A shocking new study shows that ocean water around Hawaii is rapidly reaching levels of acidification not seen in thousands of years. Even under the most optimistic emissions scenarios, coral reefs around the islands are expected to experience chemical changes beyond their ability to adapt. Using fine-scale models, scientists reveal that these reefs may soon be entering a completely new ocean environment, with windward coasts being hit hardest.

Coral and red sea urchins in Maui, Hawaii. Photo credit: Andre Seale

While some corals are already showing signs of recovery, time is running out, and researchers stress that continued emissions could reshape Hawaii's underwater ecosystem forever.

Globally, oceans are acidifying as they absorb carbon dioxide from the atmosphere, posing a serious threat to coral reefs and many species of marine life. A recent study by oceanographers at the University of Hawaii at Manoa found that ocean waters near the main Hawaiian Islands could become more acidified than ever before in the next 30 years.

Growing acidity can damage marine ecosystems by weakening the shells and skeletons of marine life such as corals and clams. It can also exacerbate the effects of other environmental stressors, putting additional pressure on already fragile habitats. Despite these threats, there is some hope. Researchers have observed that some species may be adapting to changing environments. The findings provide important insights for scientists, environmental groups and policymakers working to protect Hawaii's coral reefs and preserve marine ecosystems into the future.

The research team, led by Brian Powell, a professor in the Department of Oceanography in the School of Ocean and Earth Sciences and Technology (SOEST) at the University of Hawaii at Manoa, used high-resolution computer models to predict changes in ocean chemistry near the Hawaiian Islands during the 21st century. Their projections are based on various climate scenarios reflecting different levels of carbon dioxide emissions.

"We find that even under a low-emissions scenario, where carbon emissions are flat by mid-century, ocean acidification in surface waters around the Hawaiian Islands is projected to increase significantly," said Lucia Hošeková, SOEST research scientist and lead author of the paper. "Across all nearshore areas, these increases in acidification will be unprecedented compared to what coral reef organisms have experienced for thousands of years."

The extent and timing of these changes depend on the amount of carbon in the atmosphere. The team found that under a high-emissions scenario, ocean chemistry would be very different from what corals have historically experienced, which could challenge their ability to adapt. Even under a low-emissions scenario, some changes are inevitable, but they are less dramatic and occur more slowly.

The research team calculated the difference between projected levels of ocean acidification and the level of acidification that corals at specific sites have experienced in recent history. They called it a "novelty" and found that different parts of the Hawaiian Islands may experience acidification processes differently. Windward shorelines consistently exhibit higher novelty, that is, future conditions deviate more from those experienced by the reef in recent history.

"We did not expect future ocean acidification levels to be so outside the range of natural changes in ocean chemistry that ecosystems are adapted to," said study co-author Tobias Friedrich, a researcher in the Department of Oceanography. "This is the first ocean acidification forecast specifically for Hawaiian waters to document this situation."

Previous research has shown that corals exposed to slightly elevated ocean acidity can adapt to these conditions, increasing coral fitness.

"The findings show the acidification that corals may experience; however, the extremes of acidification will vary depending on global climate scenarios. In the best-case scenario, corals will be affected, but this may be manageable. That's why we continue to conduct new research to explore the combined effects of various stresses on corals," said Powell. "This study is an important first step in exploring the overall changes that will affect corals and other marine life, as well as how these changes vary around islands."

Compiled from /scitechdaily