The Once and Future World Page 12
Put simply, the Hecate Strait of 1750 had more of everything. Not just larger numbers of the big, eye-catching species (two times as many whales and salmon as today, four times as many lingcod, sixteen times as many sea otters, and so on), but also huge populations of smaller creatures: more so-called “forage fish” such as herring and smelt, more shellfish, more shrimp, more crabs, more corals, more sponges, more seaweed. The trouble being that it’s not supposed to work that way. “It doesn’t fit with conventional ecosystem models, because if there were more predators, there should have been less forage fish. More cats, less mice,” says Tony Pitcher, a pioneer of marine historical ecology who worked on the Hecate Strait model.
Similarly challenging findings have turned up almost anywhere that people are looking into the question, from the South China Sea to the Mediterranean, from the North Sea to the Gulf of Maine. One possible explanation is that the assembled data overstates the past abundance of the oceans. Historical ecologists have been criticized for their reliance on the unscientific observations of early explorers, settlers and even naturalists, not to mention books like Moby-Dick—a work of fiction, after all. Yet to ignore these sources of information—which often include the only eyewitness accounts of any given place in the past—can impoverish our knowledge to a surprising degree. A groundbreaking 2006 effort led by the San Diego–based Scripps Institution of Oceanography to identify past versus present nesting beaches of Caribbean green sea turtles found references in 163 historical sources, ranging from Charles de Rochefort’s 1666 The History of the Caribby-Islands to one of the earliest American novels, William Williams’s semi-autobiographical Mr. Penrose: The Journal of Penrose, Seaman. Supported by modern nesting data and historical turtle-hunting reports, the study’s authors cast new light on the species’ supposed “recovery” from near-extinction in the early twentieth century; today’s green turtle population, they estimate, is 0.33 percent of its former plenitude. Admitting that historical records are not precise, the researchers acknowledge that the true number could be higher—but then again, it could also be lower.
The Hecate Strait computer model was built using the widest possible range of source materials, including modern fisheries data, archaeological evidence, historical records, and local knowledge from both indigenous people and later settlers—and it still produced a confounding result. Scientists have an increasingly clear idea of what the oceans contained in the past, says Pitcher, but struggle to say what it might have looked like. He likens a computer model of nature to the abstract portraits painted by Pablo Picasso: all of the parts that make up the whole are accounted for, but the sense of proportion and placement doesn’t fit with reality. The question of how oceans crowded with life actually functioned is still “back-of-the-envelope stuff” he says. While modelling Hecate Strait, for example, researchers turned up evidence that Pacific bluefin tuna once consistently appeared along North America’s northwest coast during cyclical warm-current years. The tuna left a lasting impression in indigenous oral histories—not surprisingly, given that tuna-hunting trips could involve tracking the schools by the eerie green light of phosphorescent plankton churned up at the water’s surface, then spearing fish that can be three metres long, weigh as much as five men, and swim at speeds of up to eighty kilometres per hour. Bluefin tuna today are known to migrate between waters south of Japan and the coasts of California and Mexico, passing at their nearest perhaps 1,200 kilometres to the south of Hecate Strait. They have not been a part of the Pacific Northwest’s fauna in living memory, and their former role is just one of the many mysteries of a bygone natural order.* “We don’t know how it worked,” says Pitcher. “What we know is that it did work, because it was there.”
It is an axiom from the history of nature that the planet is nowhere untouched; even remote Kingman Island, “pristine” in modern terms, is raided from time to time by fishing boats hoping to profit from Asian demand for shark-fin soup, and climate change may have affected its reefs. Yet Kingman Reef has helped reveal how the seemingly impossible bounty of the past was, in fact, possible after all.
When scientists measure the abundance of plants or animals in a given area, they frequently do so by biomass, or the weight of living things. On Kingman Island’s reef, an estimated 85 percent of the biomass was accounted for by sharks and other top predators. This defied belief. Biomass is normally expected to be organized in a basic pyramid shape, with so-called primary producers, such as plants or plankton, forming a wide base layer that feeds a middle level of secondary consumers, often thought of as prey animals, which in turn are hunted by a smaller number of predators—the capstone of the pyramid. Kingman Reef turned this bottom-heavy structure upside down. It was the first time that an inverted biomass pyramid had ever been recorded among a community of species larger than the microscopic.
It took several years of research before the improbable nature of Kingman Reef could be explained. Picture a clock with only a second hand and an hour hand. Inside the clock, a small gear counts off the seconds, its teeth engaging with a much larger gear that counts off the hours. The small gear spins rapidly, but with every rotation it turns the larger gear only a fraction. An ecosystem that is top-heavy with predators works in much the same way. Most of the prey fish move quickly through their life cycles—it’s estimated that 99 percent of small reef fish are eaten each year. Still, by hiding in the coral, growing quickly, coming into sexual maturity at a young age, and producing millions of young, enough prey fish survive to maintain their populations. Sharks and other predators, meanwhile, grow slowly, mature late in life, produce few young and live for many years. Somehow, the two have found a balance—one that is far richer than on “normal” reefs affected by fishing, pollution and other human influences. A typical stretch of reef at Kingman is home to about four times the weight of fish as a similar area on nearby Kiritimati atoll (also known as Christmas Island), which has a population of five thousand people. More heavily exploited reefs have fewer fish still.
