Some corals can build up a tolerance to marine heat waves 

The relentless march of climate change has left its mark on ecosystems worldwide, with coral reefs among the most affected, mainly by heat waves in the warming oceans.

These vibrant underwater ecosystems, vital for sustaining ocean biodiversity, are under siege from the escalating threat of marine heat waves. 

Amid these dire circumstances, some good news has emerged in a study from the University of Pennsylvania. The research team spent nearly a decade investigating the resilience of coral species in Hawaii.

Coral reefs and climate change

“Coral reefs are in jeopardy as climate change leads to increasingly frequent marine heat waves,” wrote the researchers.

Some corals survive these extreme events, and this exposure may prime corals to increase their heat tolerance.

Yet, as the time between heatwaves decreases, the accumulation of stress experienced may preclude opportunities for beneficial gains in heat tolerance.

Coral adaptability to heat waves

Professor Katie Barott and her team focused their research on two coral species in Kaneohe Bay, Oahu – rice coral (Montipora capitata) and finger coral (Porites compressa). 

The experts investigated the adaptability of these corals to the harsh challenges of marine heat waves.

The study reveals that some corals have the capability to withstand and recover from the stress of elevated ocean temperatures.

“We tracked more than 40 large coral colonies over 10 years and found that certain species have an improved ability to endure and recover from subsequent marine heat waves after surviving one such event,” Barott explained.

“It’s a bit like working out; the more often you exercise, the easier it is to go through the same exercise stress.”

Resilience and vulnerability

The study’s findings are a testament to both the resilience and vulnerability of coral ecosystems.

Through detailed observation of the corals’ responses to significant marine heat waves in 2014, 2015, and 2019, the researchers identified individuals within each species that either resisted or succumbed to bleaching. 

“One of our key discoveries is the role of “acclimatization,” says Kristen Brown, first author of the paper and a postdoctoral researcher in the Barott Lab.

“This refers to the ability of some corals to adjust to higher temperatures, thereby reducing their susceptibility to bleaching, a phenomenon wherein corals expel the algae living in their tissues, causing them to turn white and increasing the risk of death.”

Contrasting recovery patterns

The researchers uncovered contrasting recovery patterns between the two coral species studied.

Montipora capitata showed a propensity for bleaching and sustained mortality up to three years post-heatwave, indicating a struggle to acclimatize effectively. 

By contrast, Porites compressa demonstrated remarkable resilience. Individual corals that were initially sensitive were found to survive subsequent heat waves without bleaching.

These corals also showed signs of recovery and acclimatization within a year.

Further research on coral and heat waves

The researchers suggest that coral responses to climate change are diverse and influenced by a range of factors including species-specific characteristics and past exposure to environmental stressors. 

Going forward, the team plans to continue monitoring and exploring aspects like coral growth, calcification, and the impacts of recurring marine heat waves.

“Now, more than ever, seasonal and long-term studies are critically needed to identify corals that cannot just withstand and survive repeated heat stress events, but also rapidly recover ecosystem-defining traits (e.g., biomineralization) to continue providing the critical ecosystem services coastal communities directly rely on,” wrote the study authors. 

Urgent, collective global action to eliminate greenhouse gas emissions remains the only approach that may provide sufficient time for corals to acclimatize and adapt to rapid climate-induced temperature increases in order for coral reef ecosystems to persist in the Anthropocene.

The study is published in the journal Proceedings of the National Academy of Sciences.

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