Benthic habitat mapping for the nearshore ecological monitoring of Dokdo (Dok island) in the East Sea (Sea of Japan)

Abstract

The Dokdo (do means an island) volcano comprises two main islets (Seo-do and Dong-do) and the associated submerged volcanic edifice in the Ulleung Basin, the East Sea. We have been obtained the detailed bathymetry data using multibeam echosounder for the benthic habitat mapping of the southern coastal area of Seo-do. The side scan sonar survey for producing seafloor backscattering images was carried out. High-resolution underwater photograph images and surface sediment samples were acquired by scuba diving surveys. The precise topographical maps of the survey area show that the range of water depth is about from 1 to 28 m and the underwater reefs are irregularly scattered and extended from inland of Seo-do in the shallow water area. In the underwater reefs area, the flank slopes are very steep and irregular, overlain by many large or small submerged rocks, indicating partial erosion due to waves, strong currents and weathering. And below ~15 m, the bathymetry gradually transitions to a relatively even undulation with a smooth slope. The seafloor backscattered image maps show that many large or small submerged rocks occur in the shallow water and other seabed area is covered with small gravels. Based on the analysis of the sediment samples, gravels were dominated in shallow water whereas sand particles increased in deep water. High-resolution underwater composite photograph image maps are draped on the bathymetry for