'Marine vomit' can smother other species, including oyster beds

  • Francisco Manzo works on a barge filled with oysters pulled from Drakes Estero on Thursday, June 14, 2012.

    (Christopher Chung/ The Press Democrat)

A newly discovered invasive species capable of blanketing shallow bay bottoms has turned up in Drakes Estero, prompting calls for immediate action to curb the biological threat and entering the debate over the future of a commercial oyster farm in the scenic Marin County estuary.

A fast-growing sea squirt, Didemnum vexillum, is actually thousands of tiny animals that cluster under a common membrane. It is called "marine vomit" for its unappealing gelatinous mass and has been likened to "The Blob" for its capacity to smother other organisms, possibly including the estero's $1.5 million a year oyster crop and its abundant eelgrass beds.

Tan blobs of D. vex appear on the Pacific oysters hauled from the estero's cold, clear water by workers for Drakes Bay Oyster Company, and a scientific survey in 2010 found it on the wooden oyster growing racks and eelgrass that forms the base of the estero's food chain.

"We have the opportunity to nip this in the bud," said Rick Johnson, a Marin Audubon Society member from Inverness. He cited studies that suggest the invader species may use the oysters and racks as a springboard into the estero's relatively pristine ecosystem.

The society, with 1,855 dues-paying members, wants the oyster farm removed from the 2,500-acre estero, designated by Congress 36 years ago as potential wilderness in Point Reyes National Seashore.

A nasty dispute over the farm's fate erupted about five years ago, and legislation by California Sen. Dianne Feinstein granted Interior Secretary Ken Salazar sole discretion to renew for 10 years the permit that expires Nov. 30.

A 500-page draft environmental report issued by the National Park Service last year discussed D. vex in one paragraph, calling it "an aggressive colonizer" of places like oyster farms and noting that it can "cause serious ecological consequences" for small organisms as well as harming eelgrass.

"This is a very serious matter," said Amy Trainer of the West Marin Environmental Action Committee, which opposes renewal of the oyster farm permit.

The Park Service largely overlooked D. vex's threat to the estero, she said, and should "give it the attention it deserves" in the final report, expected sometime this fall.

Two marine biologists familiar with the situation declined to comment, with one citing in an e-mail the "charged political atmosphere" surrounding the oyster farm.

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