Australia’s Great Barrier Reef is an intricate city of brightly coloured corals stretching more than 2,000km along Queensland’s coast. Home to one of the most complex ecosystems on Earth, climate change is presenting significant challenges to the Reef’s long-term survival.

The impacts of coral bleaching, caused by warmer sea temperatures, are widely known. However in the past decade, scientists have discovered a new threat to the Reef from ocean acidification.

Dr Bronte Tilbrook, principal research scientist with the Commonwealth Scientific and Industrial Research Organisation (CSIRO), explains how research is helping scientists better understand the impact of ocean acidification on one of the seven natural wonders of the world.

About Dr Bronte Tilbrook

About Dr Bronte
Tilbrook

Dr Bronte Tilbrook is a biogeochemist with Australia’s CSIRO Oceans and Atmosphere team.

Dr Bronte Tilbrook is a biogeochemist with Australia’s CSIRO Oceans and Atmosphere team.

He leads a number of research projects on ocean acidification and carbon cycling in the Southern ocean and in the waters around Australia.

The research provides key data for determining trends in CO2 levels stored by oceans, and for detecting changes in acidification and how marine animals and plants respond.

 

Image: Dr Bronte Tilbrook, principal research scientist with the CSIRO. ©CSIRO

Q: How does ocean acidification occur?

 A: Gases are regularly exchanged between the surface ocean and the atmosphere. As part of this exchange, the ocean absorbs large amounts of carbon dioxide (CO2) from the atmosphere.

The carbon dioxide reacts with water to make a weak acid – similar to what is found in carbonated drinks. This alters the water chemistry by reducing the seawater pH and the amount of dissolved carbonate in the water. These changes are referred to as ocean acidification.

Did you know?

One third of carbon dioxide produced by humans has been absorbed by the oceans over the industrial era. In 2015, the oceans took up about 30 million tonnes of carbon dioxide emissions every day. This is helping offset the increase of carbon dioxide in the atmosphere, but comes at the expense of ocean acidification.


Q: Why is acidification a problem?

A: Human activities – such as driving cars, generating electricity, and land use change – have increased the amount of carbon dioxide in the atmosphere, causing more carbon dioxide to be absorbed by the surface ocean and increasing ocean acidity.

Ocean acidification could have a big effect on things living in our ocean. Since pre-industrial times, the ocean’s acidity level has increased by about 25 per cent and conditions are not going to get better as CO2 emissions continue to rise.

Q: How does acidification affect the Great Barrier Reef?

A: Acidification could have a significant impact on the overall health of the Great Barrier Reef.

It can reduce coral growth, weaken reef structures and also affect the ability of some marine organisms – such as shelled plankton and molluscs – to create shells. And these changes can have knock-on impacts that weaken the Reef’s overall ecosystem.

Not all species are susceptible to the changes, but evidence suggests that as acidification increases, corals will take longer to build reefs, and structures may be more fragile and vulnerable to erosion and storm damage. As a result, ecosystems and biodiversity may change and coral’s ability to provide ecosystem habitats is likely to decline. With coral bleaching and other stresses adding to the problem, we are likely to see a shift away from healthy reefs towards more algal-dominated ecosystems.

Q: How do you monitor ocean acidification?

A: We’re partnering with the Great Barrier Reef Foundation and Rio Tinto to conduct the Future Reef 2.0 research project. As part of the project, we have fitted one of Rio Tinto’s bauxite carriers with a mobile laboratory and specially designed ocean sensor system.

The ship travels along the shipping channel between Weipa and Gladstone, providing water samples along the length of the Great Barrier Reef Marine Park. It is the only regular monitoring system of its kind that runs along the entire length of the Reef.

The sensors take measurements every one to two minutes along the entire route, providing important data on surface CO2, pH, temperature, salinity and dissolved oxygen levels.

About the Great Barrier Reef

About the Great
Barrier Reef

The World Heritage Listed Great Barrier Reef is the largest living structure on Earth, and is the only living thing visible from space.

The World Heritage Listed Great Barrier Reef is the largest living structure on Earth, and is the only living thing visible from space.

It covers almost 350,000km2 – to put that into perspective that’s roughly the size of Japan or Italy.

The Reef features the world’s largest collection of corals, more than 1,600 species of fish, more than 30 species of marine mammals, and six of the world’s seven species of threatened marine turtles.

 

Image: Australia’s Great Barrier Reef is the largest living structure on Earth. ©Gary Cranitch at Queensland Museum

Q: How will the research help?

A: Understanding changes in water chemistry is essential to protecting the Reef. It is providing a large-scale view of how the Reef is growing and responding to changing environmental conditions.

This research is testing for the vital signs of reef health – it will provide indicators of what is happening in the system. This will help us to understand how ocean acidity is influencing the growth of corals and other marine organisms. The changes in water chemistry will also provide information about Reef stressors, and may provide early warning signs if we are approaching tipping points in Reef growth.

It is providing data to test and improve models of the Reef water chemistry, as well as temperature data to help detect ocean heat waves that cause bleaching events.

Discussing ocean acidification

An interview with Dr Tilbrook and Anna Marsden, chief executive of the Great Barrier Reef Foundation, as they discuss the work being done to counteract acidification.

Q: What is your opinion on the overall health and long-term outlook of the Reef?

A: There is no doubt the Reef is under increasing stress from a number of factors like bleaching events and ocean acidification, and sustaining a healthy Reef ecosystem is going to be a big challenge.

A first step is to determine how conditions are changing on the Reef and if there are parts of the Reef more or less vulnerable to the changes, and why. An understanding of the stress points on the Reef will help efforts to adapt to changing conditions or mitigate them.

Find out more about how scientists are working in partnership with Rio Tinto and the Great Barrier Reef Foundation.

An iconic beauty under pressure

An iconic beauty
under pressure

In recognition of its significance, UNESCO listed the Great Barrier Reef as a World Heritage Site in 1981 – marking it worthy of protection so that future generations can appreciate and enjoy it.

In recognition of its significance, UNESCO listed the Great Barrier Reef as a World Heritage Site in 1981 – marking it worthy of protection so that future generations can appreciate and enjoy it.

A few years earlier, in 1975, the Australian Government had officially recognised the Reef’s importance by declaring a Great Barrier Reef Marine Park.

The Great Barrier Reef Marine Park Authority manages the Great Barrier Reef Marine Park and regularly reports on its current state and actions being undertaken to protect the Reef.

According to the Great Barrier Reef Foundation, major threats to the Reef include climate change impacts such as coral bleaching, extreme weather events and ocean acidification; declining water quality from land-based run-off; coastal development; and illegal fishing.

 

Image: The Reef features the world’s largest collection of corals. ©Gary Cranitch at Queensland Museum

Top image: The Reef features the world’s largest collection of corals. Image ©Gary Cranitch at Queensland Museum