Deadly Worldwide Coral Bleaching Episode Underway--Earth's 3rd on Record

By Bob Henson
Published: 12:47 PM GMT die 09o October, anno 2015

Earth is entering its third worldwide coral bleaching event of the last 20 years--a disturbing example of how a warming planet can harm vital ecosystems--NOAA announced on Thursday. NOAA also released an eight-month outlook that projects even more bleaching to come in 2016. The only other global-scale bleachings in the modern era of observations happened in 1998 and 2010. Global bleaching is defined as an event that causes bleaching in each of the planet’s major coral-reef areas. "We may be looking at losing somewhere in the range of 10 to 20 percent of the coral reefs this year," NOAA coral reef watch coordinator Mark Eakin said, in an interview with Associated Press. Florida started getting hit in August. The middle Florida Keys aren't too bad, but in southeast Florida, bleaching has combined with disease to kill corals, Eakin said. It has also hit Cuba, Haiti and the Dominican Republic and is about to hit Puerto Rico and the Virgin Islands, he said, adding, "you kill coral, you destroy reefs, you don't have a place for the fish to live."

The current global bleaching is the culmination of regional problems that began in mid-2014, when very warm conditions emerged in several parts of the tropics. Hawaii is one of those areas: as Jeff Masters reported in July, Hawaii experienced its worst bleaching on record in 2014 when record-warm ocean temperatures caused 50 - 70% of the corals sampled in Northeast Oahu's Kāneʻohe Bay to bleach. Another hard-hit area was the coral-rich Papahānaumokuākea Marine National Monument, which extends hundred of miles northwest of the main Hawaiian Islands. “Last year’s bleaching at Lisianski Atoll was the worst our scientists have seen,” said Randy Kosaki, NOAA’s deputy superintendent for the monument. “Almost one and a half square miles of reef bleached last year and are now completely dead.” This year, the same warm waters that have fed record numbers of tropical storms and hurricanes have laid the foundation for additional bleaching in and near Hawaii. "Hawaii is getting hit with the worst coral bleaching they have ever seen, right now," Eakin said. "It's severe. It's extensive. And it's on all the islands." In one part of northwestern Hawaii, "the reef just completely bleached and all of the coral is dead and covered with scuzzy algae."

Figure 1. NOAA's four-month bleaching outlook (top) shows a threat of bleaching continuing in the Caribbean, Hawaii and Kiribati, and potentially expanding into the Republic of the Marshall Islands. An extended bleaching outlook (bottom) showing the threat of bleaching expected in Kiribati, Galapagos Islands, the South Pacific, especially east of the dateline. The bleaching may affect Polynesia and most coral reef regions in the Indian Ocean by May 2016. Corals experiencing "Alert Level 2" conditions (dark red colors) can expect widespread mortality due to severe bleaching. Image credit: NOAA.

Figure 2. Healthy corals play host to microscopic algae (zooxanethellae) that live in their tissues (panel 1). The coral reef helps protect the algae and provides the plants with carbon dioxide and key nutrients. At the same time, the algae serve as food for the coral and are the source of coral reefs’ often-spectacular colors. During stressful conditions (panel 2), algae leave the coral tissue. If the stress continues for weeks to months, the food-deprived corals experience bleaching: they lose their color and become more susceptible to disease or death (panel 3). Image credit: NOAA.

El Niño isn’t helping
Rising global temperatures are increasing the likelihood of bleaching, but it is often El Niño that pulls the trigger for the most widespread events. A strong El Niño can suppress upwelling and raise sea-surface temperatures across much of the central and eastern tropical Pacific and other low-latitude areas. Because the algae embedded in coral depend on photosynthesis to survive, coral reefs are limited to the uppermost reaches of the ocean, where sunlight can filter through. When the sea surface temperature is 1°C warmer than the highest monthly mean temperature corals usually experience, coral polyps will expel the symbiotic algae that live in their tissues, exposing the white skeleton underneath and resulting in a "bleached" appearance. Death can result if the stress is high and long-lived--for instance, if unusually warm ocean temperatures persist for months.

Figure 3. Divers laid out transect lines to guide surveys that took place in the coral reef habitats of American Samoa and the Pacific Remote Islands Marine National Monument from January to May 2015. Image credit: NOAA.

