Lethal Seas

PBS Airdate: May 13, 2015

NARRATOR: It covers more than two-thirds of the earth; its power is tremendous; its importance to life is unquestioned, but now something is changing in the sea, threatening some of our planet's most spectacular treasures...

GRETCHEN HOFMANN (University of California, Santa Barbara): They can move, they can adapt or, unfortunately, they die.

NARRATOR: ...and attacking the ocean's fundamental web of life. Scientists are in a race against time to discover the real risks and come up with solutions. Off a remote island, an amazing discovery: a spot that could hold the key to our future.

KATHARINA FABRICIUS (Australian Institute of Marine Science): We really hit a jackpot. This is such a scientific goldmine, like nowhere else in the world.

NARRATOR: Can we crack the code of a rapidly changing ocean, to understand what it means for life, before it's too late? Lethal Seas, right now, on NOVA!

In a remote corner of the Pacific, a natural wonder: a coral reef filled with exotic creatures. Reefs like these aren't just stunning to look at, they're some of the most fertile places on Earth, home to about a quarter of all species living in the seas.

Now, this abundance of life is under threat by an invisible killer, one that's taking its toll, not just here, but in our own backyard. Off America's northwest coast, the riches of the sea look like this: Pacific oysters, a keystone of a $250-million shellfish industry. But not long ago, a mysterious threat emerged from the depths, putting the oysters and all who depend on them in jeopardy, including oyster growers, like Mark Wiegardt.

Mark and his wife, Sue Cudd, run an oyster hatchery. In giant tanks of seawater, they grow baby shellfish, called “larvae,” the foundation of the region's oyster population. Business was booming, until recently.

MARK WIEGARDT (Oyster Farmer): We first noticed a real solid change in 2007. We actually could not produce any larvae at all, and that definitely gets your attention.

SUE CUDD (Oyster Farmer): All of the larvae in the whole place were pink. They were not feeding. They looked terrible. We just knew they were all going to die.

NARRATOR: For months, the couple struggled to solve the mystery of the dying baby oysters.

MARK WIEGARDT: We saw behavior in the larvae that we'd never seen before. They would circle around and then just, kind of, lay on the bottom. We call them lazy larvae. They'd actually dissolve in the water, and we didn't know what was going on.

NARRATOR: Sue hunted for clues under the microscope and found some disturbing evidence.

This is a magnified image of a healthy larva, a one-day old oyster. It's already started producing its shell. And this is what Sue was seeing in her microscope: the shell was deformed and pitted.

The question was, “Why?” The couple searched for a possible killer, but they never suspected that the culprit could be the seawater itself, specifically, the water's pH.

MARK WIEGARDT: I think the initial reaction from a lot of people was “Don't worry about the pH of the water. That's, that's never going to be a problem.” It was a problem. The pH was dropping too low.

NARRATOR: pH is the standard measurement for acidity. The lower the pH, the higher the acidity.

One of the hatchery workers suggested they run a simple pH test on the water in the oyster tanks, water pumped from the bay. The results were shocking. The acidity of the bay water was a staggering six times higher than normal seawater. The baby oysters couldn't handle it.

MARK WIEGARDT: What we've realized about the chemistry of the water is it's everything. If the chemistry's not right, the larvae can die. They can stop eating; they can stop growing. Basically, you're not able to grow larvae.

NARRATOR: With the mystery solved, the hatchery has found a temporary solution to the problem. Soda ash, a common water softener, lowers the acidity, back to a level most of the young oysters can tolerate.

Now, enough baby oysters survive and grow, so that Mark and his crew can transfer them out into the bay, but at a huge cost.

MARK WIEGARDT: We pump 75,- to 100,000 gallons a day. And that's making a lot of your own special seawater. And there's goodies in the water the larvae like that I don't even know about, you know? Mother Nature provides. So how do you duplicate what they like? It's a tough question.

NARRATOR: Mark and Sue are not alone in their struggles. Fisheries throughout the northwest are having the same problem: water chemistry that's changing, shellfish that won't grow. And scientists are finding it's not just here. Samples taken around the globe over the last 40 years, reveal that average ocean acidity is increasing by about five percent every decade.

Why is this happening?

It turns out, the driving force of ocean acidity is the same thing that's responsible for global warming. When we burn fossil fuels, they release carbon dioxide gas, or CO2, into the atmosphere. Much of that CO2 blankets the planet and raises the global temperature, but about a quarter of that gas is absorbed into the oceans.

