The marine research using the training vessel "Toyoshio-maru" of the Hiroshima University

Abstract

In this presentation, we will present the marine research using the training vessel "Toyoshio-maru" of the Hiroshima University, especially for the environmental changes of the Hiroshima Bay in the last three decades. Secchi depth will be controlled by the suspended particles in the water, especially soil, chlorophyll and/or phytoplankton biomass. Their relationship with primary production should be an important factor in coastal marine environments. In this presentation, we present the Secchi depth data obtained in the Hiroshima Bay in the last three decades by using "Toyoshio-maru". The Secchi depths in the whole station in the Hiroshima Bay tended to be increased during recent 30 years. Similar increases in the Secchi depth have been reported in Osaka Bay, Harima Bay, and Suo Nada. This may be one of the evidence of recent oligotrophication of the Seto Inland Sea. In this presentation, we will discuss the relation between Secchi depth and photon intensities under water.