Chloe Stevenne - AIMS@JCU

Chloe Stevenne

College of Science and Engineering

Chloe Stevenne

College of Science and Engineering
Physiological characterization of a coral holobiont and its microbiome in response to nitrate enrichment and temperature stress

Chloe grew up in Belgium where she obtained a BSc degree in Biological Sciences at the University of Liège. She then followed with a MSc degree in Biology of Organisms and Ecology at the University of Liège and at the University of Bergen, Norway. During her studies, her interest grew for marine biology, particularly the study of marine benthic ecosystems, their dynamics, vulnerability, and resilience in the face of climate change and anthropogenic stressors. During her master thesis project conducted at the Institute of Marine Science (Bergen, Norway), Chloe investigated the impacts of acute crude oil exposure on the physiological responses and microbiome dynamics of a deep-sea boreal sponge. This research project further sparked her interest in physiology, genomics and holobiont studies.
She started a PhD at the University of Liège, investigating the nitrogen metabolism in coral holobionts, with a particular focus on understanding the pathways of nitrate assimilation and regulation between the coral host, the algal endosymbionts and the associated micorbiome. During the course of PhD, she worked on a variety of research projects, some of which in partnership with the Scientific Center of Monaco: assessing oxidative stress in Symbiodiniaceae in response to nitrogen treatment and thermal stress, nitric oxide production in Symbiodiniaceae, and deciphering expression and regulation of the enzyme nitrate reductase in both free-living and symbiotic Symbiodiniaceae. To conclude her PhD research, Chloe is currently working on a research project at AIMS investigating the interplay between nitrate enrichment and thermal stress on the coral physiological responses and microbiome dynamics.

Physiological characterization of a coral holobiont and its microbiome in response to nitrate enrichment and temperature stress

2019 to 2023

Project Description

Using a mesocosm set-up and high-throughput technologies, this research project aims at holistically characterising the physiological responses and microbiome dynamics of a Great Barrier Reef coral species in response to a combined nitrate enrichment and thermal stress. Along with physiological monitoring of the corals throughout the experiment, the surrounding water, coral mucus and tissues will be sampled to identify the microbial communities through 16S rRNA gene sequencing. This experiment aims to characterize the response of the coral holobiont to nitrogen enrichment and to identify any synergistic effect with thermal stress.

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.


Climate change,
Controlled Environment,
Coral reefs,
Manipulative experiments,
Molecular techniques,
Ocean warming,

Supervised By:

David Bourne (AIMS)

Yui Sato (JCU)