Ocean acidification has now surpassed the “safe operating space” for our planet’s marine systems, according to a recent study published in Global Change Biology.
Ocean acidification doesn’t look like a wildfire or feel like a hurricane. There are no dramatic visuals and seldom are there viral headlines. Ocean acidification unfolds silently as the sea absorbs increasing carbon dioxide (CO₂) from the atmosphere, causing a subtle but steady drop in pH that threatens the very skeleton of marine life.
When CO₂ dissolves in seawater it forms carbonic acid, which then breaks apart into hydrogen ions and bicarbonate. The increase in hydrogen ions lowers the pH of the water, making it more acidic. Those hydrogen ions then bind with carbonate ions, which are essential components that marine organisms rely on to build their shells and skeletons.
For some, this sounds like an abstract problem. Chemistry, numbers, graphs. But let me paint it another way: imagine you are a baby oyster. You are just starting to grow, and the seawater around you no longer has enough “building blocks” for your shell. You try, but the walls are thin. Fragile. Permeable. Some days, the water is so acidic, your shell starts to dissolve before it’s even fully formed. You never had a chance.
This isn’t fiction. It’s the reality for animals like corals, oysters, clams, and even some plankton.
We see it in Australia’s Great Barrier Reef, one of the most iconic reef systems on the planet. Ocean acidification is weakening coral skeletons, making it harder for them to grow, heal, and rebuild after major stress events like mass bleaching. When corals lose their strength, they become more vulnerable to storms, disease, and die-offs. Recovery slows or stalls entirely. And the loss isn’t just structural — it’s ecological.
Coral reefs are home to thousands of species, with fish, crustaceans, mollusks, and countless other marine organisms relying on the complex architecture of reefs to hide from predators, lay eggs, or find food. As the reef structure collapses, so do these intricate food webs. Some species may leave in search of better habitat, while others may simply disappear. Millions of people also rely on healthy coral reefs for food security, income from fishing, and protection from coastal storms. The decline of reefs threatens these livelihoods, especially in countries like Australia where reefs also drive significant tourism revenue.
Acidification is already costing Australians money, with Australian oyster growers losing their crops and their income. In many estuaries along the south-east coast, where oysters are farmed, acid sulfate soils are a common feature. When disturbed or drained, these soils can release acid into surrounding waterways, further increasing acidity levels.
This region, already identified as a climate hotspot, is also experiencing more extreme and unpredictable weather. That means not only more acidic water, but bigger swings in temperature and salinity, two conditions that are especially challenging for marine life like oysters. Researchers at the Port Stephens Fisheries Institute (PSFI) have been studying how temperature, salinity, and pH affect oyster health for years. But with climate change accelerating, that research has intensified. According to PSFI director Dr. Wayne O’Connor, ocean acidification may be a long-standing issue, but it’s now being seen through a new lens: “A whole variety of people have been looking into the same room through different windows. Now one of those windows is climate change. From our perspective, this interest is helping us understand oyster physiology more deeply — and that’s a good thing.”
“I wanted to do research that could help the industry prepare for what’s coming,” she explains. Thanks to previous work at PSFI focused on breeding Sydney Rock Oysters (Saccostrea glomerata) for faster growth and resistance to diseases like QX, her team has had a head start. Now, those selectively bred strains are being tested for their ability to withstand the chemical and physical stressors linked to climate change. The hope is that by identifying and cultivating more resilient oysters, the aquaculture industry can adapt to the changing ocean, and maybe even thrive in it.
But the challenges posed by ocean acidification to shellfish aquaculture in Australia are similarly affecting other regions in the Pacific, including New Zealand and various Pacific Island nations. New Zealand’s shellfish aquaculture industry — which involves green-lipped mussels (Perna canaliculus), oysters, and clams — is a significant sector of the country’s economy. Researchers have identified ocean acidification as a potential threat to the growth, condition, and survival of these species and field experiments have tested mitigation strategies, such as using waste shells and aeration, to alleviate acidification around mussel farms. To monitor the ongoing threat, New Zealand has established the New Zealand Ocean Acidification Observing Network (NZOA-ON), which collaborates with international partners to document the status and progress of ocean acidification in various marine environments. Additionally, the Shellfish Aquaculture Research Platform (ShARP) supports research aimed at enhancing the resilience and sustainability of shellfish aquaculture, including selective breeding programs to develop strains more tolerant to changing ocean conditions, similar to the work being done in Australia.
In the greater Pacific area, while commercial oyster farming is less prevalent, communities here heavily rely on reef ecosystems and local shellfish harvests for food security and cultural practices. Ocean acidification poses a significant threat to these communities by weakening coral reefs, which, combined with other stressors like warming and pollution, jeopardizes marine biodiversity and the livelihoods of people dependent on these ecosystems. The decline in fish species here can also pose long-term food security risks to Pacific communities. Fish will become harder to find. Catch sizes will (and already are) shrinking. Oral histories passed through generations about where and how to fish no longer match the shifting reality of the sea. Recognizing these challenges, regional organizations and governments are working to develop strategies to mitigate the impacts of ocean acidification and enhance the resilience of marine ecosystems and the communities that depend on them.
We often talk about ocean acidification as a scientific phenomenon: just some changing levels of pH and carbon uptake, of shifting baselines and skeletal erosion. But, at the heart of it, it’s also a justice issue because it’s the coastal communities who contributed the least to this crisis who are now on the frontlines of its consequences. The fisher in Fiji who notices fewer shellfish in their nets. The oyster farmer in Tasmania whose crop collapses after a sudden shift in water chemistry. The reef guide in Palau who no longer sees the familiar schools in once-vibrant coral gardens. The grandmother in Louisiana watching saltwater creep inland, knowing her grandchildren may not grow up with the same abundance of seafood or the same sense of place. These people are not passive victims of a distant problem. They are experts of their ecosystems, caretakers of coastlines, bearers of stories and knowledge systems refined over generations. And yet, their voices are too often missing from climate negotiations, funding decisions, and research priorities. Ocean acidification is also eroding sovereignty, stability, and connection.
“A lot of people think it’s not so bad,” said Nina Bednaršek, one of the study’s authors and a senior researcher at Oregon State University. “But what we’re showing is that all of the changes that were projected, and even more so, are already happening — in all corners of the world, from the most pristine to the little corner you care about. We have not changed just one bay, we have changed the whole ocean on a global level.”
The publication of the study is timely, as leading ocean policy experts and marine scientists convened in France for the United Nations Ocean Conference, where they’re tackling the growing threats facing the world’s oceans.
“We live in times where studies like this are not making an immediate impact on policy anymore, which is unfortunate,” Bednaršek said. “But I think it’s extremely important to document these changes, and hopefully this will have an impact on policy and politics.”