At first, scientists thought this was beneficial, since the more CO2 that goes into the ocean means less in our atmosphere, reducing the warming effect.

GRETCHEN HOFMANN: Oceanographers knew, for years, that carbon dioxide from the atmosphere was absorbing into the oceans. And everyone thought, “Oh, perfect. This is a service that the ocean is performing for us; storing the gas that we're releasing, as it's a pollutant, as a product of our activities.” And so everybody thought, “Ooh, this is awesome!”

NARRATOR: But scientists soon realized that this service comes at a cost. The extra carbon dioxide absorbed by the ocean is dramatically changing the water's chemistry.

MARK GREEN (Saint Joseph's College of Maine): We're dissolving 30-million metric tons of carbon dioxide into the surface of the ocean each and every day. And that is what's driving down the pH, or increasing the acidity.

NARRATOR: This is how it works:

When carbon dioxide dissolves into the ocean, it reacts with water, H2O, to form a weak acid called “carbonic acid.” This almost immediately breaks apart, releasing hydrogen ions. Those are hydrogen atoms stripped of their electrons. This is what increases the water's acidity. And it can have a devastating effect on marine life, like oysters.

Healthy baby oysters are busy building their shells. They pull the ingredients they need from the surrounding water, including calcium and a substance called “carbonate,” combining them into a tough matrix: calcium carbonate. But when too much carbon dioxide gets into the mix, the resulting acid can radically alter one crucial ingredient: carbonate.

MARK GREEN: There's plenty of calcium in the ocean. The carbonate is, kind of, what we call the limiting ingredient. There's not a lot carbonate.

NARRATOR: When acidity rises and there are lots more hydrogen ions floating around, they react with carbonate, taking away this essential molecule.

MARK GREEN: Instead of carbonate being all over the place, they're few and far between. And so, what happens is, you know, physiologically, it's just much more difficult to, to make shell.

NARRATOR: Without enough carbonate in the water, the baby oysters simply can't build their shells, and, as a result, they die.

It's not just oysters that need carbonate to survive. The changing chemistry of the ocean threatens all kinds of shelled creatures. Scientists now face an urgent challenge to understand what this will mean for life in the sea.

Along with the oysters, how many other species will struggle to survive?

GARETH LAWSON (Woods Hole Oceanographic Institution): From a, from a biological standpoint, predicting what will happen to individual animals, populations and ecosystems is, is incredibly difficult.

DAN MCCORKLE (Woods Hole Oceanographic Institution): I don't think, right now, we have a clue how that's going to change the development of any given species. And, and, then, well, how one species grows up, influences its prey, and it influences its predators, and it influences its competitors. And so it is really complicated.

NARRATOR: The problem is most urgent here, on the world's coral reefs.

These are some of the most spectacular places on Earth. Filled with exotic creatures, coral reefs occupy less than one percent of the ocean floor, yet they provide a home for at least a quarter of all marine species. And they're a key resource for survival for an estimated half-a-billion people.

The foundations of these beautiful reefs are made of the skeletons of countless corals, built up over thousands of years. Like the oyster shells, these skeletons are made of calcium carbonate, sometimes known as limestone. And this makes them especially vulnerable to the ocean's rising acidity.

KATHARINA FABRICIUS: Corals are incredibly sensitive to high carbon dioxide conditions, because they're forming a skeleton that's made out of limestone. And limestone and acid just don't go together.

NARRATOR: Katharina Fabricius has spent a lifetime diving on some of the world's most pristine reefs.

KATHARINA FABRICIUS: It's just one of the most amazing ecosystems in the world. And seeing them degrading over time…it's just a real shame. It's also a moral and ethical responsibility for us to protect the reefs for our children and our grandchildren.

NARRATOR: Many coral reefs, worldwide, are already suffering because of warming seas. How will the changing ocean chemistry affect them?

Katharina believes she's discovered a clue, a very special reef, located in remote Papua New Guinea.

KATHARINA FABRICIUS: The site is that straight stretch in the reef flat, there. We'll be able to see the bubbles from the surface.

NARRATOR: Set among the volcanic islands of Milne Bay, lies one reef that Katharina found by accident, more than a decade ago. It's a place where the water looks a bit like champagne, filled with streams of gas bubbles rising up through the seafloor, caused by volcanic activity.

Samples reveal they are pure carbon dioxide. And just like the carbon dioxide that's mixing into the oceans from the atmosphere, these bubbles react with water to form an acid, lowering the water's pH.

