Effects of pH and inorganic carbon concentration on growth ofGracilaria secundata

Abstract

The growth of Gracilaria secundata was studied in sea-water media with different concentrations of dissolved inorganic carbon (0·4–11·5 mm DIC), pH values between 7 and 9, and in the presence and absence of carbonic anhydrase (CA). The growth rate of G. secundata was saturated at c. 2·5 mm DIC. The apparent K_m(DIC) for growth was estimated at 0·7 mm. Maximum growth occurred at pH 8·0. Addition of CA stimulated growth strongly. The results indicate that G. secundata utilizes HCO^- ₃ as a carbon source for growth. In cultivation tanks the growth rate of G. secundata was greatest when pH was stabilized by additions of NaOH/HC1 and CO₂ rather than controlled by CO₂ additions alone.