Yasutsugu　Yokohama^*　and　Keiko　Aioi^**

　　It　is　well　known　that　″moba"（algal　beds　and　sea‐grass　beds）is　important　in　the　coastal ecosystems. However,disappearance　of　″moba″is　eminent　in　the　recent　phenomena　of　the coastal　ecosystems,and　the　cause　is　not　clarified.An　effective　countermeasure　has　not　been worked　out,although　it　is　urgent.The　present　situation　of　vanishing　should　be　seized　at first.In　this　survey　the　areas　of　existing　″moba″were　estimated　in　each　prefectural　area from　1989　to　1991　and　extinct　area　of ″moba″during　13　years　from　1978　to　1991.According to　the　analytical　estimation　of　″moba″,the　cause　of　desappearance　could　be　clear　up.

　　The　total　area　of゛moba″on　the　coasts　of　Japan　is　201,212ha　in　1991.Extinct　areas of　″moba″was　6,403ha　from　1978　to　1991.Seventy　percent　of　the　extinct　area　is　occupied by　the　10　localities.The　biggest　area　was　in　Amakusa‐nada（western　side　of　Kyushu）,which　occupied　14.8% of　the　extinct　total　area.The　2nd　was　Akita（11.8%）and　the　3rd was　Hyuga‐nada　（eastern　side　of　Kyushu：6.8%）.

　　The　types　of　extinct　″moba″were　classified　into　the　following　four　types,Sargassum bed（22.2%）,seagrass　bed（19.9%）,Eisenia　bed（16.2%）,Undaria　bed（14.9%）.Dominant　types of　゛moba″were　different　in　each　locality.for　example,seagrass　beds　occupied　100% of extinct　″moba″in　Mutsu　Bay　and　seagrass　and　Sargassum beds　did　50%respectively　in　Ariake-kai　（western　side　of　Kyushu）.

　The　causes　were　reformation　of　the　coasts　such　as　reclamation（28.1%）,global　die　off so‐called ゛isoyake″（14.7%）,change　of　sea　circumstances（16.2%）and　indistinctness（40.6%）.The　present　situation　of　″moba″ habitats　is　quite　serious,because　most　of　the disappearing　area　has　been　damaged　and　destroyed　during　human　activities, mostly reclamation.The　conservation　of　″moba″as　an　important　coastal　ecosystem　is　urgently required.