Salinity adaption and toxicity of harmful algal blooms in three bays of Great Salt Lake (USA)

Cyanobacterial blooms can be harmful to animals and humans exposed to their toxins; however, their environmental drivers and boundaries still need to be elucidated. Salinity has been demonstrated to be an important driver of community composition that sets boundaries of species migration and survival. The filamentous cyanobacteria Nodularia spumigena forms dense blooms in estuaries around the world, produces the hepatotoxin nodularin, and has been thought to not survive or fix nitrogen (N) in high salinities. From 2005-2009 we studied three bays of Great Salt Lake (USA), two of which are estuaries with salinities ranging from 0 to >90 g l^-1 while the third, Gilbert Bay, had a salinity near 160 g l^-1. Bear River Bay and the larger Gilbert Bay were meso‑eutrophic, while Farmington Bay, which receives direct inputs of secondary-treated sewage, was hypereutrophic with mean chlorophyll concentrations of 149 µg l^-1 and dense blooms of N. spumigena. Cell densities were >500 times those of Nodularia studied in the Baltic Sea. In Farmington Bay blooms occur at salinities ranging from 8-50 g l^-1, which are much higher than usually reported for this taxon. Concentrations of the cyanotoxin nodularin reached 660 µg l^-1 (mean = 41 µg l^-1), far above critical thresholds for contact recreation and above those causing bird mortalities elsewhere. The mean N₂ fixation rate of Nodularia measured over a salinity range of 14 to 52 g l^-1 was 47 mg N m^-2d^-1, which is among the highest reported values for freshwater and marine ecosystems. The local adaptation of Nodularia to the extreme salinity conditions in Great Salt Lake furthers our understanding of salinity adaptation and the potential spread of this species to new regions.