Climate change and disease: bleaching of a chemically defended seaweed

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.

The Second Skin: Ecological Role of Epibiotic Biofilms on Marine Organisms

“…There is some evidence that under warming stress the prevalence of diseases increases (e.g., Ainsworth and Hoegh-Guldberg, 2009; Mydlarz and McGinty, 2010; Campbell et al, 2011). Either pathogens become more abundant, or biofilm components turn virulent, or the defensive capacities of biofilm and/or host are weakened.…”

Evolution of Resistance to Quorum-Sensing Inhibitors

“…In natural marine environments, quite a few bacteria have been found to be associated with D. pulchra [144, 145]. Bacterial isolates from the distal portion of the thallus of D. pulchra had the ability to form biofilms.…”

Community Structure and Functional Gene Profile of Bacteria on Healthy and Diseased Thalli of the Red Seaweed Delisea pulchra

“…We have recently described a bleaching phenomenon in this alga, in which portions of the thallus lose their pigmentation and decay [9], [10]. The consequences of this bleaching disease are severe; because of the pattern of bleaching on the thallus relative to the production of reproductive tissue, bleached D. pulchra are essentially neutered, with the amount of reproductive tissue an order of magnitude less than that of healthy individuals [11].…”