Seasonal and spatial shifts in the volatile chemical profile of Cymodocea nodosa across marine and lagoon ecosystems.

Biogenic volatile organic compounds (BVOCs) are produced by marine organisms but remain largely understudied in seagrasses. To address this gap, this study investigates BVOC profiles from Cymodocea nodosa across seasons and between two ecosystem types: open-sea sites (Antibes, Saint Tropez, Porto Vecchio) and coastal lagoons (Thau, Urbino, Carteau). BVOCs were collected using headspace solid-phase microextraction (HS-SPME) and analyzed by gas chromatography-mass spectrometry (GC-MS). A total of 171 compounds were identified (145 in summer, 117 in spring, 115 in winter, and 103 in autumn). Volatilome composition varied significantly with season, explaining 26.1% of the explained variance, followed by site differences (14.1%), while ecosystem type had minor effects (< 5%). Functional diversity indices supported these patterns, indicating higher richness and abundance in summer, including 31 volatile compounds solely detected in summer. Cymodocea nodosa exhibited stress-related profiles, with geranyl acetone, β-cyclocitral, β-ionone, dimethylsulfide (DMS), and dihydroactinidiolide positively correlating with light, temperature, and salinity. Molecular networking showed the highest metabolite diversity and abundance in Urbino, including additional terpenoids and chlorinated and nitrogen-containing compounds. These findings highlight a haline- and heat-responsive phenotype and demonstrate strong seasonal and spatial variability in C. nodosa BVOC profiles, suggesting the presence of distinct Mediterranean site-specific chemical signature requiring further integrative metabolomic and genetic investigation.