ALL AT SEA - The New Wild: Why Invasive Species will be Natures Salvation - page 25

happen out of nothing. The Black Sea was a fetid haven for the blob. Europe's most polluted sea was a
blocked toilet bowl. It collected raw sewage from about 170 million people in thirteen countries, sewage
floating down from rivers such as the Danube and Dneiper. Its catchment extended from southern Ger-
many almost to Moscow, but it had only a tiny outlet into the Mediterranean through the half-mile-wide
straits of the Bosphorus. A full exchange of water with the Mediterranean took about a thousand years.
Because the sea could not flush itself clean, the poison built up. The sea's depths had long been devoid
of oxygen. But about fifty years ago, the anoxic waters reached the surface and spread across the sea's
large, shallow northwest shelf, which had previously been its most fertile zone.
The final straw that let in the blob was the death of huge beds of red Phyllophora algae on the north-
west shelf, according to Lawrence Mee, a Scottish marine biochemist who ran the UN's effort to save the
sea at the height of the blob's reign. “In the 1950s, these underwater meadows covered an area the size
of the Netherlands. They were the lungs of the Black Sea,” he said. They emitted oxygen and provided
nourishment and shelter for the sea's large stocks of anchovy, turbot, mackerel, flounder, and sturgeon.
“As the meadows died,” said Zaitsev, “there was a colossal death of bottom-dwelling organisms, such as
sponges, sea anemones, shrimps, and crabs, and a domino effect right through the marine ecosystem.” 4
Just like water hyacinth's invasions of Lake Victoria, the blob did not so much eat the Black Sea as
move in when the sea had died. A healthy sea would in all probability have fought off the invader.
That said, ships' ballast water certainly provides migrating species with an opportunity to cause mis-
chief. It is probably the most important means by which alien species spread around the world today.
There is a strong case for avoiding disruption by preventing discharges of ballast water containing or-
ganisms from distant waters. Most cargo ships and tankers need to add weight when empty, in order
to avoid capsizing. So they take on ballast, which they dump when they fill up with cargo. Once this
ballast was rocks or soil. Ships crossing the Atlantic routinely grabbed chunks of the geology of South
West England before they left. Days later, they deposited it—with Cornish plants, worms, and other or-
ganisms—onto the shorelines of the United States and Canada. But ever since the introduction of steel-
hulled ships in the late nineteenth century, seawater has been the ballast of choice.
We are talking about a lot of water. A large ship can carry sixty thousand metric tons of ballast, and
there are tens of thousands of vessels at sea. Altogether, an estimated seven billion metric tons of ballast
water is shipped around the world each year, and it is usually discharged into foreign coastal waters.
Often it is rich in seeds, spores, plankton, bacteria, and the eggs and larvae of larger creatures. Marine
biologists estimate that at any one time, the ballast water traveling the world's oceans contains seven
thousand species. Some of that biological cargo will be ready to take advantage of whatever ecosystems
they encounter on arrival.
Soon after the jellyfish from Maine made its fateful journey to the Black Sea in the early 1980s, the
Central Asian zebra mussel ( Dreissena polymorpha ) hitched a ride in the opposite direction. It ended
up discharged into the Great Lakes. Around a decade later, an unknown ship, probably from the Bay of
Bengal, discharged ballast water into the coastal waters of Peru. That water contained a strain of cholera
that was absorbed by local shellfish. People ate the shellfish, and the disease spread in excrement and
waterways, killing twelve thousand people across Latin America in the succeeding months. 5
Ballast water often delivers dinoflagellates, forms of algae that cause toxic “red tides” in polluted
waters round the globe. It is how Chinese mitten crabs reached Europe, how Asian kelp made it to
Southern Australia, and how Mediterranean mussels came to carpet the coast of South Africa. It is also
the biggest reason why the Mediterranean itself, the world's busiest sea, contains an estimated nine hun-
dred marine species that biologists regard as alien. A new one arrives every nine days, according to the