Bleaching-Resistant Coral Used to Build Better Reefs

A turtle swimming over a reef destroyed by the 2016 bleaching event in the Indian Ocean. (Kristen Brown/ ARC CoE for Coral Reef Studies)

(CN) – Researchers say they found a new way to fight the ravages climate change wreaks on coral reefs, which could be wiped out by the end of the century by pollution, warming oceans, and ocean acidification.

Coral may seem inert, like living rocks, but they are animals – complete with a mouth, a gut, and stinging tentacles that stretch out at night to grab the zooplankton they eat. Algae live protected in the bony structures corals build and in exchange, they feed their coral and cause them to develop their characteristic bright hues. But warm water events like El Nino weather patterns break up this reciprocal partnership. Water temperatures just one or two degrees above normal cause coral to spit out their algae – usually a death sentence, and one that drains their color.  Coral bleaching has decimated an estimated 80% of reefs in the Caribbean and about half of Australia’s Great Barrier Reef.

Marine biologist Stephen Palumbi at Stanford’s Hopkins Marine Station said the race is on to save coral reefs.

“If CO2 keeps rising in the atmosphere, then by end of century there could be enough CO2 in the atmosphere to severely damage corals in every way,” Palumbi said. “That’s a future that it is very hard to image coral reefs surviving in.”

With oceans continuing to warm, scientists are scrambling to find ways to keep them from disappearing. Projects are underway around the globe to breed “super corals” that can withstand future climate conditions and to breed corals in the lab before broadcasting their larvae over a likely ocean floor. Others are trying to establish nursery beds of young coral polyps that might be better able to withstand warmer ocean temperatures.

Those are the projects Palumbi and his team of researchers wanted to improve. Some coral species are naturally more heat resilient. But researchers didn’t know if that tolerance was an individual coral’s intrinsic characteristic, like height in humans, or if it was caused by one of two factors that might not withstand transplanting: an individual coral’s adaptation to a niche microclimate or the specific species of algae that each coral hosts.

A living, vibrant coral reef.

The researchers wanted to know: could they choose individual corals that showed exceptional heat tolerance and move them to reefs where less resilient species had died, creating coral reefs capable of surviving into the future? In 2014, the team transplanted 800 cuttings from four species originating from 80 different coral colonies to a site in the waters surrounding the Samoan Islands where the native reef had been leveled by hurricanes. Eight months later, the young corals were able to survive a bleaching event caused by El Nino’s warm ocean temperatures. They had retained their resilience.

Dr. Angelo Jason Spadaro, a coral researcher with Old Dominion University who was not involved with the Stanford study, told Courthouse News the study will help researchers choose the right coral for the conditions of the future, and could “substantially improve the survival of corals transplanted for restoration.”

He added that the study may even help researchers choose corals for propagation that are resistant to other types of stress, like disease and pollution that affects the zooplankton they eat.

“Using these “super corals” could give restoration programs a leg up right out of the gate,” Spadaro said. 

Palumbi told Courthouse News the team’s findings applied to all species of coral and would help those working to regenerate coral reefs choose cuttings that would thrive in their new environment.  While heat tolerance varies among the species of coral, it also varies among the individuals within each species, Palumbi said. That gives restoration efforts one more tool to improve the survival of the reefs they create. The results are detailed in an article published Monday in the scientific journal Proceedings of the National Academy of Sciences.

But Palumbi added that there is only one way to truly save coral reefs: halting climate change.

“The approach here is not to say, go ahead and keep emitting CO2 into the atmosphere while we help corals develop heat resilience,” Palumbi said. “The approach is to say coral resistance with heat resilient corals will help corals survive a little longer while we solve this CO2 problem. But solving that problem is the key to everything.”

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