DIFFUSION BOUNDARY-LAYER TRANSPORT IN GRACILARIA-CONFERTA (RHODOPHYTA)

A theoretical framework on the combined effect of water velocity and solute concentration on the photosynthetic performance of the red alga Gracilaria conferta (Rhodophyta) is developed. This is based on the balance between the rate of transport through boundary layers and Michaelis-Menten-type equations for carbon consumption and for production of oxygen and hydroxyl ions. By comparing the theoretical models with experimental data, we found that the mechanism of enhancing photosynthetic rates by increasing water velocity cannot be attributed to enhanced bicarbonate and CO2 transport, nor to CO2 as a sole source of carbon. Velocity-facilitated photosynthesis may be due to the enhanced removal of OH- ions, which inhibit photosynthesis when accumulated on the algal surface. Oxygen had no inhibitory effect on Gracilaria conferta.