Growth response of the picoplanktic Picocystis salinarum and the microplanktic Limnospira (Arthrospira) fusiformis strains from Lake Nakuru (Kenya) to rapidly changing environmental conditions

Abstract

The East African soda lakes are known worldwide for their huge populations of lesser flamingos. Their phytoplankton community is often dominated by the cyanobacterium Limnospira fusiformis, the main food of lesser flamingos. In the early 2010s, the population of the cyanobacterium collapsed and the picoplanktic green alga Picocystis salinarum became dominant in Lake Nakuru. Consequently, lesser flamingos had to migrate to other lakes in search of food. To establish the reasons for the success of P. salinarum, photosynthesis measurements have been performed on monoalgal cultures of both species. The examined environmental variables (temperature, light intensity) were not responsible for the dominance of P. salinarum either alone or in their any combination. Moreover, photosynthetic activity of the cyanobacterium was higher by an order of magnitude during all light and temperature treatments. Co-cultivation of L. fusiformis and P. salinarum in a chemostat revealed that a possible reason for the Limnospira replacement can be a rapid and remarkable increase of conductivity, as P. salinarum showed higher level of tolerance to this rapid change. Shortly after returning to the initial conductivity levels, the population of L. fusiformis recovered quickly.