Healthy coral and bleached coral at Guam’s West Agana site in 2014. (Photo by Laurie Raymundo)

Corals in one of the world’s most diverse corners of the ocean have been ravaged by the ongoing effects of a global bleaching event, scientists say — and nobody’s sure how long it may take them to recover or what they might look like afterwards. The reefs around the U.S. territory of Guam and other nearby islands in what’s known as the Marianas archipelago have been suffering since 2013, and the pattern is only expected to continue through the rest of this summer.

If you’re up on your marine biology news (or if you’ve been scanning headlines at all over the past few months), you’ve probably heard that the world’s coral reefs are in trouble. An ongoing global bleaching event — brought on by warming ocean temperatures and the most recent El Niño effects — has been ravaging reefs for several years now, and reports suggest that the pattern is continuing this summer.  

But while the devastation is apparent in reefs all around the globe, some have received more notice than others. Australia’s Great Barrier Reef, for instance, made headlines back in April when scientists announced that a whopping 93 percent of its corals had bleached. Corals in U.S. waters, as well as other reefs scattered throughout the Pacific, have turned heads recently as well. But the plight of the corals surrounding Guam and its neighbors has largely gone unreported in mainstream media.  

Nevertheless, the region is a big area of concern for marine biologists — and has been for going on four years. According to coral ecologist Laurie Raymundo of the University of Guam, the island of Guam is located just outside of the “coral triangle” — a kind of coral hotspot including the Philippines, Papua New Guinea, Malaysia, Indonesia, Timor-Leste and the Solomon Islands. It’s known for having the most diverse coral ecosystems in the world.

“Guam is right outside that ring of highest diversity, so the diversity is generally fairly high,” Raymundo said, adding that the area is believed to be home to more than 300 species of coral. Prior to 2013, she said, the corals there had not experienced much of a problem with bleaching like reefs in other parts of the world had.

“But in 2013, 2014 and 2015, we have gotten hammered,” she said. “And we’re getting hammered again. For the past four years we’ve had bleaching episodes, and we have not had them to this extent in recent history.”  

According to Raymundo, recent analyses have suggested that more than 50 percent of the corals there died between 2013 and 2014, and about 85 percent in total had bleached. Those estimates were made in 2015, so Raymundo estimated more corals may have died in the meantime.

And there’s been no sign of a break this summer. After a recent dive in Guam’s Tumon Bay, Raymundo took to Facebook to describe her shock at the devastation.

“I consider myself to be fairly objective and logical about science,” she wrote. “But sometimes that approach fails me. Today, for the first time in the 50 years I’ve been in the water, I cried for an hour, right into my mask, as I witnessed the extent to which our lovely Tumon Bay corals were bleaching and dying.”

While not all of the shallow reefs around Guam have been so severely affected, the damage to the Tumon Bay corals is particularly worrying because that area is so important for tourism, Raymundo said. The conditions were all the more shocking considering it was only July at the time — relatively early as far as bleaching season goes. According to Mark Eakin, head of the National Oceanic and Atmospheric Administration’s Coral Reef Watch, Guam’s bleaching event likely won’t even peak this summer until September.

As in other places around the world, corals around the Marianas archipelago are suffering from a combination of climate change-driven ocean warming and the lingering effects of a particularly severe El Niño event last year, which has caused unusually warm water temperatures in many regions. And around Guam, Raymundo said, El Niño’s effects have also caused extreme low tides and shallow waters, which have left certain parts of the reef exposed to the air.


Low tide exposure and coral bleaching at the Togcha reef flat in Guam in 2015. (Photo by Valeri Lapacek)

According to Eakin, the Coral Reef Watch will likely assign Guam’s reefs an Alert Level 2 by September, which will probably last through November or so. This is the highest alert level that NOAA issues and suggests that coral death — not just bleaching — is likely. As of August 1, the area around Guam has been mostly assigned a “warning” level, meaning that bleaching is possible.  

As the winter sets in, water temperatures will cool and the reefs will receive a bit of a respite. The problem is that corals can take years to recover from a bleaching event, and temperatures have been unusually warm in the region every summer for the past four years — meaning that the corals haven’t gotten adequate time in between bleachings to recover. This is likely a major reason conditions have gotten so bad in the past few years, Raymundo noted.  

And because scientists can’t say for sure how much worse it will get in the coming years, it’s difficult for scientists to make a prediction about how long it will take Guam’s reef to fully recover or what it will look like in the future. Because some species tend to withstand temperature stress better than others, Raymundo suspects that the reef’s composition will eventually become dominated by hardier species, while more sensitive ones (such as the staghorn coral, which has suffered particularly severe losses around Guam recently) may begin to die out.  

“I think we’re probably going to lose certain groups that may not be able to come back,” Raymundo said.