Coral Bleaching Update: It’s Not As Bad As We Thought


In 2018, the Woods Hole Oceanographic Institution revealed that, during the 2015/16 El Nino, 95% of corals bleached through heat stress around Jarvis Island in the equatorial Pacific. Upon investigating the reef further, they also found that the reef recovered from past severe bleaching events, though the 2015/16 event was the severest on record, which is unsurprising, because the last El Nino comparable to 2015/16 was way back in 1876/78 and their study only documented bleaching events since 1960. The research team were optimistic that there would be a similar recovery from the latest severe bleaching event, due entirely to a temporary spike in water temperature induced by a very powerful super El Nino, not climate change™.

Now the Scripps Institution of Oceanography and engineers at UC San Diego tell us that another coral reef in the central Pacific north east of Australia, located at Palmyra Atoll, not a million miles from Jarvis Island, which also suffered the same fate in 2015/16, has indeed largely recovered from severe thermal bleaching during the 2015/16 El Nino.

In 2015, Palmyra experienced its warmest water in recorded history, prompting a widespread bleaching event that affected over 90 percent of the corals surrounding the island. Researchers found that despite the widespread bleaching, most of the corals recovered, with less than 10 percent dying.

The conclusions are based on comprehensive monitoring of the reefs and is providing for more precise observations of how reefs are changing over time. The researchers used a long-term data set of thousands of pictures of the same  area collected over eight years. These images were stitched together using custom software to create 3-D photo mosaics of the ecosystem—a virtual representation of the corals. The technology was developed by the 100 Island Challenge team, a collaborative group of marine ecologists and engineers using the latest technology to monitor coral reefs around the world.

Oh dear, so some reefs at least do have the ability to rapidly recover from extreme thermal bleaching exceeding even 90%.

“Using a combination of novel technology and more traditional approaches, our team was able to show that the reefs of Palmyra did not suffer the same fate as many other reefs during the recent global bleaching event,” said Jen Smith, a Scripps researcher and senior author on the paper, and co-founder of the 100 Island Challenge. “Despite extreme heating, corals were able to recover without experiencing widespread mortality. These findings certainly provide an important counterpoint to the general decline in reef health being reported globally.”

Oh dear, oh dear, definitely not on message. What these studies show is that remote reefs not subjected to other environmental stressors, in particular those associated with local human activities, which may be better adapted to extreme marine heat stress due to their location where El Nino surface warming is most intense, are able to recover very rapidly from widespread severe thermal bleaching. There is no a priori reason to suppose that corals located in regions not so regularly exposed to thermal heat stress will be wiped out by future extremely powerful El Nino events (if any more come along soon – not guaranteed), combined with the modest secular ocean warming trend which is attributed to climate change™. There is certainly no reason to suggest that coral reefs globally will become extinct any time soon because of a marine thermageddon induced by CO2 and other GHGs. Corals are both adaptable and resilient.