ALL AT SEA - The New Wild: Why Invasive Species will be Natures Salvation - page 24

CHAPTER 3
ALL AT SEA
They called it the blob that ate the Black Sea. Sometime in 1982, a previously harmless New England
jellyfish—a plankton-grazer the size of your hand, known to marine biologists as Mnemiopsis
leidyi— got into the ballast tanks of a ship delivering cargo to the US East Coast. A few weeks later, the
jellyfish was discharged into the Black Sea, probably near the Ukrainian port of Odessa.
Sometimes a newcomer strikes it lucky. For a while, the tentacled, translucent jellyfish lurked un-
remarked, but in 1988 it went on maneuvers. Mnemiopsis leidyi may not sting, but it packs a punch. A
self-fertilizing hermaphrodite, it bred as quickly as it ate, reaching maturity within two weeks and pro-
ducing eight thousand eggs a day. With no predators around to eat those eggs, its rate of reproduction
was staggering. It found a ready food supply and began munching its way through the sea's plankton,
crustaceans, and the eggs and larvae of local fish. 1
Soon its gelatinous mass was breaking records. A snorkeling marine biologist from Ukraine, Yu
Zaitsev, counted five hundred of the blobs floating in a single cubic meter of water in Odessa Bay. That
meant almost more jellyfish than water. It was clogging fishing nets. Before long it was the only thing
caught in the nets. Nothing could live with it, especially not the local jellyfish, Aurelia aurita . Catches
of anchovy, mackerel, and other fish crashed. Dolphins disappeared. By 1990, biologists estimated the
total weight of the jellyfish in the Black Sea at nine hundred million metric tons. If true, that was 95
percent of the animal biomass in the sea and equal to ten times the annual fish catch in all the world's
oceans. 2
It couldn't last. With little left to eat, Mnemiopsis began to go hungry. And before too long, its
nemesis showed up. Another shipload of ballast water dumped into the sea in 1997 brought another
American jellyfish, Beroe ovate , which eats nothing but its cousin. Since then, Mnemiopsis has been in
modest decline in the Black Sea, reaching an uneasy balance with its food supply and the new predator,
but it had already started moving on. In 1996, fishers from Turkmenistan reported finding strange jelly-
fish in their nets in the Caspian Sea. Mnemiopsis had hitched a ride aboard ships traveling the Volga-Don
Shipping Canal between the two seas. By 2000, its insatiable appetite had cut fish stocks in the Caspian
by more than 50 percent, outcompeting local seals and beluga sturgeon for a local delicacy, the kilka
fish. Since 2006, Mnemiopsis has turned up, less problematically so far, in the North and Baltic Seas.
And it is spreading through the eastern Mediterranean, clogging the intake pipes of Israeli desalination
plants. 3 The blob is not done yet.
That is the conventional story. As on land, when we are looking at the spread of alien species at
sea the temptation to demonize them is strong. But this usually ignores the context—the way our own
activities typically pave the way for the invader. Blaming a chance arrival in American ballast water for
the collapse of Black Sea fisheries may be convenient, but it is not good enough. Such invasions do not