Humpbacks are adaptive animals. Researchers at the Alaska Whale Foundation have witnessed humpbacks diving below schools of krill or fish and blowing bubbles around the schools, essentially herding them into a tighter group, after which the whale comes up beneath the group, its mouth open wide to capture everything possible.
At one time scientists held the idea that the ocean might be a legitimate sink for growing amounts of CO2 on land. Some scientists were even looking for ways to improve the uptake of CO2 by the sea, but it turned out the ocean was doing a good job of taking in CO2 all by itself. CO2 in the ocean reacts with the water to form carbonic acid, and this leads to increased ocean acidity. The result is that the oceans are 30 percent more acidic than before. And there are consequences to pay.
Acidification of ocean water is bad for krill, the preferred food source of a number of whales. Studies from the Australian Antarctic Division show that most krill embryos exposed to high levels of acidification (2,000 parts per million) did not develop and none hatched successfully. Cold waters absorb more CO2 than warmer waters. Southern ocean carbon dioxide levels could rise to 1,400 parts per million by the year 2100, three and a half times higher than current rates closer to the equator. This could devastate marine life.
Ocean creatures that wear their skeletons on the outside, such as shrimp, clams, and coral, will find that an increasingly acidic environment could start dissolving those shells. Krill look like tiny shrimp whose skeletons are wrapped around their bodies like a thin suit of armor. These exoskeletons protect them from the elements, but ocean acidification could destroy that protection.
Plus, acidification interferes with the ability of whales to hear others sing. Researchers at the Monterey Bay Aquarium in California found that acidification reduces the ability of the sea to absorb low-frequency sound. This amplifies the ambient noise level from currents, animals, and man, making it more difficult to hear whale sounds, which are broadcast at similar frequencies. The ocean absorbs at least 12 percent less sound now than it did in preindustrial times. And this is projected to rise to 70 percent in 2050. As the ocean gets noisier, whale sounds may get muffled—a critical component of their mating system.
Humpbacks and other whales evolved from the same terrestrial animals that gave rise to sheep and deer. About 60 million years ago these animals moved back into the sea, slowly evolving the ability to drink salt water as their nostrils moved higher up their foreheads until they became blowholes. Their ancestors spawned different lineages of marine mammals, including whales. Some, like killer whales, preyed on different marine mammals, including other whales; others, like the humpback, evolved fine, fibrous combs called baleen in their mouths to filter shrimp, krill, and other creatures that traveled in large schools.
Though originally from the ocean, they were unable to get their gills back: “Evolution doesn’t move backwards,” said Hans-Dieter Sues when I visited him. So whales had to learn to breathe air only at the surface. They gradually lost their legs, though some whales still have small vestiges of legs near their tails. That any animal could go through such an enormous range of changes is testament to evolution’s incredible ability to morph its creatures.
Commercial whale hunting in the first seven decades of the twentieth century reduced their numbers by over 99 percent. From pre-whaling estimates of 250,000 animals, humpback whales had been nearly hunted to extinction, with only about 2,000 then remaining. In 1970, they were put on the endangered list, and since then humpback numbers have rebounded to more than 20,000 in the North Pacific. But acidification could change that progress, particularly since acidification goes hand in hand with warming (both caused predominantly by CO2).
Warming could result in a loss of polar ice. Some biologists refer to it as the “Atlantification” of the Arctic. A loss of sea ice could affect Arctic whale natives like ivory-white belugas and the single-tusked narwhals, which look like unicorns. These two whales lack a prominent dorsal fin—the main fin located on the back of fishes and certain marine mammals—which makes it easier for them to hunt under the ice. But as the ice cover melts, killer whales—whose prominent dorsal fins have foiled their ice cap hunting so far—could have free rein over the Arctic natives. Killer whales might target bowhead whale calves, while minke whales could provide increasing competition for food to all.
The prospect of a polar-ice-free future concerns many researchers. Gretchen Hofmann, a marine biologist at the University of California at Santa Barbara, makes annual visits to McMurdo Station in the Antarctic to study the effects of acidification. She likes to go down in the southern hemisphere’s spring, and she told me: “There are twenty-four hours of daylight but the ice is still strong enough for us to move around on it and support our weight.”
