Planktonic crustacean assemblages in a system of three reservoirs in the mexican Central plateau: Seasonal and spatial patterns

Planktonic crustacean assemblages were examined monthly for one year in a system of three reservoirs in the Mexican Central Plateau (Rio Grande de Morelia)—Lorna Caliente, Umécuaro and Cointzio. Temperature, dissolved oxygen, pH, conductivity, transparency, nitrites, nitrates, total phosphorus, iron, hardness, turbidity, and suspended solids were quantified. Fourteen species of planktonic crustaceans were observed, including four copepods and ten cladocerans; major phytoplankton taxa were Chlorophyceae, Bacillariophyceae, Dinophyceae and Cyanobacteria. The first two reservoirs were dominated by cladoceran assemblages, and species of Chlorophyceae and Bacillariophyceae were common. In Cointzio, the downstream reservoir, a seasonal shift in dominance from copepods to cladocerans was observed and cyanobacteria blooms prevailed. Canonical correspondence analysis showed an environmental gradient from the two upstream reservoirs (with cold, transparent, softer waters) to the downstream reservoir (with highly turbid, more mineralized waters). Specific richness, diversity. and the speed of the shift in dominance from cladocerans to copepods between the dry and wet seasons all increased in line with the mineralization gradient.