Competition between the Cyanobacterium Limnothrix redekei and Some Spring Species of Diatoms under P-Limitation

The nutrient saturated growth and the competition between Limnothrix redekei and some spring diatoms for phosphate were studied in semi‐continuous cultures at 10°C with a 6/18 h light/dark cycle and at 15 °C with a 12/12 light/dark cycle. Under these conditions in unialgal cultures, the maximum specific growth rate of Limnothrix redekei was two to three time lower than that of the diatoms. However, Limnothrix redekei was the superior competitor for phosphate under both conditions in mixed cultures. The diatoms in mixed cultures from each species with Limnothrix redekei were competitively displaced but at a different rate. This allowed the diatoms to be ranked in terms of their competitive ability for phosphate at 10°C as follows: Synedra acus > Asterionella formosa > Stephanodiscus minutulus > Nitzschia acicularis > Cyclotella meneghiniana > Stephanodiscus neoastrea > Stephanodiscus hantzschii. The competitive ability of Limnothrix redekei at 15 °C was increased and the rank order of diatoms slightly changed. The hypothesis that cyanobacteria are promoted by phosphate because they are inferior competitors for phosphate is incorrect for Limnothrix redekei.