Severe low temperatures devastate coral reefs in Florida Keys

Study: Severe low temperatures devastate coral reefs in Florida Keys
Temperature from an inshore patch (Admiral Reef) and offshore (Little Grecian) reefs. Dotted line is the average winter (January and February) seawater temperature for Admiral Reef from 2007-2009 (panel a). Photos of Admiral Reef taken in February 2010 show Montastraea faveolata skeletons being overgrown by macroalgae (indicated by arrow, panels b, c). Dead M. annularis (panel d). Tissue necrosis and skeleton of M. cavernosa (panel e). Tissue necrosis from a dead octocoral (panel f). Dead M. faveolata colony with visually unharmed Gorgonia ventalina (panel g). Visually unharmed Siderastrea siderea (panel h). Credit: Dustin Kemp/University of Georgia

Athens, Ga. – Increased seawater temperatures are known to be a leading cause of the decline of coral reefs all over the world. Now, researchers at the University of Georgia have found that extreme low temperatures affect certain corals in much the same way that high temperatures do, with potentially catastrophic consequences for coral ecosystems. Their findings appear in the early online edition of the journal Global Change Biology.

Lead author Dustin Kemp, a postdoctoral associate in the UGA Odum School of Ecology, said the study was prompted by an abnormal episode of extended cold weather in January and February 2010. Temperatures on inshore reefs in the upper Florida Keys dropped below 12 C (54 F), and remained below 18 C (64 F) for two weeks. Kemp and his colleagues had planned to sample corals at Admiral Reef, an inshore reef off Key Largo, just three weeks after the cold snap. When they arrived, they discovered that the reef, once abundant in hard and soft corals, was essentially dead. "It was the saddest thing I've ever seen," Kemp said. "The large, reef-building corals were gone. Some were estimated to be 200 to 300 years old and had survived other catastrophic events, such as the 1998 El Niño bleaching event. The severe cold water appeared to kill the corals quite rapidly."

Study: Severe low temperatures devastate coral reefs in Florida Keys
Photographs of coral colonies from Admiral Reef before (panels a, c, e) and after (panels b, d, f) the cold-water anomaly. Photographs were taken in May 2009 (before) and February 2010 (after). Coral species shown are Montastraea faveolata (a, b), Porites astreoides (c, d), and Siderastrea siderea (e, f). “After” photographs of M. faveolata and P. astreoides (panels b, d) show dead colonies, whereas S. siderea (panel f) remained alive. Pigmentation of dead M. faveolata (panel b) is due to overgrowth of the coral skeleton by cyanobacteria and filamentous algae. Credit: Dustin Kemp, University of Georgia

Odum School Professor William Fitt, Kemp's doctoral advisor and one of the paper's co-authors, realized that the team had a unique opportunity. "Nearly 100 years ago, Alfred Mayer described the temperature tolerance of different corals in the Dry Tortugas and found very similar results," Kemp said. "We decided to take the next step and learn how and why the cold temperatures caused the corals to die."

The researchers took samples of Siderastrea siderea—one of the few reef-building corals to survive—from Admiral Reef. They also took samples of three common Florida Keys corals, Montastraea faveolata, Siderastrea sidereaand Porites astreoides from Little Grecian Reef, a nearby offshore reef that had not experienced the temperature anomaly to the extent of Admiral Reef. Kemp explained that Little Grecian Reef is far enough offshore that the cold-water temperatures were likely buffered by the warm waters of the Gulf Stream, which resulted in offshore coral reefs being less severely affected by the cold air mass that was pushed by an unusual weather pattern over much of the U.S. during that two-week period.

Back in the lab, they simulated the temperatures that had been recorded at Admiral Reef during the cold weather event, testing the different corals' physiological responses at 12 C and 16 C (61 F), and then, after the corals' exposure to the cold, returned the temperature to 20 C (68 F). They found that although responses varied depending on the coral species, in general the stress of extended cold temperatures had an effect similar to that of high temperatures.

