Limnetica 40

In the present study, six reservoirs of the Ebro watershed were sampled during summer and autumn of 2016, with the objective of recognizing the zooplankton community, the environmental variables that are correlated with them and update the species checklist. We identify 40 zooplankton species among reservoirs: 21 rotifer species, 10 cladocerans, 8 copepods, and the veliger larvae of the invasive zebra mussel. Species that had higher abundances and biomass were: the rotifer Polyarthra dolichoptera (up to 278 ind/L), the cladoceran genera Daphnia spp. and Ceriodaphnia spp., the copepods Copidodiaptomus numidicus (83 ind/L), Acanthocyclops americanus (72 ind/L), Eudiaptomus vulgaris (62 ind/L) and zebra mussel Dreissena polymorpha (540 ind/L). In general, the smaller species were dominant during the summer while the larger species were dominant in the autumn. The density and biomass of zooplankton in four out of six reservoirs during the summer were double that in autumn. The main physicochemical variables correlated with the zooplankton species through a Canonical Correspondences Analysis (CCA) were: chlorophyll a, Secchi disk, total phosphorus, pH and depth. We report for the first time the species presented at the Ullibarri-Gamboa reservoir, and present new species registered in the reservoirs compared with those reported in previous studies. For the first time, the presence of the zebra mussel was detected at La Sotonera reservoir. This indicate its expansion throughout the watershed, suggesting that knowledge of zooplankton species and the changes that occur through time can be a tool for reservoirs and watershed management.