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NSF Web Site

Press Release 09-168

Global Warming Causes Outbreak of Rare Algaein Caribbean Corals

Scientists take advantage of 'experiment of nature' to discover new insightsinto coral bleaching

This image was taken in October, 2005, during a coral-bleaching event in the Caribbean.Credit and Larger Version

September 9, 2009

A rare opportunity has allowed a team of scientists to evaluate corals--and theessential, photosynthetic algae that live inside their cells--before, during, and after aperiod in 2005 when global warming caused sea-surface temperatures in the Caribbeanto rise.

The team, led by Penn State biologist Todd LaJeunesse, found that a rare species of algae that's tolerant of stressful environmental conditions proliferated in corals at atime when more sensitive algae that usually dwell within the corals were being

expelled.

The results will be published in the online version of the journal Proceedings of theRoyal Society B on September 9, 2009.

Certain species of algae have evolved over millions of years to live in symbioticrelationships with species of corals. These photosynthetic algae provide the corals withnutrients and energy, while the corals provide the algae with a place to live.

"There is a fine balance between giving and taking in these symbiotic relationships,"said LaJeunesse.

Symbiodinium trenchi is normally a rare species of algae in the Caribbean, according toLaJeunesse. "Because the species is apparently tolerant of high or fluctuatingtemperatures, it was able to take advantage of a 2005 warming event and becomemore prolific."

Symbiodinium trenchi appears to have saved certain colonies of coral from thedamaging effects of unusually warm water.

The white corals pictured have losttheir symbiotic algae and appear"bleached."Credit and Larger Version

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"As ocean temperatures rise as a result of global warming, we can expect this speciesto become more common and persistent," said LaJeunesse. "However, since it is notnormally associated with corals in the Caribbean, we don't know if its increasedpresence will benefit or harm corals in the long term."

If Symbiodinium trenchi takes from the corals more than it gives back, over time thecorals' health will decline.

"'Experiments of nature' provide unique opportunities to discover important newinsights," said Michael Mishkind, program director in the National Science Foundation(NSF)'s Division of Integrative Organismal Systems, which funded the research.

"These scientists took advantage of just such an event--with the unexpected discoverythat an alternate algal species was waiting in the wings. Whether this 'understudy'helps or hinders its host remains to be determined."

In 2005, sea surface temperatures in the Caribbean rose by up to two degrees Celsiusabove normal for a period of three to four months, high enough and long enough toseverely stress corals.

The process of damaged or dying algae being expelled from the cells of corals is knownas bleaching because it leaves behind bone-white coral skeletons that soon will diewithout their symbiotic partners.

During the summer of 2005, prior to the bleaching event, LaJeunesse and hiscolleagues collected samples of coral and algae from two locations near Barbados in theCaribbean.

By late November, water temperatures had peaked and many corals were bleached.

The team collected samples of coral and algae during the bleaching event and againtwo years after ocean temperatures returned to normal. In the laboratory, theysequenced the organisms' DNA to identify the species.

"During the bleaching event, we found that Symbiodinium trenchi , which is rarelyfound in the Caribbean, had increased in frequency by 50 percent or more in coralspecies that are most sensitive to warm water," said LaJeunesse.

"We also saw this species in corals where it had never been before. Two years later,we found that the abundance and occurrence of Symbiodinium trenchi had diminishedsignificantly. Today the symbioses have mostly recovered to their normal state, and thecorals have been repopulated by their typical algal symbionts."

Although Symbiodinium trenchi saved some corals from dying in 2005, LaJeunesse isconcerned that the species might not be good for the corals if warming trends continueand Symbiodinium trenchi becomes more common.

"Because Symbiodinium trenchi does not appear to have successfully co-evolved withCaribbean coral species, it may not provide the corals with adequate nutrition," hesaid.

LaJeunesse plans to further investigate the relationship between Symbiodinium trenchi and Caribbean coral species.

"We're interested in looking at how it behaves in other regions of the world where it'snaturally common," he said.

The research also was supported by Florida International University, Penn StateUniversity, and the University of the West Indies.

-NSF-

Media ContactsCheryl Dybas, NSF (703) 292-7734 [email protected] Kennedy, Penn State (814) 863-4682 [email protected]

The National Science Foundation (NSF) is an independent federal agency that supportsfundamental research and education across all fields of science and engineering. Infiscal year (FY) 2009, its budget is $9.5 billion, which includes $3.0 billion provided through the American Recovery and Reinvestment Act. NSF funds reach all 50 statesthrough grants to over 1,900 universities and institutions. Each year, NSF receivesabout 44,400 competitive requests for funding, and makes over 11,500 new fundingawards. NSF also awards over $400 million in professional and service contracts yearly.

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Algas Afectan Corales Del Caribe Calentamineto Global