SAN FRANCISCO--A jellyfish invasion might sound like the plot of a bad movie banished to late night TV. But the pulsing, tentacled predators were a star attraction at the Second Symposium on Marine Conservation Biology here earlier this week. Jellyfish populations appear to be exploding in several parts of the world, U.S. and Russian scientists reported, raising fears that they are taking over ecosystems that nurture key commercial fish stocks. It's often unclear whether the blooms are unusual or just natural population fluctuations, says Claudia Mills, a jellyfish expert at the University of Washington's marine laboratory in Friday Harbor.
In the Bering Sea off Alaska, the population of Chrysaora melanaster has jumped at least 10-fold over the past decade, reaching record numbers last year, reported biologist Richard Brodeur of the National Marine Fisheries Service in Newport, Oregon. Brodeur suspects long-term climate shifts may explain the increase. But whatever the cause, the huge summer blooms could deliver a two-fisted punch to the Bering's fish stocks, which account for 5% of the world's catch. Not only do the 2-meter-long jellyfish compete for food with young pollack--one of the Bering's most valuable fish--but they also eat them.
In the Gulf of Mexico, a foreign jellyfish produced a huge bloom off Alabama's coastline last summer, reported Monty Graham of the state's Sea Lab on Dauphin Island. Native to the tropical Pacific, Phyllorhiza punctata apparently drifted in from the Caribbean. Now, Graham and colleagues are waiting to see whether the species becomes a permanent resident, perhaps encouraged by declining coastal water quality and a growing thicket of offshore oil drilling platforms, which may provide the perfect hard substrate for a bottom-dwelling life stage.
Russian scientists, meanwhile, are keeping a close eye on booming Black Sea jellyfish, which may be implicated in the falling anchovy catches of the past several decades. Tamara Shiganova of the Russian Academy of Sciences noted that two species--one apparently native and the other introduced from the western Atlantic--now appear in often alternating blooms, vacuuming up the plankton that feeds young fish. The Atlantic invader, Mnemiopsis leidyi, may soon get its comeuppance, however, as yet another exotic jellyfish has arrived--and it feasts on M. leidyi.
On the flip side, notes Mills, some jellyfish have disappeared with little notice from polluted coastal waters. Determining how such departures and arrivals influence complicated marine food webs will be difficult work, she says, involving laborious field surveys and careful counts of jellyfish stomach contents. And given their gelatinous, watery bodies and stinging tentacles, it may be a nasty job, she adds: "Jellyfish can be real unpleasant to handle."