In the Baltic Sea, lush meadows of brown, red, purple, and pink weeds struggled as light penetration faltered under the increasing plankton growth stimulated by excess fertilizing nutrients. The dead bodies from these blooms piled up on the seabed and drove down oxygen levels, so that a thick organic soup began to churn above the bottom, cutting light levels further and driving out animals that once called the weedy forest home. On coral reefs, seaweed again causes problems, when mass coral mortality from high temperatures or disease opens up space. Where grazers have been overfished, seaweeds rapidly take hold, especially in places where nutrient-rich water also bathes the reef. Just as in the Mediterranean, these seaweeds trap sediment, which makes the coral comeback much harder, and the weeds may themselves harm tiny corals by poison, or by contact abrasion to make them more susceptible to diseases, some of which the seaweeds harbor.18
In many cases, loss of habitat-forming species, such as oysters, sponge, or coral, opens the way for invasions by other species. Sometimes it is the invaders themselves that oust the habitat creators, such as the rampant Caulerpa weed that engulfed the native sea grasses in the Mediterranean. Invaders complicate the business of projecting the future for marine life still further. In part, the wave of new species advancing into habitats is a product of climate warming. Some arrivals can be predicted quite easily, because they live nearby, but their effects may be hard to judge because of the complex ways in which they ripple through the web of life. Other introductions are more capricious and come about through the chance arrival and unlikely survival of creatures from far afield. The red lionfish that have so rapidly settled into Caribbean coral reefs seem certain to cause a major reorganization of life there whose outcome we can only guess at.
Habitats have been opened up and flattened out and the new regimes usually support fewer species and are less productive than the old. The contrast between kelp forest and turf pavement is like the difference between woodland and pasture. Think of how rich is the life of the forest. Its multiple layers and kaleidoscope of conditions produce communities within communities: the lush and open canopy; the fuzz of lichen and fern on trunk and branch; the dark, mossy wrinkles and cavities; the tangled undergrowth and deep loam beneath. Compare that to open grassland grazed by rabbits or livestock. A close look might reveal a miniature world more varied than is apparent at first glance, but the simple fact is that grasslands offer fewer ways to make a living than woods, and while some species do well (the Serengeti’s rivers of wildebeest in full migration come to mind), the abundance of life they support is less.
Complex habitats offer more ways to make a living than the simpler, flatter habitats that remain in the wake of degradation. They also sustain more big fish, who in turn keep productivity high by recycling nutrients. Just as gardeners love horse manure, so fish shit is great for seaweed and phytoplankton, the engines of production in the sea. They liberate nutrients to the legions of detritus feeders and animals such as corals, mollusks, and sponges that feed on floating particles. A recent study based on computer-simulated removals of fish species from food webs in tropical freshwater lakes and streams showed how some species play disproportionately important roles.19 Inconveniently for us, the most important species are often those favored by fishermen, because they tend to be large, or abundant, or both. When the simulated extinctions followed the sequence of importance of species in catches, the loss of nutrient recycling function was far greater than when species were removed at random.
In these simulations, when species with similar ecological roles were allowed to increase in abundance following the removal of others, they were often able to compensate for the roles played by their vanished colleagues. Diversity is a key to resilience. Where there are lots of species and much overlap in what they do, there is more scope for some of them to disappear before losses trigger catastrophe. The trouble with fisheries is that they are often unselective and take out several species at a time. And when one declines, fishers switch to others, so the scope for compensation is limited. This is certainly what I have seen on Caribbean coral reefs, where fewer and smaller species are left behind as fishing intensifies. The dainty little parrotfish that pluck seaweed from Jamaica’s ransacked reefs are all that are left after fishermen have taken their fill. They cannot possibly control the runaway seaweed growth that is overwhelming coral there, while the dense groups of bulky parrotfish that exist on lightly fished reefs easily strip seaweed back to a green baize film.
