Grazing impact of two aquatic invertebrates on periphyton from an Andean-Patagonian stream

DÍAZ VILLANUEVA, VERÓNICA; ALBARIÑO, RICARDO; MODENUTTI, BEATRIZ

ARCHIV FUR HYDROBIOLOGIE

Año: 2004 vol. 159 p. 455 - 471

0003-9136

The mayfly Meridialaris chiloeensis and the snail Chilina dombeiana wereobserved to coexist and develop abundant populations in several Andean streams. Inthis study we examined and compared the mouthpart morphologies and the grazingmechanisms of these two species. In addition, through field experiments we analysedthe grazing effect on periphyton composition and biomass. Results showed that theherbivores contrasted in their mouthpart morphology and foraging behaviour butwould play a similar ecological role, since they both can be considered as scrapers.Experimental results indicated that the individual mayfly effect on - chlorophyll-a and ash free dry mass was lower than that of the individual snail. However, considering thespring and autumn abundances of both populations in a natural environment, theirgrazing impact might be similar or even higher for the mayfly. In addition, M. chiloeensisdepressed the rosette forming algae and favoured the prostrate ones. As a result,the mayfly grazing produced a community dominated by Nitzschia palea instead -of Achnanthes minutissima that dominated the grazer-free controls, while the snailchanged the taxonomic composition very little.