Labelling kelps with 13C and 15N for isotope tracing or enrichment experiments v1

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 protocol details the steps involved in successfully culturing and isotopically enriching (13C & 15N) juvenile sporophytes of two common North Atlantic kelp species (Laminariales): Saccharina latissima and Laminaria digitata. A first-order successful isotopic enrichment study of S. latissima, as well as the first inclusion of 15N enrichment for L. digitata, is 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.