Abstract
AIM: This study evaluated the use of oligochaetes at different levels of taxonomic resolution as environmental indicators in Argentine lowland streams affected by different land uses. METHODS: Sampling sites were grouped based on the physicochemical and habitat characteristics (low-, moderate-, and high-impact disturbance). Collection of the oligochaetes samples was carried out seasonally in sediment and vegetation habitats. RESULTS: The increases in nutrients and organic matter produced elevated densities of the Oligochaeta, but when the disturbance also involved changes in the physical habitat or enhancements in toxic substances, the abundance decreased significantly to values even lower than those of non-impacted environments. The responses of Naidinae and Tubificinae were similar. The density of the Pristininae decreased with increasing impact, but those of the Enchytraeidae and Rhyacodrilinae increased at the most highly impacted sites. The Opistocystidae were not recorded in high-impact sites. Species richness and diversity (H') were lower in high-impact sites and even lower in sediments. Some species presented no restrictions in the habitat type or with the contamination level: Limnodrilus hoffmeisteri, Dero furcatus, D. digitata, D. pectinata, Pristina longiseta, and P. aequiseta. Moreover, Trieminentia corderoi, Slavina appendiculata, and Aulodrilus pigueti exhibited the highest abundances at low-impact sites and were not registered in high-impact sites. CONCLUSIONS: The Oligochaeta show a relatively wide ecological valence through their extensive number of species. Although lower taxonomic levels can give information about environmental status, test-species' sensitivities to different types and degrees of contamination will be of utmost relevance to the evaluation of ecological quality.
Highlights
In freshwater systems, the oligochaetes are often the most diverse and/or abundant group of benthic invertebrates
We evaluated the role of the main habitats available within pampean streams in determining the spatial distribution and abundance of the various oligochaete species
The sampling sites were arranged in 3 main groups: In the first group, M1, M2, M3, DC1, and B1 had the highest levels of dissolved oxygen
Summary
The oligochaetes are often the most diverse and/or abundant group of benthic invertebrates. From the 5,000 species described worldwide, 1,700 are aquatic with 1,111 being from continental aquatic environments, 100 from underground waters, and the rest from the oceans (Wetzel et al, 2006) These annelids participate in the trophic networks of the aquatic systems as a feeding resource of turbellarians, hirudins, chironomids Tanipodinae, crayfish, amphipods, amphibians, fish, and birds (Ezcurra de Drago et al, 2007). Oligochaetes inhabit all types of substrata, but reach a higher density and richness mainly in fine sediments (Marchese, 2009). Due to their ecological prevalence and presence in all environments, the oligochaetes are widely utilized as indicators of environmental conditions. Because of the difficulty of their taxonomic determination, even though they are present in samples of benthic macroinvertebrates, the Oligochaeta worms are generally referred down to only the class or family level, or even are omitted entirely from any analysis of the faunistic structure and composition of lotic environments (Alves et al, 2006)
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