El Niño warming causes significant coral damage in central Pacific

Georgia Institute of Technology Science Daily 1 Dec 15;

Current El Niño conditions in the Pacific Ocean have created high water temperatures that are seriously damaging coral reefs, including those on Christmas Island, which may be the epicenter for what could become a global coral bleaching event, report scientists.

Researchers from the Georgia Institute of Technology recently returned from the Island and are reporting that 50 to 90 percent of corals they saw were bleached and as many as 30 percent were already dead at some sites. The situation could worsen as water temperatures remain well above normal into the early months of 2016.

"This El Niño event is driving one of the three largest global scale bleaching events on record," said Kim Cobb, a professor in Georgia Tech's School of Earth and Atmospheric Sciences who has studied long-term El Niño conditions. "Ocean temperatures exceeded the threshold for healthy corals back in the summer, and are continuing to warm. Bleaching occurs when temperatures exceed a threshold that is function of the amount of warming, as well as the length of time at that temperature."

Bleaching is an outward sign of stress on the corals, which release the symbiotic algae that normally help provide them with energy to sustain their metabolism during prolonged episodes of warm ocean temperatures. The loss of these alga turns the coral colonies white, and opens them to disease and death. Bleached corals can recover if water temperatures return to normal, but continued stress could lead to widespread coral death, Cobb said.

Cobb has studied reef systems on Christmas Island for 18 years, and recently returned from a two-week visit to the area. She and other researchers measured water temperatures of 31 degrees Celsius, (88 degrees Fahrenheit), well above normal water temperatures of 27 degrees Celsius (81 degrees Fahrenheit).

"There's an astounding amount of warming at this particular site," said Cobb. "These reefs are under dramatic stress which is leading to severe coral loss. It will take years for these reefs to recover."

Some coral species are more sensitive to thermal stress than others, and the researchers saw responses that varied from mild bleaching in some species to coral death in others. If the high temperatures continue as projected, species that have been only mildly affected so far may be pushed toward 100 percent bleaching, while species already bleached may be killed.

The last time water temperatures reached such levels was during the 1997-98 El Niño event, which was the largest ever recorded -- until now. Until the current record-breaking El Niño event, the Christmas Island reefs had been thriving and healthy.

Georgia Tech researchers are planning to return to Christmas Island in March to assess the full impact of the damage. Cobb says the disaster will provide a unique opportunity to study the long-term ecological impacts of major bleaching events, which could become more frequent as Earth warms.

"We are determined to turn this environmental catastrophe into a scientific gold mine by being out there before, during, and after this event to document what is going on at this reef," she explained. "There is incredible interest in understanding how reefs recover from an event of this scale. If you fast-forward 50 years, this may be what a majority of the coral reefs around the world will be experiencing."

Information gathered may help project how reefs will stand up to rising sea temperatures and increasing acidification, both caused by rising levels of atmospheric carbon dioxide. In the March trip, Cobb's group plans to work with a research team led by marine ecologist Julia Baum from the University of Victoria.

The El Niño Southern Oscillation (ENSO) is a cycle of warm and cold temperatures that occurs naturally in the central Pacific approximately two to seven years. By studying fossil coral records from Christmas Island, Cobb and her research team have seen evidence of these cycles back at least 7,000 years. However, there is increasing evidence that El Niño events have changed in the past few decades.

"It's clear from the data that El Niños have been strengthening in the recent past," said Cobb. "Even without considering the current event, we have already documented that the recent spate of large El Niño events in the late 20th century stands out against a background of natural oscillations embedded in the coral records."

While her work alone cannot demonstrate a cause-and-effect relationship between strengthening El Niño events and global warming, Cobb says that the combination of many different studies suggests that the rise in carbon dioxide levels is a major factor.

Though associated with the Pacific, El Niño events have worldwide impacts. In the United States, for instance, the strong El Niño is expected to help make this winter's weather cooler and wetter than normal in the South, and warmer than normal in the North.

Coral reefs are important to the people who live in the Pacific area because they provide a nursery for fish and other aquatic life that provide a food source. The reefs also protect low-lying islands from storms and high waves. But their impact is global.

"From an ecological perspective, they are the nurseries of the global oceans," Cobb said. "The loss of this habitat will have vast implications for ocean ecosystems and ocean services that we depend on, not just for the Christmas Island area, but on a global scale."

