Pelagic occurrences of the ice amphipod Apherusa glacialis throughout the Arctic

Abstract

<i>Apherusa glacialis</i> 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 <i>A. glacialis</i> have also been reported. It was recently suggested that <i>A. glacialis</i> 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 <i>A. glacialis</i> 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, <i>A. glacialis</i> was found in Atlantic Water both in winter and summer. Additionally, we analyzed <i>A. glacialis</i> 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 <i>A. glacialis</i> 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 <i>A. glacialis</i> can no longer be regarded as an autochthonous sympagic species.