It saddens me to see the loss of beauty and wild energy of the sea. Tangled forests of mangrove that teemed with life have been replaced by the bare embankments of shrimp ponds. Verdant green meadows of sea grass have withered or been buried under blanketing mud. The labyrinthine creeks of salt marsh where once you could leave the modern world behind have been drained and built over time after time. These are just the places that are easy to see, but we find similar losses in less accessible corners. Cold water coral reefs in the North Sea were already half destroyed by trawlers when they were first discovered in the 1990s. The deep reefs off Miami where liveried grouper once held court in palaces of coral are now mostly rubble, their trawled ruins inhabited by tiny fish and worms. At some level these losses discomfort every one of us. But the disintegration of untamed nature reaches beyond aesthetics. It is undermining the ability of the oceans to sustain human needs and well-being.
CHAPTER 15
Ecosystems at Your Service
To people who allege that we
Incline to overrate the sea
I answer, “We do not;
Apart from being colored blue,
It has its uses not a few;
I cannot think what we should do
If ever ‘the deep did rot.’”
—Sir Owen Seaman, 1861–19361
My graduate student Ruth Thurstan spent the summer of 2010 sampling seabed sediments around Britain, wrestling with coring equipment and a sometimes restive team who didn’t share her enthusiasm for 5:00 A.M. starts. They pounded coring tubes into the bottom, raising clouds of mud that thickened as they worked until they had to communicate by touch alone. Once the cores were removed, she split them from top to bottom, and half went to be dated using radioisotopes while she spent the next six months sifting fragments of shell, spine, and test from the other half. These remains help trace the transformation of the bottom from an exuberance of oysters, horse mussels, and clams to silty scarcity. The change happened when trawlers and dredgers scraped the bottom clean in pursuit of fish and oysters. They sundered the layer of invertebrate life that once crusted the bottoms of estuaries and great expanses of continental shelves. Over years, decades, and centuries, the trawlers pulverized and buried creatures that once enlivened the seabed. Ironically, oysters introduced to Europe from North America to replenish exhausted beds set loose a disease that wiped out the remaining natives.
British fishers immediately regretted the loss of the invertebrate crust over the bottom, because it destroyed their source of bait for longline fisheries for cod, haddock, turbot, and the like. Some also saw that it would undermine the productivity of the fishing itself, since a breakdown in habitat would compromise living conditions. The British surgeon and naturalist John Bellamy predicted as much in 1843:
[T]he employment of the Trawl, however, during a long series of years, must assuredly act with the greatest prejudice toward these [fishy] races. Dragged along with force over considerable areas of marine bottom, it tears away promiscuously, hosts of the inferior beings there resident, besides bringing destruction on multitudes of smaller fishes, the whole of which, be it observed, are the appointed diet of those edible species sought after as human food.… An interference with the economical arrangement of Creation, of such magnitude, and of such long duration, will hereafter bring its fruits in a perceptible diminution of those articles of consumption for which we at present seem to have so great necessity.
Like all good Victorians, Bellamy continued in poetic vein,
[W]e might suppose the species thus injured by an abstraction of their food, to utter some such expressions as the following:
Nay, take my life, and all, pardon not that:
You take my house, when you do take the prop
That doth sustain my house; you take my life,
When you do take the means whereby I live.2
Bellamy’s warning and those of many less poetic scientists after him went unheeded, and the trawlers obliterated habitats formed over thousands of years, not just around Britain but around the world. More than 150 years later, Bellamy’s prediction has been proved true. A study of fish on southwest British trawling grounds showed that several species are skinny and stunted compared to those in less trawled areas, because they cannot find enough food.3 Had there been any places left that trawlers had not worked over, the contrast would have been more obvious still. Productivity has fallen not just as a result of direct removal of the plants and animals, but because simple habitats offer fewer living spaces and sustain less life than complex ones. The citadels and piazzas, avenues and apartments of these underwater worlds have crumbled, and their flattening, not just by trawlers and dredges but by the panoply of stresses I have described, has left room for only a fraction of their former inhabitants.
