title: Global patterns of kelp forest change over the past half-century.
abstract: Kelp forests (Order Laminariales) form key biogenic habitats in coastal regions of temperate and Arctic seas worldwide, providing ecosystem services valued in the range of billions of dollars annually. Although local evidence suggests that kelp forests are increasingly threatened by a variety of stressors, no comprehensive global analysis of change in kelp abundances currently exists. Here, we build and analyze a global database of kelp time series spanning the past half-century to assess regional and global trends in kelp abundances. We detected a high degree of geographic variation in trends, with regional variability in the direction and magnitude of change far exceeding a small global average decline (instantaneous rate of change = -0.018 y-1). Our analysis identified declines in 38% of ecoregions for which there are data (-0.015 to -0.18 y-1), increases in 27% of ecoregions (0.015 to 0.11 y-1), and no detectable change in 35% of ecoregions. These spatially variable trajectories reflected regional differences in the drivers of change, uncertainty in some regions owing to poor spatial and temporal data coverage, and the dynamic nature of kelp populations. We conclude that although global drivers could be affecting kelp forests at multiple scales, local stressors and regional variation in the effects of these drivers dominate kelp dynamics, in contrast to many other marine and terrestrial foundation species.
authors.affiliation: School of Resource and Environmental Management, Hakai Institute, Simon Fraser University, Burnaby, BC, Canada V5A 1S6; kkrumhan@sfu.ca.
authors.forename: Kira A
authors.initials: KA
authors.lastname: Krumhansl
authors.affiliation: School of Resource and Environmental Management, Hakai Institute, Simon Fraser University, Burnaby, BC, Canada V5A 1S6.
authors.forename: Daniel K
authors.initials: DK
authors.lastname: Okamoto
authors.affiliation: Department of Biological Science, Florida State University, Tallahassee, FL 32306.
authors.forename: Andrew
authors.initials: A
authors.lastname: Rassweiler
authors.affiliation: Department of Integrative Biology, Oregon State University, Corvallis, OR 97331.
authors.forename: Mark
authors.initials: M
authors.lastname: Novak
authors.affiliation: Department of Biological Sciences and Marine Research Institute, University of Cape Town, 7701 Rondebosch, South Africa.
authors.forename: John J
authors.initials: JJ
authors.lastname: Bolton
authors.affiliation: Department of Geography, University of California, Los Angeles, CA 90095.
authors.forename: Kyle C
authors.initials: KC
authors.lastname: Cavanaugh
authors.affiliation: Southern Seas Ecology Laboratories, The Environment Institute, The University of Adelaide, Adelaide, SA 5005, Australia.
authors.forename: Sean D
authors.initials: SD
authors.lastname: Connell
authors.affiliation: Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, 7001 TAS, Australia.
authors.forename: Craig R
authors.initials: CR
authors.lastname: Johnson
authors.affiliation: College of Fisheries and Ocean Sciences, University of Alaska, Fairbanks, AK 99775.
authors.forename: Brenda
authors.initials: B
authors.lastname: Konar
authors.affiliation: Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, 7001 TAS, Australia.
authors.forename: Scott D
authors.initials: SD
authors.lastname: Ling
authors.affiliation: Hopkins Marine Station, Stanford University, Pacific Grove, CA 93950.
authors.forename: Fiorenza
authors.initials: F
authors.lastname: Micheli
authors.affiliation: Norwegian Institute for Water Research, 0349 Oslo, Norway.
authors.forename: Kjell M
authors.initials: KM
authors.lastname: Norderhaug
authors.affiliation: Subtidal Ecology Laboratory and Marine Conservation Center, Estación Costera de Investigaciones Marinas, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Casilla 114-D, Santiago, Chile.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Pérez-Matus
authors.affiliation: Interdisciplinary Centre for Marine and Environmental Research, 4450-208 Matosinhos, Portugal.|Department of Biology, Faculty of Sciences, University of Porto, 4169-007 Porto, Portugal.
authors.forename: Isabel
authors.initials: I
authors.lastname: Sousa-Pinto
authors.affiliation: Marine Science Institute, University of California, Santa Barbara, CA 93106.
