Nodularia spumigena, like many cyanobacteria, produces specialised reproductive structures, known as akinetes, which are believed to allow survival under unfavourable conditions. This study investigated the effects of salinity, nitrogen and phosphorus concentration at two irradiances on akinete differentiation in a N. spumigena isolate from the Gippsland Lakes, Victoria, Australia. A computer image analysis program was used to photograph filaments and assess production of akinetes over time in separate experiments for each environmental parameter. Heterocyst production and cell morphology were also examined. The results suggest that akinete production increases over time. Production of akinetes is further increased at low and high salinities and with the addition of nitrate. Higher irradiance increases akinete differentiation, although in combination with different phosphorus concentrations causes varied effects. The development and sedimentation of akinetes may provide an inoculum for reoccurring blooms. Heterocysts were only observed during experiments with varying salinity and nitrogen exposures. Light quantity appeared to play a large role in heterocyst production. The ability of N. spumigena to produce akinetes and heterocysts is likely to be part of the reason for its success and continual occurrence in estuarine environments low in nitrogen, such as the Gippsland Lakes, Victoria, Australia. Factors known to reduce heterocyst and akinete production will provide new insight to possible management controls for this species.
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