Ecophysiology of a successful phytoplankton competitor in the African flamingo lakes: the green alga Picocystis salinarum (Picocystophyceae)

Picocystis salinarum is a globally widespread picoplanktonic green alga of saline lakes . This tiny alga has been recorded in four continents, and in some cases, it has become the dominant phytoplankton species. We examined the ecophysiology of a Kenyan strain of P. salinarum , collected from Lake Nakuru. The photosynthetic activity of the species was measured in seventy-two combinations of light intensity and temperature. The photosynthetic activity was low along the temperature gradient with an optimum at 31.9 °C; it varied between 0.097 and 1.233 μg C μg −1 Chl a h −1 . The ability of P. salinarum to utilize low light intensity ( α varied between 0.0061 and 0.1 (μg C μg −1 Chl a h −1 ) (μmol photons m −2 s −1 ) −1 ) and its susceptibility to photoinhibition at different temperatures confirm the species’ preference for low light intensity, which is already shown by its I k values (1.0–89.3 μmol photons m −2 s −1 ). The salinity tolerance of P. salinarum , more specifically the effect of changes in the concentration of chloride (NaCl) and carbonate forms (Na 2 CO 3 and NaHCO 3 ), was investigated in continuous cultures. The dominant ion of the medium greatly affected the growth of P. salinarum : significantly higher growth rates were recorded in carbonate form-dominated media as compared to chloride-dominated ones; the highest growth rate was observed at the highest concentration. The observed physiological properties (slow growth, low photosynthetic activity) are not typical of a dominant species; however, the high conductivity tolerance could be a key factor explaining the success of P. salinarum .