# Chemical Diversity of Mediterranean Seagrasses Volatilome
## 1 Introduction  
Volatile organic compounds (VOCs) are low-molecular compounds (<300 Da) characterized by low boiling points and high vapor pressures [1]. Biogenic VOCs (BVOCs), emitted by terrestrial plants, bacteria, algae, fungi, and animals, make up over 90% of global VOC emissions [2, 3]. Terrestrial vegetation is the largest source, with estimated emissions exceeding 1 PgC yr\({}^{-1}\) (10\({}^{15}\) gC yr\({}^{-1}\)) [2, 4]. Plant-emitted BVOCs are extremely diverse such as terpenoids (e.g., isoprene, monoterrenes, and sesquiterpenenes), benzenoids and phenylpropanoids (e.g., benzaldehyde and cinnamyl alcohol), nitrogen and sulfur compounds (e.g., isothiances and dimethyl sulfide called afterward DMS), and green leaf volatiles (GLVs) [5]. Each plant species has a unique BVOC profile or volatilome, influenced by its genome. For instance, Brassicaceae species emit isothiances [6] rarely emitted by other plant families. BVOC emission rates vary with biotic (e.g., herbivory and parasitism) and abiotic (e.g., light, temperature, and drought) factors [7, 8] and act as defense compounds againstthese stresses [9; 10; 11]. Additionally, BVOCs play key roles in regulating interactions between species (e.g., plant insects) including pollination [12], herbivory [13], or response to pathogens [14]. BVOCs influence atmospheric chemistry by forming ozone (O\({}_{3}\)) and secondary organic aerosols (SOA) through reactions with oxidants like OH\(\bullet\) and NO\({}_{3}\bullet\)[15]. SOA influences atmospheric radiation by extending methane's lifetime and acting as cloud condensation nuclei [15]. These processes affect air pollution, climate, ecosystems, and human health, emphasizing the importance of characterizing BVOC sources [16]. While BVOCs from terrestrial ecosystems have been extensively studied since the 1980s with over 2500 articles published since 1990 [17], marine environments remain comparatively understudied [18; 19]. Oceans emit a large diversity of BVOCs including alkanes and alkenes [20; 21], aromatics hydrocarbons (benzene, toluene, and xylenes) [22; 23; 24], and oxygenated VOCs (OVOCs, e.g., acetone and methanol) [25; 26; 27; 28] as terrestrial vegetation. Oceans emit terpenoids, the largest class of specialized plant compounds [20; 29; 30; 31], as well as BVOCs seldom or never documented in terrestrial environments, such as sulfur-containing compounds (e.g., DMS) [31; 32; 33; 34; 35], halogenated compounds [36; 37; 38] including brominated (e.g., CHBr\({}_{3}\)) and iodinated compounds (e.g., CH\({}_{3}\)I) [24; 39]. These emissions, primarily highlighted in pelagic zones, are linked to sea surface processes [40], phytoplankton [41], and bacteria [19; 42]. Recent reviews reveal limited research on benthic organisms, with 112 studies on macroalgae, 4 on seagrass, and 2 on corals [19; 43]. It can be speculated that BVOCs have a similar role in marine ecosystems to that in terrestrial environments. In the context of global change (rising temperature, ocean acidification, and salinity shifts [44]), studying BVOCs could reveal insights into ecosystem adaptation and resilience. Benthic ecosystems, covering vast coastal areas, may significantly influence the oceanic BVOC budget and atmospheric processes, as phytoplankton does [45; 46]. However, emissions from benthic systems, particularly seagrass meadows, remain underexplored due to limited data [19; 43]  
Seagrasses, around 70 marine flowering plant species [47; 48], form vast meadows that span over 300,000 km\({}^{2}\) globally [49]. Seagrasses are an important component of marine and coastal lagoon ecosystems providing essential ecological services such as nursery habitat, food source, coastal protection, sediment stabilization [48; 50], and carbon sequestration [51; 52]. Despite representing less than 1% of total marine primary production, seagrasses are responsible for sequestering 10% of carbon in ocean sediments for millennia and mitigating the effects of climate change [53; 54].