GROWTH, NITROGEN-FIXATION, AND NODULARIN PRODUCTION BY 2 BALTIC SEA CYANOBACTERIA

In late summer nitrogen-fixing cyanobacteria Nodularia spumigena and A phanizomenon flos-aquae form blooms in the open Baltic Sea. N. spumige na has caused several animal poisonings, but Baltic A. pos-aquae is no t known to be toxic. In this laboratory study, performed with batch cu ltures, the influences of environmental conditions on the biomass and nitrogen fixation rate of N. spumigena and A. flos-aquae were compared and the toxin (nodularin) concentration produced by N. spumigena was measured. Several differences in the biomasses and nitrogen fixation r ates of N. spumigena and A. flos-aquae were observed. A. flos-aquae pr eferred lower irradiances, salinities, and temperatures than N. spumig ena. The biomass of both species increased with high phosphate concent rations and with accompanying bacteria and decreased with unnaturally high inorganic nitrogen concentrations. Nodularin concentrations in ce lls and growth media, as well as nitrogen fixation rates, were general ly highest under the conditions that promoted growth. Intracellular no dularin concentrations increased with high temperature, high irradianc e, and high phosphate concentration and decreased with low and high sa linities and high inorganic nitrogen concentrations. Nodularin concent rations in growth media increased with incubation time, indicating tha t intracellular nodularin was released when cells lysed. The different responses of A. flos-aquae and N. spumigena to changes in salinity, i rradiance, and temperature may explain the different spatial and tempo ral distribution of these species in the Baltic Sea. According to the results, toxic N. spumigena blooms may be expected in late summer in a reas of the Baltic Sea with high phosphorus concentrations and moderat e salinity.