Late last year, a flotilla of fluorescent jellyfish covering 16 sq km of ocean was borne by the tide into a small bay on the Irish Sea. These mauve stingers, venomous glow-in-the-dark plankton native to the Mediterranean, slipped through the mesh of aquaculture nets, stinging the 120,000 fish in Northern Ireland's only salmon farm to death.

Closer to home, the Asian carp, which has been working its way north from the Mississippi Delta since the 1990s, is now on the verge of reaching the Great Lakes.

This voracious invader, which weighs up to 45 kg and eats half its body weight in food in a day, has gained notoriety for vaulting over boats and breaking the arms and noses of recreational anglers.

Having out-competed all native species, it now represents 95 percent of the biomass of fish in the Illinois River and has been sighted within 40 km of Lake Michigan. The only thing preventing this cold-water-loving species from infesting the Great Lakes, the largest body of fresh water in the world, is an electric barrier on the Chicago Sanitary and Ship Canal.

One of the great unsung epics of the modern era is the worldwide diaspora of marine invasive species. Rising water temperatures brought on by global warming have allowed mauve stingers and harmful algae to thrive far beyond their native habitats. Supertankers and cargo ships suck up millions of gallons of ballast water in distant estuaries and ferry jellyfish, cholera bacteria, seaweed, diatoms, clams, water fleas, shrimp and even good-sized fish halfway around the globe.

The first recorded case of species invasion dates to 1245, when Norse voyagers brought a soft-shelled clam to the shores of the North Sea on the sides of their wooden ships. What is new is the rate of introduction and the extent of impact - 80 percent of world trade is conducted by ship, and a new marine invader is now recorded in the Mediterranean every four weeks.

Zebra mussels have to be power-hosed from the intake pipes of Great Lakes electric companies, and sea squirts form dense colonies that smother the scallops and clams of Georges Bank. According to one estimate, invasive species in the United States cause major environmental damage and losses totaling about $137 billion per year.

There is an easy solution, however: If cargo ships were required to empty and refill their ballast tanks at sea, rather than in harbors and estuaries, marine invasions could be brought to a near standstill. Unfortunately changing ballast water at sea takes time - and time in the shipping industry is money. So far, ship owners the world over have blocked laws seeking to limit shipping's role in spreading bio-invaders.

In the absence of any concrete action by the shipping industry, I would like to make a modest proposal. To save our oceans and lakes from their apparently inexorable slide back to the Archaean Eon - when all that was moving on the face of the waters was primitive cyanobacteria - it is high time we developed a taste for invasive species.

Diners in Asia, where sesame-oil-drenched jellyfish salad has long been considered a delicious, wholesome dish, are way ahead of us.

The increased the amount of phosphorus and nitrogen in the waters off China reportedly created an ideal breeding ground for Nomura's jellyfish, a monstrous 200 kg creature that can tear apart fishing nets.

In the summer of 2005, a half-billion were estimated to be floating from the shores of China to the Sea of Japan every day, forming a ring of slime around the entire nation.

The citizens of Fukui, a northern Japanese island, coped by marketing souvenir cookies flavored with powdered jellyfish.

Returning from a fact-finding mission to China, a professor from Japan's National Fisheries University offered up 10 different recipes for preparing Nomura's jellyfish. "Making them a popular food," he told a Japanese newspaper, "is the best way to solve the problem".

Precisely. And if we want to forestall our looming carp quagmire, this is the kind of attitude we need to adopt on our shores. Sports fishermen are already doing their part by angling for the pests.

Restaurateurs from Tupelo to Toronto could pitch in by replacing the bland-fleshed channel catfish on their menus with equally bland-fleshed Asian carp. It seems only fair: it was catfish farmers in the South who imported the fish to filter algae from their ponds in the 1970s and allowed them to escape into the wild during the Mississippi floods of 1993.

For years now, fisheries scientists have been telling us that, for our own health and the health of the oceans, we need to start eating down the food chain - closer to the level of oysters than tuna. So, next time you are in the mood for seafood, ask the chef to whip you up a jambalaya of rapa whelks and Asian mitten crabs.

The New York Times

(China Daily February 21, 2008)