Spatial and Temporal Variability of Ice Algal Trophic Markers—With Recommendations about Their Application

Eva Leu,Michael J Greenacre,Michael J Greenacre,Jozef Wiktor,Thomas A Brown,Agneta Fransson,Martin Graeve,Melissa Chierici,Melissa Chierici,Ane C Kvernvik,Sander Verbiest,Clara J M Hoppe

doi:10.3390/jmse8090676

Abstract

Assessing the relative importance of sea ice algal-based production is often vital for studies about climate change impacts on Arctic marine ecosystems. Several types of lipid biomarkers and stable isotope ratios are widely used for tracing sea ic-associated (sympagic) vs. pelagic particulate organic matter (POM) in marine food webs. However, there has been limited understanding about the plasticity of these compounds in space and time, which constrains the robustness of some of those approaches. Furthermore, some of the markers are compromised by not being unambiguously specific for sea ice algae, whereas others might only be produced by a small sub-group of species. We analyzed fatty acids, highly branched isoprenoids (HBIs), stable isotope ratios of particulate organic carbon (POC) (δ13C), as well as δ13C of selected fatty acid markers during an Arctic sea ice algal bloom, focusing on spatial and temporal variability. We found remarkable differences between these approaches and show that inferences about bloom characteristics might even be contradictory between markers. The impact of environmental factors as causes of this considerable variability is highlighted and explained. We emphasize that awareness and, in some cases, caution is required when using lipid and stable isotope markers as tracers in food web studies and offer recommendations for the proper application of these valuable approaches.

Highlights

In a rapidly warming Arctic, primary production regimes are expected to change, and probably shift towards a larger contribution of phytoplankton, relative to sea ice algae, in response to increasingly open waters and thinning sea ice [1]
Sea ice algae abundance and taxonomy were studied from early March to early May, but only from April onwards did biomass concentrations become high enough to measure all trophic markers in sea ice samples
The particulate organic carbon (POC):Chlorophyll a (Chl a) ratio clearly reflected the impact of increased light under lower snow cover, and increased from 23 (23/4, high snow cover) to 93 (2/5, no snow) within only two weeks

Summary

Introduction

In a rapidly warming Arctic, primary production regimes are expected to change, and probably shift towards a larger contribution of phytoplankton, relative to sea ice algae, in response to increasingly open waters and thinning sea ice [1]. The relevance of sea ice algal production for different parts of the polar ecosystem, ranging from key pelagic grazers to mammals has been studied extensively [4,5,6,7]. Another important aspect addressed in various studies has been assessing the overall strength of sympagic-pelagic or sympagic-benthic coupling [8,9,10]. We will focus on two common types of trophic markers: (a) lipid-based trophic markers (fatty acid trophic markers, and highly branched isoprenoids), and (b) δ13C as one example of a stable isotope-based marker technique

Objectives

Methods

Results

Discussion

Conclusion