ALL AT SEA - The New Wild: Why Invasive Species will be Natures Salvation - page 30

Birds do not always travel alone. They take with them in their feathers and gullets and feet, seeds
and insects and pathogens and much else. Some of these fellow travelers will hop off at the other end
and stay put. And where birds don't go, the weather may lend a helping hand. A surprising range of
smaller organisms like algae, pollen, fungi, and bacteria are routinely wafted into the air and travel with
the wind on long journeys.
In 2005, Ruprecht Jaenicke of the University of Mainz reported that up to a quarter of the dust
particles in the atmosphere are biological rather than geological in origin. 18 Some of those particles are
far from benign. The atmosphere, like the ocean, is rich in bacteria, and nobody knows how far they can
travel. 19 The winds have for hundreds of millions of years been a ready mode of long-range transport
for a range of nasty pathogens, says Gene Shinn, now of the University of South Florida in Tampa. He
discovered that outbreaks of coral diseases on the reefs of the Caribbean often coincide with dust storms
blowing in on trade winds from Africa. On a closer look, he found that during major dust storms in the
Sahara, 130 species of pathogens were blown into the air and wafted to the West Indies. He reckons that
tens of millions of metric tons of African dust settles on the Caribbean most years, and much more when
African droughts leave the soil bare. 20
Shinn has identified one West African culprit as a soil fungus called Aspergillus sydowii . It was first
spotted in the Caribbean in 1983 during an intense drought in Africa. It went on to kill 90 percent of the
region's sea fans, a form of soft coral. The same year saw a big decline in the number of Diadema sea
urchins, as well as infestations of algae on the reefs where the urchins normally graze. Some researchers
contest that the fungus came from Africa, but Shinn reckons other diseases have made the same journey.
Soybean rusts from Africa have crossed the Atlantic by means unknown and infected plants in the Un-
ited States. One might speculate that microbes picked up by dust storms in China's Gobi Desert cross
the Pacific too.
It seems likely that the occasional appearances in Europe of foot and mouth ( Aphthae epizooticae ),
a highly contagious viral disease that afflicts cloven-hoofed animals, may have a similar explanation.
The disease is rife in the Sahara region of Africa. In 2001, British government veterinarians slaughtered
ten million sheep and cattle, and large areas of the English countryside were cordoned off in an ulti-
mately successful effort to halt the disease's spread there. There was no proof, but Dale Griffin of the
US Geological Survey said at the time: “Satellite images show a dust cloud moving [from the Sahara]
over the Atlantic and reaching Britain on 13 February 2001. One week later, foot and mouth broke out
in the UK. Given that the disease's incubation period is seven days, that is one heck of a coincidence.” 21
This kind of talk can feed our paranoia about alien species. Security types have started researching
such outbreaks, fearful that bioterrorists might take nature's hint. 22 The US Department of Homeland
Security funds studies into microbes in the air. The aspergillus fungus implicated in killing Caribbean
soft coral also causes lung disease in humans. Epidemics of meningitis and asthma and several crop
diseases have all likely been spread by aerosols of living organisms. 23 The risks are real, but the wider
ecological lesson is that microbes have always been in the air. Nature has always been rearranging itself.
We may think of volcanic islands like Ascension as unusual because their recent origin and remote-
ness mean their ecosystems are made up of a motley crew of mariner migrants. But much of the world
is like that. Nature is constantly in flux, and few ecosystems go back very far. Only ten thousand years
ago, much of Europe and North America were covered in thick ice. All soil had been scraped away and
with it most forms of life. Everything we see today in these former glaciated zones has either returned
or arrived for the first time since the ice retreated.
Looked at from this perspective, the spread of alien species today is merely a continuation of a natur-
al process of the colonization begun when the ice retreated. A broad time horizon shows there is no such