Recent invasion of Didymosphenia geminata (Lyngbye) M. Schmidt in a Patagonian regulated river promotes changes in composition and density of macroinvertebrate community

Abstract

Didymosphenia geminata is a stalked freshwater diatom, which forms large blooms in ultra-oligotrophic conditions, and it has been declared a nuisance species inmany lotic systems worldwide. Its presence is verified in Argentine Patagonia since 2010. To understand the differences in the community of macroinvertebrates between non-invaded sites and D. geminata blooms, three non-invaded sites and three sites with 80?90% blooms coverage were sampled seasonally at Futaleufu´ River. Physical and chemical variables (pH, suspended solids, total dissolved solids, conductivity, dissolved oxygen, and nutrients) showed no significant differences between sites. Sites with D. geminata blooms were associated with significantly higher values of periphyton biomass and chlorophyll a. Macroinvertebrate community differed between D. geminata infected sites and sites with native periphyton. Higher total macroinvertebrate density, higher tolerant groups (Orthocladiinae and non-insect taxa) density, and total richness were found in the presence of blooms. Trophic structure changed at D. geminata blooms, where shredders and collectorgatherers increased in abundance. The diatom blooms may constitute a new complex micro-habitat that provides refuge from harsh current and predators, as well as new foraging opportunities, producing a bottom-up effect on the benthic community.