Phytoplankton Counts Surge In SF Bay - Scientists Seek Answers

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The amount of phytoplankton — nature's most important building block in the food chain that feeds fish, clams, birds, harbor seals and other animals — is increasing dramatically in San Francisco Bay. For now, experts say, the growth appears to be a good thing. But if it keeps steadily expanding in the years ahead, fish and wildlife could be threatened. Scientists aren't sure what's behind the phenomenon.

Levels of the floating, microscopic plants have increased 75 percent in Bay waters between San Jose and Napa County since 1993, according to a study released Tuesday by researchers from the U.S. Geological Survey in Menlo Park and the University of California,Davis.

So far, so good, researchers say: More plankton means more food for clams, mussels and other aquatic creatures. In turn, that means more food for fish, which eat these smaller marine species. That means better food conditions for birds, such as pelicans or diving ducks, or for harbor seals, which eat the fish. But too much plankton also can be dangerous, causing harmful algae blooms that choke oxygen from the water. Fertilizers running off farmers' fields have caused such blooms in parts of the Gulf of Mexico, Chesapeake Bay and other places, creating massive "dead zones."

"Phytoplankton are a lot like red wine. If we have a glass each day it's good for us, but if we drink a bottle a day, it's bad for us," said Jim Cloern, a marine ecologist at the U.S. Geological Survey in Menlo Park, who was lead researcher on the study. "There's some level at which the health of the ecosystem starts degrading," he said. "We're not at that point yet. We're at a point where the increase has been beneficial for animals that use it as their food source."

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