Mytilus galloprovincialis (mussel) is a dominant species that attach to seawalls in eutrophied enclosed ports in Japan. Mussel drop-off occurrs every summertime causing sediment contamination at the sea bottom. To avoid the occurrence of mussel drop-off, we suggest to harvest an attached mussel just before the drop-off and composting it. To predict the occurrence of the mussel drop-off, we have to investigate it's biological reaction to influential factors, especially water quality variation. Therefore, we conduct the field observation and reaction experiment of mussels. As a result, we clarified that adhesion characteristics of mussels are affected by the pattern of water quality variation and caused by internal seiche which improves the number of byssus of the mussels.
