Representative photo of the coral tanks after 22 months of exposure to “current” ocean conditions.
Rowan McLachlan, OSU College of Science
A study spanning nearly two years suggests that some Hawaiian corals may tolerate warming and ocean acidification more than previously thought.
Understanding how corals respond to climate-related stressors is becoming increasingly urgent, especially as the Great Barrier Reef is currently grappling with yet another mass coral bleaching event – its fourth one since 2016. Coral bleaching has also occurred in Hawai’i. For example, reefs under protection from the state suffered ongoing bleaching for multiple years in Hanauma Bay, with nearly half the corals become bleached.
During these bleaching events, stressed corals eject the photosynthetic algae that live within them that they depend on for food. While corals can recover these zooxanthellae, consistently bleached corals are less able to do so. Since Hawaiian reefs may deal with lingering environmental challenges, longer-term studies are quite valuable.
“The majority of research that has been done investigating the capacity for coral reefs to survive and persist under ocean warming and acidification has been gained from short-term experiments, one-month duration on average, based in indoor laboratories in empty glass tanks,” says lead author, Rowan McLachlan, “While informative, these studies are limited in their ability to predict how coral will respond in the wild where the environment is much more complex.”
Representative photo of the coral tanks after 22 months of exposure to “future” ocean conditions.
Rowan McLachlan, OSU College of Science
During the 22-month project, researchers collected samples of three of the most common Hawaiian coral species and placed them in tanks with different seawater temperature and acidity levels that signify present and future oceanic conditions. At the end, the study showed that more of the corals that experienced warmer waters did perish, but 61 percent of them still survived.
A branching finger coral species known as Porites was especially tolerant of ocean warming and acidification, with 71 percent of the corals surviving after almost two years had elapsed. As key components of Hawaiian coral reefs, their resilience may help sustain some ocean biodiversity within Hawai’i.
“Our study found that in the absence of local stressors such as nutrient pollution, overfishing, bottom trawling, physical damage from tourism, etc., at least half of Hawaiian reef corals will be able to survive and persist in up to 22 months exposure to ocean warming and acidification,” said McLachlan, “The results provide hope that if we can mitigate climate change and keep within the targets of the Paris Climate Agreement, coral reefs will persist in some form.”
