Seagrasses are flowering plants in the coastal waters. They grow in the muddy, sandy, coral rubble and massive dead coral in intertidal dan subtidal areas. They form monospecific- and mix vegetation. Seagrass research in Indonesian waters was pioneered by Zollinger (1848) until Kostermans (1962), they collected seagrasses for herbarium collection. Ecological seagrass studies was started in 1984 during Snellius Expedition II. Decline of seagrass beds accelerating globally from a median of 0.9 % yr-1 before 1940 to 7 % yr -1 since 1990. It is estimated that 29 % of seagrass global distribution has been lost since late 19th century. Threats to seagrass are natural (over grazing, wave and
current), and anthropogenic (reclamation, dredging, sand mining, sand sucking, eutrofication, seaweeds culture, and land base pollution). Function of seagrass beds as carbon stock and carbon sequestration is “old stuffs with new name”, old stuff (values of biomass and production of seagrasses in gr.DW/area/time)-> Seagrass beds, new name (the values of biomass and production in gr.C/area/time)->Global change. Study on community structure and productivity of seagrasses, biomass and production data in the dry weight is converted into carbon. There