| "We're ramping up for a bleaching year." | |
| Dave Score, Florida Keys National Marine Sanctuary |
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At the end of July, coastal resource managers in the Florida Keys were reporting that isolated coral colonies were beginning to show signs of paling or partial bleaching. If conditions continued, the threat of mass coral bleaching would be high.
Widespread coral bleaching means that these normally colorful ecosystems are being subjected to starvation and could face disease, and even death. The primary culprit, scientists say, is rising sea temperatures fueled by climate change.
The consequences of major bleaching events could include millions of dollars in lost tourism revenue, communities left more vulnerable to coastal storms, and less seafood for people around the country to eat.
"Based on observations in the Florida Keys, it is clear that coral bleaching events have been intensifying over the past two-and-a-half decades on a local scale. This is consistent with other observations reported on regional and global scales," says Billy Causey, regional director of the Southeast Atlantic, Gulf of Mexico, and Caribbean Region of the National Oceanic and Atmospheric Administration's (NOAA) National Marine Sanctuary Program.
While coastal resource managers cannot address the global rise in sea temperatures, Causey and others say there are things resource managers can do to help improve corals' chances of survival, such as reducing nonpoint source pollution and other coral stressors, conducting baseline monitoring of corals and other ecosystems, identifying and protecting resilient reefs, and communicating with managers, scientists, and the public.
This advice is suggested not only for managers of states or territories with coral reefs off their shores, but also for all environmental managers who may not realize the impact their state or local storm runoff may be having on coral reefs.
Florida managers also warn that corals are one of the first indicators of ecosystem change related to climate change and that the lessons they are learning are a warning to other managers who should be preparing now for the potential of environmental impacts.
Benefits of Coral Reefs
The Florida Keys receive about four million visitors a year, who spend more than $1 billion. Many of these visitors come to scuba dive, snorkel, and sport fish—activities that are all dependent on healthy reefs.
The reefs provide habitat for finfish and shellfish, helping commercial fishermen in the Keys land $50 to $70 million worth of seafood every year. Coral reefs absorb constant wave energy from the ocean, protecting coastlines from increased storm damage, erosion, and flooding.
The U.S. and world economies also benefit from coral reefs, says Mark Eakin, coordinator of NOAA's Coral Reef Watch.
About 45 million tourists visit U.S. coral reefs every year, generating $17 billion in income, and U.S. reefs generate $247 million from commercial fishing. Globally, coral reefs have a value of $375 billion and provide food to about one billion people in Asia alone.
Getting Warmer
"The biggest issue we're seeing in global climate is that ocean temperatures are rising, and we expect them to continue to rise in the future," says Eakin. "Corals are sensitive to extremes in water temperatures and are already living at their uppermost thermal limits."
Less than a two-degree Fahrenheit temperature increase can trigger a major bleaching event.
"Coral bleaching can be caused by many adverse environmental conditions, but unusually high sea temperatures have been found to be the primary driving factor in mass coral bleaching events where entire reef systems and regions bleach," says Derek Manzello, marine biologist with the Cooperative Institute for Marine and Atmospheric Studies at the University of Miami.
"Without a doubt, in the late 1970s and early 1980s we started seeing signals of elevated sea surface temperatures affecting coral reefs in the Keys," says Causey. "We're already in a situation where the water temperature has risen high enough that we're seeing bleaching events occurring with greater frequency and intensity."
Bleaching
Corals often respond to stress by expelling the colorful algae that live within their otherwise clear tissues. Because these algae give corals their color, bleached colonies often appear stark white.
"If it's a mild event, coral will regain algae, and they will recover," Eakin explains. "If it is severe, or if the event is long-lasting, corals will die."
Secondary impacts to corals from bleaching events include disease, loss of living tissue, and low recruitment.
Manzello points out that "nearly every reef in the world has undergone temperature-related bleaching, and the increase in the frequency and severity of coral bleaching events over the past 25 years is unprecedented."
Ramping Up
In 1997 and 1998, coral reefs worldwide bleached for the first time, killing about 16 percent of the world's living coral reefs.
Since 1996, more than 35 percent of the Florida Keys' shallow coral reefs have died. The number of coral species within particular reef areas is declining as well, says Brian Keller, science coordinator at the Florida Keys National Marine Sanctuary.
The risk of mass bleaching is higher when weather forecasts call for high air temperatures and extended periods of low winds and low cloud cover. In 2005, the Florida Keys escaped the impacts of a Caribbean-wide bleaching event when four hurricanes churned past the area, lowering water temperatures.
"We're ramping up for a bleaching year," notes Dave Score, superintendent of the Florida Keys sanctuary. "We're seeing higher temperatures in mid-July than we did last year."
Vulnerability
Coral reefs typically cannot withstand continued exposure to sea temperatures colder than 68 degrees Fahrenheit or warmer than 86 degrees, or great changes in water quality or salinity.
