[A-HW22] Material transportation and cycling in watershed ecosystems; from headwaters to coastal areas

[AHW22-P22] The effects of groundwater runoff on the coastal bacterial communities near the Ryukyu Limestone area

*Nanami Mizusawa¹, Akira Iguchi², Mariko Iijima², Rio Maruyama¹, Jun Yasumoto³, Ko Yasumoto¹, Mina Hirose⁴, Shugo Watabe¹ (1.Kitasato University School of Marine Biosciences, 2.National Institute of Advanced Industrial Science and Technology, 3.Faculty of Agriculture, University of the Ryukyus, 4.Tropical Technology Plus)

Corals are exposed to various stressors such as high water temperature and anthropogenic activities. For example, those inhabiting the coastal area are thought to be strongly affected by terrestrial runoff rich in nutrients and other anthropogenic contaminants. Groundwater is believed to act as a carrier for terrestrial materials running into coastal waters in the southern part of Okinawa Jima Island. However, its lineage to the damage of corals has not been well understood. Because the microbial community plays key roles in biogeochemical cycles, we performed as a first step metagenomic analysis on the coastal seawater as well as on the groundwater in the southern part of Okinawa Jima Island to evaluate the effect of the groundwater runoff on the coastal ecosystem including coral reefs. Coastal water and groundwater samples were collected from Yaese Town and filtered through 0.2 µm pore size filters. Amplicon libraries were constructed using Pro341F/Pro805R primers targeting the V3-V4 region of the bacterial 16S rRNA gene and analyzed by an Illumina MiSeq system, then obtained fastq files were processed by QIIME2. As a result, four prokaryotic phyla, Proteobacteria, Bacteroidetes, Cyanobacteria and Actinobacteria, were found to be dominant in both the coastal water and groundwater samples. Cluster analysis revealed that the samples were divided into 2 groups; one included 16 samples from the coastal waters, and another included 8 samples from the coastal water and 7 samples from the groundwater. Clustering of the latter group comprised of both the coastal water and groundwater samples suggest that the groundwater from certain areas in this study affects the coastal ecosystem at the bacterial community level. We are currently surveying environmental factors in the groundwater which may affect the coastal bacterial communities.