KATHARINA FABRICIUS: It was just so exciting. And I realized, maybe we can use that as a natural laboratory.

NARRATOR: There's so much carbon dioxide, the acidity is much higher than normal. In fact, the water chemistry here, today, is similar to what scientists think could happen to the rest of the ocean in 50 to 100 years if carbon dioxide emissions continue to rise. So it could offer a unique window into the future of coral reefs across the globe.

KATHARINA FABRICIUS: So, I thought, “Bingo! That's it. We've got to go back.”

We're going to the site at Ili Ili Bua Bua, which is the best bubble site we've got.

NARRATOR: Katharina and her team are now into their fourth year of study here, one of only a handful of coral reefs in the world with naturally high acidity.

KATHARINA FABRICIUS: My hope is very high that these guys, here, are cracking it and producing the world-class science that is so needed to understand ocean acidification.

NARRATOR: For the team, these waters offer a unique opportunity to compare two marine environments very close together, the control site, where the ocean chemistry is normal, and the bubble site, where carbon dioxide is dramatically raising the water's acidity.

How is life here—the corals and the creatures that depend on them—responding to the changes? Are some adapting to new conditions? How many are struggling to survive?

With just two weeks to get the work done, the team dives into their experiments.

KATHARINA FABRICIUS: Each of us is focusing on two or three different projects. I'm looking at how the conditions for corals is changing. That is stuff you cannot do in the laboratory.

NARRATOR: Corals are unusual creatures. Each of these branching clumps is actually a colony, made up of thousands of tiny building blocks, called “coral polyps.”

KATHARINA FABRICIUS: This is all one organism, but, like a plant having individual leaves, the corals have individual polyps that are feeding separately from each other. They can share the food, but each polyp can respond to plankton, touching its tentacles and grabbing it. Once they're digesting it, they're spreading the juices across the colony.

NARRATOR: Corals are happiest and healthiest where the water is clear and well-lit by the sun and where they don't get too much competition from seaweed. But their unusual lifestyle makes them especially vulnerable to a changing environment.

KATHARINA FABRICIUS: Corals are actually animals, but they're glued to the ground like a plant is. They're not able to pack their bags and, and move to another site, if the conditions is no good for them.

NARRATOR: Where the carbon dioxide bubbles are most intense, few corals seem to be finding the conditions favorable.

These large, extremely tolerant corals are called Porites. They have thick skins and now dominate the reef. The colorful branching corals and soft corals that flourish in most coral reefs are gone.

The team works around the clock, in all kinds of weather. Some days, nothing goes according to plan.

KATHARINA FABRICIUS: I think there is some problem with one of the generators. One of the exhaust pipes had a bit of a breakdown.

NARRATOR: Underwater conditions are difficult.

LAETITIA PLAISANCE (Smithsonian Fellow): This site, we have massive rocks, so it's really hard to drill inside the structure.

NARRATOR: And some of the coral experiments have become dinner for some hungry snails.

SCUBA DIVER: At least 50 percent of the little coral branches we made have been eaten by these snails.

LAETITIA PLAISANCE: Yeah, not happy.

KATHARINA FABRICIUS: Experiments, by nature, quite often fail. It's requiring a lot of patience. But, eventually, we'll sort it, and we'll find some other ways to test the same questions.

NARRATOR: While Katharina is studying the impact of high acidity on the corals themselves,…

LAETITIA PLAISANCE: So probably, first, jump in and have a look around.

NARRATOR: …another team member, Laetitia Plaisance, is studying the many other sea creatures who depend on them.

Where the water chemistry is normal, the coral gardens of Papua New Guinea are among the richest on the planet, home to more than 500 species of coral and hundreds of thousands of different kinds of tiny sea creatures. The entire ecosystem rests on a coral foundation, built from calcium carbonate.

LAETITIA PLAISANCE: Everything is a balance in the ocean. The reef is made of calcifying organisms, so that means they need a higher pH to be able to build their skeleton. And this skeleton then provides the structure of the reef, where all the other associated species can find shelter. And they can mate and they can feed and they can hide, in that structure.

NARRATOR: Today, Laetitia is focusing on one particular habitat: the dead coral head.

LAETITIA PLAISANCE: I'm on my way to find a coral head, a nice, dead coral head.

NARRATOR: Living coral heads provide homes for tiny fish and many other animals. Even on normal, healthy reefs, coral heads will eventually die, but their calcium carbonate structure remains and, just like a dead tree, new creatures move in.

