Previous Article |
Table of Contents
| Next Article 
BIOLOGICAL SCIENCES / ECOLOGY
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)
Ecological observations sustained over decades often reveal abrupt changes in biological communities that signal altered ecosystem states. We report a large shift in the biological communities of San Francisco Bay, first detected as increasing phytoplankton biomass and occurrences of new seasonal blooms that began in 1999. This phytoplankton increase is paradoxical because it occurred in an era of decreasing wastewater nutrient inputs and reduced nitrogen and phosphorus concentrations, contrary to the guiding paradigm that algal biomass in estuaries increases in proportion to nutrient inputs from their watersheds. Coincidental changes included sharp declines in the abundance of bivalve mollusks, the key phytoplankton consumers in this estuary, and record high abundances of several bivalve predators: Bay shrimp, English sole, and Dungeness crab. The phytoplankton increase is consistent with a trophic cascade resulting from heightened predation on bivalves and suppression of their filtration control on phytoplankton growth. These community changes in San Francisco Bay across three trophic levels followed a state change in the California Current System characterized by increased upwelling intensity, amplified primary production, and strengthened southerly flows. These diagnostic features of the East Pacific "cold phase" lead to strong recruitment and immigration of juvenile flatfish and crustaceans into estuaries where they feed and develop. This study, built from three decades of observation, reveals a previously unrecognized mechanism of ocean–estuary connectivity. Interdecadal oceanic regime changes can propagate into estuaries, altering their community structure and efficiency of transforming land-derived nutrients into algal biomass.
climate variability | coastal eutrophication | ocean–estuary connectivity | regime shift | trophic cascade
Author contributions: J.E.C. and A.D.J. designed research; J.E.C., J.K.T., and K.A.H. performed research; J.E.C., A.D.J., J.K.T., and K.A.H. analyzed data; and J.E.C., A.D.J., and J.K.T. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0706151104/DC1.
To whom correspondence should be addressed. E-mail: jecloern{at}usgs.gov
© 2007 by The National Academy of Sciences of the USA
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg What's this?
