Kevin Lunny thought he was doing the right thing when he bought the Drakes Bay Oyster Company off the Marin County coastline in Northern California. He spent hundreds of thousands of dollars fixing environmental concerns, and prides himself on a sustainable agriculture operation, one which needs no feed at all to produce succulent and delicious animal protein, prized by shellfish aficionados (like me).

"We are producing very high-quality food with very, very low impacts," said Lunny, who also raises certified grass-fed cattle on a nearby ranch. Like virtually all oyster producers in California, Lunny raises an Asian oyster that must be "seeded" on racks of shells or raised in mesh bags because it cannot reproduce naturally in cold water.

"Acre for acre, I can produce 10 times the protein in the estuary than I can on my cattle pastures," he said. "And the oysters are produced with hardly any inputs -- no fertilizers, very little fuel. The tides provide the feed for them in the form of plankton."

Don Neubacher, superintendent of the national seashore, produced aerial photos showing propeller damage from oyster boats in the estuary's eelgrass flats.

"Eelgrass is incredibly important to an entire complex of species," said Neubacher. "And Drakes Estero has 7 percent of all the eelgrass in California. We need to protect it."

Allen said harbor seals have declined from 250 to 50 in the area Lunny recently has developed. And park biologist Natalie Gates said cultivated oysters have an impact on estuarine life even if they do nothing more than repose in the water and suck up plankton.

"We're talking millions of oysters and millions of gallons of plankton," Gates said. "All the plankton the oysters consume is plankton denied to native fish and other marine organisms."