Labelling kelps with ¹³ C and ¹⁵ N for isotope tracing or enrichment experiments

Abstract Isotope tracing experiments can be used to trace organic material flow through the ecosystem by artificially adding labelled biomass into a system. The advantage of this process is the direct control of carbon and nitrogen addition to the system for measuring uptake rates by consumers, which can substantially reduce the uncertainties associated with food web models. This article details and discusses the steps involved in successfully culturing and isotopically enriching ( 13 C and 15 N) juvenile sporophytes of two common North Atlantic kelp species (Laminariales): Saccharina latissima and Laminaria digitata . A first successful isotopic enrichment study of S. latissima , as well as the first inclusion of 15 N enrichment for L. digitata , are detailed. This protocol provides a comprehensive description of the stable isotope enrichment process in two kelp species, potentially serving as a foundation for its application in other macroalgal taxa.