Trophic positioning and microphytobenthic carbon uptake of biofilm-dwelling meiofauna in a temperate river

Abstract

1. δ13C and δ15N stable isotope signatures combined with an in situ microphytobenthic 13C labelling experiment were performed in epilithic biofilms of a large temperate river (the Garonne, France) to infer the trophic positioning and the microphytobenthic carbon (MPBC) uptake of biofilm-dwelling meio- and macrofauna. 2. Chironomidae larvae and Chromadorina spp. nematodes rapidly incorporated freshly produced MPBC contrary to Rhyacophilidae larvae and Naididae oligochaetes. Quantitatively, macrofaunal Chironomidae daily incorporated more MPBC than did meiofauna. Moreover, Chironomidae seemed more involved in MPBC spatial export than nematodes. 3. Rhyacophilidae larvae were predators feeding on large meiofauna (Naididae and Chironomidae) but not on nematodes. Naididae oligochaetes primarily gained their carbon from allochthonous and/or microbial-loop recycled sources. 4. A rapid and important loss of labelled MPBC was observed. Feeding activity of biofilm-dwelling invertebrates seemed not primarily involved in this loss.