Ice Algae-Produced Carbon Is Critical for Overwintering of Antarctic Krill Euphausia superba

Doreen Kohlbach,Thomas Krumpen,Carmen David,Jan A Van Franeker,Hauke Flores,Martin Graeve,Martina Vortkamp,Benjamin A Lange,Fokje L Schaafsma

doi:10.3389/fmars.2017.00310

Abstract

Antarctic krill Euphausia superba (‘krill’) constitute a fundamental food source for Antarctic seabirds and mammals, and a globally important fisheries resource. The future resilience of krill to climate change depends critically on the winter survival of young krill. To survive periods of extremely low production by pelagic algae during winter, krill are assumed to rely partly on carbon produced by ice algae. The true dependency on ice algae-produced carbon, however, is so far unquantified. This confounds predictions on the future resilience of krill stocks to sea ice decline. Fatty acid (FA) analysis, bulk stable isotope analysis (BSIA) and compound-specific stable isotope analysis (CSIA) of diatom- and dinoflagellate-associated marker FAs were applied to quantify the dependency of overwintering larval, juvenile and adult krill on ice algae-produced carbon (αIce) during winter 2013 in the Weddell-Scotia Confluence Zone. Our results demonstrate that the majority of the carbon uptake of the overwintering larval and juvenile krill originated from ice algae (up to 88% of the carbon budget), and that the dependency on ice algal carbon decreased with ontogeny, reaching less than 56% of the carbon budget in adults. Spatio-temporal variability in the utilization of ice algal carbon was more pronounced in larvae and juvenile krill than in adults. Differences between αIce estimates derived from short- versus long-term FA-specific isotopic compositions suggested that ice algae-produced carbon gained importance as the winter progressed, and might become critical at the late winter-spring transition, before the phytoplankton bloom commences. Where the sea ice season shortens, reduced availability of ice algae might possibly not be compensated by surplus phytoplankton production during wintertime. Hence, sea ice decline could seriously endanger the winter survival of recruits, and subsequently overall biomass of krill.

Highlights

Antarctic krill Euphausia superba Dana (1850) is a highly abundant key species in the Southern Ocean, often channeling the majority of dietary carbon from marine microalgae to fishes, seabirds, and marine mammals (Hempel, 1987; Ward et al, 2012)
To assess the potential influence of spatio-temporal variability of ice algae samples on the results, we investigated algal Fatty acid (FA) profiles and isotopic values separately for the two ice camps
In the two dinoflagellate-associated marker FAs, significant differences in the mean δ13C values ranged between 9‰ (22:6n-3) and 14‰ (18:4n-3; Table 3)

Summary

Introduction

Antarctic krill Euphausia superba Dana (1850) (hereafter “krill”) is a highly abundant key species in the Southern Ocean, often channeling the majority of dietary carbon from marine microalgae to fishes, seabirds, and marine mammals (Hempel, 1987; Ward et al, 2012). Besides their ecological importance, krill constitute an increasingly harvested fisheries resource. There remains uncertainty in sea ice extent predictions for the Southern Ocean (Turner et al, 2013), the majority of simulations indicate more widespread sea ice decline in the coming decades, during winter and spring (Turner et al, 2014)

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Discussion

Conclusion