Zooplankton Seasonal Abundance of South AmericanSaline Shallow Lakes

Abstract

The central provinces of Argentina are characterized by the presence of a high number of shallow lakes, located in endorheic basins, many of which have elevated salinities as well as eutrophic or hypereutrophic condition. The zooplankton of four saline shallow lakes of the province of La Pampa was studied on a monthly basis during a 2-year period to determine its temporal and spatial variation.The surface of these shallow lakes (< 2.5 m depth) varied between 56.8 and 215.9 ha, and some have from 8.4 to 20.8 g · l -1 . The more saline lakes have "clear" water and the less saline lakes "turbid" water. Fishes, Jenynsia multidentata, were present in only two lakes during the last two months of the studied period.The zooplankton was composed of 17 taxa of Rotifera, 5 taxa of Cladocera and 4 taxa of Copepoda. The low diversity and the faunistic composition are characteristic of saline environments. Although the studied lakes share 38% of the species, the faunistic similarity was higher between the two least saline lakes. The lowest diversity was found in the two most saline lakes.All four shallow lakes were characterized by their very high zooplankton density, especially in the least saline lakes (< 80000 ind · l -1 ). The abundance is significantly correlated with the water transparency but not with salinity.The zooplankton temporal variation was characterized by the alternation of macro-and microzooplankton, probably regulated by competition and intrazooplanktonic predation. In each lake, the spatial abundance distribution of the macro-and microzooplankton was homogeneous. It was related to the shallow depht of the lakes and their polymictic condition.The SCHEFFER model on alternative states in shallow lakes acknowledges that it cannot be applied to saline lakes because Daphnia, the main responsible for the clear water state, is not tolerant to high salinity. Our study shows that the most saline lakes, where the halophylic Daphnia menucoensis is abundant, have also the most clear waters. Another difference that we found with regards to the mentioned model is that, in turbid lakes, it could not have had a top-down control on macrozooplankton exerted by fishes because in these lakes fishes were practically absent.

Zooplankton richness, abundance and biomass of two hypertrophic shallow lakes with different salinity in central Argentina

“…These species are more commonly found in other environments of low salinity of La Pampa (Vignatti et al 2007, Echaniz et al 2008. The species that prevailed in Bajo de Giuliani were the halotolerants Cletocamptus deitersi, M. mendocinus and B. poopoensis (Menu-Marque & Locascio de Mitrovich 1998, Echaniz et al 2006, Vignatti et al 2007). The highest number of shared species was recorded among rotifers and most of the taxa recorded were of cosmopolitan distribution (Segers & De Smet 2008) and euryhaline (Fontaneto et al 2006).…”

“…The presence of large-sized cladocerans, especially that of the genus Daphnia, was sporadic and never reached high densities, possibly due to the predation exerted by fish (Grosman & Sanzano 2003, Boveri & Quirós 2007, Manca et al 2008) present in both lakes. The high standard deviation values found in the abundance and biomass of both lakes were due to the pronounced seasonality of the pampean environments, that have produced marked differences in both parameters (Echaniz et al 2006(Echaniz et al , 2009.…”

“…In the central semiarid region of Argentina (Province of La Pampa), there are many shallow lakes with a wide range of concentrations of dissolved solids, ranging from subsaline to hypersaline (Echaniz et al 2006, Vignatti et al 2007). Many of these lakes have suffered marked deterioration due to the human activities carried out in their basins, such as livestock breeding, growing of cereal and oilseed crops and development of urbanized areas of increasing size.…”

“…We have previously carried out several studies on the composition and density of zooplankton in several shallow lakes of La Pampa (Echaniz et al 2006, 2008, 2010b, Vignatti et al 2007), but not compared the zooplankton biomass in the studied environments. Therefore, the aim of this study was to determine the taxonomic composition, abundance and biomass of zooplankton in two shallow lakes of La Pampa with different salinity and test the hypothesis that in presence of zooplanktivorous fishes and at equal concentrations of nutrients and chlorophyll-a, saline lakes have higher biomass of zooplankton than lakes of low salinity.…”

Trophic interactions among sympatric zooplanktivorous fish species in volume change conditions in a large, shallow, tropical lake

“…However, different interaction patterns between species pairs appear at distinct lake areas reflecting the heterogeneous prey taxa distribution, and other niche dimensions-such as spatial distribution, could promote partitioning. As the lake volume recovers, a reduction of niche overlap values reflects less contact among the species and more ready prey availability, probably as a consequence of the increasing transparency of the deeper lake (Echaniz et al, 2006;Castro et al, 2007).…”