SAN FRANCISCO - Hundreds of dead or injured seabirds have washed up on the shores of Monterey Bay in recent weeks, and scientists believe a red tide of marine algae is to blame.

About 600 birds have been found stranded on beaches in Monterey and Santa Cruz counties since a large rust-colored algal bloom began circulating in the bay about three weeks ago, scientists say.

About 70 of the birds have died, while 530 have been taken to wildlife rescue centers, said Michael Ziccardi, director of the Oiled Wildlife Care Network.

The affected birds include loons, pelicans, western grebes, northern fulmars and surf scoters, said Dave Jessup, a veterinarian with the state Department of Fish and Game. Fish and marine mammals do not appear to be affected.

Officials initially believed the birds were victims of the San Francisco Bay oil spill that has killed or injured at least 2,800 birds. But tests found that the sticky, yellow substance found on the Monterey Bay birds was not petroleum or vegetable oil.

Scientists now believe the birds were injured by a protein that sticks to the birds' feathers and disrupts their ability to stay dry and warm, forcing them from the water where they live and feed.

"The birds are in distress because their feathers are no longer keeping them warm," Ziccardi said. "It's doing something to their waterproofing."

Researchers believe the protein is produced either directly or as a byproduct of the red tide, which is common in Monterey Bay this time of year.

Red tides that produce a neurotoxin have been known to kill sea lions and other marine mammals, but such algal blooms have not occurred in several years.

Many of the beached birds are cold and wet but otherwise healthy when they arrive at the rescue centers, and they recover quickly after their feathers are cleaned, Ziccardi said.

Algal blooms are increasing in frequency and intensity around the world, a trend scientists say may be linked to climate change as well as the use of pesticides and fertilizers.

The algal bloom likely will stay in Monterey Bay and continue injuring birds until a major weather system pushes the red tide out, Jessup said.