by Carl Safina
Since first becoming human, we have mainly been burning things to harness energy. To become fully human we’ll have to fully come out of the cave, quench the fires, and harness nonburning energy. But until then there is this problem: burning things—like coal, gas, oil, and wood—releases carbon dioxide.
Back in 1956, Roger Revelle and Hans Suess started measuring the air’s carbon dioxide to get “a clearer understanding of the probable climatic effects.” And that’s what they got.
There’s a third more carbon dioxide in the air than at the start of the Industrial Revolution. The current concentration is higher than it’s been for several million years; it’s rising one hundred times faster than at any time in the past 650,000 years. The planet has survived much higher greenhouse gas concentrations; civilization hasn’t. Our species invented agriculture about 10,000 years ago; writing and towns are about 5,000 years old. All of civilization and agriculture developed with the help of a relatively stable atmosphere, and rather stable weather. Now human-caused greenhouse gases have reversed a long, slow natural cooling.
Just to clarify, the greenhouse effect—caused mainly by the heat blanket properties of water vapor, with an assist from carbon dioxide and other so-called greenhouse gases—is natural and crucial; it prevents Earth from looking like a snowball. The concern is over how much additional heat heat-trapping gasses will trap. We now have too much of a good thing.
Stabilizing the climate requires that the world cut greenhouse gases by 80 percent by 2050. But unlike the payoff of improving, say, sewers, cutting emissions won’t actually stabilize the climate for perhaps another fifty years, because the planet will continue adjusting to gas already out of the box. Doubling the atmosphere’s carbon dioxide—expected by between 2050 and 2080 unless we quench the fires—would create a planetary-average warming of roughly five degrees Fahrenheit. If we let that happen, we’ll hand our kids a different planet, far outside the range that any humans have ever experienced, with no return possible within any foreseeable future generation. So it’s our children’s world we’re mainly talking about. But some of what will happen next is starting to happen now to people, and to corals.
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When Bob talks about “coral bleaching,” he means the corals’ loss of their internal sugar-making algae partners (called zooxanthellae) when unusually hot weather drives the seawater temperature abnormally high. Because “zoox” give corals their color, reefs without them turn porcelain white. Prolonged “bleaching” can kill corals. It’s already killed large swaths of reef. In 1980, coral bleaching was brand-new. Now it’s frequent and widespread.
About half the human-produced carbon dioxide has dissolved into the ocean. We’re producing it so fast, it’s “backing up” near the ocean’s surface. The North Atlantic is absorbing only half the carbon dioxide it did in the mid-1990s. That will warm the climate faster. By 2080, bleaching will likely hit 80 to 100 percent of the world’s tropical coral reefs every year. That could be the end of them. To outrun that, corals would have to continually adapt their temperature tolerance.
But even if corals outran warming, they’d still run into the pH problem.
In seawater, carbon dioxide triggers a short series of reactions that form carbonic acid and lock up carbonate molecules. Corals, corallines like Titanoderma, and other creatures that make skeletons and shells of calcium carbonate need those same carbonate molecules.
Chemistry buffs, this is for you: When a molecule of carbon dioxide (CO2) enters the ocean, it soon finds itself attracted to water (H2O). These two molecular parents spawn carbonic acid (H2CO3), which then releases one hydrogen ion (H+), leaving a molecule of bicarbonate (HCO3−). The concentration of those hydrogen ions is measured as pH. The more hydrogen ions, the more acid, but the lower the pH (a pH of 1 is a very strong acid). Because increasing hydrogen ions push seawater pH toward the acid end of the scale, this is being called “ocean acidification” (even though the ocean is still slightly alkaline). Compared to before the Industrial Revolution, the upper ocean already has about 30 percent more hydrogen ions.
The problem is that those hydrogen ions easily bind with carbonate ions (CO32−). Using up carbonate ions deprives animals like hard corals, clams, snails, and various plankton of building material for making their calcium carbonate skeletons and shells. Carbonate scarcity slows their growth; they become fragile and, sometimes, fatally deformed. Carbonate concentrations in the upper few hundred feet of the ocean have already declined about 10 percent compared to seawater just before steam-engine times.
