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Biogeographical patterns of rocky intertidal communities along the Pacific coast of North America

Authors

  • Carol A. Blanchette,

    Corresponding author
    1. Marine Science Institute, University of California, Santa Barbara
      *Carol A. Blanchette, Marine Science Institute, University of California, Santa Barbara, CA 93106, USA.
      E-mail: blanchette@msi.ucsb.edu
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  • C. Melissa Miner,

    1. Department of Ecology and Evolutionary Biology, Long Marine Laboratory, University of California, Santa Cruz
    2. Department of Biology, Western Washington University, Bellingham, WA
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  • Peter T. Raimondi,

    1. Department of Ecology and Evolutionary Biology, Long Marine Laboratory, University of California, Santa Cruz
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  • David Lohse,

    1. Department of Ecology and Evolutionary Biology, Long Marine Laboratory, University of California, Santa Cruz
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  • Kristen E. K. Heady,

    1. Department of Ecology and Evolutionary Biology, Long Marine Laboratory, University of California, Santa Cruz
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  • Bernardo R. Broitman

    1. National Center for Ecological Analysis and Synthesis, Santa Barbara, CA, USA
    2. Centro de Estudios Avanzados en Zados Aridas, Facultad de Ciencias del Mar, Universidad Catolica del Norte, Coquimbo, Chile
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*Carol A. Blanchette, Marine Science Institute, University of California, Santa Barbara, CA 93106, USA.
E-mail: blanchette@msi.ucsb.edu

Abstract

Aim  Our aim in this paper is to present the first broad-scale quantification of species abundance for rocky intertidal communities along the Pacific coast of North America. Here we examine the community-level marine biogeographical patterns in the context of formerly described biogeographical regions, and we evaluate the combined effects of geographical distance and environmental conditions on patterns of species similarity across this region.

Location  Pacific coast of North America.

Methods  Data on the percentage cover of benthic marine organisms were collected at 67 rocky intertidal sites from south-eastern Alaska, USA, to central Baja California Sur, Mexico. Cluster analysis and non-metric multidimensional scaling were used to evaluate the spatial patterns of species similarity among sites relative to those of previously defined biogeographical regions. Matrices of similarity in species composition among all sites were computed and analysed with respect to geographical distance and long-term mean sea surface temperature (SST) as a measure of environmental conditions.

Results  We found a high degree of spatial structure in the similarity of intertidal communities along the coast. Cluster analysis identified 13 major community structure ‘groups’. Although breaks between clusters of sites generally occurred at major biogeographical boundaries, some of the larger biogeographical regions contained several clusters of sites that did not group according to spatial position or identifiable coastal features. Additionally, there were several outliers – sites that grouped alone or with sites outside their region – for which localized features may play an important role in driving community structure. Patterns of species similarity at the large scale were highly correlated with geographical distance among sites and with SST. Importantly, we found community similarity to be highly correlated with long-term mean SST while controlling for the effects of geographical distance.

Main conclusions  These findings reveal a high degree of spatial structure in the similarity of rocky intertidal communities of the north-east Pacific, and are generally consistent with those of previously described biogeographical regions, with some notable differences. Breaks in similarity among clusters are generally coincident with known biogeographical and oceanographic discontinuities. The strong correlations between species similarity and both geographical position and SST suggest that both geography and oceanographic conditions have a large influence on patterns of intertidal community structure along the Pacific coast of North America.

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