Variacion estacional de la estructura y funcionamiento de las comunidades microbianas de sistemas hipersalinos en el Alto Guadalquivir

Resumen

Abstract This doctoral thesis deals with a comparative study of planktonic microbial communities from water hypersaline exploited solar salterns in the Alto Guadalquivir (southern Spain).These systems are not only a cultural heritage of great significance in our region but are characterized by the presence of communities of high ecological value, for its uniqueness and ability to adapt to stressful conditions. In these circumstances, the fundamental objectives of this study were to characterize the microbial communities in a set of solar salterns in the mentioned above region and the analysis of variations in the composition and functioning of such communities along a seasonal cycle. This objective was approached in an integrative mode based on the study of the taxonomy and the size structure analysis of these communities. Microbial components that have been analysed were: bacterioplankton, picoplankton, nanoplankton, microplankton and ciliated protozoa. The pico-nanoplankton analysis was carried out by the automated technique of flow cytometry, that we have had to make up for this special type of ecosystem. The results of this set-up are presented in the first chapter of this thesis. To achieve this goal we have sampled two solar salterns, Barranco Hondo (Jaén) and San Carlos (Jaén), and the saline wetland Laguna Honda (Alcaudete). The analysis of bacterioplankton and microplankton (phytoplankton and ciliates) was performed by using different techniques based on direct analysis of automatic image connected to both epifluorescence and inverted microscopy. The size and biomass spectra were related to physical-chemical properties relevant to this type of systems, such as total dissolved solids, alkalinity or ion concentration. These variables were measured using a multiparametric field probes and through laboratory techniques.The characterization of the analyzed solar salterns (Chapter 2) highlighted the lack of correlation between levels of salinity and biological variables. However, some trends were clearly observed, especially in the case of the presence of certain phytoplanktonic groups in relation to the different ionic composition of the water. The Chlorophyceae were dominant in all studied systems, being present in all of them. The presence of these species, mainly Dunaliella salina and Dunaliella viridis, are a constant in most of the hypersaline ecosystems of the world. The analysis of the seasonal variation (Chapter 3), was conducted in two solar salterns characterized by a different exploit situation, the solar salterns of Barranco Hondo (abandoned) and Don Benito (in operation). During this study, remarkable changes in the size spectra were recorded with a clear difference between the changes at the small cells range, keeping the same size structure, and the big cells range, with an irregular behaviour. The most remarkable feature of these distributions is the low biomass of individuals with sizes between 1 and 10 m3, while that the highest biomass was present in some cases in the size ranges between 128 and 1024 m3, and in another cases in higher size ranges, theses ranges belonging of the phytoplankton known as microplankton, between 1,6x104 and 105 m3. The occurrence of diatoms as Niztchia is probably responsible of the biomass increasing at these size ranges. Finally, the composition and size spectrum of ciliated protozoa communities was studied in seven different solar salterns. At the same time, the characterization of the "seed-bank" was carried out through laboratory manipulation experiments (Chapter 4). These experiments consisted in dilutions from original sample wich were cultured and regularly analysed on microscope. The size spectra of the microbial community of these solar salterns have been characterized by the presence of discontinuities, as have been described in some freshwater and marine systems, due to the lack of some functional groups. Ciliates covered a fairly wide range of sizes thanks to the presence of a significant number of cryptic species