Slower ship speeds have also been prompted by a growing awareness of the greenhouse gas emissions of the global fleet. The biggest ships emit more carbon dioxide pollution than the world’s smallest countries, and collectively, the world’s merchant fleet releases about 4.5 percent of global carbon dioxide pollution. Critics argue that speeds will rise again as soon as the price of oil goes down, but there are ways to reduce both noise and fuel emissions through better design. The military has developed propellers that minimize cavitation at high speeds to make ships harder to detect, and cruise ships have also found ways to minimize noise. There is no reason why the merchant fleet shouldn’t adopt similar designs, and many ships could be retrofitted. Ships could also reduce the need for noisy engines and fuel by using kites or skysails to catch the wind, which has the added benefit of being free.
The world’s shipping fleet is governed by the International Maritime Organization, which has overseen a huge improvement in the safety of oil shipments over the last forty years. Oil spillage has fallen considerably as a result of the imposition of double hulls, the compartmentalization of oil in the hold, pinpoint satellite navigation, and a raft of better sailing practices. It is high time for them to tackle the twin problems of noise and fuel efficiency.
CHAPTER 12
Aliens, Invaders, and the Homogenization of Life
Charles Darwin and Alfred Russel Wallace discovered the principles of evolution by natural selection around the same time, each working entirely alone, by obsessing over patterns in the distribution of species. As both of these astute naturalists traveled the world they noticed that some species came and went, while the characteristics of others changed from place to place. Eventually it became clear to them that species were not fixed by some godly act of creation. Rather, life’s forms were constantly reworked by evolution. It is Darwin we celebrate for this theory, but it was Wallace who spurred him to publish it when he later came upon the same idea. Geographic history has left some places with more species than others, and some with more unique species. Other places, by virtue of environmental stress, isolation, or lack of habitat are less rich.
The geographic ranges of species are circumscribed by many factors, most notably physical barriers such as landmasses, currents, or insurmountable gaps in suitable habitat, like ocean basins. When natural barriers divide regions, as the Isthmus of Panama did when it separated the Atlantic from the Pacific three and a half million years ago, evolution may take life in different directions.1 Over great stretches of time new species arise and others go extinct. Some natural barriers to the dispersal of species rise or fall slowly, others more quickly in relative terms, like shifts in current patterns or the appearance of a new island from a volcano under the sea.
Humankind has lowered or entirely removed these barriers. For the last several thousand years, but especially during the last several hundred, we have made long-distance voyages with animal and plant passengers in our cargo and attached to our ships’ hulls or carried in ballast. These journeys opened up new areas for colonization. The distances species could be carried underwent a steep change in the fifteenth and sixteenth centuries as the voyages of Dias, da Gama, Magellan, Columbus, and others began the age of global exploration by sea. When Columbus sailed to America he unwittingly took a bunch of freeloaders with him. Early Arab and Chinese voyages would also have carried species long distances in the Indian and Pacific Oceans.
Getting there is only the first hurdle for a would-be colonist. Conditions must be right for survival, and a sufficient concentration of colonists have to be introduced to establish a self-sustaining foothold in the new territory. In centuries past, ships often anchored or tied up for many weeks at a time on foreign shores (as opposed to only for hours or days today), allowing ample time for attached fouling organisms to shed eggs and larvae. In addition, vessels had their bottoms scraped every few months to keep them clean, and countless such voyagers would find themselves marooned in alien waters. Plants and animals could also be carried from place to place in water that sloshed around the ships’ bilges or attached to rocks used as ballast to increase the draft of lightly laden ships. Sailors carried rocks together with their hitchhikers from the Old World to the New, only to dump them on arrival to load cargo. The genes of introduced periwinkles and serrated wrack seaweeds in Nova Scotia give away origins in Scotland and Ireland, from which most of the ship traffic arrived.2 Ballast became an even more significant means of emigration from the late nineteenth century onward, as large vessels began to take in water as ballast in one port and discharge it in another. Ballast water now ranks as the foremost means by which marine species are introduced to new environments. Many marine organisms begin their lives as tiny eggs or larvae that can be transported in ballast. Even big animals can get around in ballast—fish a foot long have been found in ballast tanks.
