Effect of salinity on growth and toxin production in cultures of the bloom-forming cyanobacterium Nodularia spumigena from Australian waters

Nodularia spumigena Mertens blooms in a number of Australia's estuarine systems and coastal embayments. We investigated the effect of four salinities between fresh water (0 g kg(-1)) and sea water (35 g kg(-1)) on growth rate, cell yield, cell dry weight and toxicity of strains isolated from three Australian populations and studied under controlled environmental conditions in the laboratory. Growth rates were Significantly lower at 0 g kg(-1) than at the higher salinities, and cell yields at 0 and 35 g kg(-1) were lower than at 12 and 24 g kg(-1) salinity. This indicates that salinity extremes do not favour N. spumigena bloom development. Salinity affected nodularin content in the logarithmic phase of growth: as salinity increased, toxin content decreased, on both a dry weight and a per cell basis. In the stationary phase of growth, nodularin content was lowest at 35 g kg(-1) salinity. It increased significantly between logarithmic and stationary phases of growth. Cell mass (dry weight per cell) was not affected by growth phase. Our results indicate that mature blooms will be more toxic than developing ones because of their greater biomass and higher toxin content (on both dry weight and per cell bases).