Connections to the Deep: Deep Vertical Migrations, an Important Part of the Life Cycle of Apherusa glacialis, an Arctic Ice-Associated Amphipod

Magnus Drivdal,Stig Falk-Petersen,Jørgen Berge,Rolf Gradinger,Erin H Kunisch,Bodil A Bluhm

doi:10.3389/fmars.2021.772766

Magnus Drivdal, Stig Falk-Petersen + Show 4 more

Open Access

https://doi.org/10.3389/fmars.2021.772766

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Abstract

Arctic sea ice contains a substantial amount of living biota of which part is lost through melt and export out of the Arctic Ocean every year. It is unclear how populations can be maintained within the Arctic Ocean. A representative ice inhabitant, the amphipodApherusa glacialiswas previously assumed to spend its entire life in the sea ice habitat, hence being dependent on sea ice to complete its life cycle. However, several recent studies report pelagic occurrences and suggest that seasonal vertical migrations might be an adaptive life history trait enabling a viable population size in the Arctic Ocean. In this study we use a particle-tracking model to investigate to what extent vertical migration might affect the species’ retention in the Arctic Ocean and the sea ice habitat. The modeled trajectories ofA. glacialiswere calculated based on ice drift and ocean currents from a coupled ocean – sea ice model covering the Arctic Ocean. We test two scenarios: (1) trajectories ofA. glacialisthat stay attached to the ice or follow the surface currents if they melt out of the ice and (2) trajectories ofA. glacialisthat undertake a seasonal vertical migration to drift with the currents at depth for parts of the year. In the multi-year model simulations it is assumed that after an initial period of 2 yearsA. glacialisthat are located outside sea-ice cover each spring will perish while those located within the ice-covered region will reproduce. The model results show that a seasonal vertical migration both increases the total number of individuals and leads to a population distribution within the Arctic Ocean more in line with previous findings than the results from the non-migratingA. glacialis. Our results support the hypothesis that a seasonal migration may be an adaptive life history strategy in this species.

Highlights

The Arctic pelagic marine ecosystem contains very few endemic species, mostly due to the absence of barriers and isolation between the Arctic Ocean and its surrounding seas
In this study we examine a hypothesis based on the findings by Berge et al (2012) and Kunisch et al (2020), namely that deep vertical migration after grazing on the ice-algal bloom would enhance the return and retention of A. glacialis in the Arctic Ocean
In this paper we studied the possible effects of seasonal migration of the amphipod A. glacialis on their population size and distribution within the Arctic Ocean using a particle tracking model

Summary

Introduction

The Arctic pelagic marine ecosystem contains very few endemic species, mostly due to the absence of barriers and isolation between the Arctic Ocean and its surrounding seas. Arctic sea ice provides a unique habitat absent from subArctic seas, with a high biodiversity including a number of endemic species [examples in Bluhm et al (2011)]. More than 1,000 species, ranging from unicellular bacteria and algae up to larger crustaceans, mammals and sea birds are known to live on, in, or in close connection to the sea ice during at least parts of their life cycle (Poulin et al, 2011; Bluhm et al, 2017). Questions remain on how the sea ice taxa, which mainly drift passively with ice and currents, can maintain their populations within the Arctic Ocean when sea ice is continuously exported from the Arctic

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