Bay Nature magazineSummer 2009

The Bay

Exotic Jellies in the Bay

July 1, 2009

On a hot July afternoon last year, UC Davis graduate students Alpa Wintzer and Mariah Meek dipped glass jars and nets into Suisun Slough at Suisun City’s public dock in Solano County. They were capturing Maeotias marginata, small gelatinous creatures that look and act like jellyfish but technically aren’t (they’re hydrozoans, not true jellies). These jelly look-alikes, ranging in size from a large pea to a silver dollar, seemed to be everywhere and are beautiful to watch. They pump their bell-shaped bodies to the surface of the water, flip over, and float down, capturing zooplankton as their tentacles gently sway in the currents.

Despite their beauty, they are problematic. They’re one of three nonnative hydrozoans that have invaded the low-salinity reaches of the San Francisco Estuary and the only one visible to the naked eye. Originally hailing from the Black Sea, they were likely brought here in ballast water in the 1950s and have since made themselves at home in the Suisun Marsh and Napa and Petaluma Rivers.

As Wintzer and Meek dipped, they attracted an audience. Local kids came down to help, staring into the capture buckets. One came back with a washed-out peanut butter jar to use as a scoop, inviting the inevitable joke about peanut butter and jellies sandwiches.

Perhaps popularizing such a delicacy would help keep the jellies in check. Biologists are working to determine if these creatures are a factor in the fish decline of the upper estuary. “There do not seem to be any native or non-native species that consume them,” says Wintzer. They, on the other hand, are increasing in abundance and eating zooplankton of all kinds. “It is possible that the jellies are feeding on larval fish and also competing with juvenile fish for food resources,” Wintzer adds.

She and Meek, working under California fish experts Peter Moyle and Bernie May, are studying the jellies’ diet and genetic diversity and the role those factors play in the invasion. At this point, the researchers won’t hazard a guess about the outcome of their study (which they expect to be published in 2010) but say it is a first step in determining if there’s a need to actively manage the organisms.

About the Author

Writer Aleta George trained as a Jepson Prairie docent in 2009. In addition to writing Bay Nature's Ear to the Ground column, she has written for Smithsonian, High Country News, and the Los Angeles Times.