Two algal communities on unconsolidated sand, dominated by two Caulerpa populations, were studied in the southwestern New Caledonian lagoon. Biomass, growth rates and production were measured at two stations over one year. Biomass and growth rate of Halimeda were estimated monthly by counting the number of new and lost segments on tagged plants and by weighing them. Production was assessed monthly by comparing two successive measurements. The average rates measured were 0.60 s f-1 d-1 (segment frond-1 day-1 ) for Halimeda incrassata and 0. 15 s f-1 d-1 for H. discoidea. Production in terms of organic carbon amounted to 3.79 g m-2 y-1 for H. incrassata and 3.37 g m-2 y-1 for H. discoidea. The production of H. discoidea population is subject to seasonal variations.