Laetitia collects dead coral heads from both the normal site and the bubbly site, where acidity is much higher and the pH is lower.

Will she find the same variety of species living in both locations?

To find out, she cracks open the coral heads, hunting for the creatures hidden inside their nooks and crannies.

LAETITIA PLAISANCE: I'm searching for the crabs and the mollusks. And here is a little ophiuroid trying to escape, another sea cucumber, I think, here, all part of the food chain. And if you miss a link in the chain, the rest of the chain can't continue, can't go on. So, yes, all those little pretty insignificant species are extremely important.

NARRATOR: When she takes apart the coral head from the control site with normal pH and acidity, she's impressed by the number of creatures she uncovers.

LAETITIA PLAISANCE: This morning we collected a nice dead coral head from the control site, which meant regular conditions with beautiful reef. And when I opened the coral head, it was filled with life, abundance and diversity. So we have plenty of species of crustaceans here, lobsters and crabs and shrimps.

NARRATOR: But examining the coral head from the bubble site, even before Laetitia breaks it open, she is concerned.

LAETITIA PLAISANCE: The first thing that I noticed with this coral head is that it's covered with this type of algae. And the problem really is that this type of algae does not hold much diversity, which I'm used to see in other sites where the pH is, is much higher.

NARRATOR: The collection of life looks more limited, but to make sure, to get an exact inventory of all the different species, Laetitita analyzes the D.N.A. of the samples she collected. For example, two tiny shrimp may look alike, but they could actually be different species.

A D.N.A. test will reveal precisely how many different species live here.

The D.N.A. results confirm what Laetitia suspected: the highest species diversity is at the control site where the acidity and pH are normal. But as the acidity goes up and the pH goes down, the number of species drops dramatically. For each type of animal, only one or two species are tolerating the high acidity, and the rest have disappeared.

LAETITIA PLAISANCE: So, you have the same kind of shrimp a hundred times, when in the regular pH conditions, you have a hundred different species.

NARRATOR: Laetitia finds that the high CO2 site has 30 percent less diversity of small sea creatures, like hermit crabs, shrimp and starfish, than the control site. For Laetitia, this is troubling news.

LAETITIA PLAISANCE: The reason why this group is very important, it's because it's the basis of the food chain in coral reef. The fish feed on those tiny creatures. So if those tiny creatures disappear, the fish community is going to change and evolve as a result of this loss.

NARRATOR: It appears that changes in acidity aren't just affecting the corals themselves but hundreds of species living at the bottom of the food chain. And if those at the base of the food chain are at risk, so are all the creatures that rely on them for survival.

These kinds of changes aren't just happening at coral reefs.

Cold water absorbs more carbon dioxide than warm, so acidity could rise in the Arctic and Antarctic seas more quickly. And that could mean trouble for the creatures here that, like coral and oysters, rely on carbonate to build their shells and skeletons.

MAN ON AURORA AUSTRALIS: Back it up, please.

NARRATOR: Aboard the Aurora Australis, the Australian Antarctic Division's research vessel, scientists are studying tiny plankton, some the size of a pinhead.

DONNA ROBERTS (Antarctic Climate & Ecosystems Cooperative Research Centre): Now we get to throw that back over the side.

NARRATOR: Donna Roberts has spent much of her career in the Southern Ocean, and her favorite kind of plankton are tiny animals called pteropods.

These almost transparent sea snails swarm in vast numbers in the colder waters of the Arctic and the Antarctic oceans. They are at the bottom of the food chain, providing food for whales, fish and, ultimately, us.

DONNA ROBERTS: Pteropod shells are gorgeous. It's just like a garden snail, but instead of having one slimy foot, it's evolved to live in the ocean with wings. Scientists call pteropods the “potato chips of the sea,” because they're meaty, and a lot of things eat them, but they've got that added little crunch.

NARRATOR: Tucked away, in this cold room, at the University of Tasmania, are pteropod samples from Antarctica, dating back to 1997.

Donna is analyzing their shell weight to see if rising acidity has affected them.

DONNA ROBERTS: It does matter if a little organism is losing weight, because it's a measure of how healthy they are. So, if their shells become thin, then they are going to put more of their energy towards building what little shell they can than reproducing.

NARRATOR: Pteropod shells collected today are 35 percent smaller and more fragile than those caught a decade ago, yet another sign of rising ocean acidity.

DONNA ROBERTS: This is a healthy set of shells that we collected in 2002, and I'll just show you, for comparison, what unhealthy shells look like.

