Instant expert

Instant Expert: Ocean acidification

A wave of devastation for marine life.



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What is it?

The pH scale measures how acidic or alkaline a substance is. It ranges from 0 to 14, with 7 being neutral. Pure water is considered to have a pH of 7; while the oceans are normally quite alkaline at around 8.2 pH. However, since the industrial revolution, the pH of seawater has fallen to 8.1. By 2100, our oceans are expected to have a pH of 7.9 to 7.8.

What’s causing it?

As the concentration of carbon dioxide (CO²) in the atmosphere increases, so does the level of CO² that the ocean absorbs. Of CO² emissions from burning fossil fuels and the production of concrete in the last 200 years, about 25 per cent has reacted with water in the oceans.

What does this mean for oceans and marine life?

A change of 0.4 in pH levels may sound insignificant but it actually has the potential to wreak havoc. Marine life has evolved over millions of years to live in seawater of a certain pH. A rapid (in terms of the evolutionary timescale) change in the chemistry of the environment threatens their very ability to survive.

“There are two main problems with increased carbon dioxide levels: the inability of calcium-carbonate based animals to grow, and the less-publicised problem of hypercapnia,” says Maria Byrne, Professor of Developmental and Marine Biology at the University of Sydney.

Corals (which consist of colonies of tiny animals) and many shellfish need calcium carbonate to grow protective shells and skeletons. As the water becomes more acidic, the outer coating of the embryo dissolves, preventing it from growing properly. This also makes the creature particularly susceptible to the effects of hypercapnia, a condition where too much carbon dioxide is absorbed into the body of a living thing, effectively poisoning it.

At high water temperatures hypercapnia kills marine larvae, which means the combination of increasing ocean acidification and rising global temperatures is expecially dangerous.

How is it going to affect us?

Ocean acidification threatens marine biodiversity, which is something that affects all of humanity. In more concrete terms, damage to natural wonders such as the Great Barrier Reef will have a devastating effect on tourism.

Food security is a major concern. The Southern Ocean is particularly at risk of ocean acidification. Reports note that a doubling of current CO² levels would seriously jeopardise the food webs on Australia’s southern coastline. Some species of oysters and urchins have been shown to cope with increased acidity better than others; we may be forced to alter our eating habits.

What’s being done about it?

CO² emissions have increased from 316 ppm (parts per million) since the first full year’s record in 1959 to almost 390 ppm in 2010. Even if all CO² emissions stopped tomorrow there would still be enough of the gas in the atmosphere to continue making our oceans more acidic for centuries (not taking into account the controversial possibility of geoengineering to draw CO² out of the atmosphere). More resilient varieties of shellfish are being selectively bred in the hopes of providing a source of food for the world’s burgeoning population.

What the movers and shakers think

Janice Lough Senior principal research scientist, Australian Institute of Marine Science
“The oceans are absorbing a third of the extra carbon dioxide humans are putting into the atmosphere. This is changing their chemistry and will make it progressively harder for, for example, corals to form their calcium carbonate skeletons – the backbone of tropical coral reefs. Preserving the biodiversity of coral reefs requires immediate and drastic cuts in greenhouse gas emissions.”

Maria Byrne Professor of Developmental and Marine Biology, Sydney University
“What’s important is that we consider how we’re going to feed a growing human population. The oceans are a massive source of protein for us. Some species seem unlikely to be able to adapt – such as abalone – whereas others, such as some hardy oysters, should be able to adapt.”

Wayne O’Connor Principal research scientist, Industry & Investment NSW
“We have significant knowledge gaps in the potential of ocean acidification to affect our fisheries. For commercially valuable species, such as oysters, acidification can affect development, metabolism and growth. Oysters have some adaptive capacity and trials suggest selective breeding may help ameliorate impacts on key characteristics such as growth.”