Planktonic crustacean assemblages of three reservoirs from the Mexican Central Plateau: relationships with biotic and abiotic factors

Resumo

The reservoirs Trinidad Fabela (TF), Ignacio Ramírez (IR) and Tepuxtepec (T) are located along an altitude gradient in the upper Lerma Basin of the Mexican Central Plateau. Between July 1993 and June 1994, the planktonic crustacean assemblages of these systems were dominated by seven cladoceran species and five copepod species. Specific richness ranged from 13 species in TF to 16 species in T, out of a total 20 species. Nine species were common to all three systems, while the rest were absent from at least one reservoir. Canonic correspondence analysis showed that the structure and seasonal variation of these assemblages are regulated by factors directly related (transparency and dissolved oxygen) or inversely related (turbidity, temperature, mineralization and eutrophication) to the altitude at which the reservoirs are located. TF had the lowest levels of mineralization and the lowest specific richness, as well as the highest plankton diversity and mean density, while T had the highest mineralization and highest specific richness, but showed the lowest density. Crustacean mean size was smaller in T than in TF, possibly due to predation by fish in the former system and the presence of fish predators (waterfowl) in the latter, as well as the impact of the different hydrological regime and release schedules of the reservoirs.