Experimental analysis of grazing by the mayfly Meridialaris chiloeensis on different successional stages of stream periphyton

DÍAZ VILLANUEVA, VERÓNICA; MODENUTTI, BEATRIZ

INTERNATIONAL REVIEW OF HYDROBIOLOGY

Año: 2004 vol. 89 p. 263 - 277

1434-2944

In this study we determined grazing effects of the South Andean endemic mayfly Meridialarischiloeensis on periphyton at different stages of successional development. Grazing effects were studiedthrough a two-factor experimental design (colonization stages X grazer density) in a stream-sidechannel in spring and winter. Our results showed an absence of proportionality between grazer densityand periphyton decline in response to grazers at low and intermediate levels of periphytic biomass;however, when periphyton biomass was high a direct inverse relationship was observed between postgrazingbiomass and grazer density. The relationship between periphytic algae (chlorophyll a concentration)and periphyton (total periphytic ash-free dry mass) (C/OM index) was used as an estimation ofthe autotrophic fraction in the total periphyton matrix. Grazing did not alter the C/OM index indicatingthat both autotrophic and heterotrophic fractions of the periphyton components were reduced in the sameproportion. Ordination of samples using the relative abundance of diatom species showed that herbivoreeffect was less evident at intermediate and late stage of colonization than at early one. These resultssupport the statement that the outcome of the herbivore-periphyton interaction may depend on the successionalstage of the periphyton community. In spring Fragilaria pinnata relative abundance, on thebasis of cell counts, was reduced by grazing and Nitzschia palea was enhanced. In the winter experiment,grazing decreased Achnanthes minutissima relative abundance