Desiccation stress in two intertidal beachrock biofilms
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Chlorophyll a fluorescence was used to look at the effect of desiccation on the photophysiology in two beachrock microbial biofilms from the intertidal rock platform of Heron Island, Australia. The photophysiological response to desiccation differed between the beachrock microbial communities. The black biofilm from the upper shoreline, dominated by Calothrix sp., showed a response typical of desiccation-tolerant cyanobacteria, where photosynthesis closed down during air exposure with a rapid and complete recovery upon rehydration. In contrast, the pink biofilm from the mid-intertidal zone, dominated by Blennothrix sp., showed no distinct response to desiccation stress and instead maintained reduced photosynthesis throughout drying and re-wetting cycles. Spatial differences in photosynthetic activity within the black biofilm were evident with a faster recovery rate of photosynthesis in the surface cyanobacteria than in the deeper layers of the biofilm. There was no variation with depth in the pink biofilm. The photophysiological differences in desiccation responses between the beachrock biofilms exemplify the ecological niche specialisation of these complex microbial communities, where the functional differences help to explain their vertical distribution on the intertidal shoreline.
KeywordsPhotosynthetic Activity Spectral Reflectance Fluorescence Yield Heterocystous Rock Platform
We would like to thank the two anonymous reviewers for their time and helpful comments. This study was supported by grants from the Carlsberg Foundation (MK), and the Danish Research Council for Independent Research (MK) and the Aquatic Processes Group, UTS. KP is supported by a UTS Chancellor’s Fellowship. We thank Erik Trampe, Lars Behrendt and Anni Glud for assistance during the field work. Special thanks to Daniel Nielsen for comments on the manuscript. Marine Parks permit for collection of beachrock Hill R & Ralph PJ G08/27673.1.
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