GROWTH OF THE RED ALGA GRACILARIA-TENUSITIPITATA AT HIGH PH - INFLUENCE OF SOME ENVIRONMENTAL-FACTORS AND CORRELATION TO AN INCREASED CARBONIC-ANHYDRASE ACTIVITY

The ability of the red macroalga Gracilaria tenuistipitata var. liui Zhang et Xia to grow at a high pH was studied under different conditions in laboratory unialgal culture. Cultivation conditions were continuous light at 200-500 mumol photons m-2 s-1 and a temperature around 25-degrees-C in seawater of 6, 17 and 33 parts per thousand (kg m-3) salinity. Gracilaria tenuistipitata showed an euryhaline growth response. In all salinities G. tenuistipitata had the ability to increase the pH of the cultivation medium to above pH 9 (up to pH 10) and still maintain growth rates up to 47% d-1 when the cultures were aerated with ordinary air. The algae were able to grow at a high pH only if they were allowed to increase the pH by photosynthetic inorganic-carbon uptake from the cultivation medium. With addition of CO2 to the culture and the pH controlled to 8 the growth rate reaches over 60% d-1 during short periods. In the absence of pH control the pH fluctuated strongly when ammonium was used as nitrogen source but the pH was more stable when using nitrate. The influence of pH increase of the medium and the resulting low CO2 concentration on the activity of cabonic anhydrase (EC 4.2.1.1.) was studied. The relative activity of carbonic ahydrase increased when the cultures were aerated with CO2-free air. When the cultures were supplied with high concentrations of CO2 a slight decrease in carbonic-anhydrase activity was observed. The results suggest that the concentration Of CO2 in the medium influences the carbonic-anhydrase activity of the alga.