The effect of salinity on the growth, toxin production, and morphology of Nodularia spumigena isolated from the Gulf of Gdansk, southern Baltic Sea

Culture experiments on the toxic Nodularia spumigena strain NSGG-1 isolated from the Gulf of Gdanask showed a significant effect of salinity on growth and nodularin production. Growth of the NSGG-1 strain, was optimal between 7 and 18 psu, lower at 3 and 24 psu and was significantly inhibited at the extreme salinities of 0 and 35 psu. Nodularin (NOD) content of N. spumigena, estimated by the NOD/Chla ratios, correlated positively with salinity and increased from 0 to 35 psu. The NOD/Chla ratio on day 10 of growth was high, and, reached the maximum at day 30. A sudden increase in salinity from 7 to 18 and 35 psu resulted in plasmolysis of Nodularia cells. Salinity was also observed to have other effects on NSGG-1; the filaments were longest at 7 psu, while an increased number of akinetes were formed at 35 psu. The number of heterocytes was markedly reduced at the extreme salinities. This latter finding might explain why Nodularia blooms do not occur outside a certain salinity range in nitrogen-deficient waters.