[A-CG23] Coastal Ecosystems ? 1. Water Cycle and Land-Ocean Interactions

[ACG23-P06] The inflow of hot spring heat impact on fish communities around estuaries in Beppu, Oita prefecture

★Invited papers

*Makoto Yamada¹, Jun Shoji², Shinji Ohsawa³, Taketoshi Mishima³, Tatsuya Utsunomiya², Hisami Honda¹ (1.Research Institute for Humanity and Nature, 2.Center for Field Science of the Seto Inland Sea, Hiroshima University, 3.Institute for Geothermal Sciences, Graduate School of Science, Kyoto University)

Keywords:hot spring heat, fish community, around estuary, hot spring drainage

Hot spring drainage flows into a river and then flow into the coastal area in Beppu, Oita prefecture which is a region with many hot springs in Japan. In Hirata River where many hot spring drainage flow into, hot spring drainage creates a better habitat for Oreochromis niloticus (Nile tilapia), a foreign species, in terms of available food and water temperature. Hot spring drainage flow into the river except Hirata River in Beppu area. However, it is not clear that the influence of hot spring drainage on ecosystem of those rivers. In order to evaluate the impact of thermal energy from hot spring drainage on the fish communities near the estuary, we investigated water temperature, flow rate and fish communities near the estuaries of six rivers in Beppu area.
We sampled the fish using a small seine net in January 2015. Although the number of fish collected in four rivers was very small, Nile Tilapia and Opsariichthys platypus was collected in Hirata River and Haruki River, respectively. Hot spring drainage flow into these two rivers, however, there is a big difference in the water temperature near the river mouth in these two rivers. These results suggest the possibility that the difference in inflow of the hot spring heat affects the dominant species of the fish community near the estuary. In this presentation, we will discuss the inflow of hot spring heat impact on fish communities near the estuary with the result of the summer investigation.