Abstract
Climate change is characterized not only by increase an mean temperature, but also an increase in the variability around the means causing extreme events like marine heatwaves. These events are expected to have strong influence on the ecology of marine foundation species such as the eelgrass Zostera marina. Bacterial and macroscopic foulers are ubiquitous in the marine environment; they can have detrimental impacts on macrophytes and warming is known to enhance bacterial fouling. Thus, to investigate the consequence of heatwaves on the chemical defence of eelgrass against microbial colonisers, we incubated Z. marina plants in the Kiel Outdoor Benthocosm system under ambient control conditions and two different heatwave treatments: a treatment experiencing two spring heatwaves followed by a summer heatwave, and a treatment only experiencing just the summer heatwave. The capacity to deter microbial colonisers was found to be significantly up-regulated in Z. marina from both heatwave treatments in comparison to Z. marina under control conditions, suggesting defence regulation of Z. marina in response to marine heatwaves. We conclude climate extremes such as heatwaves can trigger an regulation in the defence capacity, which could be necessary for resilience against climate change scenarios. Such dynamics in rapid regulation of defence capacity as found in this study could also apply to other host plant – microbe interactions under scenarios of ongoing climate change or extreme climate events like heatwaves.
Highlights
Climate change is predicted to affect life on earth
They peaked in July (0HW: 4.71 RU; 1HW: 4.93 RU, 3HWs 4.77 RU) and had lower and similar densities in May and August, but were unaffected by the heatwave treatments (p = 0.2714, Figure 2 and Table 1)
All five tested bacterial isolates were deterred by Z. marina surface extracts (Supplementary Figure S2)
Summary
Climate change is predicted to affect life on earth. Many species have already shifted their geographical range in response to global warming and a poleward redistribution of species has been documented in both terrestrial and marine environments (Sunday et al, 2012). The eelgrass ecosystem is very productive and supports a diverse assemblage of organisms (Hemminga and Duarte, 2000; Den Hartog and Kuo, 2006). Within this system, eelgrass together with seaweeds provides a supportive nursery habitat for several fish and shellfish species that are of economic importance (Orth et al, 2006; Plummer et al, 2013) and the basis of a complex food web that supports all other organisms. At the same time incidences of infectious diseases often increase with high temperatures, including wasting disease of Z. marina (Sullivan et al, 2018; Brakel et al, 2019), which might increase the sensitivity of eelgrass further
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