title: Protection of large predators in a marine reserve alters size-dependent prey mortality.
abstract: Where predator-prey interactions are size-dependent, reductions in predator size owing to fishing has the potential to disrupt the ecological role of top predators in marine ecosystems. In southern California kelp forests, we investigated the size-dependence of the interaction between herbivorous sea urchins and one of their predators, California sheephead (Semicossyphus pulcher). Empirical tests examined how differences in predator size structure between reserve and fished areas affected size-specific urchin mortality. Sites inside marine reserves had greater sheephead size and biomass, while empirical feeding trials indicated that larger sheephead were required to successfully consume urchins of increasing test diameter. Evaluations of the selectivity of sheephead for two urchin species indicated that shorter-spined purple urchins were attacked more frequently and successfully than longer-spined red urchins of the same size class, particularly at the largest test diameters. As a result of these size-specific interactions and the higher biomass of large sheephead inside reserves, urchin mortality rates were three times higher inside the reserve for both species. In addition, urchin mortality rates decreased with urchin size, and very few large urchins were successfully consumed in fished areas. The truncation of sheephead size structure that commonly occurs owing to fishing will probably result in reductions in urchin mortality, which may reduce the resilience of kelp beds to urchin barren formation. By contrast, the recovery of predator size structure in marine reserves may restore this resilience, but may be delayed until fish grow to sizes capable of consuming larger urchins.
authors.affiliation: Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, CA 93106, USA becca.selden@rutgers.edu.
authors.forename: Rebecca L
authors.identifier: 0000-0001-7956-5984
authors.initials: RL
authors.lastname: Selden
authors.affiliation: Bren School of Environmental Science and Management, University of California, Santa Barbara, CA 93106, USA.
authors.forename: Steven D
authors.initials: SD
authors.lastname: Gaines
authors.affiliation: Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039, USA.
authors.forename: Scott L
authors.initials: SL
authors.lastname: Hamilton
authors.affiliation: Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, CA 93106, USA.
authors.forename: Robert R
authors.initials: RR
authors.lastname: Warner
mesh_terms: D000818:Animals; D002140:California; D017753:Ecosystem; D005399:Fishes; D020387:Food Chain; D044423:Kelp; D012617:Sea Urchins
keywords: kelp forest; marine reserves; size refuge; size-dependent predation; urchin