This year's unusually warm summer was the cause of many health issues for humans worldwide - poor air quality, heat stroke and fire danger were only a few examples. But humans and other land dwellers aren't the only species that suffer from hot weather. One marine ecosystem in particular has scientists worried: coral reefs.
Reefs in Indonesia suffered a large bleaching event this summer, where temperatures of 93 degrees Fahrenheit were reported in surface waters of the Andaman sea, off the coasts of Thailand and Myanmar. This is about 7 degrees above long-term averages for that area. Fortunately, temperatures are beginning to drop again in the Pacific, but scientists now warn that Caribbean reefs may be at risk of experiencing a similar bleaching event.
Data from the National Oceanic and Atmospheric Administration indicates that bleaching is likely to occur in the southern and southeastern Caribbean. Above-average temperatures have been recorded in the Caribbean throughout this summer, and it is predicted that coral reefs will continue to be stressed until mid-October.
"Based on these temperatures, NOAA has issued a bleaching warning for the western Pacific and the Caribbean," said Jon Corsiglia of NOAA's Office of Ocean and Coastal Resource Management. Bleaching has also been reported in the western Gulf of Mexico and the Bahamas.
Such environmental stresses can prompt reflection on the ecological importance of coral reefs. Closely related to jellyfish and anemones, coral reefs provide food and shelter for a myriad of fish, shellfish and crustacean species.
"A lot of fish species use coral as spawning grounds, so [bleaching] could seriously impact fish populations," Reidenbach said.
Reefs are also important to the fishing and tourism industries of many coastal and island communities worldwide.
"Coral reefs are primary producers; without them, fish can't feed and you lose the ecosystem ... for tourism, fishing and preservation," fourth-year College student Hunter Doughty said.
For example, some fish species that appear on restaurant menus can be affected.
"Groupers are heavily fished in the Caribbean and rely heavily on coral reefs," fourth-year College student Alia Al-Haj said. "So fishing for them will be severely affected [by coral bleaching]."
Overall, a single hectare - about 2.47 acres - of coral reef provides $130,000-1.2 million in services to humans per year, according to estimates made by experts at the DIVERSITAS biodiversity conference held in Cape Town, South Africa last October. Other studies estimate the total worth of coral reefs globally to be about $375 billion a year.
This economic importance causes experts to be particularly interested in why coral reefs can respond so negatively to high temperatures - as well as in what can be done to mitigate these effects.
"You often don't know the causes, but we know that coral bleach when they are stressed," said Matthew Reidenbach, an assistant environmental sciences professor at the University.
Most reef-building corals play host to an alga called zooxanthellae, Corsiglia said. The corals feed on the organic material produced by the alga, he said, but when temperatures rise, this relationship is disrupted.
"The metabolism of the algae speeds out of control, and the corals eject the algae due, in part, to buildup of toxic waste products," Corsiglia said. When this occurs, the coral pales and the white calcium carbonate skeleton of the coral can be seen.
"It doesn't necessarily kill the coral right away, but it can if they're bleached for too long a period, around two or three years," Reidenbach said.
He added that some coral species tend to be less resilient than others and are less capable of withstanding wide swings in temperature.
Despite these challenges, there are several steps that reef managers - officials tasked with protecting and preserving coral reefs - can take to help reduce bleaching of coral reefs. Officials can, for example, restrict potentially harmful activities such as diving and fishing, or they can artificially shade parts of a reef or reduce coastal runoff and pollution in the surrounding area. "A healthy coral reef is more able to recover," Corsiglia said.
Global warming mitigation may benefit the coral reefs, as well.
"In the long term, reducing carbon dioxide and other greenhouse gas emissions is vital to addressing the resulting impacts of rising temperatures," Corsiglia said. "If we fail at that, other coral ecosystem management efforts could be futile."
Ultimately, however, Reidenbach said it is likely that there will be more bleaching events in the future, especially as warming trends continue. These trends can raise a host of new issues.
"It's an interesting question. I think we're seeing more and more occurrences of bleaching worldwide, and the last big one happened after El Ni
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