Cladoceran (Crustacea, Branchipoda) assemblages diversity from lotic stretches adjacent areas of Rio de la Plata Basin (Argentina, Brazil, Paraguay and Uruguay)

Abstract

The cladocerans are one of the main functional groups of the freshwater plankton. Hence, its study is of major importance, both for the basic (e.g. aquatic biodiversity and ecosystems functional processes) as the applied (impact evaluation and conservation strategies) science. Many cladoceran species live in areas colonized by aquatic macrophytes as floodplains and littoral zone of lakes and rivers, which have high biological diversity. Along the Rio de La Plata Basin there are many and important areas like these, with natural differences regarding their latitude/climate/high and that suffer different influences from human activities. In 2010 a research about the cladocerans of areas like these in the Rio de La Plata Basin was started and the present proposition aims to continue it. The main premise is that the cladoceran communities will vary in relation to the geographical positioning, the season of the year and the local use of the watershed and that, additionally, the macrophyte community of the sampling sites will also influence in the cladoceran community composition. To test the hypotheses arising from the premises it is intended to analyze the geographical distribution and the seasonal variation of the cladoceran assemblies in order to determine if there are spatial variation patterns, if the community structure remains over the time and if they are associated with the human activities in the basin. In addition, to determine if there are association between the cladoceran community composition and the macrophyte community it is also intended to analyze the differential colonization of the macrophytes functional groups by the cladocerans species. To obtain the data for these analysis 23 points were sampled during summer and winter of 2010 in the Rio de La Plata Basin, of which only 21 could be sampled in both periods. For the cladocerans, three quantitative samples were taken in each site by horizontal hauls (68µm, 5m) in the region adjacent to the macrophytes (~1m) and one integrated (macrophy + adjacent zone) qualitative sample was taken with a "puçá" net (68µm). These samples were fixed with 4% formalin. Aiming future molecular analysis, a second integrated qualitative sample was taken and fixed with alcohol 70-90%. In each sampling site a horizontal profile (macrophyte zone, adjacent zone, limnetic zone) of the temperature, pH, conductivity, total dissolved solids and dissolved oxygen was performed with a Eureka Manta 2 water probe. One water sample from each site was taken to determine the amount of suspended matter (organic and inorganic), chlorophyll a and total phosphorus and nitrogen. Fragments of the dominant macrophyte were obtained to measure the amount of periphyton. It was also measured the depth and water transparency (Secchi disk) in each site. To obtain samples for the cladocerans differential macrophyte colonization it is intended to perform one more sampling expedition, utilizing specific sampling procedures for each functional group of macrophyte (submerged, rooted emerged and floating), in a site representative of these plant diversity. It is expected that the results of these analyses and an extensive revision of the literature will allow the drawing of a framework of the geographical distribution and ecological attributes of the cladocerans, and also identify the natural and atrophic factors determining the geographical distribution and the ecological attributes of the cladocerans assemblies, which will help in the use of these animals for management plans in the Rio de La Plata Basin. (AU)