Biomass and agar assessment of three species of Gracilaria from Negros Island, central Philippines

Biomass, cover and agar quality of three species of Gracilaria were monitor ed monthly in three sites in Negros Oriental, central Philippines, during t he period July 1992-June 1993. The biomass per unit area of G. arcuata peak ed around March while G. salicornia was maximal around November. Seasonalit y in G. blodgettii is not obvious from our data as this is a highly harvest ed species and we may have sampled after gleaners have harvested the algae. Agar yield values were for G. arcuata from Bais, 2.9 +/- 7% to 21.7 +/- 0.7 % while the same species from Siaton yielded 2.6 +/- 0.6% to 18.3 +/- 0.5%; G. salicornia yielded 2.9 +/- 0.1% to 15.7 +/- 1.3% and G. blodgettii, 0.1 % to 20.7 +/- 5.9%. Gel strength and viscosity were variable. Gel strength values were: G. arcuata (Bais), 17-260 g cm(-2); G. arcuata (Siaton), 58-27 0 g cm(-2); G. salicornia, 29.5-147 g cm(-2); G. blodgettii, 29.6-235 g cm( -2), and related to the 3,6-anhydrogalactose and sulphate content of the al gae.