Effects of the exotic willow (Salix fragilis) on benthic invertebrate communities in streams of Patagonia, Argentina

SERRA, M.N.; ALBARIÑO, R. J.; DÍAZ VILLANUEVA, V.

Bariloche

Congreso; VI Southern Connection Congress; 2010

UNIVERSIDAD NACIONAL DEL COMAHUE

We conducted a field survey and leaf litterbag experiments in three streams of the Nahuel Huapi National Park to study the consequences of the invasive Salix fragilis on aquatic invertebrate communities. In each Stream, we selected two Sites (one dominated by the native shrub chacay, Discaria trinervis, and another by willow trees). The study reaches were similar in water temperature, conductivity and stream depth but differed significantly in channel width and discharge. Leaf litter breakdown rates (k) for willow and chacay leaves were obtained from initial and final (30 days) leaf masses at each site, assuming an exponential decay model. Benthic invertebrate composition was analized in litterbags and also from Surber samples collected at each site. Differences in k values for willow and chacay leaflitter were not consistent among Streams and Sites (3-way ANOVA), being significantly higher for chacay only in two sites (one with native and other with exotic riparian plants). Abundance and diversity (H´ index) of invertebrates colonizing litterbags were higher in sites with chacay vegetation. However, H´ of the whole benthic invertebrate community did not differ among Sites and Streams. In addition, community abundance varied between Sites differently in each Stream (2-way ANOVA). Our results suggest that willow invading the study streams had no consistent effects on benthic invertebrate communities.