Potential responses of Oligochaetes (Annelida, Clitellata) to global changes: Experimental fertilization in a lowland stream of Argentina (South America).

ARMENDÁRIZ, L.; OCON, C; RODRIGUES CAPÍTULOA.

LIMNOLOGICA

ELSEVIER GMBH

Lugar: Londres; Año: 2011 p. 118 - 126

0075-9511

One of the possible consequences of climatic change for streams and rivers in the pampean region of SouthAmerica is an increment in nutrient loads. To analyze this possible perturbation on a biological scale, theresponse of oligochaetes to an experimental eutrophication of the La Choza Stream, Argentina was stud-ied. We proposed that the addition of nutrients could increase the abundance, biomass, and speciescomposition of the stream. Two stretches (Control and Treatment sites) were selected, with bimonthlysamples being taken (March 2007 through February 2009) in two habitat types: the sediments and theaquatic vegetation. On each sampling occasion the environmental variables were measured. The nutrientaddition consisted in the continuous dissolution of a commercial fertilizer. The oligochaete mean densityand total biomass, the taxonomic richness, the Shannon diversity (H′), and the evenness (E) were calcu-lated and the BACI ANOVA design used to compare the differences between the sites. Thirty-three speciesof the families Naididae (Naidinae, Pristininae, Tubificinae, and Rhyacodrilinae), Opistocystidae, Enchy-traeidae plus Aphanoneura Aeolosomatidae were collected. The oligochaete abundance and biomassincreased significantly in the sediments and on the aquatic vegetation, especially among the Naidinaeand Pristininae during their asexual reproductive phase. The diversity and evenness varied significantlyin the sediments with the nutrient addition. Significant differences in the species richness and diversitywere found on the aquatic vegetation, with both increasing at the treatment site after the fertilization.A significant correlation (Spearman) was observed between the oligochaete density in the sedimentsand the NO3-N and NH4-N concentration in the water. The increment in the naidines resistant to thefertilizer throughout the experiment could be explained by the greater nutrient availability, their modeof reproduction, and their short life cycles. The results of our study suggested that the incorporation ofnutrients modified the composition of the oligochaete assemblage in favor of herbivores and detrivores.The usefulness of these indicator organisms in monitoring freshwater systems is subsequently discusse.