Investigating the physiological ecology of mesopelagic zooplankton in the Scotia Sea (Southern Ocean) using lipid and stable isotope signatures

The mesopelagic zooplankton community plays an important role in the cycling and sequestration of carbon via the biological pump. However, little is known about the physiology and ecology of key taxa found within this region, hindering our understanding of their influence on the pathways of energy and organic matter cycling. We sampled the eight most abundant zooplankton (Calanoides acutus, Rhincalanus gigas, Paraeuchaeta spp., Chaetognatha, Euphausia triacantha, Thysanoessa spp., Themisto gaudichaudii and Salpa thompsoni) from within the mesopelagic zone in the Scotia Sea during a sinking diatom bloom and investigated their physiological ecology using lipid biomarkers and stable isotopic signatures of nitrogen. Data suggest that the large calanoid copepods, C. acutus and R. gigas, were in, or emerging from, a period of metabolic inactivity during the study period (November 15th – December 15th 2017). Abundant, but decreasing lipid reserves in the predominantly herbivorous calanoid copepods, suggest these animals may have been metabolising previously stored lipids at the time of sampling, rather than deriving energy solely from the diatom bloom. This highlights the importance of understanding the timing of diapause of overwintering species as their feeding is likely to have an impact on the turnover of particulate organic matter (POM) in the upper mesopelagic. The δ15N signatures of POM became enriched with increasing depth, whereas all species of zooplankton except T. gaudichaudii did not. This suggests that animals were feeding on fresher, surface-derived POM, rather than reworked particles at depth, likely influencing the quantity and quality of organic matter leaving the upper mesopelagic. Our study highlights the complexity of mesopelagic food webs and suggests that the application of broad trophic functional types may lead to an incorrect understanding of ecosystem dynamics.


Publication status:
Authors: Savineau, Eloise L-R, Cook, Kathryn B. ORCIDORCID record for Kathryn B. Cook, Blackbird, Sabena J., Stowasser, Gabriele ORCIDORCID record for Gabriele Stowasser, Kiriakoulakis, Konstadinos, Preece, Calum, Fielding, Sophie ORCIDORCID record for Sophie Fielding, Belcher, Anna ORCIDORCID record for Anna Belcher, Wolff, George A., Tarling, Geraint ORCIDORCID record for Geraint Tarling, Mayor, Daniel ORCIDORCID record for Daniel Mayor

On this site: Anna Belcher, Geraint Tarling, Gabriele Stowasser, Sophie Fielding
1 June, 2024
Deep Sea Research Part I: Oceanographic Research Papers / 208
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