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

Abstract

Biomass, cover and agar quality of three species of Gracilaria were monitored monthly in three sites in Negros Oriental, central Philippines, during the period July 1992–June 1993. The biomass per unit area of G. arcuata peaked around March while G. salicornia was maximal around November. Seasonality in G. blodgettii is not obvious from our data as this is a highly harvested 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), 58–270 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 algae.