Competitive Ability of Laboratory Batch Phytoplankton Populations at Limiting Nutrient Levels

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Abstract
A laboratory batch culture method, where dilute phytoplankton assemblages from Lake Mjosa, Norway, were used, was developed and used to determine the growth limiting nutrients for each of the most dominant populations. The relative competitive ability of the populations (based on growth rates) and the degree of growth limitation were also estimated under the temperature and light conditions employed. P or silicate was the growth limiting nutrient for Asterionella formosa Hass., Diatoma elongatum (Lyngb.) Ag., Tabellaria fenestrata (Lyngb.) Kutz. and Fragilaria crotonensis Kitt. Only P was growth limiting for Stephanodiscus hantzschii Gruen. and Oscillatoria bornetii f. tenuis Skuja. The experiments seemed to give results that can help to explain the development of the algal populations in Lake Mjosa. Oscillatoria competitively displaced Asterionella and the other diatoms at low silicate concentrations. Tabellaria was the most successful diatom at low P and silicate concentrations; Stephanodiscus had the lowest competitive ability at low phosphate concentrations. Classification systems for water samples based on simple chemical measurements (SRP and SRSi) [soluble reactive P and Si, respectively] and growth properties of algal populations are proposed.