Carbon dioxide emissions will put corals in Hawaiian reefs at risk through ocean acidification within the next 30 years. A new study by University of Hawai‘i scientists reveals that even under stable climate scenarios, nearshore waters will undergo more pronounced changes than reefs have experienced in thousands of years. Some coral species may adapt, offering some hope, but others may face critical stress in the altered environment.
Around the world, ocean acidification has been occurring as the oceans absorb carbon dioxide from the atmosphere, threatening coral reefs and other marine organisms. A new study, led by oceanographers at the University of Hawai’i at Mānoa, has revealed that previously unseen levels of ocean acidification are expected around the main Hawaiian Islands within the next thirty years. Increased ocean acidification can harm marine life by weakening the shells and skeletons of organisms such as corals and clams. Ocean acidification can also amplify the effects of existing stressors and threaten ocean-based ecosystems. However, some organisms have shown signs of adapting to the changing waters, which is a glimmer of hope. This study helps researchers, policymakers, and conservationists gain insight into the future challenges that Hawaiian coral reefs will face, providing information for conserving these vital ecosystems for future generations.
Researchers within the laboratory group of Brian Powell, professor in the Department of Oceanography at the UH Mānoa School of Ocean and Earth Science and Technology (SOEST), used state-of-the-art, fine-scale computer models to forecast how ocean chemistry around the main Hawaiian Islands might change over the 21st century under different climate scenarios and climate changes based on how much carbon dioxide societies continue to emit.
According to Lucia Hošeková, lead author of the paper and a research scientist in SOEST, even if carbon dioxide emissions flatline by mid-century in a low-emission scenario, ocean acidification is expected to increase significantly in surface waters surrounding the main Hawaiian Islands. In all nearshore areas, these increments will be unmatched compared to what reef organisms have seen in many thousands of years.
The range and timing of these changes vary based on the amount of carbon dioxide added to the atmosphere. In the high-emission scenario, the research team found that ocean chemistry will become drastically different from what corals have experienced previously, potentially posing hindrances to their ability to adapt. Even in the low-emission scenario, some changes are anticipated, but they will be less extreme and occur more gradually.
The team calculated the difference between forecasted ocean acidification and acidification that corals in a given location have experienced in recent times. Various areas of the Hawaiian Islands may experience acidification differently, due to the difference between projected ocean acidification and the acidification that corals in a given location have experienced in recent history, known as ‘novelty’. Windward coastlines consistently showed higher novelty, that is, future environments deviate more dramatically from what coral reefs have experienced in recent history.
“We did not expect future levels of ocean acidification to be so far outside the envelope of natural variations in ocean chemistry that an ecosystem is used to,” said Tobias Friedrich, study co-author and research scientist in the Department of Oceanography. “This is the first ocean acidification projection specifically for Hawaiian waters to document that.”
Previous research has shown that exposure to slightly elevated ocean acidity leads to the coral’s ability to acclimate to those conditions, thereby enhancing the coral’s adaptability. The results of this research show the potential conditions of acidification that corals might experience. The extremity of the conditions depends on the climate scenario that the world follows. In the best case, the corals will be impacted, but the effects will be manageable. This is why the team continues new research to observe the combined effects of stresses on corals. According to Powell, this study represents a significant stride in examining the combined effects of changes that will impact corals and other marine organisms, and how these effects vary around the islands.
The research team will continue to investigate future changes in Hawaiian waters, specifically heat stress, changes to Hawai’i’s fisheries, and the location of potential refugia for coral reefs.
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