Effects of temperature on isotopic enrichment inDaphnia magna: implications for aquatic food‐web studies

Abstract

Laboratory experiments were conducted with Daphnia magna and Hyalella sp. grown on a single food source of known isotopic composition at a range of temperatures spanning the physiological optima for each species. Daphnia raised at 26.5 degrees C were enriched in delta(13)C and delta(15)N by 3.1 and 2.8 per thousand, respectively, relative to diet. Daphnia raised at 12.8 degrees C were enriched 1.7 and 5.0 per thousand in delta(13)C and delta(15)N, respectively. Results imply a significant negative relationship between the delta(13)C and delta(15)N of primary consumers when a temperature gradient exists. Similar responses were observed for Hyalella. Results indicate a general increase in delta(13)C enrichment and decrease in delta(15)N enrichment as temperature rises. Deviations from the commonly applied isotopic enrichment values used in aquatic ecology were attributed to changes in temperature-mediated physiological rates. Field data from a variety of sources also showed a general trend toward delta(13)C enrichment with increasing temperature in marine and lacustrine zooplankton. Multivariate regression models demonstrated that, in oligotrophic and mesotrophic lakes, zooplankton delta(13)C was related to lake-specific POM delta(13)C, lake surface temperature and latitude. Temperature-dependent isotopic separation (enrichment) between predator and prey should be taken into consideration when interpreting the significance of isotopic differences within and among aquatic organisms and ecosystems, and when assigning organisms to food-web positions on the basis of observed isotope values.

δ15N and δ13C elucidation of size-structured food webs in a Western Arabian Sea demersal trawl assemblage

“…The slope derived in this study is remarkably similar to that for a component of the Galician upwelling pelagic food web (slope 0.28; Bode et al 2003 Log 2 max body weight (g) (Bosley et al 2002, Power et al 2003 and differ among systems (France & Peters 1997). It is unclear at present whether different fractionation estimates should be applied to temperate and tropical systems.…”

Trophic relationships and pelagic–benthic coupling during summer in the Barents Sea Marginal Ice Zone, revealed by stable carbon and nitrogen isotope measurements

“…Power et al (2003) showed that freshwater zooplankton raised at 26.5°C were enriched in δ 13 C by 3.1 ‰ relative to their diet, whereas animals raised at 12.5°C were enriched by only 1.7 ‰. The effect on δ 15 N values was opposite.…”

Naturally-occurring stable isotopes as direct measures of larval feeding efficiency, nutrient incorporation and turnover

“…In some cases, resolution of mixing models can be further improved by manipulation of the dietary isotopic composition, for example by feeding prey with C 3 and C 4 plant meals (Schlechtriem et al, 2004) or culturing algae with tank CO 2 , but remaining within the normal range of values for natural samples. Gamboa-Delgado, unpublished Spero et al, 1993Spero et al, 1993Spero et al, 1993Spero et al, 1993Power et al, 2003Lindholm and Hessen, 2007 Nematodes…”