So, you can see, this one here has lost a segment of shell, and this one here is incredibly thin, very paper thin. Shells like this often fall apart in my hand when I am trying to weigh them.

NARRATOR: Scientists say that, like the baby oysters, there could soon come a point at which the levels of carbon dioxide will be too great for these beautiful little sea butterflies.

DONNA ROBERTS: Most people have not heard of what a pteropod is, but they are vastly important. They are holding up the entire Southern Ocean food web, in places.

NARRATOR: Pteropods are a key food source for lots of animals that swim the seas, not only in the southern oceans, but in the northern oceans as well.

So what would happen if pteropod populations decline, or even disappear, around the globe because of rising acidity?

GARETH LAWSON: The ecosystem effects of removing all the pteropods are just completely unclear. If we take them all away, we really don't know what the effects might be, but they may be quite dire for the things that, that feed on them.

NARRATOR: Among the things that feed on pteropods are things we feed on, like salmon.

MARK GREEN: If you're a pink salmon… You can't just remove 10, 15 percent of a juvenile pink salmon's diet and expect it to, you know, just, “Oh, well, I'll just eat a little more of this instead.” Like, that's not, it's not evolutionarily hard-wired to do that. So, when you start removing huge components of, of, of what other individuals eat, what other species eat, that's a problem.

NARRATOR: If higher acidity reduces or wipes out populations of creatures at the bottom of the food chain, the consequences could be bad for those further up.

The worst possible scenario would involve a chain reaction of extinction, resulting in mass die-offs throughout the oceans.

It has happened before. The fossils that trace the history of life in the ancient oceans reveal dramatic moments when, suddenly, many living things went extinct.

SCOTT DONEY (Woods Hole Oceanographic Institution): We think many of the big extinction events in the past have been related to some rapid event, whether it was a asteroid impact or some rapid large increase in volcanism.

Temperature was changing, ocean chemistry was changing. That's where we see the big extinction events.

NARRATOR: The most famous extinction was 65-million years ago, when the dinosaurs disappeared. But an even bigger catastrophe hit the oceans 250-million years ago, when the Permian Era ended.

The leading theory is that massive volcanic eruptions caused carbon dioxide levels to spike quickly. The result was what's now known as the “Great Dying,” when up to 96 percent of all marine life went extinct, including many coral reefs.

If acidity changes slowly, many creatures may be able to adapt and evolve to cope with the new conditions, but sudden changes are often dangerous for life.

SCOTT DONEY: On evolutionary time scales, organisms are adapting to their environment. The environment's changing, and life is always changing. The more rapid that change, the harder it is for the organisms to adapt.

NARRATOR: And today, the burning of fossil fuels is releasing so much carbon dioxide, it's changing the environment of the ocean very rapidly. Scientists fear that if carbon dioxide continues to rise at high speeds we could have a major extinction event on our hands.

MARK GREEN: The rate of change is happening much, much faster than these plants and these animals can adapt. Unless it happens at a much, much slower rate, evolution will not have an opportunity to keep up with the change.

NARRATOR: Perhaps nowhere on Earth are the plants and animals of the sea more at risk than on coral reefs. Half-a-billion people rely on these unique ecosystems for their survival. The fish that live around reefs form a major part of the human diet.

So, how will rising ocean acidity affect these animals? In addition to messing up the base of the food chain, will the changing chemistry have any direct effect on the fishes' own bodies?

Researchers like Danielle Dixson are trying to find out. Until now, most of her work has been in the lab, but today, she's joining the team in Papua New Guinea, where at one unique reef, carbon dioxide bubbles are raising the water's acidity to extreme levels.

DANIELLE DIXSON (Georgia Institute of Technology): The thing about this location that makes it really, really interesting is that these fish have been living in this CO2 situation for a very long time.

PHILIP MUNDAY (James Cook University): You can see where the CO2 is coming up there, so that's the CO2 seep site, and the control's up here.

NARRATOR: Philip Munday is Danielle's former professor and collaborator. In experiments, back at the lab, they exposed fish to high levels of CO2 and saw alarming results. The damage wasn't done to the fish's skeletons, but to their brain chemistry and their behavior.

PHIL MUNDAY: What we do see that's really dramatic is the changes in their behavior. So things like how they respond to chemical cues in the water changes, their response to sound changes. And what's really cool, here, is that we can come to these seeps, and we can see fish that have probably been living for months, maybe even years, under a high CO2 environment and see if their behavior is still affected.