Kemp explained that corals depend on Symbiodinium, a type of symbiotic algae that lives inside them, for nutrition. Through photosynthesis, the algae produce sugars, which are passed on to the corals. "The cold temperatures inhibited photosynthesis in the algae, leading to a potential net loss of carbon transferred from the algae to the coral," said Kemp. He said that each coral species had its own unique type of Symbiodinium, some of which were better able to tolerate and recover from cold temperatures than others.

All of the corals experienced a significant decrease in photosynthesis at 12 C. Siderastrea siderea and M. faveolata were able to handle the 16 C temperatures, but P. astreoides was not, and did not show signs of recovery once the temperature was returned to 20 C. Siderastrea siderea was the only coral able to recover.

"Corals and their symbiotic algae have a range of stress tolerance," said Kemp. "Some can handle moderate stress, some are highly sensitive, and some are in between. But extreme cold is just one stressor among many." Other threats to coral health include increased seawater temperatures, diseases, ocean acidification, and pollution. "Adding stress from wintertime cold episodes could not only quickly kill corals but also may have long-term effects," he said. "For corals found in the Keys, winter is typically a 'non-stressful' time and corals bulk up on tissue reserves that are important for surviving potentially 'stressful' summertime conditions (i.e. coral bleaching)."

Kemp said that researchers at NOAA attribute the record-breaking cold anomaly to a negative trend in the North Atlantic oscillation, an atmospheric pressure pattern that influences the weather in the northern hemisphere. "They speculate that if the trend continues, these kinds of extreme cold events may become more frequent," he said.

Kemp stressed that the study's findings should not be interpreted to downplay the major role of higher temperatures on corals' decline. "The study shows that warming may not be the only climate-related problem for in the future," he said.

Kemp also pointed out that it was not only the corals that were devastated by the cold snap. "The corals provide the framework for the entire reef ecosystem," he said. "The lobster, shrimp, clams, fish—all the creatures that depend on the reef—were affected too. The potential consequences for coral ecosystems are extremely alarming."

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Citation: Severe low temperatures devastate coral reefs in Florida Keys (2011, August 8) retrieved 18 October 2019 from
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Aug 08, 2011
Is there anything global warming cant solve?

Aug 08, 2011

"Heat" and "temperature" are two different things.

The Heat of Melting of water-ice is so much higher than the specific heat capacity that it is easily possible for huge quantities of ICE in the Arctic circle to MELT, absorbing HEAT from the Sun and environment.

As this Ice becomes WATER at 0c, it mixes with the surrounding oceans, cooling the "Temperature," at least in the short term.

The Heat of Fusion of water-ice is 80 times greater than the specific heat capacity of the same amount of Liquid Water, so melting a big chunk of ice can actually cool 80 times as much sea water by 1C.

If you so happened to have a cold pocket in the ocean, and then have a frontal system move in and sit there with winds out of the North, you can cool water several meters deep, at least locally.

You should check Reynolds SST anomaly.

One giant pocket of water is around 3.5C hotter than normal, and just a few degrees away, another pocket is 2C colder than normal.

Aug 09, 2011
So what happened to all the coral in the last ice age and in past warming trends?

Aug 09, 2011
So what happened to all the coral in the last ice age and in past warming trends?

Obviously, it didn't go extinct.

Corals reproduce similarly to Jellyfish, through a combined "tri-sexual" reproduction system.

During the sexual phase, they release "Polyps" into the ocean water, which are carried away and take roots elsewhere. Then they enter an "asexual phase" in which they make exact clones of themselves as additional polyps which continue to do the same thing.

In the case of Jellyfish, some of them, such as box Jellyfish, actually have polyps which are capable of "searching" for the most favorable environment.

Over time, the corals will move with the ocean currents to areas with more stable temperatures.

In the most extreme cases, humans may need to give them a bit of help and move them "upstream" in some cases.

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