Transcriptional Variability Among Posidonia oceanica Meadows Reveals Pronounced Spatial Heterogeneity Across Gökova Bay (Eastern Mediterranean)

Posidonia oceanica is a key foundation species of Mediterranean coastal ecosystems and is increasingly exposed to environmental stressors and local anthropogenic pressures. Understanding its early physiological responses is therefore essential for effective ecosystem monitoring and conservation. In this study, we investigated spatial variability in gene expression in P. oceanica across contrasting habitats within the eastern Aegean Sea. Samples were collected from outer bay, transition, and inner/coastal stations, and the expression of genes related to photosynthesis, antioxidant defense, heat stress and metal detoxification was quantified using RT-qPCR. Gene expression patterns revealed pronounced spatial heterogeneity across the bay. Photosynthesis-related genes were generally downregulated at several transition and inner/coastal stations, suggesting reduced photosynthetic performance under environmental stress. In contrast, antioxidant defense- and heat stress-related genes showed localized upregulation, indicating activation of protective mechanisms. Principal component analysis explained 55.54% of the total variance within the first two components and clearly separated stations according to their transcriptional profiles. These findings demonstrate that environmental heterogeneity within Gökova Bay is reflected at the molecular level in P. oceanica, generating site-specific transcriptional responses. The study highlights the potential of multigene expression approaches as sensitive early warning indicators for detecting sublethal stress in seagrass ecosystems and supporting biodiversity conservation and coastal management.