The Ocean of Life

by Callum Roberts

  Those long-suffering dolphins of Sarasota show much the same thing. Animals carrying a heavier burden of toxic PCBs and DDT in their bodies had less responsive immune systems than less contaminated beasts. Concern is growing that immune suppression by pollutants contributed to the mass mortalities of dolphins from Morbilliviruses (related to measles) in the Mediterranean and around North America in the 1990s. In the Indian River Lagoon in Florida there have been horrible cases of dolphins whose living bodies are being engulfed by fungus, a result of immune suppression by a cocktail of pollutants. Similar concerns have also been raised about the role of immune suppression by toxic chemicals in people.14 Perhaps they have contributed to the emergence of several new diseases that have appeared since the 1970s. The jury is still out.

  There are other ways in which susceptibility to disease can increase. Physical injury can weaken animals and plants, and wounds provide relatively easy access to the body for infectious agents. In St. Lucia one of my graduate students, Maggy Nugues, noticed that diseased corals were more common in places that were heavily dived than ones that saw divers only occasionally.15 No matter how careful they are, scuba divers bump into, scratch, and scrape the delicate tissues that cover coral skeletons. These injuries could provide sites for infection. Sure enough, experiments show that injured tissues are much more readily infected than healthy ones. Resorts like Eilat and Sharm-el-Sheikh in the Red Sea are visited by millions of snorkelers and scuba divers every year, each one of whom knocks, tramples, or crushes some delicate creature or other. In some sites it is hard to find any coral that hasn’t been injured. Vast swathes of the northern Red Sea and many other places with coral reefs have been turned over to scuba diving.

  There is another form of injury to marine life that in scale and severity dwarfs the impacts from scuba divers: bottom trawling and dredging. When a trawl net is dragged across the seabed it causes immense collateral damage to anything that lives on or near the ocean floor. The footrope of a trawl is designed to run close to the seabed. Sometimes it is weighted and other times it has rollers to enable it to work over rougher areas. In many beam trawls, where the net is held open by a heavy steel beam that drags above the bottom on metal runners, there are several “tickler” chains set ahead of the net mouth to scare up fish that hug the bottom, such as plaice, sole, and flounder. Footropes and chains slice off marine life like corals, sponges, sea fans, and seaweeds. Ahead of the net, they catch boulders that can be yards across, sometimes entire chunks of living reef, and then roll them along the bottom as the net is towed.

  Dredgers are even more destructive, although generally smaller than trawls. Those used to catch scallops are made in the form of a steel frame with vertical teeth set beneath to dig up the seabed. Behind is a bag of chain mail and net to hold the catch. Scallop dredges look much like the harrows farmers use to break up clods of earth after a field has been plowed, and their effects below water are not far different. Dredges weave trails of devastation across the bottom. Within these tracks, the bottom is littered with the bodies of dead, dying, and injured animals: three-legged crabs with punctured carapaces struggle over ripped fragments of sponge; chopped pieces of sea fan lie across corals torn by ragged wounds; scallops with chunks of missing shell wait to be eaten by one of the many scavengers that this kind of fishing encourages.

  The carnage wrought by bottom trawling and dredging is multiplied from coast to horizon and beyond, from sea to sea and ocean to ocean. Virtually nowhere above three thousand feet deep is spared. Some places get hit once every five or ten years, while places where trawling is unusually intense can be trawled five times in a year. One widely regarded estimate says that an area of nearly six million square miles gets hit by trawls and dredges every year.16 That is more than fifteen thousand square miles of damaged, dead, and dying bottom life every day. For the sake of comparison, that equals an area about one and a half times the size of Europe or America hit every year. It isn’t hard to see how this could increase the number of individuals susceptible to disease.

