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 coastwatch.noaa.gov/seanettles.

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.

"We want to estimate in real time where sea nettles are, and when," said Christopher Brown, the co-author who initiated the project. Brown is an oceanographer at the NOAA/National Environmental Satellite Data and Information Service, in Camp Springs, Maryland. "If you know the habitat for a species you should be able to predict where it occurs," Brown said.

For instance Orbimage, an earth imaging company, produces "Fish Finding Maps" by tracking sea surface temperatures from government weather satellites and plankton concentrations from a private satellite, OrbView-2.

Brown's team takes a similar approach to find jellyfish. Using a computer program, they plug in data like freshwater inflow into the bay, wind speed, and water levels and temperature at the mouth of the bay. The program generates a "habitat model" for the Chesapeake that predicts salinity and water temperature throughout the bay and its tributaries.

Salinity and temperature most influence the jellyfish population. The saltier the waters, the better for the jellies. Using the habitat model they estimate where the jellies are.

Brown's original research goal was to track toxic algae blooms. But studies lag on the blooms, which depend on a complex interplay of factors.

By contrast, researchers know more about sea nettles and their habitats, which made the creatures a good target for the first forecasting.

Satellites can pinpoint some algae blooms but not necessarily determine the species that cause them. Often, people discover an outbreak by stumbling upon a fish kill.

The worst algae blooms wreak havoc on the fishing industry and on recreation along the coasts. Toxins can accumulate in fish and shellfish—and sicken the people who eat them.

The number of blooms is growing as a result, experts believe, of nutrients and fertilizers in farm and sewage run-off.

"A model that could predict the occurrence of harmful blooms could target our monitoring," said Robert Magnien, director of the Tidewater Ecosystem Assessment of the Maryland Department of Natural Resources.

Predicting blooms would allow time to post warnings and curtail fishing. Eventually researchers hope to control the conditions that cause the blooms.

"Nowcasts" on the Chesapeake are a step toward safer waters everywhere.

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