Ocean Acidification: A Growing Threat to the Great Barrier Reef 

The Great Barrier Reef is the largest coral reef system on Earth and one of Australia’s most iconic natural wonders. Stretching for more than 2,300 kilometres along the Queensland coast, it supports thousands of species of fish, corals, molluscs and other marine life. Yet alongside rising ocean temperatures, another invisible threat is increasingly affecting the Reef — ocean acidification.

Ocean acidification occurs when the ocean absorbs carbon dioxide (CO₂) from the atmosphere. The world’s oceans absorb roughly one-third of the CO₂ released by human activities such as burning fossil fuels and deforestation. When CO₂ dissolves in seawater it forms carbonic acid, which lowers the water’s pH and alters ocean chemistry. Since the beginning of the industrial revolution, the average acidity of surface ocean waters has roughly increased by 30%.

It is worth noting that even slight shifts in ocean chemistry can have major consequences for marine organisms.

Corals, the foundation of the Great Barrier Reef ecosystem, are particularly vulnerable. Reef-building corals construct their skeletons from calcium carbonate, a mineral formed using carbonate ions dissolved in seawater. As ocean acidity increases, the availability of these carbonate ions decreases. This makes it more difficult for corals to build and maintain their skeletons, slowing growth and weakening reef structures.

Scientists have already observed declining calcification rates in many reefs. Research suggests that coral calcification across the Great Barrier Reef may have dropped by roughly 15–20% since 1990. Slower growth means reefs recover more slowly from disturbances such as storms, bleaching events or outbreaks of coral-eating crown-of-thorns starfish.

Ocean acidification can also cause existing coral skeletons to dissolve more easily. In more acidic conditions, calcium carbonate becomes less stable, which can lead to erosion of reef structures over time. This weakens the physical framework that supports the entire ecosystem.

The impacts extend beyond corals themselves. Many other reef organisms — including shellfish, plankton and coralline algae — rely on calcium carbonate to form shells or skeletons. Increased acidity can reduce their growth, survival and reproductive success.

Despite these challenges, scientists emphasize that the future of the Great Barrier Reef is not yet sealed. Reducing carbon dioxide emissions remains the most important step in slowing ocean acidification. This means moving away from fossil fuels and transitioning to renewable energy as quickly as possible.

At the same time, local conservation efforts — such as improving water quality, managing fisheries, and protecting vulnerable reef areas — can help strengthen the Reef’s resilience.

The Great Barrier Reef has survived dramatic environmental changes over millions of years. However, the rapid pace of modern climate change and ocean acidification presents an unprecedented challenge. Protecting this remarkable ecosystem will require both global climate action and continued efforts to safeguard the reef locally, ensuring that future generations can continue to marvel at one of the world’s greatest natural treasures.

Contributed with thanks to Whitsunday Conservation Group.

Captions

Healthy reef

Photo supplied

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