  The hidden hand of climate change also plays its role in the emergence of disease. Raised water temperatures stress host animals, and pathogens thrive where stress prevails. It is often said that a warmer world will be a sicker world, although some people are less sure. However, there are good reasons to think that diseases might flourish in the future. It won’t just be fish or plankton on the move as climate changes. Diseases and parasites will also find opportunities as they spread with their hosts, or colonize places where new hosts are found. Such shifts have already been seen. In the early 1990s, an oyster parasite moved three hundred miles north into the waters of New England as the sea warmed enough for it to survive over winter.17 This single-celled parasite proliferates within oyster tissues and can take several years to kill its host.

  Mass coral bleaching is one of the most obvious sentinels of severe warming stress. Disease outbreaks have been reported in some places following sublethal bleaching.18 Diseases like the fungus that wiped out Caribbean sea fans seem to grow faster in warmer seas.19 Sponge mass mortality in the Mediterranean has been linked closely with unusually warm water.20

  Acidification will weaken many life-forms that use calcium carbonate to make shells. Thinner, more brittle shells and skeletons will mean greater chances of injury, and therefore sites for infection. Nutrient pollution from terrestrial fertilizers and sewage can also encourage disease. Diseases on Caribbean sea fans and corals spread faster in an experiment when nutrients were added, which suggests that fertilizer boosts the growth of pathogens as well as the crops.21 There is a possibility that the general background increase in nutrient pollution of coastal seas has helped to trigger some disease epidemics. But there isn’t yet much support for this, and its role probably isn’t decisive. Instead, nutrients are just one of a combination of conditions that on their own might be shrugged off easily but together have been lethal.

  There is one transformation of the sea that, from the point of view of diseases and parasites, makes it a healthier place. As I said earlier, diseases have not increased in all groups that have been looked at. There was no upward trend for disease in sharks and rays, or crabs, lobsters, and prawns, and fish seem to have less disease now than they did in the 1970s. All of these groups are intensively targeted by fishing, which means that the densities of most have nose-dived in the last hundred years. We can see in ourselves how a change in transmission rates can influence the development of illness. Colds and flu peak in winter in temperate and cold climates because we spend more time indoors and huddled together than in summer. Viruses may be assisted in a few other ways, such as our increased susceptibility in winter, or by greater survival outside the body in weak light. But the basic element is crowding. At low host densities diseases find it harder to get a foothold and spread, so exploited species may be less at risk of epidemics than they were before we fished them so intensely. At last, something positive about overfishing, but not a cause for celebration.

  The effect fishing exerts on disease and parasites goes beyond simple reduction of host densities.22 You will remember that fishing tends to selectively remove the big, old, and toothsome beasts while leaving the young and supple behind. By virtue of age, or diminishing resistance, old animals carry the greatest load of parasites. As we have fished down populations and felled their oldest members, we have inadvertently driven parasites below critical density thresholds that dictate whether they persist or disappear. Put another way, we can fish out parasites well before we fish out their hosts.

  When we stop fishing a place we play the tape of decline backward and the area fills up again with life. Corals, sponges, and seaweeds sprout from the seabed and coalesce into glades and thickets. Small fish grow into great stalking predators. Diminutive plankton feeders multiply from twinkling points into constellations of fish. As densities rise, diseases and parasites could make a comeback. I don’t know of any research that demonstrates such an effect as yet, but it is a possibility.
On the other hand, there are studies that demonstrate the opposite effect in prey or other species not targeted by fisheries. In a California marine reserve sea urchins were less abundant but more healthy, because population explosions were prevented by recovery of their lobster predators.23 And coral diseases in the Philippines were less common in marine protected areas with healthy fish populations, probably due to prevention of seaweed overgrowth by herbivorous fish.

