Long-term research shows ocean acidification increasing on the Great Barrier Reef

Ocean acidification is no longer a gloomy forecast for the Great Barrier Reef, but a reality today, reveals a new study.

The study, published in Scientific reports, shows carbon dioxide (CO₂) and ocean acidification is rapidly increasing on the reef. Seawater CO₂ it has increased by 6% in the last 10 years and corresponds to the CO rate₂ increases in the atmosphere, confirming the influence of atmospheric CO₂ on sea water CO₂ levels.

“People are talking about ocean acidification in terms of 50 years, but for the first time our study shows how fast ocean acidification is already happening on the reef,” said Dr Katharina Fabricius, lead author and Senior Principal Research Scientist at the Australian Institute of Marine Sciences (AIMS).

The research, a collaboration between AIMS and CSIRO, built on more than a decade of observations collected as part of Australia’s Integrated Marine Observing System (IMOS) to conclude that the reef’s rich carbonate bottom is not protecting against ocean acidification. as previously thought.

“Our research shows that acidification is rapidly changing the conditions that support coral growth on the reef. It has never been more important to address ocean acidification in plans to manage the reef,” said Dr Bronte. Tilbrook, Senior Principal Research Scientist at CSIRO who leads IMOS observation projects for CO₂ and ocean acidification.

Ocean acidification results from the absorption of excess CO by seawater₂ which was emitted into the atmosphere. The CO₂ it dissolves in seawater where the chemistry changes. This includes decreasing the pH of the water and reducing the saturation state of aragonite, which is critical for building the skeletons of reef-forming coral and other marine organisms. Under low pH conditions, their calcium carbonate skeletons take longer to form and weaken, making them more susceptible to damage and erosion.

Although long-term data exist for CO₂ and ocean acidification trends in open oceans, there has been very little long-term data on these trends in coastal waters around the world, including the Great Barrier Reef. Biological and physical processes such as respiration create large fluctuations in CO₂ in coastal areas, making it more difficult to identify trends.

The study filled this important knowledge gap by analyzing 10 years of CO₂, pH and data on the state of saturation of aragonite (2009–2019). This data was collected as part of the Australian IMOS network at two long-term monitoring stations, located 650 kilometers apart in contrasting locations.

The researchers found the minimum CO₂ it is likely that the concentrations measured today have already exceeded the maximum level of CO₂ levels predicted 60 years ago, even after taking into account the effects of temperature, nutrients, salinity and daily and seasonal changes.

“We now know that the oceans absorb about 23% of the excess CO2₂ from the air. They actually serve humanity by slowing down climate change. But the price to pay is that the carbon chemistry of seawater is changing, and we didn’t know it was happening in dynamic coastal waters at such high speeds, ”said Dr Fabricius.

In another first research, scientists from AIMS and CSIRO used data from 1384 reef sites to show the negative impacts of coastal acidification on three important indicators of reef health:

• the number of small corals and coralline algae is plummeting as CO₂ rises across the reef and
• undesirable algae thrive on high CO₂ locations.

The study, published earlier this year in the journal Biology of global change, found that these small corals and coralline algae also decreased, and the algae increased as the fine sediments suspended across the reef increased, with the highest concentration of sediment and organism changes observed closer to shore. Researchers highlighted effective water quality management as a viable solution to reduce the impact of coastal acidification on the reef.

Provided by the Australian Institute of Marine Science