San Francisco Threat: Big Oysters Invade Bay

San Francisco Bay's native oyster (top), the exotic oyster (bottom) i i

San Francisco Bay's native oyster (Ostrea conchaphila) (top) has a maximum length of 2.5 inches; the exotic oyster are as large as 9 inches. A.N. Cohen/San Francisco Estuary Institute hide caption

itoggle caption A.N. Cohen/San Francisco Estuary Institute
San Francisco Bay's native oyster (top), the exotic oyster (bottom)

San Francisco Bay's native oyster (Ostrea conchaphila) (top) has a maximum length of 2.5 inches; the exotic oyster are as large as 9 inches.

A.N. Cohen/San Francisco Estuary Institute

Mammoth mystery oysters — 9 inches long! - invade the San Francisco Bay, normally a habitat for oysters no longer than 2.5 inches. Andrew Cohen, director of the Biological Invasions Program at the San Francisco Estuary Institute, says the new species is not native. No one knows how the supersized shellfish got to this bay, and there are fears they could steal the best habitat.

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MELISSA BLOCK, host:

They've been digging up some surprises in the San Francisco Bay. Big surprises. Oysters up to nine inches long. And they don't belong there. Andrew Cohen is director of the Biological Invasions Program at the San Francisco Estuary Institute. And Dr. Cohen, you've been out there doing some of the digging. What you found?

Dr. ANDREW COHEN (San Francisco Estuary Institute): Well, a couple of weeks ago a woman who was working in the Bay on native oysters called me up to say that she'd found some exotic oysters at a site where a single shell of exotic oysters had been found two years earlier. We realized when I went out and checked over the weekend, we saw more of them out there, that we had a significant population. And decided to try and figure out how widespread they were, how abundant they were and to see whether we couldn't do something to remove as many of them as possible.

BLOCK: And how many have you removed?

Dr. COHEN: Well, we've gotten over 250 out of the Bay at this point. Based on what we've seen, I'd guess there's somewhere between 1,000 and 2,000 of them out there in the Bay.

BLOCK: And what do they look like?

Dr. COHEN: Well, they have varied shape. Some are rectangular. Some are nearly round. Some are fan-shaped and they look sort of like rocks on top of rocks many times. Barnacle covered. There are anemones growing on them. They blend in to some extent as well.

BLOCK: A nine-inch oyster sounds to me like a pretty scary thing.

Dr. COHEN: Well, it could be - it's probably scary if you're trying to swallow it in one gulp. But they are of concern to many people in the research community in the Bay because, of course, they'd be an entirely new organism here. They are a type of oyster that can be a very efficient filter feeder, removing the small floating plants, the phytoplankton that are the base of a lot of the pelagic food web in the Bay. So there's great concern that if they become abundant in the Bay that they could alter the entire economy of the Bay food web.

BLOCK: Any idea how these exotic oysters got there?

Dr. COHEN: There are a number of possible ways they could have come in. We're entirely speculating at this point. But if they are a type that's cultivated on the Pacific Coast, the larvae could have drifted in from a bay where they are grown. There are none cultivated in San Francisco Bay but there are some in nearby bays. They could have come in as larvae in the ballast water of a ship, as adults attached to the hull of a ship. Or conceivably someone could have bought some in a market and dumped them in the Bay in an effort to get them started here.

BLOCK: And what's the big fear when you confront an invasive species like this?

Dr. COHEN: Well, there are a number of different things. We try to manage San Francisco Bay and other water bodies to maintain a balance of organisms in there. And we need to understand how the system works in order to manage it effectively, and every time a new organism comes in, particularly one which has the potential to substantially alter the way that ecosystem functions, the knowledge that we've acquired over the years becomes less useful because the system has been changed. That's the sort of thing that has happened on a number of occasions in San Francisco Bay with invasions and may well happen with this one, should it become established.

BLOCK: Has anybody tried eating them?

Dr. COHEN: Well, that's always a possibility. Shellfish in San Francisco Bay and generally not thought to be terribly healthful to eat and no one on our team so far as I know has tried eating one yet but, of course, that's always an option.

BLOCK: Any pearls?

Dr. COHEN: Any pearls? No. My wife has asked me to keep a lookout but we haven't found any pearls yet.

BLOCK: Andrew Cohen, thanks for talking with us.

Dr. COHEN: Sure thing.

BLOCK: Andrew Cohen is director of the Biological Invasions Program at the San Francisco Estuary Institute. He spoke with us from El Cerrito.

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