EFFECTS OF BOTTLE VOLUME, THALLUS WEIGHT, OXYGEN-SATURATION LEVELS, AND WATER-MOVEMENT ON APPARENT PHOTOSYNTHETIC RATES IN MARINE-ALGAE

The importance of container volume, thallus weight, O, tension, and water motion to measurements of photosynthetic rates in Ulva lobata (Kütz.) Setchel & Gardner (a species with a relatively high photosynthetic rate) and Colpomenia sinuosa (Roth) Derb. & Sol. (relatively low photosynthetic rate) were examined by means of O2 changes in bottles and through pH and O2 flux in continuously monitored chambers. The photosynthetic rate of Ulva averaged 36% lower in 310-ml bottles than in 1220-ml jars. Apparent photosynthesis varied as a function of (1) the initial dissolved O2 levels (regardless of bottle size), and (2) the particular metabolic reactions of the individual producers to different O2 tensions. Although similar trends were observed for Colpomenia, the effects of bottle size and initial O2 concentration were not as pronounced as for Ulva. The larger thallus weights of both species resulted in lower photosynthetic values, even in the large containers, due to clumping and self-shading of individual thalli. Mixing had a greater effect on apparent photosynthesis than on dark respiration, and was more critical for Ulva than for Colpomenia. Specific recommendations are put forth to deal with problems arising from the variations in methodology examined. © 1979.