We call displaced species alien or nonindigenous to distinguish them from the natives. Some become troublemakers. These “invasive” species run wild, freed from the control of their natural predators, parasites, and competitors in their native haunts. Invasive species are like nature on steroids. They often multiply with extraordinary rapidity and overconsume or outcompete indigenous species for space, food, and other vital resources. The results can devastate ecosystems. Such invaders can eradicate local species and reduce other once dominant life-forms to the role of bit players. One such invasion, underway in the Caribbean right now, will change reef life there forever.
Red lionfish are natives of the tropical western Pacific and are popular aquarium fish. They have broad pectoral and dorsal fins that they hold open like delicately patterned Chinese fans. Their beguiling beauty is deceptive, for they are ruthless predators. They use their fins to usher small fish, ever so gently, into awkward corners of the reef, where they dispatch them with mouths that expand in an instant to engulf their prey. Enough lionfish were released or escaped from aquaria in the late twentieth century in south Florida that a breeding population became established.3 Consequently lionfish have few Caribbean predators. Their lacy fins conceal sharp spines that deliver a potent shot of venom to the unwary. The Caribbean was poised for invasion.
Early this century, surprised divers began to report sightings of lionfish off the coast of North Carolina. Reports followed from the Bahamas, Turks and Caicos, and Bermuda. The Caribbean has not seen anything like the lionfish for millions of years, if ever. Never having encountered such a belligerent and aggressively defended predator, the local fish don’t know what to make of them and show little fear. Lionfish are slurping them up by the millions. Indeed, speared lionfish have been brought up with their bellies packed so tightly they seem scarcely able to move. With food so easy to come by, these lionfish are growing faster and larger than they do in their native range, and with their populations increasing exponentially, they are laying waste to Caribbean reef fishes.4
Lionfish have exploded across the Caribbean in less than twenty years. They can now be found from Rhode Island south to Colombia, and from Belize east to the Windward Islands, and may ultimately range along the entire coast of Brazil. Although divers and conservationists soon rallied to challenge the threat, their efforts are futile, except for divers keeping the invader off specific reefs by means of frequent removals. Lionfish are there to stay. Mark Hixon, a biologist at Oregon State University who has studied the lionfish in the Bahamas and the Caymans, thinks “this could well become the most devastating marine invasion in history.”5 Although lionfish are not large—the record-size invader was just seventeen inches—they target small fish and invertebrates that include the young of large species. Such animals are not only valuable as food for people, like groupers and snappers, but also provide important ecological services, such as parrotfish that graze seaweeds that would otherwise overgrow corals. Imagine if some predatory beast invaded America and began to slay millions of birds, to snatch dogs in parks off their leads, and to indiscriminately kill cats from the backyard and possums and deer from
the country. To imagine this is to think of what life has become on Caribbean reefs. The lionfish are particularly ruthless, but they are only one of many pernicious invasive species that have begun to cause mayhem in marine ecosystems. One small window of hope may be that lionfish are becoming popular menu items in restaurants in the United States and the Caribbean, but whether harvesting this edible fish will suffice for control remains to be seen.
Ships have long been the most convenient route to a new home. At the last count over fifty thousand vessels grind their way around the world carrying goods.6 They move about three cubic miles of ballast water from place to place every year, and at any moment some ten thousand species are thought to be in transit.7 Being slopped around inside the dark belly of a ship, where temperatures can swing widely and food is at a premium, is not the surest way to survive a long journey. But it does select for the most tenacious and resilient, characteristics that serve alien species well in new places. Estuaries, which support many of the largest ports, have become hot spots for invasions from which animals and plants may spread like plague. Chinese mitten crabs and Japanese seaweeds are invading European and North American seas, while Asian kelp is spreading in California. In Germany’s Elbe River, where mitten crabs have been established for a century, at certain times of the year writhing legions of crabs swarm downriver like a locust plague on their way to spawn. A West Atlantic comb jelly called Mnemiopsis devastated planktonic life and fisheries in the Black Sea after it invaded in the 1980s, and has now reached the Mediterranean, Baltic, and North seas.8 European green crabs are crunching their way through naïve intertidal natives on North America’s West Coast and along the shores of Japan, South Africa, and Argentina. Throughout North America dense stands of phragmites reeds have begun to block coastal views and choke out native wetland plants. Intriguingly, the reed is native to North America, so scientists were puzzled as to why it had turned bad. Genetic analysis gave them their answer.9 A variety introduced from Europe is causing the nuisance, and in New England has entirely replaced the native variety.