  Disease epidemics are reshaping ecosystems in profound ways. Coral reefs give us a rare opportunity to compare present conditions with what has gone before. Corals constantly rebuild reefs on foundations laid by previous generations. Just as archaeologists piece together the course of history from their excavations, cores drilled through reefs tell us what they looked like tens, hundreds, and thousands of years ago. Cores through Caribbean reefs show that recent branching coral losses from disease are unprecedented on a timescale of several thousand years, as far back in time as the cores were able to show. As coral skeletons crumble in the aftermath of mass mortality, habitable space for fish, invertebrates, and hosts of others dwindles. The reef hemorrhages life, and, as it empties, its ability to support human needs and livelihoods declines. Dense palisades of branching corals once protected islands and coasts from Florida to Panama and South America. Where once divers had to thread their way gingerly through close forests of sharp coral to reach the open water beyond, today they pass over gently undulating hummocks of seaweed and flattened mounds of sponge, sea squirt, and encrusting coral. As coral ramparts tumbled, they left shores open to attack by wave and storm. Beaches in front of Caribbean resorts and condos that reefs once protected have washed away, forcing developers to replace them with ugly concrete defenses.

  Diseases can cause other economic losses. The sea grass wasting disease I mentioned earlier destroyed critical nursery habitats for commercial fish all the way up the Eastern Seaboard of the United States. It also caused the extinction of a tiny limpet whose only habitat was stolen from beneath it. As outbreaks of disease in the oceans multiply and spread, we can expect worse to come. They warn us that life there is increasingly stressed.

  CHAPTER 14

  Mare Incognitum

  Like children the world over, my daughters love turtles. At once incongruous and graceful, they connect us to the world of fifteen million years ago, when very similar turtles swam alongside megatooth sharks, or seventy-five million years ago, when they rubbed shoulders with dinosaurs. Only eight species of marine turtle remain from a lineage that stretches back little changed deep into the age of dinosaurs. The largest living reptile is the leatherback turtle, a barnacle-encrusted eminence that can reach ten feet long and weigh two tons. Today we confront the stark possibility that people will drive the leatherback turtle to extinction within the next human generation. Already there is just one leatherback left in the Pacific for every twenty in 1962, the year I was born.

  I find this prospect awful to contemplate. What will the world seem like to our grandchildren if the only leatherbacks left are those that inhabit books or computer screens? At the rate we’re going the world could by that time have been robbed of the majesty of whale sharks, the frivolity of sea otters, and the frenzy of bluefin tuna, beating the sea to foam as they hunt down prey. These animals are not just icons of children’s books and television channels; they are creatures we can pursue with our imaginations far into unknown depths. Without them, life will lose some of its grandeur.

  The last thousand years have seen our influences gather like a green wave, scarcely perceptible at first but slowly lifting and steepening over the centuries to burst across the globe in the last sixty years. Our planetary remodeling did not stop at the shore; it just came a little later to the sea. There is no precedent for the speed and variety of the changes underway today, save perhaps the asteroid impact that ended the reign of dinosaurs sixty-five million years ago. Even the cataclysms of the other great extinction events seem sedate by comparison. There is no sign of any letup. The rate of change continues to accelerate in step with human population and economic growth. Our impacts have intensified with time, and where once habitats and species were subject to just one or two influences, like fishing or siltation, now they are caught amid a morass of stresses whose effects accumulate and reverberate through every layer of the living world.

  While life’s players differ from place to place, how the play of human impact has unfolded is much the same. The abundance and sheer physical mass of life has declined over time. There has been a shift from dominance by large-bodied animals and plants to small ones. Populations have been truncated so that age and wisdom have given way to youth and inexperience. The web of life has been simplified as predators have yielded to prey and some species have vanished. Habitats built over millennia by the exertions of countless generations of creatures have crumbled from three-dimensional magnificence to two-dimensional monotony. And for our own species, perhaps uniquely gifted with a sense of aesthetics, in too many places there has been a shift from beauty to sordid poverty.

