Stress factors resulting from the Arctic vernal sea-ice melt

Rémi Amiraux,Patricia Bonin,Marcel Babin,Frédéric Vaultier,Guillaume Massé,Jean-François Rontani,Christopher Burot,Sophie Guasco

doi:10.1525/elementa.076

Rémi Amiraux, Patricia Bonin + Show 6 more

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https://doi.org/10.1525/elementa.076

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Abstract

During sea-ice melt in the Arctic, primary production by sympagic (sea-ice) algae can be exported efficiently to the seabed if sinking rates are rapid and activities of associated heterotrophic bacteria are limited. Salinity stress due to melting ice has been suggested to account for such low bacterial activity. We further tested this hypothesis by analyzing samples of sea ice and sinking particles collected from May 18 to June 29, 2016, in western Baffin Bay as part of the Green Edge project. We applied a method not previously used in polar regions—quantitative PCR coupled to the propidium monoazide DNA-binding method—to evaluate the viability of bacteria associated with sympagic and sinking algae. We also measured cis-trans isomerase activity, known to indicate rapid bacterial response to salinity stress in culture studies, as well as free fatty acids known to be produced by algae as bactericidal compounds. The viability of sympagic-associated bacteria was strong in May (only approximately 10% mortality of total bacteria) and weaker in June (average mortality of 43%; maximum of 75%), with instances of elevated mortality in sinking particle samples across the time series (up to 72%). Short-term stress reflected by cis-trans isomerase activity was observed only in samples of sinking particles collected early in the time series. Following snow melt, however, and saturating levels of photosynthetically active radiation in June, we observed enhanced ice-algal production of bactericidal compounds (free palmitoleic acid; up to 4.8 mg L–1). We thus suggest that protection of sinking sympagic material from bacterial degradation early in a melt season results from low bacterial activity due to salinity stress, while later in the season, algal production of bactericidal compounds induces bacterial mortality. A succession of bacterial stressors during Arctic ice melt helps to explain the efficient export of sea-ice algal material to the seabed.

Highlights

Primary production in the Arctic Ocean is characterized by short-lived, springtime blooms of sympagic algae and phytoplankton, which are the major sources of autochthonous organic carbon for the Arctic food web (Horner and Schrader, 1982; Gosselin et al, 1997; Pabi et al, 2008; Wassmann et al, 2011)
Stress factors resulting from the Arctic vernal sea-ice melt: Impact on the viability of bacterial communities associated with sympagic algae
Within the framework of the Green Edge project, originally designed to investigate the dynamics of the spring bloom in ice-impacted Baffin Bay (Massicotte et al, 2020), we found relatively strong cis–trans isomerases (CTI) activity in sea ice and sinking particles collected in the water column during the 2015 vernal melting period, which suggested the occurrence of salinity stress during the early stages of ice melt (Amiraux et al, 2017)

Summary

Introduction

Primary production in the Arctic Ocean is characterized by short-lived, springtime blooms of sympagic (ice-associated) algae and phytoplankton, which are the major sources of autochthonous organic carbon for the Arctic food web (Horner and Schrader, 1982; Gosselin et al, 1997; Pabi et al, 2008; Wassmann et al, 2011). Amiraux et al: Impact of the Arctic vernal sea ice melt on the viability of bacteria. The fate of algal material in the water column during its sinking depends on zooplankton grazing and on the hydrolytic and remineralization activity of bacteria associated with the sinking particles (whether by seaice or water-column bacteria). Howard-Jones et al (2002) suggested that significant fractions (25%–80%) of Arctic bacterioplankton (including the particle-associated ones) are dormant or express very low activity, based on measurements made in the water column of the Barents Sea marginal ice zone, where the percentage of active bacteria varied by measurement method. Studies suggested that heterotrophic bacterial remineralization was generally low in perennially cold environments like the Arctic (Pomeroy and Deibel, 1986), allowing organic matter to be exported from productive to oligotrophic regions or to be preserved long enough for use during times of low primary productivity. The effect of temperature on Arctic bacterial activity remains unclear (Kirchman et al, 2005)

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