title: Strong top-down control in southern California kelp forest ecosystems.
abstract: 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.
authors.affiliation: National Center for Ecological Analysis and Synthesis, 735 State Street, Santa Barbara, CA 93101, USA. halpern@nceas.ucsb.edu
authors.forename: Benjamin S
authors.initials: BS
authors.lastname: Halpern
authors.forename: Karl
authors.initials: K
authors.lastname: Cottenie
authors.forename: Bernardo R
authors.initials: BR
authors.lastname: Broitman
mesh_terms: D000818:Animals; D002140:California; D003247:Conservation of Natural Resources; D017753:Ecosystem; D004777:Environment; D056890:Eukaryota; D005399:Fishes; D020387:Food Chain; D005843:Geography; D007448:Invertebrates; D044423:Kelp; D010140:Pacific Ocean; D011156:Population Density; D011235:Predatory Behavior; D012623:Seawater