Controlling factors in planktonic communities over a salinity gradient in high-altitude lakes

This study aimed to determine the factors affecting plankton structure along a salinity gradient during the summer in high-altitude endorheic lakes in Catamarca Province (Argentina). During the summer 2013, eight lakes located between 3000 and 4300 meters above sea level were sampled in a 6-day period being analysed plankton, limnological variables and flamingo abundance. Principal Component Analysis explained 80% of the system variability, permitting lakes to be ordered by salinity: subhaline (SH), hypohaline (HH) and mesohaline (MH). A total of 101 phytoplankton taxa were registered, having Bacillariophyceae the highest richness (43 species registered). HH lakes were dominated by Bacillariophyceae (between 65 and 100%), while Chlorophyceae and Euglenophyceae were more abundant in SH and MH lakes. Zooplankton was poorly represented in richness (only 21 species were registered). MH lakes were dominated by Copepoda (> 85% of total abundance) and HH lakes by Rotifera (> 51% of total abundance). It was not found a clear pattern in SH lakes. The redundancy analysis explained 70.7% of phytoplankton variability and 75.7% of zooplankton variability. Bacillariophyceae presence was associated with availability of dissolved silica (Si), while Euglenophyceae and Chlorophyceae were associated with a higher nitrogen: phosphorus ratio. Cladocera and Copepoda abundance were linked to Euglenophyceae abundance and the area of lakes while Rotifera displayed a positive relation with the concentration of dissolved organic matter. We conclude that both phytoplankton and zooplankton abundance are mainly controlled by Bottom-Up forces including dissolved Si for Bacillariophyceae, and availability of Euglenophyceae for zooplankton while salinity and altitude have an effect on plankton richness distribution.