Salomé Coquin's thesis “Specialised volatile and non-volatile metabolites of marine Magnoliophytes: characterisation and seasonality in the Mediterranean Sea”.”

Madame Salomé Coquin, doctoral student at IMBE, team Functional ecology: from socio-ecological systems to molecules, will publicly defend his thesis work on Wednesday 10 December 2025 at 9 a.m. in the INSPE amphitheatre, Campus Saint-Jérôme. To follow the viva. 

In front of a jury made up of :

• Dr Anne-violette Lavoir, Rapporteur, Université Côte d'Azur
• Dr Philippe Potin, Rapporteur, Roscoff Biological Station, University of Brest
• Dr Jean-Baptiste Raina, Examiner, University of Technology, Sydney, Australia
• Professor Patricia Bonin, Examiner, Aix-Marseille University
• Professor Catherine Fernandez, PhD supervisor, Aix-Marseille University
• Dr Elena Ormeno-Fuentes, Thesis co-director, CNRS

Summary of work:

The specialised metabolites of plant species, both volatile and non-volatile, are key molecules in the functioning of ecosystems, playing a major role in defence against biotic stresses (herbivory, competition) and abiotic stresses (drought, temperature), and in intra- and interspecific chemical mediation. Their study sheds light on the mechanisms of plant resistance and resilience in the face of environmental change.

Although crucial, little is known about these compounds in marine environments, particularly in marine Magnoliophytes, which are essential for water quality, coastal stability and blue carbon sequestration. These services are under threat, however, as seagrass beds are in decline due to global change. An in-depth understanding of their specialised metabolites could improve our understanding of the dynamics of these ecosystems in a context of global change.

The thesis work presented falls within this framework by aiming to 1) characterise specialised volatile metabolites or Biogenic Volatile Organic Compounds (BVOCs), 2) characterise specialised non-volatile metabolites, 3) determine the impact of seasonality on BVOCs and 4) determine the impact of seasonality on non-volatile metabolites for four major species of Mediterranean Magnoliophytes: Posidonia oceanica, Cymodocea nodosa, Zostera noltei and Zostera marina. The VOCBs were sampled by SPME fibres and analysed by GC-MS, and the non-volatile metabolites were extracted by solvent and detected by UHPLC-qToF-MS on seasonal spot samples.

The volatilomes (i.e., all the volatile compounds produced by an individual) and metabolomes (i.e., all the non-volatile compounds produced by an individual) of the various species of seagrass present a high degree of chemical diversity. Several families of compounds identified are well known in terrestrial environments, such as chicoric acid, rosmarinic acid, benzaldehyde and α-ionone. However, this work also highlighted the presence of compounds characteristic of the marine environment, such as halogenated compounds (1-chlorodecane) and sulphur compounds (dimethyl sulphide - DMS). Certain compounds proved to be specific biomarkers, making it possible to chemically discriminate between species, with volatile biomarkers such as citral, humulene and alloaromadendrene as well as non-volatile compounds such as rutin and kaempferol sulphate. The results obtained confirm the phylogeny of the species studied, with volatilomes and metabolomes that are more or less similar depending on the phylogenetic separations, proving the value of chemotaxonomy as a complementary tool for distinguishing species. Seasonality also has a significant influence on the production of specialised compounds. Summer is particularly notable for the large number of specific compounds such as 3-hexen-1-ol, menthol, zonarene, succinic acid and ferulic acid. These results suggest that the specialised metabolites of marine plants could act as defence compounds, thanks to their antioxidant properties, which have already been demonstrated in terrestrial environments. In addition to seasonal variability, this study has also highlighted significant spatial variability, which could reveal specific metabolic acclimatisation to environmental conditions, suggesting chemotypes in C. nodosa. These initial results provide a basis for future mechanistic research, in particular into the functional role of these compounds in the chemical ecology of seagrass beds.