Author(s): Akira Tai; Hiroki Iyooka; Tomonori Saita

Linked Author(s): Akira Tai

Keywords: Estuarine Ecosystem; Larval Distribution; Saltwater Intrusion; Advection-Diffusion Simulation

Abstract: A brackish water region keeps an ecosystem adapting to the complicated environment. However, the mechanism of the special ecosystem has not been clarified yet. In this study, I tried to elucidate the mechanism by comprehending the habitat and behavior of crustaceans which occupy an important position in a brackish water region. I targeted the Kitagawa River Estuary in Kyushu Island, Japan, and tried to know the characteristics of physical environment and the distribution of crustacean larval using two approaches: by field investigations and by numerical advection-diffusion simulations of the larval. First, in order to observe the condition of saltwater instruction in river channel and the distribution of crustacean larval, I conducted field surveys from August 29 to September 1,2015, when the river discharge was larger than usual because of rainfall. Second, I carried out numerical simulations to show the effect of the larval salinity preference on the distribution. I tried to reproduce the physical environment and the larval behavior from August 25 to September 3,2015, and used parameters of the salinity preference which was provided by the previous laboratory experiments. The results are as follows. 1) When the river discharge is large, the salinity distribution of the Kitagawa River looks fully stratified. 2) Crustacean larval is especially found in the north of the Kitagawa River Estuary, which means a groin makes the river flow into the north. 3) Even if the river discharge is appreciably large, the salinity preference enables crustacean larval to stay in river channel.

DOI: https://doi.org/10.64697/978-90-835589-7-4_41WC-P2033-cd

Year: 2025