Stoichiometric homeostasis in the food web of a chronically nutrient-rich stream.

FEIJOO, C.; LEGGIERI, L. ; CAROLINA OCÓN, ; ISABEL MUÑOZ; RODRIGUES CAPÍTULO, ALBERTO; ADONIS GIORGI, ; DARÍO COLAUTTI, MAGDALENA LICURSI, NORA GÓMEZ ; NICOLÁS FERREIRO,; GOMEZ, N; SERGI SABATER.

Freshwater Science

University of Chicago Press

Lugar: Chicago (Ex North Amer. Benth. Society) ; Año: 2014 vol. 33 p. 820 - 831

2161-9549

The theory of ecological stoichiometry holds that heterotrophs are mostly homeostatic,exhibiting much less variation in their body stoichiometry than do autotrophs. Most studies of stream food web stoichiometry have focused on low-nutrient environments. Little is known about nutrient-rich streams, in which a higher level of stoichiometric homeostasis should be expected, mainly because imbalances between resources and consumers are low and nutrient availability may suffice to cover the biota´s requirements. In this study, we analyzed the element contents [carbon (C), nitrogen (N), and phosphorus (P)] and stoichiometric ratios (C:N, C:P and N:P) of basal resources, acroinvertebrates, and fishes in a nutrient-rich Pampean stream. These values were compared to values reported in other studies to determine whether they were elevated in comparison to values for high- and low-nutrient streams. We also performed P and N fertilization to analyze the response of the biota stoichiometry to an additional nutrient input to this naturally enriched system. The experiment lasted for one year, and the mean soluble reactive phosphorus concentration in the treatment reach was doubled in comparison to the background concentration. Consumers from the La Choza stream exhibited lower C:P and N:P ratios than did those of other lotic systems, whereas the P content and the C:P and N:P ratios of basal resources were within the ranges observed for other systems. Most components of the trophic web were not affected by the experimental fertilization performed in the stream, and only epiphyton, FBOM (fine benthic organic matter) and two macroinvertebrate species (Palaemonetes argentinus and Pomacea canaliculata) changed their nutrient content and/or stoichiometric ratios. Imbalances in C:N and C:P occurred between the primary consumers and their resources, particularly in macroinvertebrate collectors and detritivorous fishes feeding on FBOM. Most basal resources and consumers were strictly homeostatic for the P content and the stoichiometric ratios, but a lower degree of homeostasis occurred in the epiphyton, and in P. canaliculata and collectors feeding on epiphyton. Our results support the hypothesis that a high degree of stoichiometric homeostasis exists across the various components of the food web in this nutrient-rich stream, regardless of their trophic position.