We may see major areas of bleaching in 2016 well beyond the period covered in the latest NOAA announcement. It is looking increasingly possible that a significant La Niña event will occur later in 2016 in the wake of the current El Niño event (see below). A recent study led by Joanie Klepyas (National Center for Atmospheric Research) examined heat stress in the Coral Triangle of the tropical Northwest Pacific. This is one of the world’s most expansive regions of coral reefs with nearly 600 varieties of coral and more than 2000 species of reef fish. Thanks to El Niño, much of the Coral Triangle is now experiencing sea-surface temperatures a bit below average, but the SSTs could rise quickly if El Niño segues into a moderate to strong La Niña. In 1998, this sequence of events led to the region’s worst bleaching event on record.

“I'm very concerned about the probability of intense bleaching in the Coral Triangle into 2016. NOAA's projections look a lot like what happened in the 1997-98 El Niño,” Kleypas told me in an email. “It is quite possible that the Coral Triangle region will experience warming later into 2016, even into the fall.”

When bleaching occurs year after year
Coral reef experts have warned that multi-year bleaching events could become increasingly common as our climate continues to warm in the 21st century. The possibility of two or more consecutive years of bleaching in Hawaii may be a harbinger of this future. Bleaching occurred from 2010 to 2013 in the Arabian/Persian Gulf, following widespread coral disease unrelated to bleaching in 2009. This was the first time four consecutive years of mass mortality have been observed in any coral reef on Earth. In a study published this spring, Bernhard Riegl and Sam Purkis (National Coral Reef Institute) took a close look at this four-year disaster and found what they call a “degradation cascade.” About two-thirds of the coral cover in the area studied was lost during the four-year event. Disease outbreaks often followed bleaching, and the corals that survived tended to shrink. “Certain coral species are more vulnerable to warming and disease than others, and as conditions degrade, one can expect to see big shifts in the coral communities,” noted Kleypas.

Disease fostered by warmer temperatures is a major threat to coral reefs in its own right, as explored in a 2015 study led by Jeffrey Maynard (Cornell University). “There is great spatial variation in the projected timing of the disease-favoring conditions, which is in keeping with much new research highlighting that the impacts of climate change will not be spatially uniform,” said Maynard and colleagues in the paper.

NOAA’s El Niño report for October
The well-publicized El Niño event of late 2015 continues to unfold pretty much as expected, according to the latest NOAA monthly diagnostic discussion. The latest probabilistic forecast issued by NOAA in conjunction with the International Research Institute for Climate and Society shows a greater than 95% chance of El Niño conditions persisting through the period Dec-Feb 2015-16, with a greater than 70% chance through March-May 2016. By the end of the period (May-July 2016), neutral conditions are the most likely outcome (just over 50%), although the odds of La Niña are beginning to rise quickly by that point. Major El Niño events are often but not always followed by a significant La Niña during the subsequent northern fall and winter.

Figure 4. Maximum temperatures for the week ending on October 6, 2015, soared above 36°C (96.8°F) across roughly half of Australia, with the heat especially intense for this time of year across southern parts of the continent. Image credit: Australia Bureau of Meteorology.

We can expect an increasing onslaught of El Niño signs and symptoms to emerge in the coming months. Across parts of Australia, vicious summer heat has arrived prematurely. Dozens of stations across southern Australia notched records over the last few days for their hottest day so early in the warm season. On October 5, the nation’s capital, Canberra, hit 31.8°C (89.2°F), the city’s earliest 30°C reading on record. Melbourne scored its earliest 35°C day ever recorded when it hit 35.8°C (96.4°F) on October 6. This hot spell follows the third-driest September in 106 years of Australian record-keeping. Extreme heat is a common byproduct of El Niño in the populous southeast part of Australia, as noted by the Bureau of Meteorology in a special statement on the October heat wave.

On a quirkier note, tuna crabs (pleuroncodes planipes) were reported on the beaches of Monterey Bay this week, far from their usual domain around Baja California. Their last sighting in Monterey was during the super-strong El Niño of 1982-83.

Have a great weekend, everyone! We'll be back with a new post on Monday at the latest.

Bob Henson

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About The Author
Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather

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