NewsJune 7, 2011

Changing Jellyfish Season Could Alter Chesapeake Bay Food Chain

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Alyson Kenward

By Alyson Kenward

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First came hundreds of reports of jellyfish washing ashore in central Florida over the Memorial Day weekend. Since then, people have been spotting blooms of the gelatinous drifters off the coasts Connecticut, Virginia, and South Carolina, all earlier in the summer than expected.

The early appearance of jellyfish along the East Coast is more than just a nuisance for beachgoers. According to scientists, it’s a sign that coastal waters are warmer than usual for time of year, and recent studies suggest the early jellyfish blooms could upset the marine ecosystem in coastal areas, like Maryland's Chesapeake Bay.

Changes in the timing of jellyfish blooms in the Chesapeake Bay - an area prized for its crab fishery and other sea life - could affect fish populations in the area, according to a new study. Credit: Tony Alter/flickr.

“The key thing with jellies is that they do everything so much faster than everything else, they grow and reproduce and are voracious predators, that other animals like fish can’t keep up,” says ecologist Rob Condon from the Dauphin Island Sea Lab in Alabama.

For several years, Condon and colleagues from the Sea Lab and the Virginia Institute of Marine Science (VIMS) have been studying jellyfish that live in the York River, a southern tributary of Chesapeake Bay. They’ve discovered that rapidly-growing blooms of jellyfish are feeding on some of the most nutritious parts of the food web, including small crustaceans, and are converting them into products that sustain bacteria that leave little valuable energy supplies for fish and other sea life.

“It’s almost like the jellies are taking the good food and releasing it as a sports drink, like Gatorade,” says Condon. “And we drink Gatorade not as a valuable source of nutrition but as a quick source of energy.” 

Condon says the jellyfish are making a similar source of energy-rich material that bacteria feast upon, but that strips the nutritional value out of the river’s food web. 

“Ultimately, there is less food for the fish, because the jellyfish are eating it all,” he says. And because not too many animals (including us humans) eat jellyfish, it doesn't seem as though the food energy going into the jellies is moving up the food chain. This week, Condon and his colleagues published a study in the Proceedings of the National Academy of Sciences, detailing how jellyfish blooms reduce diversity in the marine food chain.

Researchers are still uncertain about how this change in food availability will affect the entire marine ecosystem in the Chesapeake Bay. So far, researchers say that blooms are occurring earlier in the year on the York River and warmer waters are helping to sustain jellyfish blooms later in the fall. However, overall jellyfish populations in the Bay haven’t noticeably increased. 

“There has been an increase in the water temperature in Chesapeake Bay in the winter and spring, and the water is also getting warmer earlier in the year,” says Condon. In a 2008 study with VIMS researcher Deborah Steinberg, Condon found that jellyfish in the York River began reproducing earlier in the season, aided by the warmer spring waters. Since the 1960’s, the average water temperature at the mouth of the York River has increased by nearly 2°F, an increase likely related to global warming.

Warming spring waters are causing early blooms some types of jellyfish, like these Atlantic Sea Nettles, in the Chesapeake Bay. Credit: Wally Gobetz/flickr.

While there hasn’t necessarily been an overall increase in jellyfish numbers in Chesapeake Bay, Condon says he is concerned about the earlier arrival of spring’s warm waters. He says that if warm waters foster earlier blooms, the jellyfish will begin to eat through a different section of the food chain, which will further alter what nutrients will be available for fish and other animals living throughout the Bay. It's unlikely, Condon says, that fish living in the Bay would be able to adapt to the rapid changes jellyfish will bring to the marine environment.

Warming waters aren’t the only threat to Chesapeake Bay wildlife. The area is also particularly vulnerable to sea level rise, and the health of its waters have been diminished by nutrient runoff from nearby farmland. According to Maryland’s Department of Natural Resources, the Chesapeake Bay coastline increased by about one foot during the last 100 years, and recent studies now suggest that by the end of the century, water could rise between two and five additional feet.

Organizations like the Chesapeake Bay Foundation and the Virginia Coastal Zone Management Program have already begun planning for the impending sea level rise, and have established conservation plans to protect coastal wetlands.

Yet while some of these efforts can help stave off the damage from rising water levels, there aren’t many local actions that can counteract the effects of warming water. The average temperatures in Chesapeake Bay are expected to keep climbing slowly throughout the century, and warm spring waters are likely to arrive much earlier than what has been the norm during the past 100 years. 

According to Condon, if these warm waters continue to arrive in the earlier and earlier in the springtime, the effects could be felt throughout Chesapeake Bay. “Jellyfish are an important indicator of the health of a marine ecosystem,” he says. “If the jellyfish blooms come earlier, there will be big consequences for fish production in the Bay.”