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Science 26 May 2006:
Vol. 312. no. 5777, pp. 1230 - 1232
DOI: 10.1126/science.1128613
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Reports

Strong Top-Down Control in Southern California Kelp Forest Ecosystems

Benjamin S. Halpern,1* Karl Cottenie,1,2 Bernardo R. Broitman1,3

Global-scale changes in anthropogenic nutrient input into marine ecosystems via terrestrial runoff, coupled with widespread predator removal via fishing, have created greater urgency for understanding the relative role of top-down versus bottom-up control of food web dynamics. Yet recent large-scale studies of community regulation in marine ecosystems have shown dramatically different results that leave this issue largely unresolved. We combined a multiyear, large-scale data set of species abundances for 46 species in kelp forests from the California Channel Islands with satellite-derived primary production and found that top-down control explains 7- to 10-fold more of the variance in abundance of bottom and mid-trophic levels than does bottom-up control. This top-down control was propagated via a variety of species-level direct and indirect responses to predator abundance. Management of top-down influences such as fishing may be more important in coastal marine ecosystems, particularly in kelp forest systems, than is commonly thought.

1 National Center for Ecological Analysis and Synthesis, 735 State Street, Santa Barbara, CA 93101, USA.
2 Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada.
3 Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, CA 93106, USA.

* To whom correspondence should be addressed. E-mail: halpern{at}nceas.ucsb.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Invasive range expansion by the Humboldt squid, Dosidicus gigas, in the eastern North Pacific.
L. D. Zeidberg and B. H. Robison (2007)
PNAS 104, 12948-12950
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Science. ISSN 0036-8075 (print), 1095-9203 (online)