The bottom environment and macrobenthic community of Osaka Bay, Japan in 2003 and 2011

The bottom sediment condition, macrobenthic abundance and community structure were investigated at 5 and 10 stations in 2003 and 2011, respectively, in Osaka Bay in April (May), July, October and January. The purpose of the study was to identify changes in the bottom sediment condition and its influence on the macrobenthic community in recent years. AVS values in 0-2 cm surface sediment at 5 stations in 2011 tended to be lower than those at the 5 stations in 2003. However, changes in TOC and TN were not found in recent years. The distribution of macrobenthic abundance and community structure in Osaka Bay in 2011 were not remarkably different from those in 2003. Macrobenthic abundance in autumn for the interior stations of Osaka Bay in 2011 was less than in 2003. The number of macrobenthic species in only part of Osaka Bay was higher in 2011 than in 2003. It is suggested that the improvement observed in the bottom condition represented by the decrease of AVS values has not yet led to changes in the macrobenthic community in Osaka Bay.