A cold phase of the East Pacific triggers new phytoplankton blooms in San Francisco Bay

*United States Geological Survey, MS496, 345 Middlefield Road, Menlo Park, CA 94025;
^‡Department of Environmental Science and Policy, University of California, Davis, CA 95616; and
^§California Department of Fish and Game, 4001 North Wilson Way, Stockton, CA 95205

Edited by George N. Somero, Stanford University, Pacific Grove, CA, and approved October 3, 2007 (received for review June 29, 2007)

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Fig. 1.
Indicators of phytoplankton change in South SFB. (A) Occurrences of autumn blooms (August through December Chl-a >10) since 1999. (B) Increases in August through December Chl-a (interquartile ranges are shown as bars) and gross primary production (GPP) (open circles). (C) Ten-year windowed trends showing statistically significant (P < 0.05; filled squares) Chl-a increases after 1999. (D) Annual inputs of dissolved inorganic nitrogen and phosphorus from the San Jose–Santa Clara Wastewater Treatment Plant [N. Van Keuren (City of San Jose), personal communication], the largest municipal discharger to South SFB.
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Fig. 2.
Monthly trends of water quality in South SFB based on USGS measurements of DIN and DRP for the years 1990–2005, and surface salinity, water temperature, Chl-a, and SPM for the years 1978–2005. Units are percent change y⁻¹. Darker bars indicate statistically significant trends (P < 0.05).
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Fig. 3.
Indices of biological community change within SFB and physical changes in the adjacent California Current. (A) Annual median biomass of filter-feeding bivalves across shallow habitats in South SFB; numbers above squares indicate sample number per year. (B) Mean annual catch ha⁻¹, normalized to 1980–2005 averages, of English sole, Bay shrimp, and Dungeness crab, from monthly sampling across the marine domains of SFB. (C) Anomalies in upwelling intensity computed by the National Oceanic and Atmospheric Administration from atmospheric pressure fields. (D) Sea surface temperature measured at the Farallon Islands. The bottom series (C and D) are 12-mo running averages of deviations from 1977–2005 monthly means.