NOAA’s Coral Reef Watch is sounding the alarm today about the global die off of coral from the very strong El Niño that has warmed sea surface temperatures. The scientists that rank El Niños say the current one is as strong as the El Niño of 1998. In that instance, there were widespread algae die-offs that occurred along some of the largest coral reefs. And based on satellite imagery, it appears the same event is happening again. But current die-off estimations may be two times too high.
The El Niño that formed in 2015 has the pronounced effect of warmer ocean temperatures, and if sea surface temperatures remain that way for too long, the algae living in coral eventually give up the ghost. This algae is what makes coral reefs so stunning to look at, especially those with brilliant, vibrant colors. NOAA also says global warming is playing a role, though a new paper indicates there has been a global warming “slowdown” from 2001-2014, with El Niño raising global temperatures in 2015.
Algae, unlike most plants that have roots and stems, enjoy a symbiotic relationship with coral, their host organism. But if the algae die, the coral expels it, giving reefs a blanched appearance. Corals are tiny animals that get their nutrients and energy from the “photosynthetic algae that live inside the coral’s cells.”
These die-offs, or coral bleaching events, normally coincide with El Niños, a naturally occurring event where the tropical Pacific Ocean along the equator becomes warmer than normal. Specifically, the sea surface temperatures (SST) are a few degrees higher than normal. This upper sea surface area is also where the vast majority of coral resides, forming the many atolls and reefs across the planet. New research has shown that corals can also live quite nicely at much deeper depths and as such are unaffected by warmer-than-normal SSTs.
After the 1998 coral bleaching event, rapid growing, branching corals grew back faster than slower growing corals that are generally considered the “backbone of reefs.” According to Scientific American, a new study shows that corals can bounce back from widespread bleaching events. The study looked at reefs off two of the central Seychelles isles in the Indian Ocean, where 90 percent of those coral had whitened in 1998. “Scientists from Australia found that reefs could rebound” even after catastrophic bleaching events.
Unlike the National Oceanic and Atmospheric Administration (NOAA), which relies on satellite imagery, the study’s team actually observed 21 reefs beginning in 1994. They took a range of measurements, including the “total number of plant-eating fish and the amount of nutrients reaching the reefs.” They found that the majority of these reefs recovered after the 1998 El Niño event. Those that didn’t recover became “seaweed-covered ruins.”
They also learned which aspects “most strongly predicted a resilient or doomed reef.” These include the water’s depth, the coral’s shape and complexity, nutrient levels, number of fish grazing, and “survival rates for young coral.” They found the deeper the water, the better the chance for a reef’s survival. Even coral living in “shallow, warm waters” weren’t necessarily going to die. That’s because the amount of nutrient and pollution in the surrounding waters boosted or doomed a reef’s survival.
They also found that reefs that survived previous bleaching events were more likely to survive the next bleaching event. Other factors that affect a coral’s survival include the acidity of surrounding seawater, which can change due to the swapping of gases in the atmosphere with the ocean. Corals that form Australia’s Great Barrier Reef are also proving to be more resilient than previously thought. After the 1998 bleaching, 50 percent of reefs recovered and 40 percent had “regime shifts to macroalgae dominated compositions.”
Researchers from Penn State also discovered in 2010 that a diversity of corals were using an “unusual species of symbiotic algae in the warm waters of the Andaman Sea in the northeastern Indian Ocean.” Up until then, scientists didn’t think that a coral’s algae (zooxanthellae) could withstand temperatures as high as in that location, so their findings were unexpected.
Last July, NOAA said that coral reefs were dying off at an unprecedented rate, even though a newly published paper showed that these statements are more alarmist than accurate. As we first reported, the paper, published in Marine Biology in April 2015, shows that even though some corals appear bleached, it doesn’t mean they are dead, as satellite tracking methods can’t distinguish between white and bleached (dead) colonies.
That’s because NOAA’s conventional tracking system (like NOAA’s 5-km Coral Reef Watch Satellite Monitoring) can’t distinguish between white, healthy coral and bleached, dead coral. The paper, by Cruz et al, says that “although bleaching leaves the coral skeleton visible under its transparent tissue, not all white coral colonies display this feature,” which “raises the question as to whether all ‘white’-shaded colonies are indeed bleached.” Accordingly, this would lead NOAA’s estimation of coral bleaching to be two times to high.
NOAA said again in October that the global bleaching event may be the third-worst bleaching event, which the aforementioned paper indicated does a disproportionate job of indicating dead coral that’s still alive. Other factors that drive algae die-offs are colder-than-normal SSTs. In 2010, “cold water temperatures in the Florida Keys caused a coral bleaching event that resulted in some coral death.”
Other factors contributing to the widespread coral bleaching event are the now-dissipating Pacific warm blob, a cooling trend in the Atlantic Ocean, a cold blob in the north Atlantic, and one of the strongest El Niños since satellite tracking began in the 1980s. And while NOAA is calling this the “longest die-off event on record,” they have only been monitoring coral reef bleaching since 1989, when “a relatively new ocean phenomenon called ‘coral bleaching’ was increasingly observed in parts of the Caribbean Sea.”
Based on marine sediments and fossil records, coral bleaching events have been occurring for millions of years. NOAA’s Coral Reef Watch Program was created in 1998 under executive order by then-President Bill Clinton and supervised by former VP-turned-activist Al Gore.