Vertical zonation and production rates of epiphytic algae on Phragmites australis

1. The vertical distribution of chlorophyll in epiphyton on Phragmites australis showed a peak in the middle sections of the submerged parts. Just below the water surface and above the sediment, chlorophyll concentrations were much less. 2. During winter and early spring, loosely attached diatoms were predominant just below the water surface and on the middle sections of the Phragmites plants. Near the bottom, adnate diatoms, parenchymatous thalli of chlorophytes and cyanobacteria were abundant. 3. At high photosynthetic active radiation (PAR) during May, filamentous species of Ulpthricophyceae and Zygophyceae developed dense populations on the middle sections of the stems. 4. Primary production rate was proportional to chlorophyll concentration although production maxima were recorded above the biomass maxima. 5. Where illumination was low, the chlorophyll-specific rate of photosynthesis (P^B rate) decreased proportionally with the vertical decrease of PAR in the littoral zone, independent of the chlorophyll concentration on the stems. 6. When illumination was high, the P^B rate decreased as biomass increased, and was independent of surface radiation. 7. The dependence of primary production rate on chlorophyll concentration produced a saturation curve with a maximum production at 4.6 μgC cm^?2h^?1.