Scientists anticipate big summer jellyfish season

Submitted by Amy Pelsinsky on Thu, 06/21/2012 - 2:16pm
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Jellyfish are not only showing up early in the Chesapeake Bay this summer, but their population is likely to be noticeable.

"The conditions are right to have a large population," said Maggie Sexton of the University of Maryland Center for Environmental Science. "But that's no guarantee."

The first jellyfish spotted this season.

Each day she does a jellyfish count from a dock in the Choptank River near Cambridge, Maryland.

"We saw the first one two weeks ago, and now we're starting to see one every day," she said. "In couple of weeks to a month, we expect to see a lot more."

June 24 is the median occurrence time for the jellyfish to arrive, but they arrived this year on June 7.

"This spring has been much warmer than average, and one of things that wakes up the polyps in the springtime is the warmth," Sexton said. 

Sexton has studied jellyfish as a graduate student with Professor Raleigh Hood at the Horn Point Laboratory. Today, she is Maryland's jellyfish expert.

"Her work has changed our understanding of what controls their abundance and distribution," said Hood. "It turns out their abundance behaves more like an algae bloom."

Scientists used to think that if the water temperature (warm) and salinity (high) were in the right range, we could expect a large jellyfish population. But Sexton's work has shown there is one other very important factor -- initial conditions.

Jellyfish produce larvae that attach to the bottom of the Bay and turn into an anemone-like polyp. In the springtime, warm temperatures combined with saltier water trigger the polyps to "bud off" tiny sea nettles that rapidly grow into tentacled adults, or medusae. If initial conditions occur at the right time, the result is a large bloom.

"Last year we had really low salinity at the beginning of the year. The salinity was so low that the polyps never really got going. We saw a few, but not a lot of them," said Sexton. "This year I would guess that we'll see more."

There has been a decline in jellyfish abundance over the last 50 years, but their presence in the Bay does have some benefit. Sea nettles help keep balance in the food chain by eating comb jellies, which are voracious consumers of fish and oyster larvae--important food for the Chesapeake's fish.

"If nettles can knock down the comb jelly population, they give a lot of fish a greater shot at survival," Sexton said.

--Amy Pelsinsky

CHECK OUT THE JELLYCAM STREAMING LIVE FROM THE CHOPTANK RIVER HERE.

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