Zooplankton Assemblages of an Argentinean Saline Lake during Three Contrasting Hydroperiods and a Comparison with Hatching Experiments

Many saline lakes are temporary, with large variations in salinity, and their biota is adapted to withstand unfavorable periods. Utracan Lake, in a protected area in central Argentina, was studied on three occasions under different environmental conditions. In 2007, depth and salinity were 2 m and 33 g/L, and six species were recorded in the zooplankton. In 2009–2010, its maximum depth was 0.3 m, its salinity exceeded 230 g/L, and only Artemia persimilis was recorded. Field studies to compare the active zooplankton of a third period were combined with laboratory tests to ascertain the composition of the egg bank (flotation with sucrose) and zooplankton succession (hatching from sediments). In 2017–2018 (third period), the depth and salinity were 1.75 ± 0.17 m and 47.19 ± 11.40 g/L, respectively. Five species were recorded, and A. persimilis was found coexisting with cladocerans, copepods, and rotifers. Brachionus plicatilis, Hexarthra fennica, Boeckella poopoensis, A. persimilis, and a single specimen of Moina eugeniae were recorded in hatching experiments; however, the latter species was not recorded again. No cladoceran ephippia were recorded in the flotation tests. Salt accumulation on the sediments during the Utracan drought (2010–2016) would have deteriorated the ephippia. The register of M. eugeniae in 2017–2018 could be largely because of recolonization by waterfowl. The conservation of Utracan Lake is therefore advisable, and the same goes for other nearby saline lakes, which can act as sources of propagules that cross terrestrial areas through transport by wind or zoochory.