* * *
“To see where this is heading,” warns Bob, “put a clamshell or an egg in vinegar for a day.”
I did. Not good. My shell began dissolving.
“Already,” Bob adds, “some corals are growing thinner, weaker walls.”
And I’ve already talked to shellfish growers who are seeing their larval oysters dying as lower-pH seawater reaches their hatcheries.
Carbonate concentration varies regionally. It’s normally highest in the tropics, lowest near the poles. It’s low around the Galápagos Islands. But Indonesia’s waters have plenty of dissolved calcium carbonate of the form hard corals need (that form is called aragonite, by the way). So Indonesia’s corals should be okay for decades. But only decades.
Since about 1800, the atmospheric carbon dioxide concentration has risen about 35 percent, from 280 molecules per million molecules of air to about 385 (in the year 2010). It’s increasing by about 2 parts per million annually. When it reaches 450 parts per million—a near certainty in the middle of this century—the aragonite concentration around Australia’s Great Barrier Reef will fall below the lowest concentration now bathing any coral reef on the planet. At 500 parts of carbon dioxide, large swaths of the Pacific and Indian Oceans will fall below the minimum aragonite concentration required by hard corals. If the atmosphere’s carbon dioxide hits 550 (actually expected later in this century) the aragonite concentration that coral reefs require will essentially cease to exist. So it appears that carbonate availability will drop too low for reef growth before 2100. If we keep running civilization with fire, and the carbon dioxide concentration reaches abut 560, the world’s seawater will begin to dissolve shellfish and coral reefs.
At the base of the food chain, some of the most important ocean drifters use calcium carbonate. They include organisms like single-celled foraminifera and coccolithophorids, which drift the ocean in uncountable trillions, plus pteropods (silent p; they’re related to snails) that can swarm at densities of up to 1,000 per cubic meter of water. Foraminifera shells are now a third thinner than those from before the Industrial Revolution. Trouble for them means trouble for everything that eats them. Most people haven’t heard of pteropods, but they’re well-known to hungry young mackerel, pollock, cod, haddock, and salmon.
Copepods are often the first animal link in the food chain. When experimenters lowered seawater pH by 0.2 units, half their copepods died within a week. The pH of the ocean’s surface has already dropped by about 0.11 units. In other laboratory experiments mimicking conditions predicted between 2040 and 2100, clams, oysters, mussels, urchins, and snails all had problems growing and reproducing.
Life often finds ways, but it needs time. Adaptation becomes less likely as changes accelerate.
While some people still argue over whether warming will generally be good or bad (though it will generally be bad), there is no argument that acidification will be anything but bad for things people care about, like shellfish and coral reefs, and all the associated fish, turtles, seafood, tourism—.
* * *
For the early Triassic period, when the air’s carbon dioxide concentration was very high, the fossil pages of the coral chapter go blank. Bob speculates that without carbonate, some may have survived “by going naked.” That is, corals may have lived like anemones, with no hard parts. “It took, I mean, millions of years for hard corals to reappear,” he says.
We sip our beer. I’m thi
nking. Hundreds of millions of people depend heavily on reefs for food and livelihood.
I must look a little fatigued, because Bob asks, almost innocently, “Am I piling on the bad news?” He mentions that letting grazing fish recover—especially parrotfish—would buy reefs a little time to solve our atmospheric crisis. He knows two places where fish have saved coral in trouble: Bonaire, in the Caribbean, and Palau, in the western Pacific. I tell him I’d like to see that.
As the sun sinks, the plump moon rises, spreading its silver cloak upon the sea and the shadowed clouds, the sandy curve of shore, and the white gleam of surf. Under this moon, any slender hope will have to do. I decide not to think, and to just feel the night sea breeze.
* * *
Bonaire, anchored off Venezuela, has wild flamingos and the best remaining coral reefs in the Caribbean. Our first dive will be from the beach. As usual, Bob and Susie are studying coral, crusting algae, and seaweed. Also as usual, Ruddy Turnstones—birds I seem to see wherever I go—are picking along the waterline.
We suit up and walk into the shallows, suck a couple of breaths to make sure our air is on, pull our diving masks down, and plunge seaward.
