Acidification, Pteropods, the Great Barrier Reef and more

You know, we’re not talking about insignificant items in the ocean. We’re talking about the cornerstone of whole ecosystems.

***– Donna Roberts, leader of the Cooperative Research Centres’ ocean acidification project


As the Southern Ocean absorbs increasing amounts of carbon dioxide, its chemistry is changing with potentially significant impacts on marine life…

The most threatened species are cold-water calcifying organisms which include plankton known as pteropods - winged snails that swim through surface waters.


“We are just beginning to understand the complexities of the physical, chemical and biological system that drives the carbon cycle.”
Dr Bronte Tilbrook, Antarctic Climate & Ecosystems Cooperative Research Centre and CSIRO.


In 2005 the Max Planck Institute  described when  “… CO2 combines with seawater, it forms an acid. Because this process reduces the naturally basic state of seawater, it is termed acidification, even though seawater remains basic (pH > 7).

A study by an international team of oceanographers published in Nature magazine September 2005, reports that ocean acidification could result in chemical conditions that will be corrosive enough to force key polar marine organisms to disappear within 50 to 100 years, much sooner than previously thought. Most threatened are cold-water organisms that build their external skeletal material out of calcium carbonate, the basic building block of limestone. Such organisms include sea urchins, cold-water corals, and plankton known as pteropods—winged snails that flutter through surface waters. And because these organisms provide essential food and habitat to others, their demise could affect entire ocean ecosystems.”

Bronte Tilbrook from the CSIRO talks about the process and cycle of ocean carbon uptake – aka ocean acidification. As ocean acidity increases there is a decrease in concentrations of calcium carbonate. This decrease is expected to affect marine species in polar and sub-Antarctic marine ecosystems, in particular marine organisms with external skeletons and shells built from calcium carbonate. For instance, pteropods are eaten by many small marine creatures which are in turn eaten by larger animals. If pteropods are adversely affected by ocean acidification there will be significant consequences for the rest of the food chain.

As carbon dioxide levels increase the oceans are absorbing more. And while that’s slowing CO2 levels in the atmosphere, it comes at a cost.

Planktonic pteropods, also called winged snails, may be so thick that they stain the waters a dark color although each animal is only 6-12mm (a quarter to a half inch) in size.


and what it means for the Great Barrier Reef…

Bronte Tilbrook and Donna Roberts interviewed by ABC radio’s Environment reporter Sarah Clarke (listen here). Video with Bronte Tilbrooke

SARAH CLARKE: The Great Barrier Reef is one region that’s been under close watch.

Scientists from the CSIRO have collected samples from the entire length of the reef, both inshore and offshore, over the last two years.

What they’ve found is it’s already under stress with the greatest impact inshore and in the southern end.

BRONTE TILBROOK: And what was surprising to us is that a lot of the waters on the reef are already in what are considered marginal growing conditions for healthy coral reefs.

That means that they probably are becoming stressed.

There is some indication that corals are not growing as well as they used to on the reef. If you make it harder for corals to grow, something else will probably take over from them.

And so the reef itself may, in 50 years’ time for example, may not look anything like we see at present – less corals, more other organisms like algae.

SARAH CLARKE: There are similar concerns further south in the cooler waters of the Southern Ocean.

Donna Roberts is the leader of the Cooperative Research Centres’ ocean acidification project.

DONNA ROBERTS: What we’ve found recently in the Southern Ocean ecosystem is that tiny marine shell-making organisms are actually getting lighter in current waters.

Pre-industrial shells are 30 to 35 per cent heavier.

And that’s because there’s not enough carbonate iron available because of the process of ocean acidification for them to actually make a robust shell.

And this has got serious implications for communities and ecosystems and things that eat them, like commercial fish.

SARAH CLARKE: That also has implications for other species in the Antarctic like whales, seals and birds.

DONNA ROBERTS: You know, we’re not talking about insignificant items in the ocean. We’re talking about the cornerstone of whole ecosystems.

SARAH CLARKE: While scientists are witnessing the most rapid responses in the Southern Ocean, they argued this is an indication of what’s in store in tropical waters elsewhere.

Pelagic opisthobranch or pteropod (wing foot),open ocean. San Diego, California, USA (from


Wider ranging consequences…

“Higher concentrations of carbon dioxide also may make it harder for some larger marine animals to obtain oxygen from seawater. For example, squid are particularly sensitive because they move by jet propulsion, which is energy-demanding and requires a good supply of oxygen.

In tropical regions, the combined effects of climate change and ocean acidification mean that corals could be rare on tropical and subtropical reefs, such as the Great Barrier Reef, by 2050.

This will have major ramifications for hundreds of thousands of other species reliant on reef systems, as well as for the people that depend on them for food, tourism, and to help to protect coastal areas from, for example, tsunamis.”

More here from the CSIRO factsheet on carbon dioxide, the ocean and climate change.