NARRATOR: The team want to find out if the behavior they saw in the lab will be repeated in the wild, where some fish have grown up in high CO2 conditions, throughout their lives. They'll compare the behavior of the fish living both near and far from the carbon dioxide bubbles.

First, they'll test how they respond to chemical cues in the water, in other words, their sense of smell.

PHIL MUNDAY: Baby fish, in particular, have very good noses. It's not on the end of their face, but they have nostrils, and water comes in and there's sensory cells inside the nostril, and then water goes back out, very much the same as we do.

NARRATOR: Just as land animals use their noses to detect certain molecules that float in the air, fish noses can sense molecules moving through the water. Their sense of smell is critical for their survival. They use it to catch food, find their way home and even to sense danger.

DANIELLE DIXSON: There's a lot of things in the water that produce a lot of smell. There's predators in the water that are trying to feed. There is prey in the water that things are trying to feed on. The corals themselves, they're also releasing chemical cues. Pretty much everything uses chemistry underwater, so, yeah, reefs would be a pretty smelly place.

NARRATOR: The first step for this experiment is to catch some fish.

DANIELLE DIXSON: They're very easy to catch. Just a little bit of clove oil and then you can use your hand to waft them out of the coral and grab them in a net.

NARRATOR: Next they must catch a predator fish.

SCUBA DIVER: So, got a fish.

NARRATOR: Danielle wants to test the smaller reef fishes' ability to identify their predators, like this rock cod, by their smell, a crucial survival strategy for animals on land or sea.

DANIELLE DIXSON: This fish is going to be used to make predator odor. I'm just going to soak it in some water, and then the cues from the fish will come out in the water, and I'll be able to test little fish to see if they can identify the predator cues over other cues.

NARRATOR: For this experiment, water with the predator odor is being pumped into the top side of the flume. The bottom side has normal offshore seawater.

DANIELLE DIXSON: The fish that we have in the flume right now was taken from the control reef where no CO2 bubbles are happening.

The fish identifies the predator through smell alone and then stays in the offshore water side, where no predator smell is.

NARRATOR: The next fish has grown up in the carbon dioxide bubble site, where the water acidity is higher.

DANIELLE DIXSON: Now the fish is sitting in the water that has the predator scent.

NARRATOR: Instead of being repelled, the fish seems attracted to the dangerous smell.

DANIELLE DIXSON: We've found that the CO2 is affecting the fish's cognitive ability. So, it can identify the smell of a predator, but something's wrong with its brain, that it's having a hard time identifying it as a bad thing. It's just identifying the smell.

NARRATOR: After testing dozens of fish, Danielle finds that the fish that grow up in higher acidity don't avoid the predator smell—behavior that makes it much more likely that they'd end up as somebody's dinner.

In addition to smell, Danielle wants to test another survival instinct: the ability to hide.

On these reefs, many fish live among the corals, using their branches for protection.

DANIELLE DIXSON: These fish are like candy on the reef. They're really liked to be eaten. It is in their best interests to be close to their habitat, so they can retreat back to it and they're not picked off as much by predators.

NARRATOR: Danielle tracks how adventurous the little fish are. Which ones will play it safe and stick close to the coral shelter?

This one is from the control site, where the conditions are normal.

DANIELLE DIXSON: You can see it retreats right into the coral. It might be exploring the habitat of the coral, but it's not really exploring the tank. The fish will stay like this for the entire trial, in general.

NARRATOR: The next fish comes from the carbon dioxide bubble site.

DANIELLE DIXSON: You can see it's checking out the water a lot. It's going quite far from the coral. It's not really retreating back into the coral. Being bolder can make you grow faster and get bigger, but it also makes you a lot more susceptible to predators.

NARRATOR: Danielle tests several fish.

The small fish living in the higher acidity are consistently more adventurous, behavior that could put their lives at higher risk.

Researchers don't know yet how all the different kinds of fish that live in the sea will be affected in higher acidity. Some are likely to cope better than others, and some may find some surprising benefits.

At the bubble site, one form of life that's thriving is the sea grass.

KATHARINA FABRICIUS: Sea grasses can live in very high CO2 environments. They actually like it, because sea grasses, like the terrestrial plants, they do take in the carbon dioxide and convert it into sugars.

NARRATOR: For plants, carbon dioxide is a fuel. They use sunlight to turn it into sugar, leaving oxygen as a waste product.

