Microalgal food sources greatly improve macroinvertebrate growth in detritus?based headwater streams: Evidence from an instream experiment

In forested headwater streams, inconspicuous food resources such as epilithic microalgae can play a major role owing to their content of long chain polyunsaturated fatty acids (PUFAs) that are essential for macroinvertebrate development. Yet, the use these and consequences consumers life-history traits remain scarcely studied, especially non-herbivorous taxa. Using instream mesocosms, we aimed understand how two species, shredder detritivore (Gammarus pulex) scraper (Rhithrogena semicolorata), available organic under light versus shaded conditions (high low amounts phototrophic biofilm, respectively). We specifically focused on origin carbon (C) lipids (PUFAs, sterols) assimilated by species effects compounds survival growth. When autotrophic biofilms were (mesocosms exposed light), both experienced significantly higher growth than in mesocosms placed dark. Rhithrogena nymphs, imago emergence rates positively affected access biofilms. stable isotope analysis (?13C ?15N), demonstrated dark macroinvertebrates C detrital origin. Under conditions, most R. semicolorata was derived from around 11% fine particles (FPOM). Gammarus pulex part its sources (mainly FPOM) The results isotopic analyses (?13C) (FAs) sterols showed entirely dependent meet dietary FAs sterol requirements. contrast, quantitatively important G. terms supply, irrespective tested. For consumers, seemed be complementary source, but yet cover large requirements long-chain PUFAs. This study clearly confirmed ecological importance functional feeding groups streams providing new insights trophic PUFAs diet.