Effects of light intensity and nutrients (N and P) on growth, toxin concentration, heterocyte formation and akinete germination of Nodularia spumigena (Cyanobacteria).

Harmful effects of the toxic cyanobacterium Nodularia spumigena were observed in experimental marine shrimp production ponds in Brazil. Strains of this cyanobacterial species were isolated and cultured, and in the present study, we evaluated the influence of light intensity and the concentration of dissolved inorganic nitrate and phosphate on the growth, toxin concentration, heterocyte formation and akinete germination of N. spumigena. A factorial experiment (3 × 3) was performed to test three light intensities and nutrient concentrations with a reduced nitrate concentration, a reduced phosphate concentration and a nutrient-replete f/2 medium. The influence of light intensity on growth and akinete formation was varied: the highest cell density and chlorophyll a were recorded at the lowest light intensity, while the high light treatment stimulated akinete formation. The availability of phosphate was the main factor favouring the growth of N. spumigena and the formation and germination of akinetes, while the concentration of nodularin per cell was highest under phosphate deficiency. This information is useful in the management of aquaculture ponds and other brackish and marine environments where the goal is to reduce N. spumigena blooms. [ABSTRACT FROM AUTHOR]