Does the nature and persistence of a substrate at a mesohabitat scale matter for Chironomidae assemblages? A study in two perennial mountain streams in Patagonia, Argentina

Abstract

Chironomid substrate-specific associations regarding the nature (organic-inorganic) and stability (stable-unstable) of different habitats were investigated at two low order Patagonian streams, during high and low water periods. Nant y Fall and Glyn rivers were visited twice (October 2007 and March 2008) and seven different habitat types were identified. A total of 60 samples were collected using a Surber sampler (0.09 m-2 and 250 μm) and a set of 23 environmental descriptors including physicochemical parameters and different fractions of particulate organic matter were assessed. Thirty five Chironomidae taxa were recorded with Orthocladiinae (20), Chironominae (7) and Podonominae (4) being the best represented subfamilies. Paratrichocladius sp. 1, Parapsetrocladius sp. 2, Parametriocnemus sp. 1., Pseudochironomus sp. and Rheotanytarsus sp. were the most abundant taxa. According to the Relative Preference Index at least 14 taxa showed strong affinity for a particular substrate. The structurally complex macrophyte Myriophyllum quitense supported 11 taxa compared with only 5 taxa found on the less complex Isoetes savatieri. Generally, stable substrates (boulders, cobbles and rooted plants) supported significantly higher chironomids richness, abundance and diversity than unstable ones (gravel-sand). Canonical Correspondence Analysis revealed that detritus (leaves, seeds biomass), macrophyte biomass, and secondarily hydraulic variables had high explanatory power on chironomids species composition and structure. This work suggest that more complex substrates showing persistence in the temporal dimension supported a diverse array of chironomids, meaning that the maintenance of the natural habitat heterogeneity is essential for the community. Land-use practices having significant effects on ecological stream attributes such as turbidity, sediment deposition, runoff patterns, will alter assemblages. Understanding environmental associations of the Chironomidae community at the habitat scale is significant for conservation purposes and for the management of low order streams in Patagonia.