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Ocean acidity devastates corals

Ocean acidity devastates corals

Featured image above by Kennedy Wolfe

Increasing carbon emissions in the atmosphere from activities such as the burning of fossil fuels and deforestation are changing the chemistry in the ocean. When carbon dioxide from the atmosphere is absorbed by seawater, it forms carbonic acid. The increased acidity, in turn, depletes carbonate ions – essential building blocks for coral exoskeletons.

There has been a drastic loss of live coral coverage globally over the past few decades. Many factors – such as changing ocean temperatures, pollution, ocean acidification and over-fishing – impede coral development. Until now, researchers have not been able to isolate the effects of individual stressors in natural ecosystems.

In an article published in Nature on 24 February 2016, researchers working at the University of Sydney’s One Tree Island Research Station at the southern end of the Great Barrier Reef (GBR) found that they could improve coral development by reversing the acidity of the reef waters.

“Our oceans contribute around $45 billion each year to the economy”

The international team – led by Dr Rebecca Albright from Stanford University in the USA – brought the acidity of the reef water back to what it was like in pre-industrial times by upping the alkalinity. They found that coral development was 7% faster in the less acidic waters.

“If we don’t take action on this issue very rapidly, coral reefs – and everything that depends on them, including wildlife and local communities – will not survive into the next century,” says team member Professor Ken Caldeira.

Destruction of the GBR would not only be a devastating loss because it’s considered one of the 7 Natural Wonders of the World, but would be a great economic blow for Australia.

Our oceans contribute around $45 billion each year to the economy through industries such as tourism, fisheries, shipping, marine-derived pharmaceuticals, and offshore oil and gas reserves. Marine tourism alone generates $11.6 million a year in Australia.

Impact of acidification on calcification

Corals absorb carbonate minerals from the water to build and repair their stoney skeletons, a process called calcification. Despite the slow growth of corals, calcification is a rapid process, enabling corals to repair damage caused by rough seas, weather and other animals. The process of calcification is so rapid it can be measured within one hour.

Manipulating the acidity of the ocean is not feasible. But on One Tree Island, the walls of the lagoons flanking the reef area isolate them from the surrounding ocean water at low tide – allowing researchers to investigate the effect of water acidity on coral calcification.

“We were able to look at the effect of ocean acidification in a natural setting for the first time,” says One Tree Reef researcher and PhD candidate at the University of Sydney, Kennedy Wolfe.

ocean acidity
The University of Sydney’s Kennedy Wolfe collecting water samples on One Tree Reef. Photo credit: Ken Caldeira

In the same week, an independent research team from CSIRO published results of mapping ocean acidification in the GBR. They found a great deal of variability between the 3851 reefs in the GBR, and identified the ones closest to the shore were the most vulnerable. These reefs were more acidic and their corals had the lowest calcification rates – results that supported the findings from One Tree Reef.

Marine biologists have predicted that corals will switch to a net dissolution state within this century, but the team from CSIRO found this was already the case in some of the reefs in the GBR.

“People keep thinking about [what will happen in] the future, but our research shows that ocean acidification is already having a massive impact on coral calcification” says Wolfe.

– Sue Min Liu