Following the Water Framework Directive (2000/60/EC), macroinvertebrates are required
biological elements for monitoring European aquatic ecosystems. Several efforts have been
made towards establishing a biomonitoring programme for the Azores freshwater systems
using benthic macroinvertebrates. However, little was previously known concerning
Azorean freshwater macroinvertebrate fauna. Data from a major ongoing survey of
macroinvertebrate freshwater fauna for two islands are presented and the use of
macroinvertebrates as water quality indicators for the Azorean streams is evaluated. The upper, middle and lower reaches of streams longer than 10 km from São Miguel (10) and Santa Maria (1) were surveyed (a total of 33 samples). A total of 21 taxa were collected; Diptera, in particular chironomidae, were dominant; chironomids were collected from all
sampling sites. The Azorean lotic fauna is characterized by low levels of abundance and the absence of macroinvertebrate groups commonly associated with continental systems.
Traditional biotic indices, used to classify ecological quality, yielded poor to bad
classifications despite little or no environmental impacts at the sampling sites. The paucity of macroinvertebrate fauna is probably due to the result of geological and physicochemical processes, the oceanic character of the islands, their volcanic origin, small size and geological youth and climate related factors such as seasonal peaks in rainfall. Considering these constraints, we demonstrate that watershed age plays a determinant role in shaping
Azorean macroinvertebrate freshwater communities which can confound the water quality classification via the use of traditional biotic indices