Kingman Island is not a freak anomaly. Several other reefs—all of them relatively remote from human interference—are now known to be top-heavy with predators. In fact, it’s quite possible that this is what many if not most reefs would look like in a pristine condition. Countless sharks appear in the histories of coasts that today are densely populated with people: Accounts from Florida in the 1880s describe sharks “swarming” around fishing wharves, and, as late as 1920, driving fishermen from their grounds by attacking their catch. Sea shanties once warned of the blue and porbeagle sharks that lurked just offshore of the British Isles, and as recently as the 1960s some six thousand sharks a year were being hooked off southwestern England; the same fishery brings in less than 5 percent of that number today. In just the past forty years, the worldwide population of great sharks—those species that grow to more than six feet in length—has likely declined by 90 percent or more. Reef sharks are down by as much as 97 percent.
When Sala and his colleagues first circulated their research from Kingman Island, they met with flat scepticism from their scientific peers. Then they sent out the paper again, this time with photos of the schools of sharks included. The doubters grew quiet. Before long, some were saying they wanted to visit the reef, just to experience it for themselves.
Abundance begets abundance. Consider another ecological puzzle, this time involving shrimp-like animals called krill in the Southern Ocean that surrounds Antarctica. Before industrial whaling, baleen whales in the Southern Ocean ate a mass of krill equal to more than half the weight of all the fish caught by people worldwide each year today, with the critical difference that we are severely depleting our fish stocks, while the krill catch by whales was apparently sustainable. When Antarctica’s great whales were nearly wiped out in the 1960s, scientists expected krill populations to boom. Instead, they did the opposite, crashing by some 80 percent by the end of the century. Climate change was suspected. Then in 2008, Victor Smetacek, a polar biologist based in Germany, prop
osed a more intriguing explanation. Perhaps, he argued, whales not only eat krill, they also produce the conditions in which krill can thrive. In turn, larger numbers of krill support a growing population of whales, and both increase on an upward spiral. He called it “the food chain of the giants.”
It is sometimes known by a different name: “the whale-shit hypothesis.” Here, roughly, is what the theory proposes. While whales feed on krill, krill feed on plankton. In order to bloom, however, plankton need sea water that contains sufficient iron, and the Southern Ocean receives only a small amount of iron from natural sources, such as fallout from the atmosphere or runoff from Antarctic soil.
Whales, though, boost the iron content of the ocean in two important ways. First, they recycle the iron that’s available. When krill eat plankton, the krill themselves end up loaded with iron; whales then eat the krill and, later, defecate in liquid form near the surface of the sea. The quantity of iron-rich excrement produced by individual whales is impressive: one research team described whale manure, almost poetically, as “flocculent fecal plumes,” each “about the size of our inflatable boat, and the colour of oversteeped green tea.” The feces refertilizes the ocean with iron, spinning the nutrient through the food chain multiple times before it inevitably sinks to the sea floor.
Second, whales have the capacity to retrieve the sunken iron. Sperm whales, along with a surprisingly long list of smaller toothed whales, dive to incredible depths. Adult sperm whales routinely dive one kilometre below the surface, and are thought to be capable of diving three times that depth during epic aquatic journeys that can last two hours. (By way of comparison, the deepest human dive without mechanical assistance plunged just one hundred metres into the sea and lasted only four minutes.) Despite being as dependent on air as you or I, sperm whales spend more than 70 percent of their time holding their breath. When diving to terrifying depths, where the water is pitch black and presses in with crushing force, the whales shut down every bodily function not essential to survival. That includes digestion. Whales don’t excrete in the deeps. They hunt iron-rich prey such as giant squid down there, but empty their bowels at or near the surface, where the nutrients can once again feed blooms of plankton.
It all sounds like a biologist’s April Fool’s joke, but the effects are significant. The estimated twelve thousand sperm whales that currently live in the Southern Ocean draw fifty tonnes of iron to the surface every year. Now consider the fact that the estimated pre-whaling population of sperm whales is 120,000—ten times today’s numbers. Suddenly, five hundred tonnes of deep-ocean iron is reaching the surface each year, much of it then recycled at the surface by baleen whales feeding on krill. Whaling records from the Southern Ocean indicate a historical population of baleen whales that was so high that biologists couldn’t understand how there was enough food for them all in such an iron-poor environment, and some thought the numbers had been over-reported. Instead, the whales may have been boosting the productivity of the entire ocean, making their own extraordinary abundance possible. Blue whales—the largest mammal ever to live on earth—are now thought to have been as much as one hundred times more numerous in the Southern Ocean than they are today.