McMurdo is a coastal station at the southern tip of Ross Island, about 850 miles (1,360 kilometers) north of the South Pole. It is a snow-covered island surrounded by frozen seas and rimmed by jagged mountains. The annual temperature is zero degrees Fahrenheit (minus 18 degrees Celsius), but it can get even colder with the wind-chill factor. Many scientists wear “ice cream suits”—big, thick coveralls that cover the whole body—but Hofmann likes her layers better: a down jacket, topped by a layer of polar fleece, topped by another layer of polar fleece, topped by a parka to cut the wind.
She says the worst thing about McMurdo is the food. “It’s all from cans. You get used to having fresh vegetables in Santa Barbara. But down there, there’s nothing fresh, and your food habits get worse and worse. All of a sudden you realize, ‘I’m living on Pringles!’ ”
Hofmann spends about a month or two each year doing her research and teaching classes. She claims the Antarctic is a special land of snow and ice, but the poles are more affected than other areas by acidification as well as global warming, because colder water holds more CO2. Hofmann also works in the South Pacific island of Moorea and along the California coast.
Off Antarctica and off Palmyra Atoll in the mid-Pacific, Hofmann and her coworkers have found that the increase in seawater acidity caused by greenhouse gas emissions is still within the bounds of natural pH fluctuation. But areas in California such as at the mouth of the Elkhorn Slough in Monterey Bay and off La Jolla, at the top of San Diego Bay, are already experiencing acidity levels that scientists had expected wouldn’t be reached until the end of the century. Hofmann believes ocean acidification in the open ocean may still be tolerable for marine organisms, but that those animals living in tidal, estuarine, and upwelling regions may be functioning at the limits of their physiological tolerance.
Curt Stager, author of Deep Future: The Next 100,000 Years of Life on Earth and a professor at Paul Smith’s College, has studied the Eocene climatic optimum, an interglacial period that began about 50 million years ago. During this time average global temperatures rose 18 to 22 degrees Fahrenheit (10 to 12 degrees Celsius) above today’s mean temperature for several million years.
But what interests Stager most is a brief spike in rising temperatures, called the Paleo-Eocene thermal maximum (PETM), that for approximately 170,000 years forced this world into an extremely warm state, another 10 degrees Fahrenheit (5 to 6 degrees Celsius) hotter, on top of an already warming world that resembles our own extreme-emissions scenario in climate models. To date, humans have sent 300 gigatons of fossil carbon into the atmosphere. During the PETM there were at least 2,000 gigatons in the atmosphere from causes that yet remain unclear.
As greenhouse gas concentrations rose, they warmed and acidified the deep sea enough to wipe out bottom-dwelling creatures and burn a red layer into the ocean floor. Sediment cores show that it took thousands of years for the worst of it to subside. The PETM might have reduced the nutritional value of plants, stunted the growth of mammals, and encouraged insects to attack plants more vigorously. During the PETM, mammals were extremely small, about half the size of their counterparts during the periods before and after.
Increased CO2 in the bloodstream can reduce an organism’s ability
to bind and transport oxygen, which is perhaps one of the reasons for the appearance of PETM dwarfs.
Such a high CO2 scenario would have enormous effects on our present-day coral reefs. Coral reefs are breeding grounds for fish, but with acidification, corals don’t aggregate or form stony structures for other marine creatures to cling to or crevices in which to hide. Coral reefs are natural breakwaters for many South Sea islands. But acidification and sea level rise are threatening these places.
Maria Cristina Gambi, of the Stazione Zoologica Anton Dohrn, in Naples, Italy, studies natural volcanic CO2 vents off the island of Ischia in the Gulf of Naples. She and her colleagues have found fewer animal groups and lower biomass in the extreme low-pH areas near the vents. Instead, a few small acidification-resilient species have filled the gap with population booms, which decreases the number of species.