European seas are far less productive than they once were. The fact that the UK bottom trawl fleet lands only half the fish today that it did when records began in 1889, despite a massive increase in fishing power, says all we need to know about how we have squandered natural capital.4 People in wealthy nations have so far been sheltered from the impacts of overexploitation. They are rich enough to buy fish from parts of the world where there are still some to be caught. But when fish stocks collapse in the developing world, desperation follows. Nowhere has this been more potently illustrated than in the Philippines. This country should be the world’s underwater wonderland. It lies at the heart of the most diverse sea on the planet, one crammed full of a dazzling variety of fish, coral, and almost every other form of life. Filipinos have lived by and from the sea for thousands of years. They depend on it, getting some 70 percent of their animal protein from seafood. In recent years, though, their explosive population growth has upped demand far beyond the capacity of the sea to supply. The result is a cycle of overfishing that has become ever more frantic with each passing year; the most extreme manifestation in the world has got to be the practice of pa-aling.
When times were better, Filipinos fished using traditional methods, such as traps, nets, hooks, and spears. A day’s fishing would easily supply a family’s needs and leave extra to sell. In a familiar pattern, as stocks declined, people devised ways to maintain catches by upping the power of these simple methods. The process of escalation eventually led them to invent pa-aling—or drive-net fishing—in which a team of men and boys suffers extreme peril at the limits of human endurance for a few bucketfuls of fish. When reefs have been emptied of life in the shallows, there is nowhere to go but down.
A team of ten or fifteen men and boys will dive down as far as 100 feet, or 130 feet, with a huge ball of net, breathing diesel-tainted air through a length of garden hose supplied from a compressor onboard a boat. Meanwhile, another team on the boat struggles to keep the engine going and all the hoses from turning into a lethal tangle. Underwater, the fishermen unfurl the net into a dome the size of a village church. It is weighed down at the sides and one end with rocks and buoyed at the top with air-filled plastic bottles. The dénouement comes after a break at the surface, as the team swims along the bottom with a scare line to drive fish into the net, trampling and bashing the bottom with rocks in their advance. One drive can clear a place of half its fish and leave the reef in tatters.
The human cost of pa-aling is brutal: Divers frequently far exceed safe diving times and are stricken by agonizing bends that can paralyze or kill. Others drown when they are tangled in the net or air supplies are cut off. Captains often exploit child labor in their pursuit of the last fish. This is the last gasp of overfishing. When the fish have been taken from these depths there will be none left within reach of divers. The Philippines should have the world’s most spectacular coral reefs. Instead, it serves as a dreadful warning.
The world is living on borrowed time. We can’t cheat nature by taking more than is produced indefinitely, no matter how fervently politicians or captains of industry might wish it. Rich nations can outsource production to poor ones, but at some point fish stocks will collapse there too, and then there will be no fish to be had at any price. In essence, what we have done in the last few decades is to mine fish, bringing them in at rates faster than they can replace themselves. Sharks, bluefin tuna, cod, Chilean sea bass—all have declined steeply as a result of excessive fishing. The price that must be paid for today’s rapaciousness will be tomorrow’s scarcity or, in some places, seas without fish. If we follow the trajectories of loss seen today, that point may be only forty or fifty years away. Fishermen and -women of the future will have a tough time keeping their nets full.
Nature has survived planetary upheavals many times before, and life will survive this one. Natural selection is a powerful force. It has brought us life in all its wonderful guises and leaves us in breathless admiration at how such exquisite adaptations as the eye, or the color-shifting skin of a squid, or our self-aware brain could have come about. Life is endlessly adaptable and can eke an existence in some of the most hostile environments on Earth, like superheated hydrothermal vents under extreme pressure in the complete darkness of the deep sea. The planet has remained habitable for over four billion years; life has endured through times when the oceans turned more acid, when the atmosphere choked on carbon dioxide and methane, when the continents coalesced into parched desert, and when ice ages froze the sea.
