Abstract
Deterioration of coral health and associated change in the coral holobiont’s bacterial community are often a result of different environmental stressors acting synergistically. There is evidence that water flow is important for a coral’s resistance to elevated seawater temperature, but there is no information on how water flow affects the coral-associated bacterial community under these conditions. In a laboratory cross-design experiment, Acropora muricata nubbins were subjected to interactive effects of seawater temperature (27 °C to 31 °C) and water flow (0.20 m s−1 and 0.03 m s−1). In an in situ experiment, water flow manipulation was conducted with three colonies of A. muricata during the winter and summer, by partially enclosing each colony in a clear plastic mesh box. 16S rRNA amplicon pyrosequencing showed an increase in the relative abundance of Flavobacteriales and Rhodobacterales in the laboratory experiment, and Vibrio spp. in the in situ experiment when corals were exposed to elevated temperature and slow water flow. In contrast, corals that were exposed to faster water flow under laboratory and in situ conditions had a stable bacterial community. These findings indicate that water flow plays an important role in the maintenance of specific coral-bacteria associations during times of elevated thermal stress.
Highlights
Deterioration of coral health and associated change in the coral holobiont’s bacterial community are often a result of different environmental stressors acting synergistically
No visual signs of stress or bleaching were evident for coral nubbins that were exposed to high water flow irrespective of temperature, or low water flow at the control temperature
The laboratory experiment provided evidence that increased water flow can limit the capacity of potential pathogens to proliferate, while in situ observations confirmed that water flow can influence microbial community composition and, potentially, coral health
Summary
Deterioration of coral health and associated change in the coral holobiont’s bacterial community are often a result of different environmental stressors acting synergistically. Corals that were exposed to faster water flow under laboratory and in situ conditions had a stable bacterial community These findings indicate that water flow plays an important role in the maintenance of specific coral-bacteria associations during times of elevated thermal stress. Recent studies have provided compelling evidence that coral-microbial associations are more complex than previously believed, and are significantly influenced by factors specific to the physiological[6,7] and physical environment of the coral host[1,8,9] Physical factors such as temperature, light and water flow vary significantly over stony coral reefs, and have an impact on both the host and its microbial communities[10,11,12,13]. Various studies have demonstrated that health of the coral host deteriorates when seawater temperature increases, and results in greater opportunities for infection by coral-associated pathogens[7,13,35,37,38,39,40]
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