Online Jellyfish Forecast Warns Chesapeake Swimmers

Bijal P. Trivedi
National Geographic Today
July 22, 2002

Getting stung by a jellyfish is among summer's beach bummers. This summer, though, the sting may be less for swimmers in Chesapeake Bay, in Maryland and Virginia, the largest estuary on the United States' East Coast.

Regions of the Chesapeake Bay can be notorious hotbeds for the sea nettle, Chrysaora quinuecirrha—a jellyfish with a veil of transparent stinging tentacles.

Now researchers are tracking sea nettles in the Chesapeake and posting a "nowcast" map every Friday that shows the likelihood of close encounters.

The map is posted at

The National Oceanic and Atmospheric Administration (NOAA) and several universities are developing the jellyfish forecast. A report on the project appears in the July 30 issue of Eos, journal of the American Geophysical Union.

The researchers hope to use a similar technology to predict toxic algae blooms that increasingly menace the fishing industry and coastal communities worldwide. For example, red tides—toxic blooms of red and brown algae—have been reported recently along the coasts of the eastern U.S., China, South Africa, and the United Kingdom.

Though not as threatening as toxic algae, "the sea nettle can actually prevent swimming in much of the Chesapeake for the entire summer," said Raleigh Hood, a report co-author and biological oceanographer at the University of Maryland Center for Environmental Science, in Cambridge. "In some places you'd be hard-pressed to swim without hitting one," he added.

To protect themselves, some swimmers in the Chesapeake don wet suits or even pantyhose, noted Mary Beth Decker, a co-author and marine ecologist at Yale University.

In the Chesapeake's tributaries, when conditions are right, the waters are transformed into jellyfish soup, with about 16 jellies per square meter. "But even at lower densities, they are lurking around and they have very long tentacles," Decker said.

At high densities, sea nettles can cripple fish stocks by devouring the fish larvae and copepods—tiny crustaceans that serve as food for many other species.

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