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[AHW22-P17] Process of spatio-temporal variation in seagrass-seaweed meadows in intertidal areas of Seto Inland Sea, western Japan
Keywords:seagrass-seaweed meadows, spatio-temporal variation, intertidal area, submarine groundwater discharge (SGD)
Seagrass-seaweed meadows are regarded as an important coastal ecosystem with several ecosystem services such as global carbon sink, maintenance of coastal food webs, and producing biodiversity. However, the process of these spatial distributions and temporal changes are not well studied for intertidal areas. In the present research, we aimed to examine the process of spatio-temporal variation in seagrass-seaweed meadows in intertidal areas of Seto Inland Sea, western Japan.
Our target area is located on coastal areas of the island in Seto Inland Sea. Distributions of seagrass, seaweed, and bottom materials were investigated at several tens of points from 2014 to 2020. From these results, it was found that the biomass of seagrass and seaweed had decreased significantly between 2014 and 2018, and then has been recovering in recent years. The factors that influenced this result were considered to be the decrease in water depth due to long-term sedimentation, changes in the type of bottom materials, and the supply of nutrients due to the extreme rainfall event in western Japan in 2018.
The results of principal component analysis (PCA) suggests that the distribution of seagrass and seaweed were greatly affected by the type of bottom materials: green algae tended to distribute in gravel-rich area, while eelgrass in the muddy and sandy area. The analysis also suggests that submarine groundwater discharge (SGD) influences the biomass of green algae. Besides, the results of nitrogen stable isotope ratio (δ15N) analysis revealed that seagrass and seaweed in the target area are strongly affected by the nitrogen supply from the terrestrial area through SGD.
*This work is supported by the research grant of “Grant-in-Aid for Scientific Research (B), 18H03411, 2018-2021, PI: Mitsuyo SAITO”.
Our target area is located on coastal areas of the island in Seto Inland Sea. Distributions of seagrass, seaweed, and bottom materials were investigated at several tens of points from 2014 to 2020. From these results, it was found that the biomass of seagrass and seaweed had decreased significantly between 2014 and 2018, and then has been recovering in recent years. The factors that influenced this result were considered to be the decrease in water depth due to long-term sedimentation, changes in the type of bottom materials, and the supply of nutrients due to the extreme rainfall event in western Japan in 2018.
The results of principal component analysis (PCA) suggests that the distribution of seagrass and seaweed were greatly affected by the type of bottom materials: green algae tended to distribute in gravel-rich area, while eelgrass in the muddy and sandy area. The analysis also suggests that submarine groundwater discharge (SGD) influences the biomass of green algae. Besides, the results of nitrogen stable isotope ratio (δ15N) analysis revealed that seagrass and seaweed in the target area are strongly affected by the nitrogen supply from the terrestrial area through SGD.
*This work is supported by the research grant of “Grant-in-Aid for Scientific Research (B), 18H03411, 2018-2021, PI: Mitsuyo SAITO”.