Story Source:

The above post is reprinted from materials provided by Georgia Institute of Technology. The original item was written by John Toon. Note: Materials may be edited for content and length.


Coral Reefs Provide Crystal Ball for Future Change
Pacific reefs devastated by El Nino offer a glimpse of the future under global warming
Brian Kahn, Climate Central Scientific American 4 Dec 15;

Christmas Island sits about as close to the middle of the Pacific as you can get. The main island of Kiribati, a small island nation, is 3,300 miles from San Francisco, 3,800 miles from Brisbane and just 140 miles north of the equator. Its closest neighbor of note is Hawaii, which is still 1,250 miles away.

Some might say it’s as close to the middle of nowhere as you can get. But it’s at the center of one of the biggest climate events in decades. A super El Niño has raised water temperatures to unprecedented levels and it’s causing a massive coral die off.

Researchers are racing to track the impacts the warming is having on coral as well as what happens to the reefs when the waters cool. The work has implications well beyond an island in the middle of nowhere. How coral respond to this year’s El Niño offers a preview of what the rest of the world’s coral will face as the world continues to warm.

From the water’s surface, the coral reefs surrounding Christmas Island looked healthy. But as soon as Kim Cobb plunged below the azure waters that surround the world’s largest atoll, a new picture began to emerge on a November dive.

Once-vibrant reefs had lost their color. Ghostly white skeletons covered in a growing layer of green-brown algae created a desolate underwater landscape.

“Everything was structurally intact, the reef looked almost normal,” Cobb, a paleoclimate scientist at Georgia Tech, said. “But all the colors were different. The coral isn’t alive, it’s already dead. It’s an eerie, eerie thing to be in the midst of such a rapid transformation.”

Cobb has worked on the reef for 18 years. The rapid change she saw this year is being driven by El Niño, which has ratcheted up ocean temperatures to record levels in the eastern central Pacific.

A slow and steady creep starting in 2014 turned into a rapid rise in the latter half of 2015. By November, water temperatures around the island reached as high as 88°F.

That’s great for a swim but terrible for coral.

When waters warm for an extended period, they essentially cook the algae that help coral grow. If water temperatures remain that high, coral can’t recover and die off.

The world’s oceans are currently in the midst of the third major die off — termed bleaching by scientists — ever recorded and the hot waters around Christmas Island have been dealing with the heat for months.

“Christmas (Island) has been on highest bleaching alert for many months now, since at least July, and it will stay on the highest level through next March,” Julia Baum, a coral ecologist at the University of Victoria who is also doing work at Christmas Island, said. “That is almost unprecedented, if not totally unprecedented. We normally look at temperature anomalies in degree heat weeks. We’ve been saying we might have to change the scale to degree heat months because this is going on and on and on.”

Months upon months of exposure to extreme heat have cooked corals to a crisp. Cobb estimated that 30 percent of the corals she’s been monitoring are dead.

“Given that what we saw in November was a much larger level of destruction than anticipated, we’re truly braced for the worst,” she said, noting that some areas could see 100 percent die off by the time El Niño is expected to wind down in March.

A ‘Crystal Ball’ For the Rest of the World

But there’s hope that some coral could survive and both Cobb and Baum are looking out for them in hopes of unlocking what their secret to survival is. Christmas Island’s location makes it a model location to study the role of warming on reefs, but it also has a diverse array of reefs — from ones impacted by human fishing to ones that are in pristine condition — that make it ideal to see how different influences play out.

Monitoring reefs’ reaction to warm waters and how they recover (or don’t) when El Niño finally ebbs could also provide clues about how to manage reefs in other parts of the world.

Global warming has made oceans the warmest they’ve ever been and temperatures are expected to keep rising for decades to come. That could push some reefs out of their comfort zone and cause coral die offs. Add in the stress of ocean acidification and protecting coral reefs becomes even more important (and challenging).

Reefs provide protection against storm surge and when managed properly, can be an important source of subsistence for millions around the world. Researchers estimate that reefs could provide as much as $172 billion in services a year, from tourism to fishing to flood protection. In part, that’s why their survival is so important.

“It’s like holding a crystal ball. We can figure out the effect, we can figure out why, we can figure out which corals are super performers. If we understand that, we can make targeted conservation solutions, we can learn lessons and transfer them to other reefs,” Baum said. “Climate change is coming to all of those reefs. If we sit and do nothing right now, it will too late.”

This article is reproduced with permission from Climate Central. The article was first published on December 4, 2015.

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