4.4 Perspectives
Our study highlights the applicability of δ13CEAA fingerprinting in a regional sea with strong salinity and temperature gradients by differentiating among the trophic niches of both functional groups and species at an unprecedented resolution, and by identifying spatial fingerprinting differences of widely distributed species. These differences are likely driven by regional differences in basal resources, i.e. algal composition, and the strength of trophic links between various phytoplankton producers and consumers. Our study also highlights how CSIA can provide new insights into food web structuring in spatially and temporally dynamic systems, and thus complement traditional tools in trophic ecology, including insights that are complementary to those from the “traditional” bulk stable isotope analysis.
Current marine food webs are predicted to be fragile and susceptible to structural changes with consequent alterations in the functioning of the ecosystem (Marina et al. 2018). As environmental changes are accelerating, it is crucial to understand whether and how quickly marine food webs can adapt to changes in phytoplankton assemblages and overexploitation of top predators. For this reason, it is key identifying and quantifying feeding interactions across trophic levels, from phytoplankton to zooplankton to higher trophic levels, but many of these interactions remain crucial knowledge gaps (Griffiths et al. 2017). The combination of δ13CEAAand the more affordable bulk stable isotope analysis holds considerable promise to address these gaps in the future.
ACKNOWLEDGMENTS
We thank Dr. Nils Andersen, Karsten Gramenz and Robert Priester for technical assistance at the Leibniz Laboratory for Isotope Research (University of Kiel), and the scientific and permanent crew of RV Alkor cruise AL476 for their support during fieldwork. The study was supported by the Cluster of Excellence 80 ”The Future Ocean”, which is a framework within the Excellence Initiative by the Deutsche Forschungsgemeinschaft (DFG). Sampling on board of RV Alkor took place in the framework of the BONUS BIO-C3 project. TL was supported by the Germany’s Federal Ministry of Education and Research (BMBF) via LOMVIA (03V01459) and JD was in part supported by the BONUS XWEBS project, both supported by BONUS (Art 185), funded jointly by the EU and the German BMBF. We declare no conflict of interest.
CONFLICT OF INTEREST
None declared.
AUTHOR CONTRIBUTION
JD and TL conceived the study, JD collected the samples, TH determined bulk isotope values, TL conducted amino acid isotope analyses and performed statistical analysis, TL and JD wrote the manuscript, and all authors commented on it.
DATA AVAILABILITY STATEMENT
Data associated with this paper are available in the Supplementary Information.
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Table 1. Sampling summary for research cruise AL476 with research vessel ALKOR in April 2016. CSIA indicates the number of specimens analysed for compound specific stable isotope analysis and BSIA the number of specimens analysed for bulk stable isotope analysis.