Friday, October 4, 2019

Marvelously Resilient Coral

Low tide bleaching of Heron Reef

Published October 2, 2019 in California’s Battle Born Media newspapers - the Pacifica Tribune, the Novato Advance, the Sausalito Marin Scope, the Mill Valley Herald, the Twin Cities (Larkspur and Corte Madera) Times, the San Rafael News Pointer and the Ross Valley Herald. 

What’s Natural? 

Marvelously Resilient Coral

Imagine if today’s magnificent coral reefs all dried up and died - from the surface down to a depth of 400 feet. Horrifying! But that was exactly the case 20,000 years ago when growing glaciers of the Last Ice Age lowered sea level 400 feet. Yet coral reefs fully recovered as the earth warmed. So, what makes coral so resilient? 

To survive, coral must also withstand lethal effects of modern cyclones, coral-eating crown-of-thorns starfish, and El Niño related bleaching.  Rapid growth has allowed most reefs to fully recover within 7 to 30 years. For example, due to the 1998 El Niño event 12 reefs on the Seychelles, experienced greater than 95% mortality. Yet 6 reefs fully recovered within 7-12 years, and within 16 years coral cover had increased by 135% to 305% of pre-bleaching values. The others continued to recover but at a slower pace.

In contrast to climate crisis claims, cyclones cause the greatest coral mortality. Cyclones have caused 48% of lost coral cover, while crown-of-thorns feeding caused 42%, and bleaching just 10%. Yet regardless of cause, coral growth quickly restored most damaged reefs within 10 years. Known as the Phoenix effect, remnant living tissues can expand, regenerating tissue that covers dead skeletons. After several years of regeneration, plus growth of surviving colonies, coral then produce massive amounts of larvae (young coral) and complete the reef’s recovery. 

Disturbingly, an extreme advocate of a coral climate “crisis”,Terry Hughes argued global warming has impaired recruitment of new coral to the Great Barrier Reef,  despite only 2 years since the 2016 bleaching event. Internet media outlets, eager for ‘click-bait headlines’ wrote, “Great Barrier Reef suffers 89% collapse in new coral” and CNN hyped “Dead Corals Don’t Make Babies”. 

But such reduced larval production is normal whenever adult corals are reduced. For example, after a western Australian reef suffered 70 to 90% mortality, larval production was reduced by 96% for the first 6 years. Nonetheless surviving coral increased their abundance by 5-fold over a period of 12 years. After the first 6 years of increasing coral, larval production rapidly increased. Likewise, in the northern Great Barrier Reef, which was heavily bleached in 2016, an 89% decrease in larvae is expected. And consistent with the potential for rapid recovery, surviving coral in the northern Great Barrier Reef have now increased by 16%. Thus, its highly likely we will witness large increases coral larvae within four years.

Media outlets have also misleadingly conflated coral bleaching with dead coral prompting ridiculous headlines proclaiming the Great Barrier Reef is dead. But bleaching is not always lethal. When over 90% of the coral on the Palmyra Atoll experienced bleaching, there was no loss of coral on the reef flats, and only a 9% loss on the fore reefs. Similarly, despite the severe 2016 bleaching in the Coral Sea Marine Park, researchers reported total coral cover was not significantly reduced by 2017. Most bleached corals survived.  

Reef building corals depend on energy from photosynthesizing symbiotic algae.  But their symbiotic relationship requires careful maintenance. So coral naturally add and subtract symbiotic algae as the seasons change. During the winter, coral increase their symbiotic algae as lower light reduces photosynthesis. Each summer as light intensity increases, they expel symbionts. Bleaching is just an extreme of that behavior. After bleaching, coral can quickly replace their symbiotic algae within days or months with no resulting mortality. 

Scientists are increasingly observing that coral can acquire very different symbiotic algae with different genetics. To adapt to changing climates corals don’t require thousands of years to evolve. Coral get instantaneous genetic upgrades simply by acquiring new symbiotic algae. Acquiring different symbiotic algae allowed coral to adapt to dramatic temperature changes as Ice Ages came and went. And acquiring new symbiotic algae now allows coral to rapidly adapt to 60-year changes caused by ocean oscillations.

Under La Niña like conditions, warm water accumulates over the “coral triangle” in the western Pacific, promoting more rains and heavier cloud cover. This condition can dominate for 30 or more years. However, during El Niños as in 2016, that warm water sloshes towards the Americas causing sea levels to dramatically fall. Falling sea levels expose coral to drying winds and shallower bays will more rapidly heat. Furthermore, during an El Niño, the rains and cloud cover moves eastward. With less clouds, the Great Barrier Reef is exposed to more sunshine and more heatwaves. Scientists now recognize a strong connection between ocean heat waves and El Niños. Coral bleaching correlates best with El Niños. 

Climate models do not agree on how El Niños will change in the future. But there is good news. Michael Mann, who promotes “dire predictions” due to rising CO2, also published that during past warm periods, the oceans remain in more La Niña-like conditions. And La Niña-like conditions are good for the Great Barrier Reef.

Jim Steele is director emeritus of the Sierra Nevada Field Campus, SFSU and authored Landscapes and Cycles: An Environmentalist’s Journey to Climate Skepticism