Bay / delta habitats suffer big declines

I've long been intrigued by mollusks and their filtering role in our waters -- as well as bellwether of ecological health. This article not only reports on biodiversity of the No.California Bay, but the role of mollusks in today's ecological system.

Bay, delta habitats suffer big declines

Most of 39 species studied have lost half of original populations

David Perlman, Chronicle Science Editor

Friday, November 3, 2006

For more than a thousand years the waters of San Francisco Bay and the rivers that feed the delta have been losing critical species of fish, wildlife and plants, and the loss rate is steadily increasing today, say marine biologists.

Scientists studied long-term trends in 39 species of marine mammals, birds, fish, shellfish, plankton and plants around the bay, the Sacramento-San Joaquin River Delta and the rivers that feed the delta, tracing their population trends back for 1,000 years.

They found that more than 90 percent of the original water-dwelling species in those waters have lost at least half their populations, and a third of those populations collapsed close to extinction before their numbers partially recovered in more recent times.

San Francisco's waters, she said, are top contenders for historic damage with only a little recent relief from conservation efforts around the bay's shorelines to restore salt ponds and revive vegetation that serves as habitat for fish and shorebirds.

Of the 12 bays and estuaries Lotze and her colleagues studied, the biodiversity of San Francisco Bay's waters has fared worse than similar areas in Canada and Australia, she said, but is about the same as the Chesapeake Bay and the Bay of Fundy on the Atlantic coast.

Her team recorded 145 alien plants and animals that have invaded San Francisco Bay since historic times, a number that far exceeds the count of invasive species recorded in several European coastal estuaries, she said.

The bay's water quality, however, "is a bit of an outsider," she said, compared to the other bay and river systems she studied.

It shows no signs of oxygen depletion that could threaten fish, she said, and the reason is a bit ironic:

The native oysters, clams and mussels that once filtered organic matter from water and prevented algae from blooming in the bay disappeared, but varied species of alien invading clams from Japan, the Philippines and the Atlantic coast have replaced them and taken on the filtering role.

Dangerous blooms of algae no longer threaten the bay's ecology, Lotze said.

SOURCE: SFGATE.com