CE20 - Biologie des animaux, des organismes photosynthétiques et des microorganismes

Contrasting adaptive/acclimatization potentials of fire coral holobionts (Millepora spp) facing global change – the role of the Symbiodiniaceae photosymbiont – SymbioFire

Contrasting adaptive/acclimatization potentials of fire coral holobionts (Millepora spp) facing global change – the role of microbiome

Coral reefs directly support half a billion people and are home to a quarter of marine biodiversity. However, they have been facing an increasing number of local and global stressors that threaten their existence and the services they provide to human societies. The acceleration of massive bleaching events, more and more frequent, weakens the reefs which do not have time to recover between two events. It is therefore urgent to better characterize the adaptive capacities of corals.

hope for rapid adaptation in coral reefs ?

The microbiome, the set of microorganisms living in symbiosis with the coral, represents hope for their adaptation. It is now essential to characterize the coral-microbiome dynamics in order to elucidate its role in the acclimatization/adaptation capacities of organisms and in the resilience of coral reefs. The SymbioFire project has three main objectives: i) the fine characterization of the partners present in the fire coral holobiont (Millepora spp): host-Symbiodiniaceae-bacteria on 21 sites spread over 3 Indo-Pacific islands (Réunion, Moorea , Taiwan); ii) the study of the temporal stability of these associations thanks to a temporal follow-up of 2.5 years (4 monitorings per year and per island) and iii) the search for the transcriptomic responses of the partners in thermal and acid stress conditions .

SymbioFire is based on quarterly temporal monitoring in 3 Indo-Pacific islands coupled with spatial sampling around these 3 islands. Temporal monitoring is necessary, but sorely lacking so far, to be able to reveal the drivers of coral-microbiome dynamics. SymbioFire also takes advantage of the existence of a true natural laboratory along the Taiwanese coast: a temperature gradient linked to the Kuroshio current can thus demonstrate the possible evolution of the coral microbiome linked to ocean warming. Finally, acid and thermal stress experiments in the aquarium will complete these field samplings. The heart of the project is based on 'omics' approaches of metabarcoding, metatranscriptomics and metagenomics in order to finely characterize the dynamics of the microbiome in the natural environment and in the experimental environment.

SymbioFire is an ambitious project that will focus on studying the main drivers of the composition of microbial communities and understanding how this composition, in turn, affects the response of the holobiont when faced with various environmental pressures. By combining natural laboratory approaches, in vitro experiments, spatial sampling and temporal monitoring with the concomitant study of sediment and water samples to characterize environmental microbiomes, the project will achieve a precise and accurate picture of the major processes that shape the microbiome of fire corals in the Indo-Pacific.
SymbioFire will also focus on distinguishing the role of the environment from the role of the host evolutionary history on species assemblage, a factor often overlooked but which can influence contemporary ecological processes such as resistance and resilience.

With its eco-evolutionary framework for studying the coral holobiont in a changing environment, SymbioFire will provide an in-depth understanding of how the coral holobiont functions in time and space, and thus bring a unique perspective on the role of coral-microbiome dynamics in the persistence of populations and the resilience of coral reefs.
Eventually, if certain Symbiodiniaceae algae or certain bacterial consortia prove to be more advantageous, they could be inoculated, as is already the case in assisted evolution projects on the Great Barrier Reef.

A minimum of 4 manuscripts are envisioned:
(1) A first holobiont global diversity manuscript comparing the biodiversity of Symbiodiniaceae and bacterial communities within the 3 islands and between the 3 islands, as well as between the different species of Millepora;
(2) A second publication will focus on the changes in bacterial community and gene expression of coral host and Symbiodiniaceae during aquarium stress experiments;
(3) A third publication will focus on the viral diversity within Millepora species;
(4) A fourth publication will focus on the temporal dynamics of the microbial communities over the 2.5 years of survey.
In 2023, the results of the global diversity part will be presented at the Hydrozoan Society symposium (Norway). The final results of the project will be presented at the European and Asia-Pacific Symposia on Coral Reefs (2023). Throughout the project, the team will seek out various opportunities to attend conferences and share their findings with the scientific community.

In our context of global change and accelerated degradation of coral reefs, it is critical to better characterize coral-microbiome dynamics in order to decipher its role in the acclimatization / adaptive capacities of organisms and populations and resilience of coral reefs. The project SymbioFire has three main objectives: i) characterize each partner present in the fire coral holobiont (Millepora spp): host-Symbiodiniaceae-bacteria on 21 sites on 3 Indo-Pacific locations (Réunion, Moorea, Taiwan); ii) study the temporal stability of these associations through a temporal survey of 2.5 years (4 time points per year and per island), and iii) search for transcriptomic responses of the partners facing thermal or acidification stress. This project will use metabarcoding, metatranscriptomic and metagenomic approaches, both in situ and in vitro, with aquarium experiments. Furthermore, the study of sites along a temperature gradient on the eastern coast of Taiwan will provide a true natural laboratory showing the possible evolution of the coral microbiome linked to ocean warming. SymbioFire is an ambitious project that will investigate the main drivers of microbial community composition and how this composition can affect, in turn, the holobiont response when facing various environmental pressures. SymbioFire is based on a temporal survey, which is necessary, but crucially missing so far, to fully reveal the drivers of the coral-microbiome dynamics. SymbioFire will also focus on disentangling the role of the environment from the role of host species on microbiome assemblages. By combining natural laboratories, in vitro experiments, a thorough spatial and temporal sampling with the concomitant study of microbial composition of water and sediment samples, the project will allow reaching an accurate picture of the main processes shaping the microbiome of fire corals. Ultimately, with its eco-evolutionary framework for the study of the coral holobiont in a changing environment, SymbioFire will allow obtaining a deeper understanding of the coral holobiont functioning in space and time, and will thus bring a unique perspective on the role of the coral-microbiome dynamics on population persistence and reef resilience.

Project coordination

Emilie Boissin (Centre de recherche insulaire et observatoire de l'environnement)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Oregon State University / Vega Thurber Laboratory
CRIOBE Centre de recherche insulaire et observatoire de l'environnement
ENTROPIE Ecologie marine tropicale dans les Océans Pacifique et Indien
GM Génomique Métabolique
National Taiwan University / Institute of Oceanography

Help of the ANR 376,692 euros
Beginning and duration of the scientific project: December 2020 - 36 Months

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