Seasonal changes in the δ13C and δ15N signatures of the Lago Maggiore pelagic food web

Abstract

Seasonal variation in the relative contributions of littoral and pelagic food sources to the diets of open-water zooplankton and subsequent changes in their trophic

Defining Seasonal Functional Traits of a Freshwater Zooplankton Community Using δ13C and δ15N Stable Isotope Analysis

“…In Lake Maggiore, it has been demonstrated that δ 13 C of the primary consumer Daphnia longispina galeata gr. tracks the isotopic composition of seston (50 ≤ size ≤ 126 µm) and of the pelagic baseline [16,35]. The choice of Daphnia as a useful isotopic baseline is supported by other studies [27], considering this taxa as a short-lived organism suited for fine scale temporal integration of pelagic δ 13 C or δ 15 N signatures.…”

“…Zooplankton δ 13 C and δ 15 N isotopic signatures were referred to that of the pelagic baseline, which was expressed by the primary consumer, Daphnia longispina galeata gr. This choice came from previous stable isotope studies in Lake Maggiore [16], showing that Daphnia's δ 13 C signature in the different seasons was closely correlated with the signature of seston (r = 0.86; p < 0.01; N = 13), confirming that Daphnia was an appropriate proxy for the pelagic baseline against which the carbon isotopic signals of other zooplankton can be compared. ∆ 13 C was used to detect seasonal changes in taxa specific feeding behavior and assess the origin of carbon sources fueling the pelagic food web.…”

“…This follows the standard routine sampling for deep subalpine lakes, in which samples are collected within the upper 50 m depth, as previous research on the vertical distribution of zooplankton showed that this is the water layer in which zooplankton live [22]. Monthly samples were collected from April to November 2009, when total zooplankton biomass was ≥3 mg·m −3 , using a wide-mouth 450 µm mesh zooplankton net of diameter 0.58 m, filtering 13 m 3 lake water from three pelagic stations (G: 45 • [16].…”

“…Depending on body mass, 50 to 700 individuals of each taxa were pooled to reach a minimum dry weight (DW) of 1 mg per sample. Three replicates of each taxa were run from each of the three sampling stations, as among-station differences were statistically non-significant (p > 0.05, Friedman Analysis of Variance, ANOVA test; [16]). The isotopic composition of organic carbon and nitrogen was determined from the analyses of CO 2 and N 2 by the G. G. Hatch Stable Isotope Laboratory at the University of Ottawa, Ontario, Canada, using a CE 1110 Elemental Analyser (Vario EL III manufactured by Elementar, Germany) and a DeltaPlus Advantage isotope ratio mass spectrometer (Delta XP Plus Advantage manufactured by Thermo, Bremen, Germany) coupled to a ConFlo III interface (Conflo II manufactured by Thermo, Bremen, Germany).…”

Carbon and Nitrogen Isotopic Signatures of Zooplankton Taxa in Five Small Subalpine Lakes along a Trophic Gradient

“…Stable carbon isotope ratio (δ 13 C‰) reflects the input of carbon revealing the contributions of different food sources, and nitrogen isotope (δ 15 N‰) indicates the trophic role because a consumer is typically enriched with respect to its diet (e.g., [5][6][7][8]). Increasing δ 15 N enrichment is usually observed with the increasing lake trophic status [9][10][11].…”