San Francisco Bay is one of the most invaded ports in the world.10 Over the last 140 years, nearly three hundred alien species have settled in the bay and its rivers,11 and the rate of arrival has increased. From 1851 to 1960, a new species arrived just over once a year on average, but between 1961 and 1995 there was a new arrival every fourteen weeks. These new species have transformed the bay, much as San Francisco itself has become a cultural cornucopia. Hardly any corner has less than a third of its species count made up of aliens, and in many places they have complete control, having ousted all the natives. Atlantic smooth cordgrass has formed dense stands over areas of open mud that once were rich feeding grounds for birds. Beneath the tranquil surface three kinds of gribbles, tiny isopod crustaceans related to woodlice, are busy boring their way through wooden docks and pilings. In Seattle they have inflicted $700 million worth of damage.12 Clam diggers around San Francisco Bay are now much more likely to unearth Asian clams than native. So enthusiastic is the feeding of these clams, they are sucking the water clean of plankton, which could deprive other species of essential food and cause declines of animals whose eggs and larvae drift in bay waters.
The rise in ship traffic is part of the reason why San Francisco has been so comprehensively invaded, but there are other ways to get from place to place. Aquaculture, the farming of marine life for our consumption, is a major source. Rather than farm local species, we like to move the fish and shellfish around that we enjoy most and are best able to raise. In the 1800s, vast numbers of eastern oysters were transplanted from the Atlantic to the Pacific coast of North America, and the same happened in the 1900s with Japanese oysters. Atlantic salmon are grown along cool stretches of the Pacific coast of North and South America. East Coast oysters are cultured on the West Coast. California’s red abalone is raised in Chile. But it isn’t just the cultured species themselves that get moved: Along with the oysters came scores of unwanted hitchhikers, many of which are now abundant in San Francisco Bay. Fish feeds can also bring unintended guests, and are often responsible for outbreaks of parasites and diseases that I will come to in the next chapter. The expansion of aquaculture across the globe has been extremely rapid and will continue, which means this is a problem that will run and run.
Marsh grasses, like the Atlantic smooth cordgrass, were introduced to San Francisco Bay intentionally by the U.S. Army Corps of Engineers to “restore” wetlands and prevent erosion. It was spectacularly successful, but now state officials want it out and have launched an eradication campaign. Perhaps as much as 6 percent of marine invasions worldwide have come from unintentional introductions from aquaria. After lionfish, the most notorious is a tropical seaweed, Caulerpa taxifolia, a dark green weed that scrambles over the seabed in mats of twisted stems and has been dubbed the “killer algae.”13 Caulerpa doesn’t normally grow in cool places like the Mediterranean. But keepers at the Monaco Aquarium14 heard of a strain that German aquarists discovered could survive in similar conditions, and they imported it for their own tanks. Caulerpa escaped into the Ligurian Sea almost immediately, through discharge pipes from the circulating seawater system.
