Tidal zonation as a driver of reproductive and genetic divergence in Zostera japonica: molecular mechanisms and restoration insights

Seagrass meadows are vital ecosystems in global decline, necessitating restoration informed by adaptive mechanisms. Tidal zonation creates distinct habitats, driving adaptive divergence in the foundation species Zostera japonica . We investigated its reproductive strategies, population genetics, photosynthetic performance, and transcriptomic profiles across a tidal gradient comprising 3 distribution zones: high (longest emersion time), medium, and low (longest submersion time). Key findings include: (1) Sexual reproduction increased with tidal depth, peaking from June to October. The low zone exhibited high sexual output, linked to the regulation of key photoperiod pathway genes (e.g. CRY , COP1 ). The medium zone showed reproductive flexibility with upregulated jasmonic acid signaling genes (e.g. JAR1 , MYC2 ), while the high zone relied on asexual reproduction. (2) Genetic diversity was highest in the medium zone, with active gene flow to the low zone. The high and fragmented apical zones showed lower diversity and greater genetic distance. (3) Photosynthetic performance revealed complementary strategies: the low zone had the highest photosynthetic capacity, whereas the high zone prioritized photoprotection, accompanied by upregulated antioxidant (e.g. GGT , GSHB ) and photosynthesis-related genes (e.g. PsbA ). We conclude that tidal zonation drives fundamental trade-offs between persistence and dispersal, mediated by zone-specific physiological, genetic, and molecular adaptations. These insights provide a mechanistic framework for precision restoration, advocating for selecting source populations tailored to specific restoration site conditions.