Coral Reefs are as Good as Dead, so We Don’t have to Try Anymore?

Essay by Eric Worrall

But, but, there is still hope if we restrict fishing, reduce runoff pollution, and immediately commit to reducing CO2 emissions.

The end of coral reefs as we know them

Years ago, scientists made a devastating prediction about the ocean. Now it’s unfolding. 

By Benji Jones@BenjiSJones  Apr 26, 2024, 7:15am EDT

More than five years ago, the world’s top climate scientists made a frightening prediction: If the planet warms by 1.5 degrees Celsius, relative to preindustrial times, 70 to 90 percent of coral reefs globally would die off. At 2°C, that number jumps to more than 99 percent. 

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In not so great news, the planet is now approaching that 1.5°C mark. In 2023, the hottest year ever measured, the average global temperature was 1.52°C above the preindustrial average, as my colleague Umair Irfan reported. That doesn’t mean Earth has officially blown past this important threshold — typically, scientists measure these sorts of averages over decades, not years — but it’s a sign that we’re getting close.

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What’s become increasingly clear is that climate change doesn’t just deal a temporary blow to these animals — it will bring about the end of reefs as we know them. 

Will there be coral reefs 100 years from now?

In the next few decades, a lot of coral will die — that’s pretty much a given. And to be clear, this reality is absolutely devastating. Regardless of whether snorkeling is your thing, reefs are essential to human well-being: Coral reefs dampen waves that hit the shore, support commercial fisheries, and drive coastal tourism around the world. They’re also home to an incredible diversity of life that inspires wonder.

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Ultimately, the only real solution is reducing carbon emissions. Period. … “We really have no choice but to stop climate change.”

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Scientists also see an urgent need to curb other, non-climate related threats, like water pollution and intensive fishing. “To give corals the best possible chance, we need to reduce every other stressor impacting reefs that we can control,” Manzello told Vox. 

These efforts alone will not save reefs, but they’ll buy time, experts say, helping corals hold on until emissions fall. If those interventions work — and if countries step up their climate commitments — future generations will still get to experience at least some version of these majestic, life-sustaining ecosystems.

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Read more: https://www.vox.com/climate/24137250/coral-reefs-bleaching-climate-change

The 70-90% death rate prediction, let alone the 99% death rate prediction, doesn’t pass the smell test.

If the ocean warms a few degrees, beyond current reef survivability, coral organisms will just migrate slightly further away from the equator.

Reef coral is highly mobile.

The adult form of coral is immobile, but every year, when conditions are right, coral produces uncounted billions of highly mobile microscopic larvae which seek out new locations to colonise. Coral is continuously probing the boundaries of its range, and establishing new colonies when conditions permit.

And that range of acceptable conditions is enormous. I live on the southern edge of the Coral Sea on the East Coast of Australia. There are plenty of suitable sites to the south of me, stretching well over a thousand miles South, which could be colonised overnight by coral if the water was a little warmer. That water near my home is too cold for swimming much of the year – but coral does just fine in the waters off my section of the coast. The Great Barrier Reef which starts near where I live stretches thousands of miles North into the sun drenched bathtub warm waters of the tropics.

Further evidence of reef adaptability is that reefs like the Great Barrier Reef have only been in their current location for a few thousand years. During the great melt which marked the end of the last ice age, when in just a few thousand years sea level rose over 300ft, the reef had no problem keeping up with the rising sea level, and immediately colonised former coastland which were inundated by the rising seas. In fact, during the Holocene Optimum, around 6000 years ago, when sea level was around 6ft higher than today, the Great Barrier Reef occupied parts of coastal Australia which are now dry land.

If you want to see the limits of modern coral adaptability, there are corals growing in the Persian Gulf which tolerate sea water temperatures > 36C / 97F.

Even the dinosaur killer asteroid failed to kill off coral. Coral survived mile high tsunamis, earthquakes and volcanic upheavals which blackened the skies and poisoned the waters of the Earth, and also survived the billions of tons of mud and organic detritus which must have gushed into the oceans when those mile high Tsunamis receded. Much of the organic detritus washed from the land by giant tsunamis would have been caught in coastal areas, and would have rapidly rotted and turned stagnant, releasing nitrates and toxic chemicals into the shattered remains of the world’s coral reefs.

Yet coral survived all this and recovered.

Then there was the Palaeocene – Eocene Thermal Maximum. That temperature excursion was so extreme, one recent theory which tries to explain the PETM temperature excursion is a close encounter with another star perturbed Earth’s orbit, causing radical changes to the global climate.

At least 5-8C hotter than today. Yet coral survived the PETM – the lack of abundance was because of geography, not because of survivability.

Paleobiological Traits That Determined Scleractinian Coral Survival and Proliferation During the Late Paleocene and Early Eocene Hyperthermals

Anna M. Weiss, Rowan C. Martindale
First published: 21 January 2019

This article was corrected on 18 MAR 2019. See the end of the full text for details.

Abstract

Coral reefs are particularly sensitive to environmental disturbances, such as rapid shifts in temperature or carbonate saturation. Work on modern reefs has suggested that some corals will fare better than others in times of stress and that their life history traits might correlate with species survival. These same traits can be applied to fossil taxa to assess whether life history traits correspond with coral survival through past intervals of stress similar to future climate predictions. This study aims to identify whether ecological selection (based on physiology, behavior, habitat, etc.) plays a role in the long-term survival of corals during the late Paleocene and early Eocene. The late Paleocene-early Eocene interval is associated with multiple hyperthermal events that correspond to rises in atmospheric pCO₂ and sea surface temperature, ocean acidification, and increases in weathering and turbidity. Coral reefs are rare during the late Paleocene and early Eocene, but despite the lack of reef habitat, corals do not experience an extinction at the generic level and there is little extinction at the species level. In fact, generic and species richness increases throughout the late Paleocene and early Eocene. We show that corals with certain traits (coloniality, carnivorous, or suspension feeding diet, hermaphroditic brooding reproduction, living in clastic settings) are more likely to survive climate change in the early Eocene. These findings have important implications for modern coral ecology and allow us to make more nuanced predictions about which taxa will have higher extinction risk in present-day climate change.

Key Points

• There is no extinction of coral genera in the late Paleocene; however, there are extinctions at the species level
• Differences in habitat, reproductive strategy, diet, coloniality, and photosymbiotic ability make some corals more susceptible to extinction than others
• The early Paleogene is an important case study in how coral communities survive extreme environmental perturbations

Read more: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018pa003398

Given the evidence of coral survival during the PETM, 5-8C hotter than today, and the modern day extremophile descendants of that warm epoch which thrive in the Persian Gulf, how can anyone seriously claim a 2C global temperature rise will kill 99% of all Coral?

Nothing we are doing to the planet is any kind of threat to the survival of Coral and Coral reefs. At worst, a few species might be outcompeted by other corals, a dance of survival which has occurred unchecked since modern corals first appeared over 200 million years ago.