Coral reefs as we know them are doomed, a new paper reports. What we have to do now is try to save and conserve as much of them as we can — but even experts are at a loss as to how we might accomplish that.

Image via Pixabay.

For decades, marine scientists have been trying to warn us that coral reefs can’t survive in the warmer world we are creating. Those warning calls have peaked and now, they make way for silence. Researchers today watch in stunned despair while the coral reefs as we know them limp their last sickly strides.

A new study published this Thursday, by a team of the world’s top coral experts, comes to sound the death knell of the oceans’ megalopolises. Surveys of over 100 reefs scattered all across the world revealed that extreme bleaching events — which occurred every 30 to 25 years before the 1980s — now take place every five or six years.

A frightful way to go

Corals start bleaching when they overheat. When faced with high temperatures, the host polyps (phylum Cnidaria) have a last-ditch survival strategy — they turn on the symbiotic algae which help feed them (zooxanthellae) and start to consume them alive. The algae that can’t survive the heat or the polyp’s voraciousness get thrown out in a bid to keep the coral as cool as possible.

It’s a desperate shot at survival, a heart-breaking attempt that effectively rips the coral family apart and turns it on each other. It’s ruthless and tragic, but in short bursts, it works. If conditions don’t improve rapidly, however, the wavering algae can’t supply enough photosynthesis to feed the polyp. Starved, the polyp stops its growth and becomes sickly. In the mid-long term, the increase in temperature will kill the corals outright.

Reefs can and do recover from bleaching events. Polyp larvae have no qualms about moving in an unclaimed coral and rebuilding. It does take time, however — about 10 years or so for the fastest-growing corals in a reef — to properly heal.

With the interval between bleaching events shortened five-fold, there simply isn’t enough time for the ecosystems to recover. These damaging events occur so frequently now that the reefs’ chances for recovery in the long term are virtually nil, the authors write. Huge swaths of today’s reefs — which collectively cover an area about the size of France — face almost certain death.

A bleached coral reef. Image credits: NOAA.

It’s getting worse and worse

“These impacts are stacking up at a pace and at a severity that I never had anticipated, even as an expert,” said Kim Cobb, climate scientist and coral researcher at the Georgia Institute of Technology, not affiliated with the study, in an interview for Grist.

“It’s really the rapidity of it that is so sobering and shocking — and for me personally, life-altering.”

According to lead author Terry Hughes, a coral scientist at Australia’s James Cook University, “mass bleaching of corals was unheard of” before the 1980s.

Since then, things have gone horribly wrong. The paper reports that 94 of the 100 coral reefs the team surveyed have experienced at least one severe bleaching event since the 80s. The remaining six aren’t in a single solid chunk, but they’re scattered across the world — meaning there’s virtually no ocean basin on Earth whose coral reefs have been spared.

Study coauthor and coordinator of the National Oceanic and Atmospheric Administration’s Coral Reef Watch program, Mark Eakin, says that by 2050, ocean temperatures will be warm enough that 90% of all the world’s reefs will experience at least one bleaching event — every year.

“It is clear already that we’re going to lose most of the world’s coral reefs,” he confesses.

And when the corals go, oceans will heave and buckle. We won’t be spared either.

Neptune’s starving trident

Coral reefs provide a slew of essential services for humans and for ecosystems. Despite taking up only 0.1% of the ocean floor, up to 25% of all marine species depend on them for food, shelter, and mating habits. Fish from coral reefs feed over a billion people worldwide, my colleague Elena wrote last year. Those people will still need food — but we won’t have the reefs any longer.

Reefs also rake in billions of dollars every year from tourists visiting coastal areas or island chains to see the “rainforests of the sea”. These reefs will go, or at least change into a very, very different version of their current selves. Conservation biologist Josh Drew, not affiliated with the study, told Grist that the interval between bleaching events is, fundamentally, a “death warrant for coral reefs,” at least  “as we know them”.

“I’m not saying we’re not going to have reefs at all, but those reefs that survive are going to be fundamentally different,” he explains.

“We are selecting for corals that are effectively weedy, for things that can grow back in two to three years, for things that are accustomed to having hot water.”

The economies that today’s reefs prop up will crumble. The societies that depend on them for food will waver, some may not be able to recover. That’s only part of the price humans will pay for coral bleaching.

Right now, researchers are trying to understand what the loss of these linchpin ecosystems will do to the Earth in coming decades. Previous research suggests that the full impact may play out in a domino effect with disastrous consequences. Scientists such as Eakin are desperately trying to save whatever crumbs they still may, considering even “much more radical actions” than they would have previously.

Work is being done to breed genetically-modified super coral species that can live in the warmer, more acidic waters. Other groups are trying to identify the last few dozen reefs that have a shot at surviving. They plan to turn these into seed-banks to be called upon by future generations after climate change has stabilized. Even geoengineering is being considered as a last-ditch attempt to stabilize the climate in time to give reefs a fighting chance.

There’s no consensus on what will work. There’s no agreement on which one is most feasible. But that doesn’t matter because there’s one thing every expert agrees on — the reefs seem doomed, and this is our final shot at saving what’s left.

The paper “Spatial and temporal patterns of mass bleaching of corals in the Anthropocene” has been published in the journal Science.