Seasonal links between metabolites and traditional seagrass metrics in the seagrass Halophila ovalis in an estuarine system

•Metabolomics and traditional monitoring enhance seagrass performance assessment.•Relative leaf metabolite abundance differed seasonally with environmental conditions.•Metabolomics helps unravel molecular stress mechanisms in seagrass Halophila ovalis.•Correlations between metabolites and seagrass metrics mainly driven by leaf δ13C. Monitoring of seagrasses has mainly relied on traditional seagrass metrics (e.g., biomass), which deliver reliable information about mortality but are unable to inform about impacts on seagrass health at the very early stages of stress exposure. Metabolomics is a novel molecular technique which can be used for early stress-detection in plants and also for unravelling the underlying mechanisms of stress response. In the Swan-Canning Estuary, south-west Australia, the seagrass Halophila ovalis is impacted by seasonal changes in sediment-and nutrient-stress. To date, it is unknown how H. ovalis responds to these seasonal stressors on a molecular level. Here, we used a combined approach of traditional seagrass metrics and metabolomics to create a holistic picture of seasonal influences on seagrass condition. Leaf samples of H. ovalis were collected from six different locations in the Swan-Canning Estuary in both summer and spring. We detected strong differences in metabolite profiles and relative metabolite abundance between seasons, with growth- and/or development-related metabolites being up-regulated in spring and stress-related (secondary) metabolites being up-regulated in summer. Metabolites were mostly related to leaf δ13C signatures, a metric that has been previously associated with variation in light and pH in the Swan-Canning. We demonstrate that a holistic approach which includes metabolomics into ecological monitoring can help to improve our understanding of the mechanisms underlying molecular (stress) responses in seagrasses which is crucial knowledge for management and conservation measures locally and globally.