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A new study challenges the established principle that water quality in bays and estuaries is driven primarily by human-caused changes in the surrounding landscape.

Marine life in San Francisco Bay has flourished over the past decade in concert with a large-scale climatic shift originating far out in the Pacific Ocean, according to a U.S. Geological Survey (USGS) study released in November 2010. The study challenges the established principle that water quality in bays and estuaries is driven primarily by human-caused changes in the surrounding landscape.

Photo of a crab sitting on the grass.
The Dungeness crab (Metacarcinus magister), whose range extends from the Aleutian Islands to the coast of California, is one of the species whose populations in San Francisco Bay have increased with a large-scale climatic shift that began in 1999. Photograph courtesy of the U.S. Fish and Wildlife Service.

By documenting changes in two dominant climatic cycles in the north Pacific basin and looking at correlations with population abundances of marine life over the past 30 years, scientists have linked broader changes in climate to local manifestations, including record-high abundances of marine species in San Francisco Bay.

"While some native species of fish are near extinction in the upstream [Sacramento-San Joaquin] Delta, bottom fish, crabs, and shrimp are thriving in the marine waters of the bay," said Jim Cloern, research ecologist with the USGS. "Discovery that the bay's biological communities are linked to climate patterns thousands of miles offshore is essential information for environmental managers."

Studying trends revealed by three decades of observation, scientists from the USGS, the California Department of Fish and Game, the National Oceanic and Atmospheric Administration (NOAA), and five universities found that one particular atmospheric pattern over the Pacific Ocean developed in 1999 and has persisted through most of the 2000s. This atmospheric pattern resulted from the interaction of two large-scale climatic cycles known as the Pacific Decadal Oscillation and the North Pacific Gyre Oscillation. The atmospheric pattern altered winds, ocean currents, and upwelling to establish a coastal habitat that promotes the population growth of flatfish, crab, and shrimp species that migrate into estuaries such as San Francisco Bay. 

USGS scientists have monitored San Francisco Bay continually since 1968, resulting in hundreds of scientific articles to draw from for this study.

The report "Biological Communities in San Francisco Bay Track Large-Scale Climate Forcing Over the North Pacific" was released November 8, 2010, in the journal Geophysical Research Letters.

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