Castaways of the Millennium
By Jean-Michel Cousteaum
Introduced species, exotics, bioinvaders-these terms all refer to the same major phenomenon: organisms on the move from one place to another.
Species have always moved around, but today they are moving in unprecedented numbers and with unprecedented speed. And the main reason is us.
Humans have always had stowaways, hitchhikers and tagalongs. Bacteria, viruses, insects, pets, livestock-once you begin counting, it becomes obvious that we are biological transport mechanisms par excellence. Once we began taking to the sea in ships, we extended the reach and rapidity of our services. And today, as we criss-cross the globe, so do our guests.
For millennia, oceans have been conduits of commodities and culture. Today, they are also highways of biological invasion. The ballast tanks of ships are staterooms for invaders ranging from toxic organisms such as dinoflagellates to pathogens such as cholera. Each year 10 billion tons of ballast water is taken on and dumped. Each tankful is an important link in the global "economy" of invasion.
Most exotics fail to thrive in their new homes. And some of those that do thrive are good neighbors. But by one estimate, a full 10 percent are able to affect the functioning of entire ecosystems. Historically, introduced species have their most spectacular impact on islands-isolated ecosystems without large predators where endemic plants and animals are especially vulnerable.
In Hawaii, the world's most isolated archipelago, 50 bird and 17 mammal species have been introduced since 1780. Today, 26 of the islands' 71 native birds are now extinct, and another 31 are endangered. The same goes for plants. During the past several hundred years, 4,600 plants have been added to the nearly 2,000 endemics. Today, more than 200 native plants are extinct.
In the Galapagos, introduced mammals such as the brown rat have decimated young tortoises and native rodents. Nearly 200,000 goats alter entire plant communities, while thousands of pigs, cats and dogs ravage the nests of tortoises, turtles and nesting birds, as well as lizards and iguanas. Some came eons ago, with the Polynesians, or later with the whalers. And some are coming today, either in ships, on dredges, in airplanes, on clothing. But the negative effects are no longer restricted to islands, they are everywhere:
Red Sea jellyfish introduced via the Suez Canal have damaged fisheries and tourism in the Eastern Mediterranean.
- Black Sea fisheries have been decimated by ctenophores from the West Atlantic.
- San Francisco Bay hosts some 200 exotics, introduced by ballast dumping, at the rate of one every 12 weeks.
Are aliens inherently evil? No. Like humans who no longer inhabit the African savannah from which their ancestors emerged, nearly all species alive today are aliens, having moved around in search of food and favorable climate. But this awareness should not be an excuse for complacency in light of today's very real crisis.
Bioinvasion is now considered among the most significant threats
to biodiversity. And less diversity means less stability in the system of life on Earth.
But, even given our mobile lifestyle, we can do things to reduce the flow of organisms. The Convention on Biodiversity produced by the Earth Summit in Rio commits governments to reducing the spread of alien species. And some nations have been very active-New Zealand now bans the imports of all species that are not known to be benign.
The International Maritime Organization (IMO) is developing new regulations for the management of ballast water. Later this year, the IMO expects to implement these regulations.
The IMO is also exploring ways to keep toxic marine organisms from spreading. Besides dumping ballast in the deep ocean, which it considers less biologically sensitive, the organization is also working on various techniques for neutralizing these organisms en route. These include filtration, heat treatment, chemical additives and even irradiation.
Clearly, some of these cures may turn out to be worse for the environment than the sickness they aim to combat. But the effort is a big step in the right direction.
Even as individuals, we can have a positive impact. As planners and developers, we can conserve fragile or disrupted areas known to be more susceptible to invasion. As recreationists we can stop practices such as the stocking of lakes and streams with sport fish, which can disrupt entire food webs. As consumers, we can be more prudent and stop buying exotic nursery plants that are known to displace natives. And as responsible citizens, we should question the lifestyle choices that drive the introduction of species. We must begin to be accountable for the impacts of global trade. Trade is an important engine of prosperity, but as a contributor to biological invasion, it can undercut prosperity in the long term. So, where possible, we should choose products and services of local or regional origin.
Introduced species are the castaways of the millennium. Transported to distant shores by human negligence, they have become a challenge to human ingenuity.