The remains of past Staghorn thickets were mounded on the beach. Now they carpet the shallows between patches of dazzling sand. Old-timers tell of thickets of Staghorn and Elkhorn so dense that in the 1950s people here used chains and clubs to smash paths through the coral so they could dive from shore.
I see precisely zero live Staghorn, zero live Elkhorn. Yet this is, overall, the best place in the Caribbean to experience a “healthy” reef—one that is still functioning as a coral reef and hasn’t gone over to the dark side of seaweed and gloomy shadow.
Past where those thickets once grew, the seafloor slopes to a rather narrow—but nice—band of reef from about twenty to fifty feet deep. There’s a decent amount of live coral, covering about a quarter of the bottom. Corals shaped like brains, plates, and soft whips.
On this island, where since 1971 it’s been illegal to even possess a speargun, the fish on the reef are delightfully abundant—and tame. They don’t turn tail. Yellowtail Snappers and Bar Jacks swim almost touchingly close. You can approach parrotfish easily; they’re as likely to turn toward you as away. Over the slope swarm thousands of Blue and Brown Chromis, white-lipped Creole Fish, and platoons of Sergeant Majors. They cloud the water in schools extending halfway to the surface, nabbing invisible plankton from an imperceptibly gentle flow.
* * *
A coral reef may be the most beautiful natural system on Earth. A towering rainforest, a lakeshore by campfire light, endless tundra, the dazzle of polar ice, turquoise atolls in azure seas, crystal alpine meadows, rolling grasslands pulling down the whole horizon, any water under the influence of gravity, desert solitude, the song of the blue ocean—no natural place lacks a claim to beauty. But unlike a place that whispers intimate secrets, a coral reef parades its pageantry. It’s got to be the most spectacular cabaret in nature.
Discus-shaped surgeonfishes rove the reef here in herds of several dozen. When they descend to graze, they give close buzz cuts to coral heads, nipping any soft filaments, causing ruckus enough to dust up the place with clouds of sediment. Trumpetfish follow them, hoping to pick off little swimming animals displaced from cover.
Of parrotfishes, eight kinds here are recognizable as adults: Stoplight, Queen, Striped, Redfin, Redband, Blue, Rainbow, Princess. The only juvenile I learn easily is the Queen, because Susie calls them “crackheads” for their washed-out gray-and-white appearance and the dark circles under their eyes. The parrots scrape into the reef, chipping audibly, excreting lines of fine coral sand. They’re abundant. Damsels are superabundant. Everywhere they’re chasing grazing fish from their little seaweed gardens. Butterfly fishes flutter by like pennants in a stiff breeze. Angelfishes—French Angels, Queen Angels, and the superb Rock Beauty—cruise along arrayed in blues and golds.
They can take your breath away, but so can mere time; our air is limited. As we’re swimming shoreward, Susie peeks into a pile of Staghorn rubble and a jade octopus slyly slides from its garden. And as we cross the dazzling shallows, a fencepost-sized Great Barracuda glides effortlessly into view, very much at home. It’s the first big ’cuda Bob’s seen here in a while, and he nods and signs an enthusiastic “Okay.”
Walking to shore, we notice two big parrotfish in water so shallow their tails break the surface. Over white sand, they stand out like watermelons in a porcelain sink. When an Osprey comes over, it has to see them—but it sails past. It must be full. Plenty of parrotfish, it seems to me.
But the Osprey and I know what is, not what has been, or what is coming.
A middle-aged woman who has seen a lot of sun comes over. She recognizes Bob. Turns out she’s a divemaster. Nice parrotfish right there, we agree. She’s worried, though, because parrotfish are being increasingly caught from shore by recent immigrants from South America. “Every day, I see them casting their nets, taking the big ones,” she reports.
Bob’s been counting—and he concurs; parrots are still common but are definitely suffering decline compared to past years. Parrotfish have long been protected here by the ban on spearguns, and they are vegetarians, so they usually don’t take a baited hook. But: new people, new method, new problem. Old story.
Bob’s also seeing more seaweed. He showed me. So far it’s just a tiny fuzz, in small patches. It’s not the bushy growth that turns other Caribbean reefs gloomy. Not yet. Parrotfish decline looks like the smoking gun. As elsewhere.