In 1984, divers noticed a patch of a strange new weed smaller than a tablecloth growing wild.15 Curiously, it was not removed. Five years later it covered a couple of acres of seabed. Ten years after its release people knew they had a serious problem. Six square miles of the bottom were blanketed in the weed, which blocked the light and suffocated all beneath. Where meadows of sea grass once waved in sunlight, now there was only Caulerpa, like a cancerous growth. And like cancer, this invasion soon metastasized. Fishing boats picked up the weed in their nets and pleasure craft snagged it in their anchors. Soon it flourished in hundreds of new places. Just fifteen years after its release, Caulerpa covered 97 percent of available surfaces between Toulon in France and Genoa in Italy, a distance of nearly two hundred miles. It isn’t over yet. Much more of the Mediterranean could soon fall victim to the blight. The alga has now secured bridgeheads in Spain, Italy, Croatia, and Tunisia.
Caulerpa racemosa is a related species from southwest Australia that is also highly invasive and has settled in the Mediterranean. It was first reported in 1990, and if anything is an even more vigorous competitor for light and space than its namesake. It even seems to be outcompeting it! Within six months of arrival this plant had gained complete dominance in some places, indiscriminately laying waste to sea grass beds, seaweeds, sponges, and all manner of other creatures that make a living attached to the bottom of the sea. Caulerpa racemosa has now spread from Cyprus to Spain, and beyond to the Canary Islands.
Like many invasive species, both these algae have far-reaching effects within the communities they have entered. In the space of decades their arrivals have brushed aside relationships formed among Mediterranean plants and animals over tens of thousands of years. Sea grass beds are rich in fish, crustaceans, starfish, urchins, and hundreds of other species that call them home or use these meadows for a time before moving on. Green turtles graze contentedly on the flexible green blades beneath shafts of light that dance and dapple over the lush pasture. They aren’t keen on Caulerpa. Most fish also fare badly where Caulerpa mats occlude the bottom. The hunters can no longer reach invertebrates living in the sand. Those that once sheltered among blades of grass have found their lives brought to a standstill as the thickets close around them, much as the palace and its dozing inhabitants were overgrown by a dense tangle of briar in the fairy tale “Sleeping Beauty.”
So what factors facilitate a successful invasion? The bad news is that many of the problems highlighted elsewhere in this book increase the chances that invaders will establish and make trouble. It turns out that where overexploitation or pollution have depleted local life, competition for space and other resources is less intense and invaders can establish a beachhead from which to spread. Some pollutants may also render conditions more amenable for invaders. Nutrient pollution in the B
lack Sea, for instance, is thought to have favored the establishment of the Mnemiopsis comb jelly. The simplification of marine ecosystems by multiple stresses opens up opportunities for invaders. And the creation of structures such as seawalls, rigs, and wind farms can facilitate the spread of invasive species that require hard bottoms across expanses of otherwise unfavorable habitat.
One of the great paradoxes of invasive species is that they can spring to life from just one or a handful of individuals, like a forest fire caught by a lone spark. Yet we struggle so hard to keep life’s spark alive when endangered species have been reduced to the last few dozen individuals. What makes invaders different is freedom, opportunity, and of course luck. We forget that some invasive species may have failed many times to settle successfully before they eventually do. We only see the winners. America drew settlers from all over the world as a land of freedom and opportunity, and still does. When a species is plucked from its homeland and thrust into a new world, it can find itself reborn, freed from the shackles of traditional enemies. The burden of disease and parasites may be lifted. Likewise, predators and competitors can be thin on the ground for a stranger. Life is good.
The contrast between old haunts and new can sometimes create conservation ironies. Sea lamprey invaded North America’s Great Lakes after a canal was opened around the natural barrier of Niagara Falls in 1919. These primitive fish are slippery, slim as eels, and mottled like leopards. They have a ring of conical teeth around a jawless mouth with which they attach to bigger animals. Lampreys rasp holes in the flesh of their hosts, leaving their flanks pocked with bleeding sores. So many now live in Lake Superior that there is hardly a big fish left that has not been attacked. For lamprey the Great Lakes have been one long lunch. Sea lamprey numbers back in their native Europe have plunged in the last half century, a decline usually blamed on poor water quality in the rivers where they spawn. But I suspect the real cause is loss by overfishing of the big animals they use as hosts while at sea. In Europe the sea lamprey is protected; in the Great Lakes it is vermin.
The Ocean of Life Page 20
