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Regional and local environmental factors structuring undisturbed benthic macroinvertebrate communities in the Mondego River basin, Portugal

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The relative contribution of environmental variables in explaining the structure variation of undisturbed benthic macroinvertebrate communities was investigated over three seasons at 18 sites of the Mondego River basin, Portugal. Sampling sites located at distinct altitudes (2–840 m), presented a consistent pattern of water conductivity values through seasons, always showing the highest values in lowland water-courses. Streams showed highly variable hydraulic conditions from intermittent to perennial systems, so discharge-related factors were expected to influence their communities' structure. Ninety-nine macroinvertebrate taxa were recorded at the undisturbed sites, ranging from a minimum of 32 during spring to a maximum of 63 during summer. Taxon richness at a site was the only significantly different descriptive measure among seasons. Regression analysis applied to undisturbed data revealed spring (−), channel width (−), dissolved oxygen (+), total dissolved solids (−) and chlorophyll-a (−) as the strongest predictors of family richness, while invertebrate abundance was highly related to organic content of sediment (+) and levels of dissolved oxygen (+) (ordered by significance). Community family composition was related with environmental variables through canonical correspondence analyses which showed that the most significant natural environmental-gradient affecting invertebrate distribution was a spatial variation of sediment grain size, altitude and stream bed geology explained by conductivity. As expected, discharge-related variables such as dissolved oxygen, current speed and channel width were main factors in defining a secondary seasonal gradient. This was reinforced by the results of a similarity percentage breakdown procedure, which showed differences in the invertebrate composition between seasons and between sites within the same season. These findings recognize the importance of local factors but also indicate the significance of larger-scale factors such as stream geology and altitude in structuring the undisturbed benthic invertebrate communities in this area.
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Document Type: Research Article

Publication date: August 1, 2005

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