Australia's Great Barrier Reef experienced its second consecutive year of mass coral bleaching in 2017, and an international team of researchers say the time between bleaching events is likely to continue decreasing.
According to a report published Jan. 5 in the journal Science, researchers analyzed the coral bleaching records at 100 reef locations across the world from 1980 to 2016.
"The time between bleaching events at each location has diminished five-fold in the past 3-4 decades, from once every 25-30 years in the early 1980s to an average of just once every six years since 2010,” said Terry Hughes, the lead author and director of the ARC Centre of Excellence for Coral Reef Studies (Coral CoE).
The National Oceanic and Atmospheric Administration (NOAA) explains that increased ocean temperature caused by climate change is the leading cause of coral bleaching, but runoff, overexposure to sunlight and extreme low tides can also cause bleaching events.
Coral can survive bleaching events, but they are put under more stress and shorter recovery windows put them at higher risk.
As coral reef degradation continues to occur, the non-profit SECORE International is working to come up with a new technique to achieve large-scale restoration.
Restoration efforts have been limited to areas less than a hectare in size, or about 2.47 acres, at a time. Currently restoration efforts are also hindered by the fact that they are labor-intensive and costly.
"So this is a big bottleneck if you look at the current state of restoration because to plant a single coral takes a few minutes," explained Dirk Petersen, the executive director of SECORE International. "If you’re dealing with several thousands of corals, it takes a long time.”
SECORE International's most recent study, published in Scientific Reports, offers a more efficient alternative.
In SECORE's recent research pilot in Curaçao, the non-profit tested its "seeding units," which consist of a substrate and a coral polyp. A substrate is basically just the place where an organism grows and, in this case, the substrates are specifically designed to enhance the coral's chance of survival.
“What happens around this little coral will determine whether it will survive or die."
First, the research team collected larvae released by colonies of golf ball corals and then settled the larvae on the cement tetrapod-shaped substrates.
In the study, SECORE used a brooding species of coral, which release larvae that are already fertilized. Most of their work outside of the study, however, involves broadcast spawners, which release egg and sperm bundles that need to be fertilized by sperm from other coral colonies. In this case, SECORE takes the bundles back to the lab for in vitro fertilization.
Three weeks into the study, the coral larvae had turned into initial coral polyps and the each of the "seeding units" were sown on the reef in front of the Curaçao Sea Aquarium. The substrate's shape made it possible for researchers to easily wedge the "seeding units" in the natural crevices of the reef rather than having divers manually attach lab-grown corals using nails.
“What happens around this little coral will determine whether it will survive or die," Petersen said. "So with the design of the substrates, we tried to create a very diverse micro-habitat.”
Petersen added that coral larvae prefer to settle in the grooves of the substrate, which gives them more shelter and protection.
Researchers are still working to enhance the substrate's design and eventually hope to sow the substrates in large numbers using boats or underwater drones.
One year after the "seeding units" were planted on the reef in Curaçao, researchers said more than half had at least one coral.
Petersen said SECORE International has partnered with the California Academy of Sciences, the Nature Conservancy and others to launch the Global Coral Restoration Project. Going forward, Petersen said they hope to test the technique on a much larger scale.
In addition to refining each step of the sowing technique, SECORE is also hoping to develop different "seeding unit" shapes to cover a wider range of reef habitats.
While coral restoration is very important, Petersen said it's only "one tool in the tool box of coral reef conservation.
"It’s not the ultimate solution; it can only assist the natural recovery process of coral reefs," he said. "So the most important thing we have to do is to address climate change. Restoration can only buy us some time if we don’t deal with the huge problem of climate change."
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