Drastic change of bivalves and gastropods caused by the huge reclamation projects in Japan and Korea

Abstract

In this study, I compared faunal change of bivalves and gastropods after the construction of the reclamation dike in case studies in Japan (Isahaya Bay) and South Korea (Saemangeum). In April 1997, the inner part of Isahaya Bay was isolated from the rest of Ariake Bay by a reclamation dike. In the inner part of this bay, 15 species of marine bivalves and gastropods were collected in large numbers before the dike was completed. These species were still alive in May 1997, but most of them had died by August 1997. However, a brackish bivalve species, Potamocorbula sp. that was not found prior to isolation of this bay, replaced the pre-isolation bivalve community from August 1997. In the outer part of Isahaya Bay, hypoxic water masses appeared around the mouth of the bay in June 1997, and most of the bivalve species distributed near the hypoxic regions decreased rapidly from 1997 to 1999. Thereafter, only a few bivalve species such as Modiolus (M.) comptus increased rapidly in abundance from June 2002. These faunal changes were strongly influenced by environmental changes, such as occurrence of hypoxic water and decrease of grain size of bottom sediments, and those are caused by isolation of Isahaya Bay. In Saemangeum area, Potamocorbula sp. and a few other species of bivalves and gastropods also increased temporarily after the dike construction. These results suggest that drastic changes of bivalves and gastropods after isolation are very similar in the Yellow Sea and Ariake Bay.