Cladocera in the eutrophic reservoir of Valle de Bravo. Annual study on its diversity, distribution, abundance, and new records

Background. The Valle de Bravo reservoir is part of the Cutzamala system that supplies drinking water to Mexico City. For this reason, it is essential to guarantee its conservation and the quality of its waters. Due to the increased discharge of agrochemical pollutants and domestic wastewater discharges into the reservoir, the eutrophication of its waters has been accelerated. Eutrophication is associated with developing harmful cyanobacterial blooms (HCBs), which can affect aquatic communities. Goals. This study aimed to evaluate the diversity, species richness, and abundance of cladocerans in the Valle de Bravo reservoir and to determine the impact of this eutrophic environment. Methods. Zooplankton samples were obtained at six sampling stations through vertical throws, monthly during an annual cycle. Results. In total, 12 species of cladocerans were recorded, of which eight are new records for Valle de Bravo. The highest density of cladocerans occurred in March and June, with a notable decrease from August to November. Sampling sites S1, S2, and S4 had cladoceran densities higher than 60 ind. L-1. The species with the highest density was Bosmina longirostris, and five species were recorded throughout the year. The Shannon diversity index showed low values (1.0 a 1.48) associated with a eutrophic aquatic system. Conclusions. Even though the Valle de Bravo dam had blooms dominated by cyanobacteria at all times, the species richness was high compared to other freshwater ecosystems in Mexico, possibly reflecting that previous collection efforts were not intense enough to reflect the diversity and richness we recorded. Finally, the harmful effects of cyanobacterial blooms on aquatic biota cannot be ruled out.