During the Permian, ocean acidification left a unique legacy in its sedimentary layers, the “Lazarus taxa”—“taxa” meaning biological groups. Certain species seem to disappear at the end of the Permian but then resurface millions of years later, apparently coming back from the dead, as Lazarus did in the Bible.
The resurrection of these creatures may be due to ocean acidification. Without a shell or an exoskeleton, many creatures would leave no fossil or other evidence of their existence. It could be that many of these creatures survived “in the nude” for a while and came back when the oceans were less acidic and more hospitable to building shells.
Mary L. Droser, a paleontologist at the University of California, Riverside, believes Lazarus taxa may actually represent not a resurrection of old species but the convergent evolution of other animals. In other words, they are different species evolving to fill the same ecological niche. Such is the case when a number of different animals evolved to have crocodile-like jawbones and bodily features. They weren’t all crocodiles, it’s just that the crocodile had for some reason proved evolutionarily successful at that time, and evolution loves a winner. Droser likes to refer to them not as Lazarus taxa but as “Elvis taxa” in that most forms were primarily imitations. But there were a lot of them. About 30 percent of all such groups were Lazarus taxa during some point between the mid-Permian and the mid-Triassic.
One of the most crucial problems with acidification is the loss of coral. Coral reefs build up over time and offer shelter for smaller fish and other organisms. The coral reefs of the world are home to 25 percent of all marine species, yet they occupy a total area about half the size of France. Global warming and acidification have already led to increased levels of coral bleaching, which eliminates algae in reefs. Coral have a symbiotic relationship with various species of algae. They provide algae a place to live, and algae provide coral with vital nutrients. But coral bleaching eliminates the algae, and as a result coral starve.
About two-thirds of coral species live in deep, cold reefs, far outnumbering the more famous shallow, near-shore habitats of the Indian and Pacific Oceans and the Caribbean Sea, which are better known to vacationing snorkelers. Like shallow reefs, deep coral reefs provide shelter to an enormous and colorful bouquet of sea life. Fish that live in both deep, cold coral reefs and shallow, warm reefs represent a quarter of the annual marine catch in Asia, and feed about a billion people.
There are effects in the Southern Ocean encircling Antarctica as well. Acidification there dissolves the shells of sea snails. Geraint Tarling with the British Antarctic Survey in Cambridge captured free-swimming sea snails called pteropods and found that under an electron microscope they showed signs of strong corrosion. Experiments have shown that coral and mollusks use calcium carbonate in the water to make their shells. But increasing levels of ocean acidification means there is more carbonic acid in the water and this attacks shell building.
Certain types of phytoplankton, which have calcium carbonate shells, may be devastated by acidification in our oceans. Plankton that live in reef communities will suffer a double whammy, since acidification will destroy corals and raise temperatures above reef animal tolerances.
What happens then? Well, considering that atmospheric oxygen comes from two major sources—the tropical rain forests and marine plants such as kelp, algal plankton, and phytoplankton—deforestation and acidification may literally be attacking the air we breathe.
With ocean acidification, we may be harming the environment less purposefully than by overfishing, but the two combined are a bombshell to our present-day marine environments. It’s amazing to consider, but it hasn’t been that long since we started taking fish from the ocean. Archaeologists studying fish bones at 127 archaeological sites across England found a remarkable change in catches starting around 1050. According to Callum Roberts, a professor of marine conservation at the University of York, England, and author of The Unnatural History of the Sea, it was only in the beginning of the last millennium that people who were used to eating freshwater fish and freshwater/ocean migrants (such as salmon) began eating fish primarily from the sea.
Fish from rivers and ponds, such as pike, trout, and perch, as well as migratory fish like salmon, smelt, and sea trout dominated archaeological sites from the seventh to the tenth centuries, but from the eleventh century onward the fish bones in English digs changed to mostly herring, cod, whiting, and haddock—all sea-based creatures. New fishing technologies as well as bigger boats stoked the fishing fires, but the truth was there simply weren’t enough inland fish left to feed the growing British population.
Trawling, the dragging of nets across the seafloor, goes back to the late fourteenth century. It’s a destructive type of fishing that indiscriminately catches fish both big and small. Trawling nets are, however, a boon to ocean fishing.