  The shifting baseline syndrome has blinded us to these alterations. A trip to the seaside appears to hold the same joy and wonder for my children as it did for me some forty years ago, when there was more to find amid rockpools and waves. But what disturbs me, as my own perspective extends into middle age, is how rapid the alteration has been. The vibrant coral reefs I dived as a youth seem less bright, less imposing, and less wild today, as indeed most of them are. In that time the carpets of stony corals that build reefs and give them much of their vivid color and complexity have shrunk by a third to a half. The fat beady-eyed groupers that skulked beneath ledges have become rare, and the walls of predatory snappers and emperors have thinned. In many places silt washed off the land has fogged visibility, so the vistas are less impressive and their colors dimmed.

  Just fifty years ago there were thirty times more Atlantic bluefin tuna swimming wild than now exist. The shoals that raced into the North Sea each spring to thrash among the herring have disappeared. Vast ice shelves have broken free in the Southern Ocean, the Arctic ice thins, and open water near the North Pole has allowed the surface waters of the North Pacific and the Atlantic to mix for the first time in eight hundred thousand years. Sea grass meadows in the Mediterranean have been swallowed beneath choking blankets of invasive seaweed. Dead zones have grown and multiplied. Mighty currents have slowed. In sum, humanity has achieved dominion over the oceans and marine life is in difficulty.

  It is hard to grasp the prospect of seas so compromised that they no longer sustain the ecological processes that we take for granted and upon which our comfort, pleasure, and perhaps even our very existence depends. What will the future look like? Prediction is difficult, given that we have never been here before. In the early days of European seafaring, unexplored areas of ocean were marked on charts as “Mare Incognitum,” or Unknown Seas, and the truth is that we are voyaging into such seas again today. But we have a special interest in the outlook, so prediction is worth a shot. After all, as the American engineer Charles Kettering once said, the future is where we will spend the rest of our lives. To see where the ocean world is going is a good place to begin to look at the drivers of change.

  Fishing is the most ancient of human influences on the sea, but it is only in the last 150 years that its effects spread beyond the local. The late-nineteenth-century industrialization of fishing came when we added engines to boats. Technological innovation gathered pace through the twentieth century in a race to snag fish and beat others to profit, and has carried on since. The footprint of fishing spread from traditional fishing grounds to distant seas in the early twentieth century, and then in the mid–twentieth century from coasts to the high seas, and shallow water to deep. Over time we have substituted new species as past favorites waned. The price of fish has outstripped inflation for decades, reflecting the increasing difficulty and cost of sustaining supplies. In the last third of the twentieth century, developed countries turned to the
developing world to supply their fish after having exhausted their own grounds. The UN Food and Agriculture Organization’s scorecard of the world’s major fisheries shows an increasing rate of collapses since 1950, when it began to collect statistics.

  Growing demand for fish from the rapidly expanding human population has driven these trends. In 1880, on the cusp of the industrial fishing revolution, there were 1.4 billion mouths to feed. By 2011 that number had reached seven billion, five times more. Demand is set to rise by another third in the next forty years with the addition of at least another 2.1 billion people, so pressure for fish protein isn’t about to diminish.1 If we exploit the oceans as we have done for the last century, then overfishing will continue to eat away at the populations of the world’s big fish; some will be driven to extinction, while many more will become too rare to play any further meaningful role within their ecosystems. As they disappear, we will continue the switch from large predators like cod and hake to animals low in food webs, like prawns and anchovies. But they too will become overexploited (as some already are), and we will have to seek seafood from other sources, such as Antarctic krill, which will be processed into more palatable looking foods, like fish cakes and fish sticks.

  In fact, fisheries for krill and jellyfish are already on the rise. FAO figures show jellyfish catches rose exponentially from almost none in the 1960s to more than half a million tons today. If we fish as we do now, it is doubtful that catches from these animals—which, based on their fleeting lifestyles, could be dubbed the mice and cockroaches of the sea—will be able to substitute for the peak landings reached in the 1980s, so wild seafood will get ever scarcer. A billion people rely on seafood as their main source of animal protein today, most of them in the developing world.2 The continued decline of wild fisheries threatens malnourishment for many more by the middle of this century.