I came to this last best place in the Caribbean to see a reef without obvious overfishing. As usual, it seems I’m a little late.
Old-timers say there were vastly more groupers and snappers—big ones—years ago. Easy to catch on a hook, they remain fished out. Among other things, they ate damselfish. And damselfish, though they eat seaweed, effectively defend their little seaweed gardens against other grazing fish. Fewer groupers and snappers mean more damsels, which means more gardens, more seaweed. And reduced parrotfish also means more seaweed.
Bob says, “I’m hearing alarms.” One, a drop in parrotfish; two, increasing seaweed. “It worries me. Every coral reef in the world where seaweed got a foothold has unraveled—no exceptions.” Susie’s data show that baby corals have declined by fully half in the last few years. Getting a grip on life is becoming increasingly difficult for corals, even here.
* * *
Bob loves parrotfish. The few new immigrants love them too—mainly steamed. In most of the Caribbean, fishing pressure is much harsher than here in Bonaire, and the problems worse. Throughout the Caribbean, about 60,000 small-scale fishers set nets and traps and baited hooks on, in, over, and around coral reefs, dropping 180 kinds of fishes onto the tables of fish markets and high-end resorts. In Belize, where fishing has depleted groupers and snappers, fishermen sell parrotfish as “snapper.” Tourists don’t know the difference; locals don’t care. But it boomerangs.
In Belize I once went out with some fishermen who’d set a half-kilometer-long gill net overnight. At dawn we began hand-hauling the net, and at first, no fish appeared. After twenty minutes it was clear these guys were in for a meager catch. By the time they’d hauled the entire five hundred meters of net into the boat, they’d caught not one single fish. Not one. It was a brutal lesson: if you take all, you get nothing.
Rising tides of people accelerate the strains on food, freshwater, forests, and fish. And as a man from nearby Nicaragua who is here studying the reefs points out, “Many poor Latin American places have a dual problem: poverty is hard to solve when the Catholic church forces people to choose between birth control and God.”
What can a poor person do? The Nicaraguan man added, though, that it’s usually not the local community that depletes the resources; it’s the market. But the market is just a distant community that has come to buy resources because it can’t feed its own beast. The “market” is overpopulation looking for a place to shop.
The market is people living elsewhere who can support themselves only by sticking their straw into other communities, other countries. The market is immigration that stays at home but arrives on your doorstep dressed as cash.
The big cities and crowded corridors of the world pull nature into the vortex of their appetites, from across town and across the planet. People inside that vortex who don’t get enough may decide to leave. Emigration is just overpopulation looking for a place to eat. And so a few have arrived here, and elsewhere, bringing a taste for, say, parrotfish. Enough parrotfish for the reef may look to fishers like plenty for them, and too many people for the reef might look like just a few more people.
* * *
Bob’s hearing a third alarm besides declining parrotfish and increasing seaweed: Titanoderma is rapidly declining. So are other crusting algae. Bonaire, with the best reefs in the Caribbean, has also had the Caribbean’s highest density of Titanoderma, helping give coral babes a boost. In under a decade, crusting algae have shrunk from covering 20 percent of the bottom to, now, under 5 percent. Bob says warily, “You don’t want to lose such an important coral starter.” Bob thinks Titanoderma’s decline might result from acidification.
But if that’s true, wouldn’t corals be having the same problem? “No, probably not,” Bob explains. Corals use the much more common form of calcium carbonate, aragonite. Crusting algae use the scarcer form called calcite. Getting enough calcite from the seawater demands more energy. As ocean acidification makes calcium carbonate scarcer, calcite users might be the first in their neighborhood to show the strain.
* * *
Bonaire’s government understands that luring crucial tourists depends on Bonaire’s ability to boast the region’s best reefs. But “best” doesn’t mean Bonaire is immune from the region’s problems. Bonaire was not spared the diseases that killed the Caribbean’s branching coral and grazing urchins. It’s been spared the plague of excess seaweed only because, compared to the rest of the region, it better protected its fish. But it’s not immune to the possibility of overfishing. The reefs need fish. That’s not all they need, but as Bob had said, keeping fish on the reef is the best time buyer against climate changes.
