Behavioural interactions between ecosystem engineers control community species richness

Authors

  • Paul E. Gribben,

    Corresponding author
    1. Department of Environmental Sciences, University of Technology, Sydney, PO Box 123, 2007, Australia
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  • James E. Byers,

    1. School of Biological Sciences, University of Wollongong, Wollongong, NSW 2522, Australia
    2. Department of Zoology, University of New Hampshire, Durham, NH 03824, USA
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  • Michael Clements,

    1. Centre for Marine Bio-Innovation and School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney 2052, Australia
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  • Louise A. McKenzie,

    1. Centre for Marine Bio-Innovation and School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney 2052, Australia
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  • Peter D. Steinberg,

    1. Centre for Marine Bio-Innovation and School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney 2052, Australia
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  • Jeffrey T. Wright

    1. National Centre for Marine Conservation & Resource Sustainability, Australian Maritime College, The University of Tasmania, Locked Bag 1370, Launceston, TAS 7250, Australia
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  • 1

    The periostracum is an organic layer, secreted as the outermost layer of most mollusk shells that protects the underlying shell from erosion.

*E-mail: paul.gribben@uts.edu.au

Abstract

Behavioural interactions between ecosystem engineers may strongly influence community structure. We tested whether an invasive ecosystem engineer, the alga Caulerpa taxifolia, indirectly facilitated community diversity by modifying the behaviour of a native ecosystem engineer, the clam Anadara trapezia, in southeastern Australia. In this study, clams in Caulerpa-invaded sediments partially unburied themselves, extending >30% of their shell surface above the sediment, providing rare, hard substrata for colonization. Consequently, clams in Caulerpa had significantly higher diversity and abundance of epibiota compared with clams in unvegetated sediments. To isolate the role of clam burial depth from direct habitat influences or differential predation by habitat, we manipulated clam burial depth, predator exposure and habitat (Caulerpa or unvegetated) in an orthogonal experiment. Burial depth overwhelmingly influenced epibiont species richness and abundance, resulting in a behaviourally mediated facilitation cascade. That Caulerpa controls epibiont communities by altering Anadara burial depths illustrates that even subtle behavioural responses of one ecosystem engineer to another can drive extensive community-wide facilitation.

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