The idea of fertilizing the oceans with iron has recently inflamed debate in a much different sphere: the fight against climate change. When a kind of plankton known as diatoms bloom, they not only take up iron from the sea, they also remove carbon from the atmosphere—the same carbon that, mainly due to pollution from the burning of fossil fuels, now threatens human civilization with catastrophic global warming. Researchers theorized that when diatoms died, their bodies would sink to the ocean floor, where the carbon they contained would be kept out of the atmosphere for centuries or even millennia. Scientists are now testing whether ocean iron fertilization could produce and sink enough diatoms to combat carbon pollution from human activities. One of the most important studies so far was led by Smetacek himself—he of the “food chain of the giants” hypothesis. In 2012, his team reported that they had successfully used iron seeding to create a plankton bloom, with at least half the carbon that the plankton removed from the atmosphere ultimately ending up at the bottom of the sea.
Ocean iron fertilization is known as “geoengineering,” or tinkering with the earth’s biggest systems in order to stabilize the climate; other proposals include spreading reflective particles in the atmosphere to bounce the sun’s warming rays back into space, and using artificial “super trees” to capture atmospheric carbon for storage in underground chambers. Even among its advocates, geoengineering is widely considered a perilous, last-ditch response by a world community that appears unable to find a way to rapidly reduce its dependence on fossil fuels. Potential risks from iron-seeding experiments, for example, include irruptions of toxic algae or “dead zones” where plankton blooms starve every other species of oxygen. On the other hand, iron fertilization’s potential as a tool to fight climate change has made it impossible to ignore. Marine policy experts estimate that the carbon that could potentially be removed from the atmosphere by ocean iron fertilization would be worth $1 billion on the emerging international carbon-trading market, which puts a price on carbon pollution.
In the past, however, large numbers of whales fertilized the ocean with iron, probably with few if any risks. But how much carbon did they really remove from the atmosphere? “To date, the role of whale defecation in influencing carbon export has been overlooked,” writes one team of scientists, perhaps stating the obvious. Researchers, however, have begun to crunch the numbers. Calculating the impact of sperm whales alone, they estimate that even today’s small population triggers the removal of 240,000 tonnes of carbon from the atmosphere each year. Bring sperm whales back to their pre-whaling numbers, and the amount of carbon removed would reach 2.4 million tonnes—a carbon reduction worth more than $20 million on today’s carbon exchange. Sperm whales, meanwhile, are only one of thirteen great whale species, nearly all of them decimated during the twentieth century.
Individual whales are themselves remarkable storehouses of carbon. Using conservative estimates of the pre-whaling population, rebuilding just the Southern Ocean population of blue whales would turn 3.3 million tonnes of atmospheric carbon into living bone, muscle and blubber, much the way old-growth trees store carbon in their trunks, limbs and roots over their long lifespans. When compared to the most successful iron-seeding experiments to date, restoring the Southern Ocean’s blue whales would be equivalent to two hundred such projects—and that only includes the carbon stored in the whales themselves, without the reductions in atmospheric carbon they catalyze through the iron cycle.
When living things die, their embodied carbon is normally released through decomposition. Most whales, however, sink down—I picture a cradled, rocking motion—through the abyssal depths to the sea floor. Each sunken whale removes its mass of carbon from the atmosphere for hundreds or thousands of years. They once did so in such numbers that whale ear bones, which are the size of a large man’s fist, turned up regularly in fishers’ nets when they first trawled new sections of sea floor. Whole communities of other species erupt wherever a whale carcass touches down, including at least twenty-eight creatures known only from “whale falls”—meaning that such bonanzas were once common enough that specialized scavengers could successfully evolve. It can take fifty years for a huge carcass to fully decompose, meaning that a whale can “live” after death as long as it did in life.
How much did the ecological abundance of the past shape the atmosphere? No one can say. Climate change ecology is such a new science that the first major workshop on the subject, at Yale University, took place in 2012. But the first glimmers are fascinating. Research on the kelp forests off North America’s west coast found a startling difference in carbon storage between those areas where sea otters have recovered and those where they have not. In the restored areas, kelp is one hundred times more plentiful; a totally restored kelp forest would store an amount of carbon worth $90 mil
lion on the carbon market today. In another study, maintaining the vast herds of wildebeest on the Serengeti plains of Africa was found to control wildfire so successfully that enough carbon was stored to equal the carbon footprint of every tourist who flies in from around the world to witness the animals. At the very least, according to Yale ecologist Oswald Schmitz, full-force nature was “another wedge, a stabilization wedge” in the face of climate change.
At the most, it was something more. The time period in which atmospheric carbon has rapidly increased is not only the era in which fossil fuel use soared, it’s also the era in which the planet’s ecology was stripped down and transformed more rapidly and radically than it had been in thousands of years. It is just possible, in other words, that much of the reason we have a new climate is because we have made ourselves a new world.
* Another shift: The average size of individual animals appears to shrink under hunting pressure in many species. Some shellfish have steadily decreased in size over 10,000 years of human impacts on the Channel Islands off California—red abalone have gone from whoppers that would span a dinner plate to mouthfuls that would have to be served by the dozen. Tiger sharks off North America’s east coast have shrunk from a typical length of eight feet to about half that size, and silver seabream have grown smaller by about 50 percent since European arrival in New Zealand. Even the seabream’s behaviour appears to have changed. Where once they were frequently seen from boats or shore, and even fished for with rifles or spears in shallow water, they are now considered “spooky,” avoiding even divers.