Evaluación del estado ecológico de medios fluviales a través del uso de biondicadores en cuencas mediterráneas y tropicales

Abstract

Fluvial ecosystems contain a substantial portion of the total planetary biodiversity, but are at the same time among the most threatened on the planet. This is the result of the drainage network being the summary of all the basin activity. All events occurring In the basin end up having some hierarchical and progressive reflection in the watercourses that drain it This phenomenon is accentuated in areas with structural water deficits, such as the Mediterranean. Here the endemic lack of water conditions the greater alteration of the rivers, more regulated, receiving less diluted discharges and subjected to a greater general human pressure. The opposite should happen in areas of the planet with more water surplus, such as the tropics: less human settlement, less anthropic impacts, and more capacity to dilute the waste water discharges. In this work we study different bioindicators, macroinvertebrates and fish, useful to evaluate the ecological status of aquatic ecosystems, In two types of highly contrasted media: Mediterranean and Amazonian. In addition, the aim is to characterize the status/conservation value of watercourses from their fish communities, a fundamental toof, complementary to that of ecological status. In the first place, it was addressed a topic of maximum interest in the study of rivers, the accuracy and reliability of the measurement of their ecological status through their communities of macroinvertebrates. Usually, in the majority of cases, as is usual in ecology, the estimates' error made using bioindicators is not delimited, and automatic protocols are followed that avoid this fundamental issue. In the Múrtigas River (Hueiva) the study of the macroinvertebrate family richness in consecutive series of samples was carried out to estimate the real richness value by means of accumulated curves. The conclusion was that the wealth estimate was always dependent on the applied sampling effort, so the determination of the ecological status using these bioindlcators is easily manipulated. The Water Framework Directive (DMA) requires that the ecological status of water bodies be assessed using different groups of aquatic organisms as bioindicators. In all of them there is general agreement on the procedure for carrying out this, except in the case of inland fish, especially in Mediterranean areas. In this thesis we proposed to apply in the Guadalquivir basin an adapted version of an ecological status index useful for the DMA, developed for the Júcar basin,. This index solves the major drawbacks assigned to other previous proposals (easy to use, independent of reference areas, correlated with indices of other types of organisms, etc.) and also allows to evaluate the state of conservation of rivers and streams, from its ichthyofauna. To use the fish as bioindicators it is necessary to know its distribution in reference localities, that is not modified by the human action and / or to know its distribution in the past, when the human environmental intervention was much less to the current situations. In this thesis we have defined the distribution area of some common fish species in the Guadalquivir basin in the past, usually by the middle of the 19th century, and at the same time we have considered the role of invasive alien species in the high dynamics of these aquatic vertebrates communities. Finally, we have investigated the situation of the fish communities in environments radically different from those in the Mediterranean, such as tropical forests, in order to evaluate their potential bioindicator of ecological status and, secondarily, their state of conservation. The extraordinary biodiversity of these vertebrates in the Amazon rainforest of Madre de Dios in Peru is sensitive to the environmental conditions and it has been possible to characterize species and communities that are indicative of particular environmental conditions, both alien to human activity and determined by it. In this sense it has been possible to conclude that the fish are a useful tool in the management of these spaces so relevant for the planetary biological diversity.