August 3, 2009

Predatory snail wrecks California oysters

A predatory snail indigenous to the Atlantic Ocean is decimating native oysters living in Tomales Bay north of San Francisco, scientists said Monday.

About half of the Olympia oysters in the coastal estuary fell to a predatory whelk snail, a California Sea Grant-funded study published in the July issue of the Oecologia journal said. The grant's operation is based at the University of California-San Diego, which distributed a news release.

The type of oyster drill savages oysters by boring into their shells and digesting soft tissue inside, the researchers said. The snail was inadvertently brought to the West Coast decades ago with shipments of Atlantic oysters that people tried unsuccessfully to cultivate in California locales such as Tomales Bay.

Although both native and non-native oyster drills inhabit the West Coast, in the salty Tomales Bay, red rock crabs keep native oyster drills in check and hunt Atlantic drills to near local extinction. In the bay's freshwater, seasonal deluges kill rock crabs, resulting in the Atlantic drills invade low-salinity zones, at the expense of native oysters, researchers said.

It is a characteristic of successful invasive species that they tend to be highly tolerant to salinity extremes. For Tomales Bay, this means that nearly half the habitat is inhospitable to re-establishing native oysters, the article's lead author David Kimbro, a post-doctoral associate at Florida State University who was a Sea Grant trainee in the University of California system at the project's onset.