Stable isotopes dissect aquatic food webs from the top to the bottom

Abstract

Abstract. Stable isotopes have been used extensively to study food-web functioning, that is, the flow of energy and matter among organisms. Traditional food-web studies are based on the natural variability of isotopes and are limited to larger organisms that can be physically separated from their environment. Recent developments allow isotope ratio measurements of microbes and this in turn allows the measurement of entire food webs, in other words, from small producers at the bottom to large consumers at the top. Here, I provide a concise review on the use and potential of stable isotopes to reconstruct end-to-end food webs. I will first discuss food web reconstruction based on natural abundances isotope data and will then show that the use of stable isotopes as deliberately added tracers provides complementary information. Finally, challenges and opportunities for end-to-end food web reconstructions in a changing world are discussed.

Reviews and syntheses: to the bottom of carbon processing at the seafloor

“…Interactions among food-web members are considered the key to understanding carbon flows (Pimm et al, 1991;. During the last 2 decades, 13 C-labeled phytodetritus addition experiments have been performed to identify the organisms involved in the immediate processing of organic matter delivered to the seafloor (Middelburg, 2014). These studies often covered all size classes (animals and microbes) and could show that respiration was the major fate of added phytodetritus and that all size classes directly profited from recently deposited organic matter (Blair et al, 1996;Moodley et al, 2002Moodley et al, , 2005aWoulds et al, 2007Woulds et al, , 2009Woulds et al, , 2016Witte et al, 2003;Nomaki et al, 2005;Sweetman and Witte, 2008).…”

Stable carbon isotope biogeochemistry of lakes along a trophic gradient

“…The δ 13 C of terrestrially derived organic carbon is therefore often distinct from that of organic matter produced within the lakes and this difference can be used to trace carbon flows and origins in plankton food webs. A major challenge in stable isotope studies is to elucidate the isotopic composition of microbial organisms (Middelburg, 2014), such as phytoplankton and bacteria, since it is difficult to separate these potential carbon sources from bulk particulate organic carbon (POC). Therefore, most studies use indirect methods to determine δ 13 C of phytoplankton (δ 13 C phyto ), bacteria (δ 13 C bac ) and allochthonous carbon (δ 13 C allo ).…”

Use of Multi-Carbon Sources by Zooplankton in an Oligotrophic Lake in the Tibetan Plateau

“…This isotope-mixing model solves iteratively for possible carbon source composition and provides a frequency distribution of the contribution of each carbon source to the consumer [28]. We used tolerance parameters of 1‰-3‰, reflecting the high uncertainty of the sources, no trophic enrichment factor for ∆ 14 C (because of its definition), and a trophic adjustment of 0.4‰ for δ 13 C [24,25]. The ∆ 14 C of DIC was used as a surrogate for the ∆ 14 C of phytoplankton since algae biomass production is based on in situ DIC and therefore tracks that of DIC [29][30][31].…”

“…The stable C isotope value is calculated as δ 13 C (‰) = (R sample /R standard − 1) × 10 3 , i.e., parts-per-thousand (‰) deviations from international standards (PeeDee Belemnite for δ 13 C), where R = 13 C/ 12 C. The analytical error between repeated measurements was typically within ±0.1‰ [24]. Radiocarbon 14 C isotope measurements were performed by the Accelerator Mass Spectrometry Facility at the Beta Analytic Radiocarbon Dating Laboratory, which is an ISO 17025-accredited radiocarbon dating laboratory in Miami, Florida.…”