Verena Witt (Germany) – Bourses IRCP 2013

Title of the project : Bacterial diversity and metabolism in tropical coral reef biofilms and sponges.

Abstract : Water quality in coastal regions around the world is declining in response to global (i.e., ocean warming and acidification) and local (i.e., land-based activities) anthropogenic impacts. Terrestrial runoff leads to decreased salinity, increased nutrient and reduced light availability to nearshore coral reefs with adverse effects. Bacterial communities associated with biofilms and sponges shift rapidly in response to changes in water quality and hence may serve as bioindicators for reef health. However, the potential of microbial bioindicators in reef organisms and whether microbial community shifts also alter community functioning remain unexplored. This study will therefore aim to identify microbial target indicator species, investigate the recovery/adaption potential of biofilm and sponge-associated microbes and determine potential consequent changes in organism functioning. Biofilms will be established on artificial substrates for 30 d in aquaria and sponges will be collected in situ along a water quality gradient comprising of inshore and offshore sites. Biofilms and sponges will then be exposed to inshore coastal sites highly exposed to terrestrial runoff (low light, high nutrient availability) and more pristine sites (high light, low nutrient availability). Transplant experiments will be performed with biofilm and sponge replicates (transplanted from impacted to pristine and vice versa) and sampled after 3 and 10 d exposure to the new site. 454 Tag-pyrosequencing will provide in-depth insight into the bacterial community composition and diversity. A metagenomic approach and direct measurement of biogeochemical O2 fluxes (dark/light incubations/luminescent optode) will reveal whether community shifts also alter the function of whole bacterial communities in biofilms and sponges. Findings may contribute to understanding consequences of terrestrial runoff on ecosystem functioning and resilience, and to the application of microbial biofilms/sponges in long-term water quality monitoring programmes and future coastal management.

Main results and perspective : It is important to investigate the diversity and function of bacteria in order to investigate their potential as bioindicators and furthermore to understand the resilience of coral reef ecosystems. Understanding qualitative and metabolic responses of biofilms to terrestrial runoff will contribute importantly to understanding coral reef ecosystems and further, may contribute to future coastal management which may be readily adaptable to other tropical regions.

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