A new study headed by University of Victoria biologists offers first-of-its-kind evidence that coral reefs with little human disturbance may be able to withstand climate change longer than expected.
The study, released on Dec. 8, presents the findings of an international research team that tracked hundreds of coral colonies around Christmas Island during the 2015-2016 El Niño – a periodic warming event of sea surface temperatures in the eastern and central Pacific Ocean. What made this El Niño noteworthy was that it lasted an unprecedented 10 months, triggering the worst global coral bleaching and mass mortality event on record.
Because coral reefs are stationary animals, they rely almost entirely on microscopic algae living inside their tissues to feed them. When these “symbiotic partners,” as UVic marine biologist and senior study author Julia Baum describes them, photosynthesize they provide food for the coral.
The reason coral reefs are so susceptible to climate change is that they are extremely sensitive to changes in water temperature. As little as one degree Celsius can completely throw off the relationship between coral and their feeders.
|A coral reef site on Christmas Island before and after the 2015-2016 marine heatwave. (Courtesy of Danielle Claar and Kevin Bruce)|
“Suddenly, their symbiotic partners will start producing toxic chemicals and, no longer recognizing them as partners anymore, the coral will kick the algae out,” Baum said. This is what is known as coral bleaching.
“That then sets the coral on a trajectory of starving to death,” Baum explained.
Normally, coral reefs can survive a couple-week heatwave before needing their symbiotic partners back. So, as the 2015-2016 El Niño stretched on for months, researchers feared all of the coral reefs would die. Instead, the extended heatwave allowed them to discover something no researchers had before – that coral reefs that hadn’t been exposed to human stressors were able to recover some life even while the heatwave raged on.
These coral reefs developed new relationships with more thermotolerant symbiotic partners and were able to obtain some sustenance.
This discovery, Baum said, proves that protecting coral reefs from coastal development, dredging and water pollution can significantly impact their ability to survive climate change. Long-term, the only solution for saving coral is stopping climate change.
Now, it’s up to people to let their governments know that climate action is a priority, she said. “We want economic recovery from COVID-19 that is aligned with addressing climate change.”
The full study can be found at nature.com.
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