Trophic Enrichment Factors of Carbon and Nitrogen Isotopic Ratios (Δ13C and Δ15N) in Four Marine Ciliates.

Jun Young Park,Heum Gi Park,Chang-Keun Kang,Jae-Ho Jung,Hyun Je Park,Jung Hyun Kwak

doi:10.3389/fmicb.2021.721157

Abstract

Understanding the magnitude and causes of isotopic fractionation between organisms and their dietary resources is crucial for gaining knowledge on stable isotope ecology. However, little is known regarding the diet-tissue fractionation values of marine ciliates, which play a critical role in the reconstruction of microbial food webs. In the present study, we conducted experiments on two benthic (Pseudokeronopsis pararubra and Protocruzia labiata) and two pelagic (Strombidium sulcatum and Uronemella filificum) marine ciliates, where they were fed with isotopically constant foods (Chaetoceros calcitrans and Isochrysis galbana) under laboratory culture conditions to determine their carbon and nitrogen isotopic fractionation values (Δ13C and Δ15N). The stable isotope values (δ13C and δ15N) of ciliates for all experiments rapidly increased after the initial feeding, with half-lives ranging from 6.1 to 23.0h for δ13C and from 3.1 to 24.9h for δ15N. The Δ13C and Δ15N for all ciliates represented significantly positive enrichments, with overall mean fractionations of 0.6±0.2 and 1.2±0.4, respectively. Irrespective of the dietary type, both Δ13C and Δ15N were very similar for the same ciliate species. These results suggest that Δ13C and Δ15N for marine ciliates are similar to those found in common marine organisms with very little food-dependent variation. Overall, quantifying the specific isotopic fractionation of marine ciliates is expected to provide fundamental information on the trophic transfer of carbon, nitrogen, and energy flow through the microbial pathway in marine ecosystems.

Highlights

Stable isotope ratios of carbon and nitrogen have been used to identify trophic pathways of organic matter and trophic relationships within animal communities, and the isotopic ratios of an organism’s tissues reflect those of its dietary sources (Fry and Sherr, 1984; Peterson and Fry, 1987; Michener and Schell, 1994; Layman et al, 2012)
There were no significant differences in the δ13C and δ15N values of both C. calcitrans and I. galbana at various sampling times, showing overall mean values of
Our results showed that despite the significant differences in Δ13C and Δ15N, benthic and pelagic ciliates feeding on different microalgae had similar patterns of isotopic fractionation (i.e., TEF and isotopic turnover rate) under controlled laboratory conditions to those previously reported for other aquatic organisms (McCutchan et al, 2003; Dubois et al, 2007)

Summary

Introduction

Stable isotope ratios of carbon and nitrogen have been used to identify trophic pathways of organic matter and trophic relationships within animal communities, and the isotopic ratios of an organism’s tissues reflect those of its dietary sources (Fry and Sherr, 1984; Peterson and Fry, 1987; Michener and Schell, 1994; Layman et al, 2012). Isotopic Fractionations of Marine Ciliates isotopes in animal tissues occurs during the course of physiological metabolism, in the range of ≤1‰ for carbon (DeNiro and Epstein, 1978; Fry and Sherr, 1984) and 2–4‰ for nitrogen (Vander Zanden and Rasmussen, 2001; Post, 2002). Understanding the magnitude and causes of isotopic discrimination between consumers and resources is crucial for understanding trophic ecology using stable isotope tracers

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Discussion

Conclusion