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Climate change and disease: bleaching of a chemically defended seaweed

Authors

  • ALEXANDRA H. CAMPBELL,

    1. Centre for Marine Bio-Innovation, Evolution and Ecology Research Centre, School of Biological, Earth and Environmental Sciences, Sydney, New South Wales 2052, Australia
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  • TILMANN HARDER,

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

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

    1. Centre for Marine Bio-Innovation, School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, New South Wales 2052, Australia 2052
    2. Singapore Centre on Environmental Life Sciences and Engineering, Nanyang Technical University, Singapore 637551, Singapore
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  • PETER D. STEINBERG

    1. Centre for Marine Bio-Innovation, School of Biological, Earth and Environmental Sciences, Sydney Institute of marine Sciences, Sydney, New South Wales 2052, Sydney, Australia
    2. Institute of Marine Sciences, Chowder Bay 2088, Australia
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Alexandra H. Campbell, Evolution and Ecology Research Centre, University of New South Wales, Sydney, New South Wales 2052, Australia, tel.+61 2 9385 8775, fax:+61 2 9385 1554, e-mail: alexandra.campbell@unsw.edu.au

Abstract

Disease is emerging as an important impact of global climate change, due to the effects of environmental change on host organisms and their pathogens. Climate-mediated disease can have severe consequences in natural systems, particularly when ecosystem engineers, such as habitat-formers or top predators are affected, as any impacts can cascade throughout entire food webs. In temperate marine ecosystems, seaweeds are the dominant habitat-formers on rocky reefs. We investigated a putative bleaching disease affecting Delisea pulchra, a chemically defended seaweed that occurs within a global warming ‘hot-spot’ and assessed how patterns of this phenomenon were influenced by ocean temperature, solar radiation, algal chemical defences and microbial pathogens. Warmer waters were consistently and positively correlated with higher frequencies of bleaching in seaweed populations, but patterns of bleaching were not consistently influenced by light levels. Bleached thalli had low levels of antibacterial chemical defences relative to healthy conspecifics and this was observed across entire thalli of partially bleached algae. Microbial communities associated with bleached algae were distinct from those on the surfaces of healthy seaweeds. Direct testing of the importance of algal chemical defences, done here for the first time in the field, demonstrated that they protected the seaweed from bleaching. Treatment of algal thalli with antibiotics reduced the severity of bleaching in experimental algae, especially at high water temperatures. These results indicate that bleaching in D. pulchra is the result of temperature-mediated bacterial infections and highlight the potential for warming to influence disease dynamics by stressing hosts. Understanding the complex ways in which global change may affect important organisms such as habitat-forming seaweeds, is essential for the management and conservation of natural resources.

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