pacific and Atlantic Oceans to measure the impact of future seawater acidity in dissolving the sands that make up coral reef systems. They then developed a model extrapolating their results for 22 coral reefs across three ocean basins.

Once the ocean reaches a tipping point in acidity, the reef sediments begin to dissolve. The time it takes to reach this threshold will depend on the rate of seawater acidification on the reefs. One study suggests more rapid acidification of seawater on reefs – which could mean that reef sediments start to dissolve by 2020. A slower rate of open ocean acidification would still mean that reef sediments will be dissolving at 20 of the 22 reefs modelled, before the end of this century.

“It may be possible to reduce the impact of ocean acidification on the dissolution of reef sediments by managing the input of organic matter at local and regional scales, providing some hope for reefs, but much more research on this topic is required,” Professor Eyre said.

The paper’s second author, Dr Tyler Cyronak, completed his PhD and first postdoctoral work at Southern Cross University.

The Science paper ‘Coral reefs will transition to net dissolving before end of century’ can be found here: https://www.science.org/doi/10.1126/science.aao1118