Ecotypic differentiation in response to nutritional factors in the algal genusStigeocloniumKütz. (Chlorophyceae)

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Abstract
Growth responses of several Stigeoclonium strains to increasing levels of phosphate, ammonia and chloride in the culture medium were studied in an attempt to explain the distribution of the strains according to the nutrient levels of their habitats. The strains show relatively high saturation values and tolerances towards phosphate and ammonia, which is in accordance with the often severe eutrophication at their locations. No close correlation between demand or tolerance to phosphate and ammonia in culture and the field situation was found, apart from some incidental cases. With regard to chloride a positive correlation between salinity tolerances of the strains and mean chloride levels in the field could be established. Apparently chloride is an important factor in the distribution of at least several of the tested strains. One strain, originating from a brackish pond (5·5 g 1-1 chloride), was found to be clearly adapted. It grew well in medium with 10 g 1-1 chloride, a concentration at which the other strains did not survive.