Influence of Seasonal Abiotic Factors and Co-Existing Salt Marsh Plants on the Growth and Reproduction of Zostera japonica in Fluctuating Estuarine Environments

In the biodiverse Nakdong River estuary, the predominant seagrass and salt marsh species, Zostera japonica and Bolboschoenus planiculmis , are declining due to human and natural pressures. Our study investigated how environmental factors and co-existing salt marsh vegetation impact the growth and reproduction of Z. japonica . Understanding the reproductive dynamics of Z. japonica in this estuary is crucial, as sexual reproduction ensures the resilience and stability of seagrass populations in challenging environments. This study revealed that approximately 49% of Z. japonica shoots flowered, yet none persisted to the subsequent growth season, indicating a reliance on sexual reproduction for population resilience. The presence of competing B. planiculmis shoots and Ulva pertusa indirectly suppressed the growth and reproduction of Z. japonica by reducing light availability. Additionally, environmental stresses that occurred during summer, such as elevated temperatures, reduced salinity, and sediment transport, likely affected the vegetative and reproductive performance of Z. japonica in this estuary. Consequently, Z. japonica in this estuary has adopted a mixed annual life history strategy in response to these environmental oscillations. Our findings highlight the vulnerability of the Z. japonica population to seasonal environmental shifts and interspecies competition in this estuary, offering essential considerations for its conservation and effective management.