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Reed
authors.affiliation: School of Resource and Environmental Management, Hakai Institute, Simon Fraser University, Burnaby, BC, Canada V5A 1S6.
authors.forename: Anne K
authors.initials: AK
authors.lastname: Salomon
authors.affiliation: Leigh Marine Laboratory, Institute of Marine Science, The University of Auckland, Auckland 0941, New Zealand.
authors.forename: Nick T
authors.initials: NT
authors.lastname: Shears
authors.affiliation: Oceans Institute, University of Western Australia, Perth, WA 6009, Australia.|School of Biological Sciences, University of Western Australia, Perth, WA 6009, Australia.
authors.forename: Thomas
authors.initials: T
authors.lastname: Wernberg
authors.affiliation: Department of Biological Sciences and Marine Research Institute, University of Cape Town, 7701 Rondebosch, South Africa.|Department of Agriculture, Forestry and Fisheries, Roggebaai 8012, South Africa.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Anderson
authors.affiliation: Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, 7001 TAS, Australia.
authors.forename: Nevell S
authors.initials: NS
authors.lastname: Barrett
authors.affiliation: Centro de Investigación y Desarrollo en Recursos y Ambientes Costeros, Universidad de Los Lagos, Puerto Montt 5480000, Chile.|Centro de Biotecnología y Bioingeniería, Universidad de Los Lagos, Puerto Montt 5480000, Chile.
authors.forename: Alejandro H
authors.initials: AH
authors.lastname: Buschmann
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95064.
authors.forename: Mark H
authors.initials: MH
authors.lastname: Carr
authors.affiliation: Marine Science Institute, University of California, Santa Barbara, CA 93106.
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Caselle
authors.affiliation: Muséum National d'Histoire Naturelle, Station Marine de Concarneau, 29182 Concarneau Cedex, France.
authors.forename: Sandrine
authors.initials: S
authors.lastname: Derrien-Courtel
authors.affiliation: Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, 7001 TAS, Australia.
authors.forename: Graham J
authors.initials: GJ
authors.lastname: Edgar
authors.affiliation: Department of Biology, San Diego State University, San Diego, CA 92182.
authors.forename: Matt
authors.initials: M
authors.lastname: Edwards
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95064.
authors.forename: James A
authors.initials: JA
authors.lastname: Estes
authors.affiliation: Centre for Environmental Data and Recording, National Museums Northern Ireland, Holywood, Co. Down BT18 0EU, United Kingdom.
authors.forename: Claire
authors.initials: C
authors.lastname: Goodwin
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95064.
authors.forename: Michael C
authors.initials: MC
authors.lastname: Kenner
authors.affiliation: Channel Islands National Park, Ventura, CA 93009.
authors.forename: David J
authors.initials: DJ
authors.lastname: Kushner
authors.affiliation: Institute of Marine Research, 4817 His, Norway.
authors.forename: Frithjof E
authors.identifier: 0000-0002-0790-4593
authors.initials: FE
authors.lastname: Moy
authors.affiliation: Centre for Environmental Data and Recording, National Museums Northern Ireland, Holywood, Co. Down BT18 0EU, United Kingdom.
authors.forename: Julia
authors.initials: J
authors.lastname: Nunn
authors.affiliation: School of Marine Sciences, University of Maine, Walpole, ME 04573.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Steneck
authors.affiliation: Departamento de Biología Marina, Universidad Católica del Norte, Coquimbo 1781421, Chile.
authors.forename: Julio
authors.initials: J
authors.lastname: Vásquez
authors.affiliation: Biology Department, Vancouver Island University, Nanaimo, BC, Canada V9R 5S5.
authors.forename: Jane
authors.initials: J
authors.lastname: Watson
authors.affiliation: Ecology and Evolutionary Biology, Brown University, Providence, RI 02912.
authors.forename: Jon D
authors.initials: JD
authors.lastname: Witman
authors.affiliation: Department of Biology, University of Massachusetts, Boston, MA 02125.
authors.forename: Jarrett E K
authors.identifier: 0000-0002-9791-9472
authors.initials: JE
authors.lastname: Byrnes
mesh_terms: D001110:Arctic Regions; D057231:Climate Change; D017753:Ecosystem; D065928:Forests; D044423:Kelp / Q000254:growth & development*; D009792:Oceans and Seas
keywords: Laminariales; climate change; coastal ecosystems; global change; kelp forest