Pelagic occurrences of the ice amphipod Apherusa glacialis throughout the Arctic.

Erin H Kunisch,Øystein Varpe,Rolf Gradinger,Malin Daase,Jørgen Berge,Igor A Melnikov,Haakon Hop,Bodil A Bluhm,Xabier Irigoien

doi:10.1093/plankt/fbz072

Erin H Kunisch, Øystein Varpe + Show 7 more

Open Access

https://doi.org/10.1093/plankt/fbz072

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Abstract

Apherusa glacialis is a common, sea ice-associated amphipod found throughout the Arctic Ocean and has long been considered permanently associated with the sea ice habitat. However, pelagic occurrences of A. glacialis have also been reported. It was recently suggested that A. glacialis overwinters at depth within the Atlantic-water inflow near Svalbard, to avoid being exported out of the Arctic Ocean through the Fram Strait. This study collated pelagic occurrence records over a 71-year period and found that A. glacialis was consistently found away from its presumed sea ice habitat on a pan-Arctic scale, in different depths and water masses. In the Svalbard region, A. glacialis was found in Atlantic Water both in winter and summer. Additionally, we analyzed A. glacialis size distributions throughout the year, collected mostly from sea ice, in order to elucidate potential life cycle strategies. The majority of young-of-the-year A. glacialis was found in the sea ice habitat during spring, supporting previous findings. Data on size distributions and sex ratios suggest a semelparous lifestyle. A synchronous seasonal vertical migration was not evident, but our data imply a more complex life history than previously assumed. We provide evidence that A. glacialis can no longer be regarded as an autochthonous sympagic species.

Highlights

Apherusa glacialis is a common, sea ice-associated amphipod found throughout the Arctic Ocean and has long been considered permanently associated with the sea ice habitat
The Berge et al (2012) model suggests that a primary e ect of being at depth in the Atlantic inflow area is that A. glacialis avoids being exported out of the Arctic Ocean, though some population loss still occurs via sea ice export through Fram Strait (Hop and Pavlova, 2008)
We cannot entirely rule out that the pelagic occurrences of A. glacialis are due to them being lost from the sea ice habitat and that they are sinking to the sea floor, pelagic individuals occurred in areas covered by sea ice outside the melt season

Summary

Introduction

Apherusa glacialis is a common, sea ice-associated amphipod found throughout the Arctic Ocean and has long been considered permanently associated with the sea ice habitat. When drifting sea ice habitat melts or is exported out of the Arctic Ocean, it is assumed that A. glacialis is lost to the water column, with little to no chance of survival, especially when sea ice is exported out of the Arctic Basin (Arndt and Pavlova, 2005; Hop and Pavlova, 2008). This led to the question, how are they able to maintain a viable population within this drifting and often ephemeral habitat? The su cient lipid stores found in the deep-water A. glacialis (Berge et al, 2012) suggest an adequate energy supply for overwintering

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