The effect of pH upon the photosynthesis of littoral marine algae

Summary

The photosynthetic rates of a number of littoral marine algae were determined over a pH range from 8.1 to 10.3, employing the Winkler technique to measure evolved oxygen. In a large number of red, brown and green algae, the rate fell to a low value, or to complete inhibition, at pH 9.5 and higher. This indicates, in conformity with general permeability theory, that the HCO₃ ^}-ion cannot readily penetrate the cells, and is hence not available for photosynthesis.

However, in two genera of coralline red algae (Bossea andCorallina) photosynthesis persists up to pH 10 or higher (though at a considerably reduced rate). This can be interpreted as due to utilization of the HCO₃ ^}-ion (though probably not the CO₃=ion). But several other non-coralline red algae (Centroceras, Botryocladia andGastroclonium), as well as the brown algaPelvetia (and possiblyFucus), and the green algaeUlva andEnteromorpha display this same ability.

Thus the utilization of HCO₃ ^}-ion cannot alone be ascribed as the cause of calcium carbonate deposition, since several other non-calcareous algae have this same power. The utilization of HCO₃ ^}-at least permits calcification, however. The question might be reversed, to ask whyUlva, Enteromorpha. Pelvetia and several red algae are not calcified. Some cell wall property may be involved.