Hook-and-line fishing enjoyed a boost in the eighteenth century when long lines with hundreds of thousands of hooks replaced hand lines with much fewer. But the true dawn of industrial fishing began in the mid-1870s when the steam trawler appeared. The fishing power of sailing trawlers had been limited by tides and wind, but the steam trawlers were forever freed from the constraints of weather. Steam trawlers quickly replaced sail power for bottom trawling. The development of the frozen food industry during the 1920s provided the next big boost.
Even so, coming out of World War II in the 1940s and 1950s, such environmentalists as Rachel Carson, author of Silent Spring, couldn’t fathom a future without fish. Most marine experts thought the oceans were inexhaustible. They were wrong.
In the decades that followed, intensive fishing became an enormous worldwide industry. Bigger boats, longer lines, and ever-larger trawls worked the sea with an efficiency not previously possible. Doctors started talking about how fish was much better than beef for one’s health, providing another big boost for the fishing industry. Global fish catches reached a peak at about 85 million metric tons a year in the 1980s. Large catches were maintained by a growing fleet with more advanced equipment.
Peter Ward, a paleontologist at the University of Washington, claims that by some estimates every square mile of the world’s continental shelves is trawled every two years. But as the continental shelves have begun to diminish, fishermen have entered the last great wilderness: the deep sea. Muddy bottoms cover much of the deep-sea floor. But here and there seamounts (underwater mountains) thrust their peaks up just shy of the surface and allow for pockets of enormous fish diversity. Giant circular currents move up and down, bathing the tops of the seamounts in phytoplankton.
In the late 1960s, Soviet fishermen discovered plentiful schools of armorhead fish around seamounts off Hawaii and began to harvest them. Fish around seamounts had to contend with stronger open-ocean currents, so they were more muscular and tastier than coastal fishes. Other countries followed the Russian lead, and seamounts off Hawaii were fished intensively. But the run didn’t last. Around 1976, catches collapsed from 30,000 tons to just 3,500 tons. If the Hawaiian fish bonanza had proved to be short-lived, no matter: there were plenty of seamounts left in the sea.
The next jackpot cam
e from Soviet ships fishing at depths of 2,600 to 3,300 feet (800 to 1,000 meters) over the Chatham Rise off New Zealand in the early 1980s. Here, fishermen ran into plentiful populations of a bright-orange fish—what scientists referred to as Hoplostethus atlanticus, a relatively large deep-sea fish and a member of the slimehead family. But “slimehead” didn’t sound like something housewives would want to unload their wallets for, so they changed the name to “orange roughy.” It is still used worldwide for breaded fillets, fish cakes, and fish sticks, along with other white fish.
Fishermen in New Zealand and Australia quickly joined the Russians in a full-scale assault on the fishery. One Australian fisherman, Allan Barnett, struck it rich at St. Helen’s Hill off the edge of the Tasmanian island shelf in 1989. In the first year, the hunt brought in a whopping seventeen thousand tons of orange roughy. But catches soon began to plummet as fishermen worked one seamount after another. Orange roughy are a very long-lived fish that do not reach reproductive maturity for over twenty years, making them extremely susceptible to overfishing and very slow to recover.
But that’s not the end. I visited Craig R. McClain, assistant director of science at the National Evolutionary Synthesis Center, in Durham, North Carolina. He is a husky, young, friendly evolutionary marine biologist whose specialties are deep-sea species and very large marine animals like giant squid.
According to McClain, “We have overfished the shallow seas and are now moving into the deeper waters and doing the same.” He claimed the next big pressure in the deep sea is going to come from industrial mining companies that want to harvest the rare minerals in the bottom of the ocean. Mining companies off Papua New Guinea are starting to explore deep-sea vents, as they are made of a lot of precious minerals needed to make things like computers and, ironically, Toyota Prius hybrids. China is now considering harvesting deep-sea sediments for their rare earth metals.
The Next Species: The Future of Evolution in the Aftermath of Man Page 18
