Does predation by the introduced rainbow trout cascade down to detritus and algae in a forested small stream in Patagonia?

BURIA, L., . ; ALBARIÑO, R.,; DÍAZ VILLANUEVA, V., ; MODENUTTI, B. ; BALSEIRO, E

HYDROBIOLOGIA

SPRINGER

Año: 2010 vol. 651 p. 161 - 172

0018-8158

Cascade effects of an exotic predator, therainbow trout (Oncorhynchus mykiss), on periphytonand leaf litter were analysed in a headwater, forestedstream of Andean Patagonia (Argentina). We conductedseasonal field sampling and two field experimentsmeasuring leaf litter mass, periphyton biomassand macroinvertebrate biomass in relation to thepresence and absence of rainbow trout. In the fieldsurvey, the presence of trout influenced resource mass:leaf litter (60% decrease in summer, P = 0.024)and periphyton (tenfold increase in chlorophyll a,P\0.001) were affected, which were mediated by adecrease in the biomass of shredders (95% decrease insummer, P\0.001) and scrapers (90% decrease,P\0.001). There was an effect on leaf litter biomassonly in the summer, whereas fish presence reducedperiphyton biomass all year except in the winter. In thefield experiments, we observed that leaf litter breakdownand periphyton development were effectivelycontrolled by consumers in the absence of fish. Incontrast, the presence of fish caused a release ofherbivory and detritivory resulting in a significantincrease in periphyton biomass (100% increase,P\0.001) and a decrease in leaf litter decay (40%decrease, P\0.001). Our results suggest that in loworder streams and in the presence of visual predators,trophic cascades may operate both on detritus andalgae, but with different timing.