Imprint of Climate Change on Pan-Arctic Marine Vegetation

Dorte Krause-Jensen,Philippe Archambault,Olga Maximova,Inka Bartsch,Karen Filbee-Dexter,Kai Bischof,Uliana Simakova,Jorge Assis,Mikael K Sejr,Kenneth H Dunton,Vassily Spiridonov,Susse Wegeberg,Carlos M Duarte,Sunna Björk Ragnarsdóttir,Mie H S Winding

doi:10.3389/fmars.2020.617324

Abstract

The Arctic climate is changing rapidly. The warming and resultant longer open water periods suggest a potential for expansion of marine vegetation along the vast Arctic coastline. We compiled and reviewed the scattered time series on Arctic marine vegetation and explored trends for macroalgae and eelgrass (Zostera marina). We identified a total of 38 sites, distributed between Arctic coastal regions in Alaska, Canada, Greenland, Iceland, Norway/Svalbard, and Russia, having time series extending into the 21st Century. The majority of these exhibited increase in abundance, productivity or species richness, and/or expansion of geographical distribution limits, several time series showed no significant trend. Only four time series displayed a negative trend, largely due to urchin grazing or increased turbidity. Overall, the observations support with medium confidence (i.e., 5–8 in 10 chance of being correct, adopting the IPCC confidence scale) the prediction that macrophytes are expanding in the Arctic. Species distribution modeling was challenged by limited observations and lack of information on substrate, but suggested a current (2000–2017) potential pan-Arctic brown macroalgal distribution area of 655,111 km2(140,433 km2intertidal, 514,679 km2subtidal), representing an increase of about 45% for subtidal- and 8% for intertidal macroalgae since 1940–1950, and associated polar migration rates averaging 18–23 km decade–1. Adjusting the potential macroalgal distribution area by the fraction of shores represented by cliffs halves the estimate (340,658 km2). Warming and reduced sea ice cover along the Arctic coastlines are expected to stimulate further expansion of marine vegetation from boreal latitudes. The changes likely affect the functioning of coastal Arctic ecosystems because of the vegetation’s roles as habitat, and for carbon and nutrient cycling and storage. We encourage a pan-Arctic science- and management agenda to incorporate marine vegetation into a coherent understanding of Arctic changes by quantifying distribution and status beyond the scattered studies now available to develop sustainable management strategies for these important ecosystems.

Highlights

Rapid warming of the Arctic with associated melting of ice sheets, glaciers, and reduced extent and thickness of sea ice is causing major changes in high latitude coastal ecosystems (Pörtner et al, 2019)
We looked for studies reporting trends in macroalgae or seagrasses from the Arctic region as defined by the Arctic Council (Huntington, 2001), including Arctic Canada, Alaska, Greenland, Iceland, Norway/Svalbard, and Russia (Figure 1)
Arctic macroalgal habitats in Alaska have been studied for decades and three time-series exist between the cold temperate Aleutian Islands in the southern Bering Sea and the High Arctic Beaufort Sea (Figure 1)

Summary

Introduction

Rapid warming of the Arctic with associated melting of ice sheets, glaciers, and reduced extent and thickness of sea ice is causing major changes in high latitude coastal ecosystems (Pörtner et al, 2019). A large component of macroalgae growing in the Arctic have a boreal origin, shaped through cycles of glaciation to unique assemblages in polar waters (Bringloe et al, 2020) Many of these macroalgae as well as eelgrass (Zostera marina), the sole seagrass species occurring in sub-Arctic areas, are characterized by optimum temperatures for growth which are considerably higher than those currently experienced in the Arctic (Müller et al, 2009; Wulff et al, 2009; Beca-Carretero et al, 2018). While the combination of reduced sea-ice cover and warming is expected to stimulate growth of Arctic marine vegetation (Krause-Jensen and Duarte, 2014), sediments delivered with glacier runoff may locally increase water column light attenuation and, thereby, counteract the effect of reduced extent of sea ice on light availability (Bartsch et al, 2016; Bonsell and Dunton, 2018; Pavlov et al, 2019)

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Conclusion