The rich supply of carbon dioxide here is fertilizing these sea grass beds. The thick lawn of sea grass appears to be an important nursery for baby fish.

Biologists are hoping that many of today's fish will find a way to survive in an ocean with more carbon dioxide and higher acidity. Their bodies may be able to adapt to changing conditions, possibly by turning on particular genes.

PHIL MUNDAY: There are mechanisms that might allow them to adjust to a high CO2 world. Some individuals will have better genes for that particular environment and so they pass their genes on, and you get genetic adaptation.

NARRATOR: Marine biologists are eagerly hunting for any signs of genetic adaptation to a rapidly acidifying ocean. Today, the race is on to find creatures that carry genes that would help them survive. And the best places to look are the ones where ocean acidity goes up and down.

On the west coast, from Washington State down to California, there's a seasonal upwelling of carbon dioxide from the deep ocean, lowering the pH and raising the acidity.

Gretchen Hofmann is trying to find out how the marine life here copes with a fluctuating pH.

GRETCHEN HOFMANN: One thing that's unique about the California coast, here, is that we have “upwelling.” And this is where wind blows across the surface of the ocean, starting in the springtime, and this wind brings up deep, cold CO2-rich water to the shores. And that water has a really low pH, and this low-pH-water has an impact on the biology on the shores.

NARRATOR: One creature that seems to have adapted to the ocean's low pH and high acidity here is the spiky sea urchin. These are the lawnmowers of the sea. They play a vital role, keeping ecosystems healthy by devouring seaweed, which, without the urchins, could grow out of control.

Unlike the oyster, which is struggling to build its shell in the high acidity of the northwest coast, the sea urchin seems to be flourishing, even though it sports a shell constructed of the same material: calcium carbonate.

Gretchen believes the key to its success may lie in its genes.

GRETCHEN HOFMANN: We found that populations, say from the north, in Oregon, that are really tougher in the face of these pH changes, they were expressing genes in a different way than, sort of, the wimpy California urchins were, that they were turning on more genes that would help them make their skeleton.

NARRATOR: By turning on certain genes, the northern sea urchins became more efficient at building their calcium carbonate shells, even when the surrounding water had higher acidity.

Gretchen wonders if this life-saving gene could be passed on to the more vulnerable urchins in the south. To find out, she sets up a cross-breeding experiment.

The sperm from both northern and southern males is used to fertilize eggs from the less hardy southern females. Once the larvae begin to mature, Gretchen compares the two samples.

GRETCHEN HOFMANN: Now, we're interested in measuring their skeleton. And the way I think about a sea urchin larvae is that it's like a free-standing back packing tent. So, the skeleton are actually like tent poles. That's the thing that's made of calcium carbonate, and that's the part of their body that could be challenged to form, under ocean acidification conditions.

NARRATOR: Amazingly, the experiment reveals that the northern urchin's tolerance to high acidity is passed on, genetically, to the southern female's young larvae.

GRETCHEN HOFMANN: What we've learned is that larvae that have fathers from the northern populations actually retain their body size. They stay bigger in the face of low pH.

So, it does matter who your daddy is, in this kind of experiment.

We know, now, that there are populations that have the genetics that will allow them to adapt, and we know how to look for them.

NARRATOR: Researchers are looking all over for other marine life that is surviving in more corrosive waters, especially corals since, so far, they seem to be some of the most vulnerable creatures in the sea.

About a thousand miles northwest of Papua New Guinea, off the Pacific islands of Palau, sits another coral reef where the acidity is naturally high.

Here, there are no carbon dioxide bubbles rising up from below. The acidity seems to be caused by the density of aquatic life, combined with very slow water circulation in these shallow lagoons.

Despite the high acidity, many corals here appear to be healthy.

Anne Cohen is trying to figure out why.

ANNE COHEN (Woods Hole Oceanographic Institution): We believe that we have found one coral reef community, which, for some reason that we don't quite yet understand—it could be a genetic adaptation or it could be a combination of environmental factors—that allows them to survive and cope with these low pH conditions.

NARRATOR: One important feature of this environment may be that, in these shallow lagoons, the corals are extremely sheltered from any waves or storms. And that may be the key to their survival, so far.

For marine scientists, places like these are precious.

ANNE COHEN: We have to put those systems at high priority for protection. Those systems might be the only ones that are left at the end of this century.

NARRATOR: Unlike this unusual spot in Palau, most reefs have to cope with powerful storms from time to time, and they rely on fast-growing corals to quickly rebuild their foundations.

