Effects of disturbances on microbial community composition and activity of biofilms from the Great Barrier Reef

Tropical coral reefs worldwide are increasingly threatened by disturbances on both global and local scales. Of particular concern are reef ecosystems in close proximity to urbanized coastal areas, where extreme weather events in the summer wet seasons result in terrestrial runoff leading to reduced light and increased nutrient availability for benthic coral reef communities. Such runoff may deteriorate water quality along the Great Barrier Reef coast and hence affect coral reef dynamics, productivity and composition. Microbial biofilms respond rapidly to changing environmental conditions and may be useful bioindicators for water quality. To test this potential, microbial communities associated with biofilms were analysed by terminal restriction fragment length polymorphism (T-RFLP) and sequencing of 16S rRNA genes. Further, O2 fluxes, biofilm biomass and chlorophyll a contents were determined. Overall, microbial communities in biofilms established on standardised substrata (glass slides) shifted in response to high temperature, nitrate, pCO2 and light availability, and thus, efficiently reflect changes in ambient water conditions. Seasonal and water quality driven shifts in the relative abundances of key microbial groups in biofilms suggest they are useful bioindicators for tropical coastal water quality and may have implications for future coastal management. Further, it is suggested that climate change and terrestrial runoff will likely impact productivity, composition and functioning in future coral reef ecosystems