Depth‐specific and spatiotemporal variation of δ¹³C and δ¹⁵N in Charophytes of Lake Constance: implications for food web studies

Abstract

Macrophytes are at the base of many lake food webs providing essential food resources for animals at higher trophic level, such as invertebrates, fish and waterbirds. However, data regarding the spatiotemporal variation in isotopic composition of macrophytes are generally missing. We measured the carbon and nitrogen stable isotope ratios of Charophytes at Lake Constance, where they constitute a major food source for waterbirds. Our data reveal seasonal and site-specific differences as well as depth-specific variations in isotopic carbon values within the littoral zone. Charophytes were enriched in (13)C at sites of higher productivity: the δ(13)C values were high in summer, at shallow and at relatively nutrient-rich sites, and comparatively low in winter, and in deeper and nutrient-poorer sites. In contrast, no temporal or spatial trend was found to explain the variability in the isotopic nitrogen values. These results imply that the seasonal timing of food intake (relative to turnover rates of consumers tissue) and the potential depth of foraging need to be taken into account when calculating the relative contribution of energy sources to diets of consumers such as waterbirds.

Nitrogen stable isotope variability in tissues of juvenile tilapia Oreochromis aureus: empirical and modelling results

“…Nevertheless, the temperature in our study was approximately the same as that of the tilapia's natural environment; thus, differences in isotope turnover among tissues could not be linked to a change in temperature. Some researchers have also reported that isotopic turnover rates varied with body size, ontogenetic state and other environmental factors, which were not responsible for the turnover variation in our study. We deduced that the variation in isotopic turnover rates was mainly attributable to the different biochemical compositions of the tissues.…”

Niche differentiation between sympatric alien aquatic crustaceans: An isotopic evidence

“…Spatial differences in isotopic signatures are commonly observed between different sites in Lake Constance (e.g. Fuentes, Güde, & Straile 2013;Matuszak, Voigt, Storch, Bauer, & Quillfeldt 2011;Yohannes, Franke, & Rothhaupt 2014). Interestingly however, the four species were not equally affected by inter-habitat isotopic differences [e.g., ␦ 13 C and ␦ 15 N; sampling year 2011 (Table 2) vs. ␦ 13 C and ␦ 15 N; sampling year 2012 (Table 3)].…”