title: Trophic cascades promote threshold-like shifts in pelagic marine ecosystems.
abstract: Fisheries can have a large impact on marine ecosystems, because the effects of removing large predatory fish may cascade down the food web. The implications of these cascading processes on system functioning and resilience remain a source of intense scientific debate. By using field data covering a 30-year period, we show for the Baltic Sea that the underlying mechanisms of trophic cascades produced a shift in ecosystem functioning after the collapse of the top predator cod. We identified an ecological threshold, corresponding to a planktivore abundance of approximately 17 x 10(10) individuals, that separates 2 ecosystem configurations in which zooplankton dynamics are driven by either hydroclimatic forces or predation pressure. Abundances of the planktivore sprat above the threshold decouple zooplankton dynamics from hydrological circumstances. The current strong regulation by sprat of the feeding resources for larval cod may hinder cod recovery and the return of the ecosystem to a prior state. This calls for the inclusion of a food web perspective in management decisions.
authors.affiliation: Swedish Board of Fisheries, Institute of Marine Research, P.O. Box 4, SE-45321 Lysekil, Sweden. michele.casini@fiskeriverket.se
authors.forename: Michele
authors.initials: M
authors.lastname: Casini
authors.forename: Joakim
authors.initials: J
authors.lastname: Hjelm
authors.forename: Juan-Carlos
authors.initials: JC
authors.lastname: Molinero
authors.forename: Johan
authors.initials: J
authors.lastname: Lövgren
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Cardinale
authors.forename: Valerio
authors.initials: V
authors.lastname: Bartolino
authors.forename: Andrea
authors.initials: A
authors.lastname: Belgrano
authors.forename: Georgs
authors.initials: G
authors.lastname: Kornilovs
mesh_terms: D000818:Animals; D017753:Ecosystem; D053476:Extinction, Biological; D005399:Fishes; D020387:Food Chain; D048388:Gadiformes; D008386:Marine Biology; D009792:Oceans and Seas; D011157:Population Dynamics