In this study we examined the importance of seasonal changes in habitat features and aquatic macroinvertebrate responses in temporary and perennial streams from two different catchments in the Western Mediterranean region in Spain. Macroinvertebrate sampling was spatially intensive to account for the relative frequency of meso-(i.e., riffles and pools) and micro-habitats (i.e., different mineral and organic-based substrata) at each site. Samples were collected at two distinctly different phases of the hydrograph: (1) during the flowing period, when poolriffle sequences were well-established, and (2) during the dry phase, when only isolated pools were expected to occur in the temporary streams. During the dry season, both a reduction in the available total habitat and in microhabitat diversity in all sites studied was observed. As a result, taxon richness decreased in all streams, but more dramatically at temporary stream sites and particularly so in the infrequently remaining discontinuous riffles. Macroinvertebrate assemblages differed among catchments (i.e., geographical identity) and sites (perennial vs. temporary). Invertebrate differences were also strong within and among meso-and micro-habitats, particularly mineral and organic microhabitat patches, and differences were due to both loss of taxa from some habitats and some taxa exhibiting certain habitat affinities.

Intermittent streams are dynamic ecosystems that alternate between dry and wet states. Despite their global dominance, we have scant information about the effects of surface flow drying on terrestrial arthropods in channel and adjacent terrestrial habitats. In the present study, we used pitfall traps to characterise the terrestrial arthropod assemblages along lateral gradients (channel, riparian, and upland habitats) in perennial and intermittent reaches of two contrasting Mediterranean intermittent streams (Rogativa and Fuirosos streams). Simultaneously, we assessed changes in assemblage composition and structure on five sampling occasions over the entire drying period (i.e. 29 days). The composition of arthropod assemblages differed among streams, flow regimes, habitat types, and sampling dates. In contrast, depending on the stream, taxonomic richness and total abundance were similar between perennial and intermittent reaches, but differed among habitat types. Formicidae, Araneae, Collembola, and Coleoptera explained most of the differences between flow regimes and habitat types in both streams. In Rogativa stream, arthropod abundances peaked in the dry channel and increased with drying time, while abundances decreased in riparian and upland habitats. It implies that the dry channel may be colonized by riparian and upland arthropods to a greater or lesser extent depending on the stream and the specific landscape context. Our results emphasize the importance of dry channels as temporary habitats for terrestrial arthropod assemblages. Thus, the dry period should be considered explicitly when assessing biodiversity of and establishing management strategies for intermittent streams and their fringing riparian and upland areas.Values in italics indicate statistical significance at P < 0.05. GROUND-DWELLING ARTHROPOD ASSEMBLAGES IN INTERMITTENT STREAMS