Zooplankton structure in high-Andean reservoirs of southern Peru: an approach to its relationship with limnological variables

Peru has over 500 dams distributed throughout its territory; however, knowledge of their ecological functioning and the effects of damming on zooplankton communities at elevations above 3000 m a.s.l. remains limited. This study characterizes the composition of major zooplankton groups in six high-altitude reservoirs and identifies the principal limnological variables influencing their distribution. Between 2018 and 2023, we sampled six reservoirs, collecting relevant environmental data (including phytoplankton) along with simultaneous zooplankton samples. The analysis focused on three main zooplankton groups: Rotifera, Cladocera, and Copepoda (including both calanoids and cyclopoids). Zooplankton densities were generally low across the reservoirs, except at two sites where high abundances of rotifers and cladocerans were recorded. Overall, rotifers dominated in half of the reservoirs, although some also exhibited co-dominance by cladocerans or copepods. Rotifer abundance was positively correlated with electrical conductivity; cladoceran abundance was negatively associated with pH; and cyclopoid copepods were linked to higher total phytoplankton biovolume. These findings improve our understanding of zooplankton abundance and distribution in high-Andean reservoirs and highlight the influence of limnological factors on their occurrence.