A disconcerting ocean event could destroy one of our most promising sources of medicine

Venomous cone snails sting passing fish, paralyzing them so they can be digested alive. Fire coral causes painful scrapes and infections when touched, a means of self-defense. And certain reef-dwelling mollusks swallow microbes to build up a protective coat of toxins on their skin.

Coral reefs and other rare environments aren't just fascinating and beautiful.

The potent and diverse chemicals created by nature might hold the key to better treatments for cancer, HIV, and many other diseases that stymie doctors - but only if we can reach them in time.

Harvesting and adapting these natural compounds is crucial to the advancement of modern medicine. But many of the best potential sources of new drugs are at risk of extinction.

Around the world, reefs - the heart of the ocean ecosystem, the most biodiverse places on the planet - are currently undergoing what could be the worst "bleaching event" ever recorded. Stress from high temperatures damages the organisms that make up the corals, causing them to lose their color, making them vulnerable to disease, and eventually, if temperatures don't drop, killing them.

A study published April 15 in the journal Science found that up to this point, corals in Australia's Great Barrier Reef have been somewhat protected from bleaching events (and able to recover) because of internal protective mechanisms. But the study argues that now, those mechanisms have been essentially overwhelmed and won't be able to keep up with ongoing temperature changes. That means more and more of that reef will die, along with others around the world.

We're losing not just a crucial ecosystem, with untold environmental consequences, but also one of our most promising sources of medicine. Countless potential new treatments will be lost before we ever have a chance to discover them.

Finding drugs in nature

The first modern antibiotic, penicillin, comes from a fungus.

Ancient Greeks used molds to fight infections. Polynesian seafarers and 14th-century Chinese people derived painkillers from reef creatures. And in recent years we've learned much more about how to extract chemicals and medicines from natural sources.

"Mother Nature has been doing her chemistry over the last 3 billion years," says David Newman, the former chief of the Natural Products Branch of the National Cancer Institute. "She isn't making anti-tumor compounds," he explains, but the same chemical that a sea sponge uses to fight predators might also be able to kill cancer cells or viruses.

Cone snail venom is now being used as a painkiller - one that's 50 times more potent than morphine - that eliminates phantom limb pain in amputees. Tunicates, marine invertebrates frequently found around coral reefs, provide anticancer and antiviral chemicals. AZT, the first effective drug against AIDS, comes from a chemical produced in a lab, but the chemical was first found in, and modeled from, a Caribbean sea sponge.

Scientists from the National Oceanic and Atmospheric Administration say that more than half of modern pharmaceuticals are derived from the natural world. In particular, they say that reefs and the creatures that live on and around them show special potential for medicine.

A 2012 review found that of the new drugs approved to fight cancer between 1981 and 2010, only 20.2% were purely synthetic - meaning purely made in a lab, not found in nature or made, derived, or copied from something natural. The same was true for new drugs used to fight infections. Just 22.6% of those were purely synthetic.

Killing off potential treatments

Nature has amazing medical potential because of its biodiversity, but finding new medicines is hard work.

For every medically useful molecule found, thousands have been tested unsuccessfully. Some of those useful molecules, and the species that produce them, can be found in only a few vulnerable places.

"When we lose a single reef or part of a forest due to changes in climate or other causes, we do not know what we have lost," says Newman.

Natural resources with great potential have been squandered before.

Newman tells the story of a researcher who in the late 1980s collected samples of biological material from a certain type of algae growing among mangroves on the coast of a Caribbean island. Tests later showed that the algae contained what seemed to be a promising new antitumor agent. But when the researcher returned, the mangroves had been uprooted, and the area filled in and turned into a golf course.

Why coral reefs matter

The ocean in particular is considered both one of the least explored and potentially most useful sources of new medicines. Called the "medicine cabinets of the 21st century" by the National Oceanic and Atmospheric Administration, coral reefs are the most biodiverse sites in the sea.

But they're also the most vulnerable.

They cover less than 1% of the ocean's floor, and more than a quarter of marine life directly depends on them. But they are in dire shape because of the effects of rising temperatures, pollution, and ocean acidification. Many researchers think it might already be too late to save reefs.

According to the latest report from the Intergovernmental Panel on Climate Change, warming and acidification will cause high extinction rates throughout the tropics, where most reefs are located.

The latest studies about the state of reefs are even more dire.

"This is a huge, looming planetary crisis, and we are sticking our heads in the sand about it," Justin Marshall, the director of CoralWatch at Australia's University of Queensland, told The New York Times.

Reefs are essential for medicine, but they do far more than that too. The ocean food chain - which provides food for one billion people, one-seventh of the world - all depends on these hotspots of life.

And right now, reefs aren't the only sites at risk.

"We are effectively undoing the beauty and the variety and the richness of the world which has taken tens of millions of years to reach," Elizabeth Kolbert told NPR's Terry Gross while discussing her book "The Sixth Extinction."

There have been five mass extinctions in earth's history, when some tragic event caused the number of species on the planet to plummet. Many people think that climate change, ocean acidification, and habitat destruction have started a sixth extinction event, which could cause the "extinction of one-third of all reef-building corals, a third of all freshwater mollusks, a third of sharks and rays, a quarter of all mammals, a fifth of all reptiles, and sixth of all birds," according to Kolbert.

A study published in Science Advances in January of 2015 said that extinction event is "already under way."

If these sites are lost

The loss of much of the world's biodiversity is only one of the expected effects of climate change. But that one effect could have an even greater impact on humanity than we know.

It can't be said with certainty that climate change will destroy the molecule that would provide the perfect cure for leukemia or breast cancer or the chemical that could universally eliminate HIV.

New compounds with medical potential could theoretically be found anywhere. A molecule that could treat anthrax was discovered in underwater sediment off the coast of California. The source of an amazing new drug for fighting cancer might exist in some rare, never-analyzed species of fungus growing in New York's Central Park.

But so far, many of the most promising sources of new medicine in the world are in the biodiverse hotspots most at risk of being lost. Sites like reefs are beautiful, interesting places. But even if they weren't, they'd be worth preserving for their medical potential alone.

Unfortunately for much of the world, it could already be too late.

This is an updated version of a story first published in July of 2014.