But timescale is everything. A starving person will not be spared by the prospect of plentiful food three years hence. His needs must be met now. Evolution can take a very long time. It works in the currencies of life and death, and the ticking hand of evolution’s clock counts out time in generations. Each generation gives forth its young to face the vicissitudes of life. As Charles Darwin deduced, those best suited to the conditions prevail to give birth to their own young, who in turn share some of the characteristics that favored their parents. So it is that species can adapt to changing conditions over periods of many generations.
Human stresses on the environment exert potent selective pressure on living organisms, winnowing those less able to cope. The hand of evolution can already be seen in the emergence of slower growth and smaller size at maturity in exploited fish, for example. The trouble is, we are changing the environment at such a breakneck pace it will far exceed most species’ ability to evolve adaptations quickly enough. For an animal like a whale, deep-sea fish, or reef coral, whose generations can span decades, there is too little time. Microbes, and many phytoplankton and zooplankton, will produce generations in hours, days, or weeks. There is plenty of scope for them to evolve their way out of trouble. But evolution imposes constraints too. The loss of coral reefs for long stretches of geological history suggests that it isn’t easy to find a way to precipitate solid carbonate from seawater when acidity gets too high. So there is probably no get-out-of-jail card to be had here.
Animals, plants, and microbes do everything they can to survive. When conditions turn, they adopt all kinds of strategies to persist, like switching to different foods, going deeper to find cooler water, or discovering pockets of favorable habitat in otherwise hostile terrain. We can draw comfort from the fact that life has been through many crises before. Pretty much everything alive on Earth today made it through the deglaciation that happened from about twenty thousand years to ten thousand years ago. This transition saw the world warm several degrees and included rapid shifts in conditions that would have tested the hardiest. Life has experienced some twenty glacial cycles in the last two million years, so it is well versed in the business of tracking environmental change, and ecosystems have undergon
e many reassortments of their component species.
Financial products these days always include a caveat in the small print below their headline claims of amazing returns: “Past performance is not necessarily a guide to future performance.” There is an important difference between those past climate swings and the present day: us. Species didn’t have to cope with the multitude of stresses they face today. We really are sailing into the unknown.
We are beginning to count the human cost of altered oceans in currencies other than food. In the far distant past, when Roman emperors ruled and North America was a patchwork of tribal territories, estuaries and coastal seas were clearer and bluer than they are today. In estuaries like America’s Chesapeake Bay, where oyster reefs lined channels and inlets, they could strain the entire volume of water in a few days, a rate that has fallen a hundredfold today with the decline of these shellfish. Species on the seabed of open coasts did much the same. The massed ranks of mollusk, sponge, and coral drew nutrients and mud from the water and locked them away in shell and sediment. We need them more than ever today to help deal with the wastes that pour from our industries and towns, streets, and fields.
In Seattle, coastal residents have suffered growing discomfort and health problems since the 1980s, due to heaps of sea lettuce rotting on their beaches. The lettuce produces the toxic gas hydrogen sulfide that wafts from the beach to cause eyes to stream, sore throats, and in some cases breathing difficulties. It may be significant that hospitalizations from asthma in Washington State are higher than the U.S. average and have increased in the past decade.5 However, it still isn’t possible to disentangle trends in ocean pollution from increasing traffic pollution or poverty as causes. The seaweed problem is due to nutrients from sewage outfalls and lawn fertilizer washed from the city’s gardens into Puget Sound. You may want to think twice next spring before liberally fertilizing your lawn. Similar problems are popping up in other parts of the world. Residents in the Western Australian town of Busselton saw their beach transform from one of the best in the country to an “environmental nightmare” within the space of a decade, as heaps of rotting seaweed piled up.
The Ocean of Life Page 25
