Effect of total dissolved solids and irradiance on growth and toxin production by Nodularia spumigena

The objective of this work was to determine the influence of total dissolved solids/salinity (TDS mg L^-1) on growth and biomass specific rates of nodularin (hepatotoxin) production by Nodularia spumigena 001E isolated from Lake Alexandrina, South Australia. Maximum biomass yield (dry matter, chlorophyll a and particulate organic carbon/POC) at 80 μmol photon m^-2 s^-1 was recorded at 3300 mg TDS L^-1 and decreased at salinities above or below this value (p < 0.05). The maximum biomass yield (dry matter and chlorophyll a) at 30 μmol m^-2 s^-1 occurred at a higher salinity of 9900 mg TDS L^-1. Cultures grown at 80 μmol m^-2 s^-1, at a TDS > 6600 mg L^-1, had significantly (p < 0.05) lower nodularin content (ml^-1 medium) than cultures grown at the same salinities at 30 μmol m^-2 s^-1. The maximum total toxin concentration (mL^-1 medium) occurred at 9900 and 3300 mg TDS L^-1 at 30 μmol m^-2 s^-1 and 80 μmol m^-2 s^-1 respectively. Toxin per unit biomass, expressed as dry matter, chlorophyll a and POC was similar for cultures grown at 30 μmol m^-2 s^-1 or 80 μmol m^-2 s^-1 at salinities < 6600 mg TDS L^-1. At salinities > 9900 mg TDS L^-1 the toxin content per unit biomass decreased at both irradiances, however, cultures grown at 30 μmol m^-2 s^-1 had a higher toxin content than those grown at 80 μmol m^-2 s^-1. The results indicate that not only do changes in irradiance and salinity directly influence growth and toxin production but that changes in irradiance affected the influence of salinity.