Presentation Information
[AOS26-P03]Seasonal variations in the nutritional status and growth condition of seagrass in coral reef estuaries
*Keisuke Umebayashi1, Kazuki Kondo1, Han Lyu1, Soh Sugihara1, Kenta Watanabe2, Kazutoshi Osawa3, Yu Umezawa1 (1.Tokyo University of Agriculture and Technology, 2.Port and Airport Research Institute, 3.Utsunomiya University)
Keywords:
Seagrass,Terrestrial element,Red soil (Red cray soil),Coral reef
In tropical and subtropical island regions, including Okinawa, Japan, terrestrial soil (hereafter “red soil”) runoff into coastal areas has become a significant threat to coral reef ecosystems. Red soil consists mainly of highly weathered fine particles, mainly silt-sized or smaller fractions, which are easily suspended in the water column and readily deposited on benthic habitats. When suspended or deposited, these particles reduce light availability and impair the physiological activity of corals and seagrasses. To address this issue, “Okinawa Prefecture Red Soil Erosion Prevention Ordinance” was enacted in 1995, resulting in a gradual reduction in red soil runoff.
On the other hand, red soil also contains elements essential for plant growth, such as iron (Fe), manganese (Mn), and silicon (Si). Coral reef sediments are primarily composed of calcium carbonate minerals derived from corals and foraminifera, and seagrass growth in such environments can be limited by Fe availability. Under the current reduction in red soil runoff, red soil–derived elements may function to alleviate nutrient limitation in seagrass.
In this study, seagrass and sediment samples were collected from coastal areas around Ishigaki Island, Japan. We evaluated seagrass nutritional status (i.e., particularly trace metals such as Fe and Mn) and health (leaf width, leaf length, number of leaves, photosynthetic pigments, etc.) during both summer and winter seasons. In selected sites and seasons, primary production measurements and carbon and nitrogen stable isotope ratio analyses were also conducted.
Although no significant seasonal differences were observed in seagrass morphology, carbon stable isotope ratios were consistently higher in summer at all sampling sites. Metal concentrations increased toward river mouths, suggesting uptake of red soil–derived elements by seagrasses. In the presentation, we will also discuss the seasonal variations of various metal elements in seagrass tissues.
On the other hand, red soil also contains elements essential for plant growth, such as iron (Fe), manganese (Mn), and silicon (Si). Coral reef sediments are primarily composed of calcium carbonate minerals derived from corals and foraminifera, and seagrass growth in such environments can be limited by Fe availability. Under the current reduction in red soil runoff, red soil–derived elements may function to alleviate nutrient limitation in seagrass.
In this study, seagrass and sediment samples were collected from coastal areas around Ishigaki Island, Japan. We evaluated seagrass nutritional status (i.e., particularly trace metals such as Fe and Mn) and health (leaf width, leaf length, number of leaves, photosynthetic pigments, etc.) during both summer and winter seasons. In selected sites and seasons, primary production measurements and carbon and nitrogen stable isotope ratio analyses were also conducted.
Although no significant seasonal differences were observed in seagrass morphology, carbon stable isotope ratios were consistently higher in summer at all sampling sites. Metal concentrations increased toward river mouths, suggesting uptake of red soil–derived elements by seagrasses. In the presentation, we will also discuss the seasonal variations of various metal elements in seagrass tissues.