Back in Papua New Guinea, Katharina Fabricius would love to find evidence that the corals here, bathed in carbon dioxide bubbles produced by volcanic activity, are adapting and finding ways to be resilient, in spite of the higher acidity.

KATHARINA FABRICIUS: Here, hopefully, some organisms have gotten used to the high carbon dioxide concentrations, which would be a good thing, because it would tell us that maybe there is a future for coral reefs after all.

NARRATOR: Fourteen months ago, Katharina placed over a hundred blank tiles at her study sites, just in time for the annual coral spawning, hoping to compare the growth of baby corals in areas with normal and high acidity.

The spawning of the coral is one of the most spectacular natural events on earth. The corals synchronize their spawning with the lunar cycle, releasing billions of eggs and sperm, usually on the same night. Within a few days, the tiny coral larvae must find the right place to call home.

Will these baby corals settle and grow on Katharina's tiles or will the high acidity ruin their chances?

Now she'll find out.

The first tiles are from the control site.

KATHARINA FABRICIUS: They are looking fantastic. All the pink color is coralline algae, which are really important for the health of the reefs.

NARRATOR: This pink coralline algae is often called “the cement of the reef.” It's one kind of algae the corals actually do like. Young corals are genetically programmed to zero in on it, because it provides a strong foundation for their growth. But it's made of a type of calcium carbonate that will dissolve even faster than the corals, if the pH drops too low.

Katharina now moves to the high acidity bubble site and collects the tiles there.

It takes hours to inventory exactly what's growing on all the tiles.

The ones from the control site where acidity is low have cultivated a healthy batch of young corals.

KATHARINA FABRICIUS: The tiles from the control site already have got a fair number of large coral colonies established. Baby coral settled on the edge here is growing quite happily, so that's about one-year-old coralline algae here, the pink stuff. There's a speck here. There's one sitting here, right at the edge. I found up to 19 coral settlers on this very small space. Not all of them will survive, but still, it's very good for the coral reefs to establish.

NARRATOR: But the tiles from the carbon dioxide bubble site tell a different story.

KATHARINA FABRICIUS: We found hardly any coral recruits on them. There's no pink left, no coralline algae. We're getting a lot of seaweed that are occupying the space for coral to settle. The fact that there are so few coral recruits is of real concern. I didn't expect the differences to be so stark.

NARRATOR: The expedition's nearly over. The findings here have been discouraging.

Along with the scientists, the locals are concerned about the future of their coral reef.

LOCAL CHILD: How does carbon dioxide concentration affect the corals in the sea?

KATHARINA FABRICIUS: The coral reefs will still be there in a 50 or 100 years' time, but they will look very different is our prediction. There will be less of those branching corals, and there will be, possibly, less fish, which is of real concern, because it's important for food.

NARRATOR: Right now, carbon dioxide emissions are rising rapidly, and if that keeps going, the acidity of the ocean will continue to rise as well.

ANNE COHEN: The problem now is that you can't fence off a coral reef island or a fringing reef or a barrier reef and protect it from acidification. This is a global threat.

NARRATOR: With coral reefs, in many places, already vanishing at a rate of one to two percent every year, finding a solution is critical. So far, evidence that coral can adapt is slim. And many marine biologists are asking, “Is it realistic to expect the creatures of the sea to adapt to an ocean that is changing so rapidly? Or should we go to the source of the problem: the rising carbon dioxide in our atmosphere and in the seas, caused by the burning of fossil fuels?”

SCOTT DONEY: The best solution is to reduce the emissions to the atmosphere or capture the carbon dioxide before it gets into the atmosphere.

KATHARINA FABRICIUS: There's no way to save coral reefs without stopping greenhouse gas emissions. There is absolutely no practical solution to protect coral reefs from warming and from ocean acidification if you don't stop carbon dioxide emissions in the world.

DAN MCCORKLE: If we know what's causing it, why don't we just fix the cause and not, not, twiddle our thumbs for 20 or 30 years, trying to sort things out?

NARRATOR: And if carbon emissions aren't cut, many are troubled by the question, “What will happen to life in the sea?

MARK GREEN: It's a big question mark, really, what the ocean's going to look like, but it is going to look a lot different, and it is, it is not going to be as resilient as it is today.

DAN MCCORKLE: We're sort of crossing our fingers that, that there's all these complicated web of changes and that somehow we're going to be happy with the outcome. And I just think that's a bigger risk than we ought to take.