"Here in the Keys, the reefs that are the most vulnerable to bleaching are the ones that are the most popular—the shallow reefs that are the most beautiful dive destinations," says Causey.
Nearshore patch reefs have shown the least amount of decline. "One might not expect that to happen," notes Causey, because these reefs are generally found in the most turbid waters in the Keys adjacent to the shoreline where sanctuary monitoring has found high levels of nutrients. They are also exposed to a wider temperature range than the other reefs.
"They have acclimated over a long geological time to a broader range of temperature shifts," Causey explains. "The algae in patch reefs also are a different type, which helps the coral communities survive."
Corals are able to adapt, says Eakin, "if the rates of change are going extremely slowly. We don't know how slow that is. The problem that we're running into now is that the changes we're seeing are at a rate that far exceeds what corals are capable of responding to."
Stressed Out
One of the problems is that the corals may be facing too many other stressors at once, such as land-based sources of pollution, habitat loss and degradation, and overfishing.
"Under normal conditions, corals can tolerate a certain level of environmental stress," says Causey. "If you add the temperature stress to the corals and you add any of the other stressors—whether it is nutrients or physical impacts—all of these are part of the multiple stressors that are pushing corals to the very brink."
The good news is that coastal resource managers can play a critical role in responding to bleaching events and in helping to control the issues that put additional stress on reefs.
Building Relationships
Some of the successful management efforts undertaken by the sanctuary include creating no-impact zones that protect reefs and species, and providing in situ and remote sensing observations to researchers who have developed prediction methods and who are working to better understand the bleaching phenomenon.
Sanctuary staff members have reached out to other reef managers and scientists around the country and world to share and compare bleaching-related information and insights, and contributed to A Reef Manager's Guide to Coral Bleaching, produced by NOAA, the Great Barrier Reef Marine Park Authority, and others, that provides information on actions local reef managers can take.
When a bleaching event is predicted, sanctuary managers alert the local dive and fishing communities, who provide information on bleaching conditions to an early-warning network of volunteers called BleachWatch.
They are also collaborating with resource managers, researchers, nonprofits, and other stakeholders to help develop strategies to support the natural resilience of reefs.
Stress Management
Other management actions that could improve reef health include working to improve water quality, or timing impacts to avoid exacerbating bleaching events. Mitigating the impacts of coastal development, commercial fishing, agriculture, and tourism could also reduce sources of coral stress.
"These are things coastal managers are looking to do anyway, and in many cases aren't doing as well as they would like because of factors beyond their control," Eakin says. "What's going on with coral reefs could serve as a catalyst to help them to take the actions they would already like to be taking."
He adds, "This truly is their issue, whether they have a reef in their backyard or not. Two-thirds of the U.S. has an influence on the reefs in the Gulf of Mexico and Florida Keys."
Harbingers
Coastal managers may also want to take the coral bleaching events in the Florida Keys as forewarning to prepare for their own environmental impacts from climate change.
"It's a matter of time before others are experiencing the impacts of climate change like we're experiencing in the Keys and other areas," says Causey. "Coral reefs are really good indicators of climate change and truly are also an indicator of ecosystem change. . . They are the canaries in the coal mine."
He adds, "One of the lessons that we've learned is the need to focus scientific efforts on understanding this change as it takes place, and being prepared to adapt management for the future."
Staying Positive
While the impacts of coral bleaching are grave, there is still hope.
"It's very serious in the short term, but over a much longer term coral reefs have adapted in various ways," says Eakin. "Coral reefs have been around for 400 million years, and corals will continue to be around in some form."
"We're not giving up," says Score, "and the colleges in South Florida are not giving up, and I don't want to send the message that the problem is too big to fix."
He adds, "Don't be afraid to do your part when it feels like you can't fix it all. It takes all of us working together to buy the time we need until we have a global solution."
For more information on coral bleaching, contact Billy Causey at (305) 809-4670, ext. 234, or Billy.Causey@noaa.gov.Contact Dave Score at (305) 809-4700, or David.A.Score@noaa.gov, or Brian Keller at (727) 553-1100, or Brian.Keller@noaa.gov. Mark Eakin can be reached at (301) 713-2857, ext. 109, or Mark.Eakin@noaa.gov.
Additional Information
- A Reef Manager's Guide to Coral Bleaching, www.coris.noaa.gov/activities/reef_managers_guide/
- The National Oceanic and Atmospheric Administration (NOAA) Coral Reef Conservation Program, www.coralreef.noaa.gov
- NOAA's Coral Reef Watch, http://coralreefwatch.noaa.gov
- NOAA's Coral Reef Information System (CoRIS), www.coris.noaa.gov
- The Florida Keys BleachWatch program, http://isurus.mote.org/Keys/bleachwatch.phtml
- The Florida Reef Resilience Program, www.nature.org/wherewework/northamerica/states/florida/preserves/art17499.html
