Guam’s Coral Reefs Ravaged by Warming Oceans

Bleaching killed 34 percent of the island’s reefs between 2013 and 2017, a study finds.

Catherine Offord
Jul 31, 2019


More than a third of Guam’s coral reefs were killed by bleaching between 2013 and 2017, according to researchers at the University of Guam. At a press conference held yesterday (July 30), the team discussed results of a study published last month (June 25) in Coral Reefs, which found that rising ocean temperatures and extreme low tides had led to the death of 34 percent of all the island’s reefs, and the disappearance of about 60 percent of reefs along the east coast of Guam.

“Never in our history of looking at reefs, have we seen something this severe,” study coauthor Laurie Raymundo told reporters, Pacific Daily News reports, adding, “The highest temperatures we’ve ever recorded in Guam happened in 2017.”

The researchers write in their paper that the data suggest several species of corals are at high risk of local extinction in Guam’s waters, and that, given the likelihood of future bleaching events, “the persistence of Guam’s current reef assemblages is in question.”

The conference was held just days after a report by The Guam Daily Post warned that huge swathes of the remaining coral reefs surrounding Guam could be dead within weeks. The report was based on forecasts released by the National Oceanic and Atmospheric Administration that predict coral bleaching (indicated by an Alert Level 1 by authorities) and death (Alert Level 2) are likely to occur through August. 

“We are expected to reach bleaching Alert Level One within one to four weeks and Alert Level Two within five to eight weeks,” states a press release from the island’s Coral Reef Resilience program, the Post reports.

To help keep track of changes in the reefs, the Coral Reef Resilience program has put out a call for volunteers to aid the work of staff at Guam’s multi-agency Coral Reef Response Team, the Daily Post reports. Participants will help monitor signs of coral bleaching, disease, and death, including outbreaks of coral predators known as crown-of-thorns starfish. More than 200 of Guam’s residents have taken part in training sessions for the work so far, according to the newspaper.

Catherine Offord is an associate editor at The Scientist. Email her at 

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