Effects of light and temperature on volatile mediated seaweed-bacteria interactions

Land plants strongly contribute to BVOCs (biogenic volatile organic compounds) which serve multiple ecological roles. Aquatic macrophytes such as seaweeds underpin some of the most extensive and productive coastal ecosystems globally. However, seaweed health and fitness can be negatively impacted through excessive bacterial colonisation on their surface. Just like land plants, seaweeds employ a range of chemicals to deter, reduce or “garden” epibacterial colonisation. Like plants, seaweeds are known to be prolific producers of BVOCs in the marine environment. However, unlike plants, the ecological roles of seaweed BVOCs, particularly in mediating seaweed-bacteria interactions, has hardly been explored, especially when compared to the role of non-volatile compounds. Although BVOC production is known to vary with abiotic factors in seaweeds, we do not know yet how such variations may alter ecological interactions of seaweeds with bacteria. Using two ecologically important seaweeds, Fucus serratus and Palmaria palmata , we investigated how different different light and temperature conditions can influence BVOCs mediated interactions of seaweeds with their bacteria We tested F. serratus and P. palmata BVOCs for their effect upon settlement in twelve common marine bacterial strains for the temperature experiment and seven common bacterial strains for the light experiment. When the seaweeds were incubated at higher temperature (21°C), the bacterial strains in contact with BVOCs from both F. serratus and P. palmata had a higher relative settlement compared to seaweeds incubated at ambient temperature (16°C). Overall temperature had a stronger significant effect than species identity. The effect of light on the BVOC mediated seaweed-bacteria interaction was less distinct but had a stronger inter-specific effect. Our results provide the first evidence from an aquatic environment that BVOC mediated ecological interactions can vary between seaweed species and with light and temperature. • BVOCs mediate multiple ecological interactions. • We investigated how abiotic factors such as light and temperature can influence BVOC mediated seaweed-bacteria interactions. • We provide the first evidence from the aquatic system that abiotic factors can alter BVOC mediated host-microbe interactions.