A team of scientists equipped with high-tech underwater cameras is documenting a coral-bleaching event in Bermuda.
The Catlin Seaview Survey -- led by researchers from the University of Queensland, Australia, and sponsored by the insurance and reinsurance company Catlin Group Ltd. -- raced to Bermuda this month after the U.S. National Oceanic and Atmospheric Administration issued a bleaching alert as water around the islands' reefs grew dangerously warm.
"As soon as we got in the water we observed bleached fire corals and minor bleaching in brain and star corals," Manuel Gonzalez Rivero, the Catlin's shallow-reef survey coordinator, said in an email.
The Caitlin Survey is on a long-term mission to photograph the world's reefs with 360-degree images and 3-D video to establish a comprehensive base line for tracking damage inflicted by climate change and other threats (ClimateWire, Aug. 6). But the team turned into coral ambulance chasers after the NOAA bleaching alert.
The team's been in Bermuda for more than a week and plans to survey up to 18 miles of reefs there, taking about 10,000 panoramic images that will ultimately be posted online in the style of Google Street View. The shots will also be included in the Coral Reef Record, an online database unveiled this week.
Coral reefs are ecologically and economically valuable ecosystems, supporting an estimated 500 million people through fishing, tourism and other benefits. But reefs are under assault from overfishing, pollution, disease, rising temperatures and acidifying water.
More than 40 percent of the world's reefs have been lost over the last 50 years. Some of the greatest losses are in the Caribbean, which has seen 80 percent of its reefs destroyed over the past 35 years.
Reef losses are expected to continue. Recent studies suggest a majority of reefs will bleach regularly by midcentury and that changing ocean chemistry conditions will make it impossible for corals to grow by 2100 if carbon emissions continue on their current trajectory.
Keeping an eye on current bleaching conditions and mortality is NOAA's Coral Reef Watch, which since 1997 has been issuing watches, warnings and alerts about abnormally warm ocean water and the potential for coral bleaching and death around the world.
Bleaching occurs when water gets too warm and wrecks a delicate relationship between corals and algae that live inside coral cells and convert sunlight into energy. As water warms, algae release toxins, so corals expel the algae. With the colorful algae gone, reefs turn white and starve for loss of their source of food and energy.
"If it is a brief event, corals can recover their algae and go back to normal," said Mark Eakin, the Reef Watch director. "If the event is long-lasting or severe enough, the coral dies."
It can take decades for reefs to fully recover from bleaching, yet widespread events are increasing in frequency and intensity since they started in the 1980s. For example, there have been six major bleaching events in the Caribbean since 1985.
"That's more than once every five years," Eakin said in an interview. "There isn't a reef in the world that can bounce back from major bleaching that fast."
Bleaching is suspected of making reefs more susceptible to other stressors like disease, pollution and overfishing, which can result in death or hinder recovery. For example, an overfished reef can be quickly overgrown by scuzzy algae because the gardeners that would graze on the algae were removed. The algae prevent new baby corals from finding a spot to grow and recolonize the reef.
NOAA alerts are based on information provided by satellites that measure sea surface temperatures around the globe twice daily, which are compared with historical averages.
When water temperatures exceed the monthly maximum average, the team issues bleaching "watches." If temperatures hit 1.8 degrees Fahrenheit higher, the team issues a "warning" that bleaching is possible.
Then there are two levels of alerts for when things get serious. The alert levels are based on a running tally of unusual temperature increases over a rolling three-month time frame, which is called “degree heating weeks.” Alert Level 1 is for when the total hits 7.2 degree Fahrenheit weeks and bleaching is likely, and Alert Level 2 if it hits 14.4 degree weeks and mortality is likely.
It’s not that the water is 14 degrees warmer but that the smaller increases added together exceed 14 degrees. This rolling total reflects accumulated stress that is likely to cause corals to bleach or die.
"We've never gone as far as having level 3 and level 4," Eakin said. "We've been thinking more about maybe we need to."
Consider that during the 2005 bleaching event in the Caribbean, the temperature stress over a three-month period added up to 29 degrees Fahrenheit, reflecting a period in which the water was slightly warmer for months.
While managers can't stop the warm water from hitting the reef, alerts provide a heads-up for when resources will be stressed. They can possibly take action to reduce compounding stressors to help the reef recover more quickly, such as closing an area to fishing, diving or a beach nourishment project that could cover reefs in extra sediment.
"There are a number of local actions that we should really be doing anyway," Eakin said. "But it gives new ammunition and new incentive to perhaps, on a short-term basis, be more strict about these things."
Managers have been asking for longer lead times, so Coral Reef Watch is now issuing seasonal bleaching forecasts. They aren't localized enough to differentiate between how reefs in the U.S. Virgin Islands will do compared with those in Puerto Rico, but they can project whether it's going to be a good year for the Caribbean or the western Pacific Ocean, Eakin said.
Coral Reef Watch is also testing out new products such as ocean-acidification monitoring and the probability of disease outbreaks.
Forecasts and alerts will become much more accurate and localized in the coming year. NOAA is incorporating data not just from the polar-orbiting satellite but also geostationary satellites that take constant readings from a single spot above the Earth. This will provide more data at 100 times finer resolution. Instead of seeing a 31-mile-wide square, they can see a 3-mile square.
That's closer to the scale of reefs, but not quite. That's why, Eakin said, the Catlin Seaview Survey observations are so valuable. They provide feedback for the forecast models and identify local differences between how corals respond under different management regimes, he said.
"We have to plan not only how do we deal with events in the short term," Eakin said, "but how do we do the best job we can to make them more resilient in the future, knowing these events are going to be continuing and probably be getting worse."
Correction: A previous version of the story incorrectly described the extent of ocean warming and the basis for issuing bleaching alerts.