Genevieve is from upstate New York, where she grew up in the Finger Lakes Region. She obtained her BSc in Biology from Haverford College, studying chemical mediation of bacterial-phytoplankton dynamics. Genevieve is working towards her MSc in Marine Biology at James Cook University, where she is excited to learn about coral holobiont dynamics.

Coral and microbial nitrogen fixation

2022 to 2024

Project Description

The main aim of this experiment is to assist Chloe Stevenne on her PhD project, working to characterize the physiological responses and microbiome dynamics of a coral from the Great Barrier Reef under enriched nitrogen and thermal stress conditions.

Project Importance

Coral reefs are amongst the most threatened marine ecosystems and are increasingly subjected to environmental stressors such as increased sea water temperature and eutrophication of oligotrophic coastal waters. Reef ecosystems constitute biodiversity hotspots and provide many vital ecosystem services which benefit both the marine environment and human populations. It is imperative that we acquire a better understanding of the physiological processes underpinning their vulnerability and/or resilience in the face of environmental change.
It is unclear whether nitrate is detrimental or beneficial to the coral holobiont or whether it benefits some partners of the symbiosis at the expense of others resulting in ambiguous responses at the holobiont level. Different lines of evidence support either higher tolerance to thermal stress of corals exposed to eutrophication or, on the contrary, enhanced vulnerability. Microbial contribution to coral ecological resilience has been overlooked for a long time but recent studies have shed light on the correlation existing between microbial communities and the top three stressors facing coral reefs (i.e. climate change, water pollution and overfishing). Changes in environmental factors seem to be driving forces for the variability observed in the functional potential of coral associated microbiomes. Such evidence emphasizes the need to better characterize the diversity and roles of coral microbiomes and to link genomic data to environmental parameters. This experiment will yield novel data that is essential towards better predicting coral responses to mixed stressors.

Project Methods

Using the SeaSim controlled environment, Acropora sp. coral nubbins will be exposed to a nitrate enrichment and a heat stress treatment using a cross-factor design over a period of 4 weeks. Throughout the exposure time, the coral’s physiology will be closely monitored and samples of mucus, tissue and surrounding seawater will be collected in order to characterise the microbial communities.
Coral nubbins’ health and photosynthesis will be closely monitored using a CoralWatch health chart and by measuring chlorophyll fluorescence emission with a PAM. The physiological status of the coral nubbins will be monitored by measuring respiration rates, photosynthesis, pigment profile, nitrogen uptake, growth rates and Symbiodiniaceae density following standardised protocols. Microbial communities will be monitored in the surrounding water, in the coral mucus and coral tissue by next-generation sequencing (NGS) of PCR amplicons targeting the 16S rRNA V5-V6 regions. Symbiodiniaceae community composition in the coral tissue will also be identified by NGS of PCR amplicons targeting the ITS2 rRNA region.

Project Results

It is expected to observe variations in the composition of the microorganisms community associated with the coral in response to the enrichment in nitrate and to the temperature rise. It is suspected that nitrogen enrichment and temperature stress act in synergy to induce changes in the coral functioning and in its associated microbial community with potentially marked health consequences for the holobiont. Often, our understanding of coral reefs health in response to environmental stressors is impaired by our lack of knowledge on coral holobiont’s functioning at the molecular and microbial level. This experiment aims at strengthening such knowledge which, in turn, will benefit our understanding of coral reef dynamics under the current pressures of climate change and anthropogenic stressors.

Keywords