[A-CG51] Coastal Ecosystems-2. Coral reefs, seagrass and macroalgal beds, and mangroves

[ACG51-P04] Adaptation and functional changes of eelgrass (Zostera marina) to changes in light quality associated with increased water depth.

*Yuji Takahashi¹, Yu Umezawa¹, Yoshikatsu Todoroki¹, Motohiro Ogawa¹, Toru Hirawake², Masakazu Hori³, Hiromori Shimabukuro³, Yuji Tsugawa¹ (1.Tokyo University of Agriculture and Technology, 2.National Institute of Polar Research (NIPR) , 3.Japan Fisheries Research and Education Agency)

Keywords:seagrass bed, Zostera marina, light quality, metabolome analysis

In coastal waters, the declline of seagrass beds results in the loss of ecosystem functions, creating a serious concern. It has been suggesuted that the degradation of seagrasses in the shallow coastal zone (0-2 m depth) is partly due to increased seawater temperatures and increased physical disturbances caused by typhoons and strong winds. Therefore, the deeper water areas (5-8 m depth) are considered a potential refuge site for seagrasses. Long-wavelength red light quickly attenuates in water with increasing depth, while light with a wavelength of around 550 nm reaches deeper depths. On the other hand, vegetables such as fruits and lettuce have been produced in the factory with added value by taking advantage of the fact that the type and amounts of metabolites accumulated vary depending on the wavelength of irradiating light. Therefore, in this study, we analyzed photosynthetic pigments and metabolites in seagrass inhabiting shallow and deep water to understand the differences in physiological adaptation and functionality of seagress depending on the depth of habitat.
Samples were collected on June 19, 2024 along the coast of Ikunoshima in the Seto Island Sea, where temperate seagrass (eelgrass:Zostera marina L.) was growing from shallow to deep water. Changes in light intensity and wavelength of transmitted light in the water were determined using an underwater spectroradiometer (RAMSES, TriOS). Photosynthetic pigment content was measured to evaluate the adaptation of seagrasses to changes in light intensity and quality. The metabolite analysis in seagrass leaves were conducted through measurements obtained with LC/Q-TOF/MS (Agilent 6546) and analysis using the mass spectrometry data processing program MS-DIAL 5.
A decrese in light intensity with increasing water depth and differences in attenuation rates among different wavelengths were observed. The light with wavelengths near 535 nm was reaching a depth of 8-10mt. Z.marina inhabiting deeper water increased photosynthetic pigment content, suggesting adaptation to a light environment with attenuated light levels. In metabolome analysis, principal component analysis (PCA) based on metabolites contained in shallow- and deep-water individuals revealed different trends in metabolite accumulation at different depths. Furthermore, the search for secondary metabolites that contribute significantly to the plot based on the results of the PCA revealed the accumulation of multiple flavonoid compounds in Z.marina inhabiting deeper water and the accumulation of sugars such as sucrose, which contribute to growth in those in shallow water. If the increase in metabolites with antioxidat and antimicrobial properties has the effect of decreasing the feeding and degradability of seagrasses, it was suggested that seagrass bed development in deeper habitats may compensate for the disadvantages of lower growth rates with the effect of higher CO₂ sequestration properties.