Flower production was very low perhaps due to self-shading in a dense population. Zostera marina L.behaves similarly, with 17% of reproductive shoots at a total shoot density of 162 shoots m(Bayer 1979), 5% reproductive at densities of 279–929 shoots m-2, (Poumian-Tapia and Ibarra-Obanda 1999) and 2% reproductive at densities of550–1400 shoots m-2(Wium-Anderson and Brorum 1984).