And yet, on a three-day trip in July to harvest coral samples, he repeatedly found himself surprised. The Rib Reef, where he was diving, had been healthy and vibrant only a year ago. But during his return visit, large sections were dead, covered in algae that looked like soot.
The samples he collected — of the Pocillopora acuta species — were often the only healthy chunks of coral to be found among canyons of dead reefs.
Near the end of their research trip, he and two other scientists dove for nearly an hour before finding just three samples, which they removed with a hammer and chisel and placed in a metal supermarket dish rack for transport to the surface.
“This is probably a three-year-old coral,” he said back on the boat, admiring a pinkish sample with a handful of healthy branches that made it look like a fist-size shrub. “We want to take the whole adult coral, collect its babies and then grow the larvae into adult coral.”
Professor van Oppen, a senior scientist who oversees Dr. Cantin’s research, said that part of what makes the Australian experiment stand out is the “sea simulator” at the Townsville marine institute. It is a complex high technology laboratory where corals live in tanks with water temperatures that can be calibrated to a tenth of a degree and simulate seasonal patterns of warming events. Lighting systems replicate the moon cycles that corals use to time their spawning.
Future generations of corals, the offspring of the those Dr. Cantin harvested, will be tested for resilience in this artificial environment, with warmer and more acidic water that mimics what scientists are predicting for the years 2050 and 2100.
The strongest corals will then become parents again, with some crossbreeding of the same species from different sections of the reef and also crossbreeding of different species to create genetic hybrids.
“If the speed of natural adaptation was fast enough to keep up with climate change, we wouldn’t see the scale of loss we’re seeing,” Professor van Oppen said. “There’s an urgent need to come up with ways to slow it down.”
Professor van Oppen is collaborating with Dr. Gates, who heads the Hawaii Institute of Marine Biology on a small island in Kaneohe Bay, off Oahu. Their joint project is partially funded by the family foundation of Mr. Allen, the billionaire philanthropist.
On a recent day at the lab, a manager, Jen Davidson, meticulously examined coral colonies growing in indoor tanks under artificial lights.
Starting with hardy coral polyps that survived past environmental assaults in Kaneohe Bay, the Gates lab is trying to make them even hardier, crossbreeding the corals and testing offspring in water treated to mimic the hotter, more acidic conditions likely to prevail in a future ocean.
Under normal conditions the animals grow and build their reefs only slowly, one of the factors that is stymying the effort to save them. “We can do all this work here, but can we scale it up enough to make an impact?” Ms. Davidson asked.
Researchers in Florida may be closest to answering that question. At the Mote laboratory in Sarasota, a researcher named David Vaughan has perfected a technique in which coral samples are broken into tiny fragments; the polyps grow much faster than normal as they attempt to re-establish a colony.
“It used to take us six years to produce 600 corals,” Dr. Vaughan said in an interview. “Now we can produce 600 corals in an afternoon, and be ready in a few months to plant them.”
Florida’s reefs have been badly damaged over the years, not just by climate change but by more direct human assaults, like overfishing that disturbs the ecological balance. Yet the Mote lab and other centers have already replanted thousands of small coral colonies.
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