Stable isotopes as tracers of trophic interactions in marine mutualistic symbioses

Abstract

Mutualistic nutritional symbioses are widespread in marine ecosystems. They involve the association of a host organism (algae, protists, or marine invertebrates) with symbiotic microorganisms, such as bacteria, cyanobacteria, or dinoflagellates. Nutritional interactions between the partners are difficult to identify in symbioses because they only occur in intact associations. Stable isotope analysis (SIA) has proven to be a useful tool to highlight original nutrient sources and to trace nutrients acquired by and exchanged between the different partners of the association. However, although SIA has been extensively applied to study different marine symbiotic associations, there is no review taking into account of the different types of symbiotic associations, how they have been studied via SIA, methodological issues common among symbiotic associations, and solutions that can be transferred from one type of association with another. The present review aims to fill such gaps in the scientific literature by summarizing the current knowledge of how isotopes have been applied to key marine symbioses to unravel nutrient exchanges between partners, and by describing the difficulties in interpreting the isotopic signal. This review also focuses on the use of compound‐specific stable isotope analysis and on statistical advances to analyze stable isotope data. It also highlights the knowledge gaps that would benefit from future research.

Chemosynthesis influences food web and community structure in high-Arctic benthos

“…The lower (i.e. more negative) δ 13 C values within this bimodal spectrum for CBC can be attributed to the use of the enzyme Rubisco I as catalyst in the carbon fixation step of the Calvin Benson-Bassham cycle (CBB) (Robinson & Cavanaugh 1995, Ferrier-Pagès & Leal 2018. The higher (i.e.…”

“…The importance of chemosynthetic carbon (CBC) in benthic food webs has been documented for cold seeps globally (Levin 2005, Decker & Olu 2012, Zapata-Hernández et al 2014. Stable isotope analysis has provided valuable insight into trophic interactions and the utilization of different carbon sources (Brooks et al 1987, Ferrier-Pagès & Leal 2018. By combining analyses of stable carbon (δ 13 C) and nitrogen (δ 15 N) isotope ratios to assess energy sources and trophic structure, it is possible to investigate community characteristics and predator−prey interactions and to generate insights into resource utilization (Brooks et al 1987, Hobson & Welch 1992, Vander Zanden et al 1999.…”

“…Such δ 13 C signatures differ substantially from photosynthesized orga nic car bon from phytoplankton (δ 13 C typically −20 to −25 ‰) and ice algae (typically −15 to −20 ‰) (Hobson et al 1995, Søreide et al 2006. Hence, due to differences in the carbon end-member isotope compositions caused by different carbon fixation pathways, trophic interactions, and carbon-source δ 13 C signatures, 13 C/ 12 C ratios in biomass provide a valuable tracer of CBC in marine food webs (Robinson & Cavan augh 1995, Zapata-Hernández et al 2014, Ferrier-Pagès & Leal 2018.…”

Toward a standardised protocol for the stable isotope analysis of scleractinian corals

“…Although, there is now a better knowledge of how corals and their algal partners cooperate to share nutrient resources, the complex aspects of metabolic interactions (i.e., flux and destination of metabolites) are still unclear . Further, carbon and nitrogen stable isotope experiments may further reveal the ecological (nutritional) functions of the dense, diverse microbial communities that scleractinian corals harbour in their tissues and skeletons …”

“…3 Further, carbon and nitrogen stable isotope experiments may further reveal the ecological (nutritional) functions of the dense, diverse microbial communities that scleractinian corals harbour in their tissues and skeletons. 25,26 Sample preparation and treatment prior to the analytical determination of stable isotope ratios are of critical importance to achieve high-quality stable isotope data. However, there are marked differences among studies concerning the methods used for sample preparation in order to determine stable isotope ratios (see Table 1).…”