| Abstract: | Some aquatic oligochaete species, mainly certain naidids and tubificids, are often associated with polluted environments, with high levels of organic matter and oxygen deficit. However, in the stations sampled in the Guadaira river basin, which can be arranged on an axis of organic pollution, the main aquatic oligochaete species (Nais elinguis and Tubifex tubifex) inhabiting these environments do not show a distribution pattern significantly related to the water physico-chemical characteristics measured. Nor, have we registered any association between these species and any kind of microhabitat, defined here: water current, presence of different types of vegetation, substrate coarseness and presence of anoxic sediments. Paranais litoralis is the exception, being related to areas without water current, located at higher altitudes, with high levels of dissolved organic matter and an anoxic substrate made up of fine particles. These results can be explained by the highly fluctuating nature of Mediterranean ecosystems and by the marked generalist character and ubiquity of the oligochaete assemblage species, able to colonize any kind of environment. |
