for National Geographic News
Invasive Australian jellyfish are appearing in large numbers this summer in waters off the southeastern United States.
The jellyfish are only mildly venomous and do not pose a threat to humans who may come in contact with them, experts say. (Related photo: "Giant Jellyfish Invade Japan" [January 19, 2006].)
But some commercial fishers and shrimp trawlers in the Gulf are finding their nets fouled with the gelatinous blobs, which may weigh up to 25 pounds (11 kilograms).
Interference with fishing operations can result in a reduced catch, said Monty Graham of the Dauphin Island Sea Lab and the University of South Alabama.
But an even greater concern for biologists and fisheries managers is that the invaders may harm native fish and other marine species.
The jellyfish feed on tiny fish larvae and may also compete with adult fish for other sources of food.
"We have good evidence that [jellyfish] can, at times, clear water of eggs and larvae of fishery species," Graham said. "The scale at which this occurs may or may not be large enough to force a reduction in [fish reproduction] over the entire range of the stock."
The same jellyfish species previously invaded Gulf waters in 2000, but had been seen only sporadically since then. Compared to 2000, Graham said, this year the jellyfish seem to be less numerous in any one place and are instead spread out across a far larger area.
"This is the first year we've heard about [jellyfish sightings] north of Florida," he said.
Reasons to Swarm
The Australian spotted jellyfish has been on the move for decades, appearing in numerous locations far from its native range in the South Pacific and Indian oceans.
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