Microbial Abundance and Enzyme Activity Patterns: Response to Changing Environmental Characteristics along a Transect in Kongsfjorden (Svalbard Islands)

Gabriella Caruso,Franco Decembrini,Federico Giglio,Maurizio Azzaro,Alice Madonia,Filippo Azzaro,Simone Bonamano,Marco Marcelli,Giovanna Maimone,Stefano Miserocchi,Rosabruna La Ferla,Daniele Piazzolla,Viviana Piermattei

doi:10.3390/jmse8100824

Abstract

Svalbard archipelago is experiencing the effects of climate changes (i.e., glaciers’ thickness reduction and glacier front retreat), but how ice melting affects water biogeochemistry is still unknown. Microbial communities often act as environmental sentinels, modulating their distribution and activity in response to environmental variability. To assess microbial response to climate warming, within the ARctic: present Climatic change and pAst extreme events (ARCA) project, a survey was carried out along a transect in Konsfjorden from off-shore stations towards the Kronebreen glacier. Total bacterial abundance and the fraction of actively respiring cells (labelled by cyanotetrazolium chloride, CTC), cultivable heterotrophic bacterial abundance, and extracellular enzymatic activities (leucine aminopeptidase (LAP), beta-glucosidase (GLU), and alkaline phosphatase (AP)) were measured. In addition, water temperature, salinity, dissolved oxygen, turbidity, total suspended matter (TSM), particulate and chromophoric dissolved organic matter (CDOM), chlorophyll-a (Chl-a), and inorganic compounds were determined, in order to evaluate whether variations in microbial abundance and metabolism were related with changes in environmental variables. Colder waters at surface (3.5–5 m) depths and increased turbidity, TSM, and inorganic compounds found at some hydrological stations close to the glacier were signals of ice melting. CDOM absorption slope values (275–295 nm) varied from 0.0077 to 0.0109 nm−1, and total bacterial cell count and cultivable heterotrophic bacterial abundance were in the order of 106 cells/mL and 103 colony forming units/mL, respectively. Enzymatic rates <1.78, 1.25, and 0.25 nmol/L/h were recorded for AP, LAP, and GLU, respectively. Inorganic compounds, TSM, and turbidity correlated inversely with temperature; AP was significantly related with CDOM absorption spectra and heterotrophic bacteria (r = 0.59, 0.71, p < 0.05); and LAP with Chl-a, Particulate Organic Carbon (POC) and Particulate Organic Nitrogen (PON) (0.97, 0.780, 0.734, p < 0.01), suggesting that fresh material from ice melting stimulated the metabolism of the cultivable fraction.

Highlights

Arctic regions are currently experiencing a rapid global warming due to climate change, with its detrimental effects, such as ice melting, glacier retreat, and/or thickness reduction
Temperature and salinity values decreased from st. 4 to 8, while an opposite trend was observed for turbidity and inorganic compounds
The variability in the amounts of total bacteria and enzymatic activity rates reflected the changes in the hydrological conditions; the inflow of Atlantic waters from the open ocean and the freshwater runoff from the melting glaciers stimulated microbial abundance and metabolism within the fjord

Summary

Introduction

Arctic regions are currently experiencing a rapid global warming due to climate change, with its detrimental effects, such as ice melting, glacier retreat, and/or thickness reduction. Besides rising temperatures and salinity variations, increased water turbidity due to particulate matter inputs from glacier meltwater outflow and river runoff are frequently recorded in coastal or close to coastal ecosystems. A significant contribution to current knowledge of the distribution, community dynamics, and metabolic activities of marine microorganisms inhabiting Arctic marine ecosystems has been provided by a number of previous investigations [2,3,4,5,6,7,8,9]. Rapidly occurring changes induced by environmental variability in polar regions stimulate further research on the response of microbial communities, since the literature available on this issue is still far from being exhaustive [11,12]

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