Climate change stimulates the growth of the intertidal macroalgae Ascophyllum nodosum near the northern distribution limit

Núria Marbà,Anissa Merzouk,Dorte Krause-Jensen,Birgit Olesen,Robert T Wilce,Joao Rodrigues,Peter B Christensen,Susse Wegeberg

doi:10.1007/s13280-016-0873-7

Abstract

Ascophyllum nodosum is a foundation macroalgae of the intertidal zone that distributes across latitude 41.3–69.7°N. We tested the hypothesis that growth of A. nodosum near the northern distribution edge increases with warming. We retrospectively quantified the growth of eight A. nodosum populations at West Greenland and North Norway (from 64°N to 69°N). For seven populations, we measured growth rates since 1997–2002 and for one of them we extended the time series back to 1956 using published estimates. Individuals at northern populations elongated between 2.0 and 9.1 cm year−1 and this variability correlated with temperature and annual ice-free days. A spatial comparison of A. nodosum growth across the species distribution range showed that Northern (and coldest) populations grew at the slowest rates. Our results demonstrate that arctic climate change enhances the growth of A. nodosum populations and suggest that their productivity may increase in response to projected global warming.

Highlights

The arctic climate is rapidly changing due to excessive anthropogenic greenhouse gas emissions to the atmosphere (IPCC 2014)
We saw a latitudinal trend of increased growth of sub-arctic A. nodosum populations from north to south along Greenland’s coast matching the higher temperatures and the reduced sea ice cover towards the south
Our data clearly show that A. nodosum populations grow much faster at 69°N along Norway’s Gulf Current-influenced coast, than at the same latitude in the colder and partly ice-covered Greenland waters

Summary

Introduction

The arctic climate is rapidly changing due to excessive anthropogenic greenhouse gas emissions to the atmosphere (IPCC 2014). The Arctic Ocean ranks amongst the oceans warming at the fastest rate, twice as fast as the global ocean, and it experiences the largest thermal marine. Arctic warming is evidenced by the rapid loss of sea ice cover during the last decades, which reached the minimum extension ever recorded in 2012 (Vaughan et al 2013). Arctic warming is expected to continue and, even under a mild scenario of greenhouse gas emissions (i.e., IPCC scenario RCP4.5), global models project a median of 4.9 °C (maximum 9.3 °C) warming by the end of the twenty-first Century (Christensen et al 2013). Footprints of current arctic climate change are already evident in marine arctic ecosystems (Wassmann et al 2011). A major limiting factor is the sparsity of long-term datasets on arctic benthic vegetation, which are limited to scattered information from Svalbard fjords (Weslawski et al 2010; Fredriksen and Kile 2012; Fredriksen et al 2014; Kortsch et al 2012; Bartsch et al 2016), Greenland coasts (Krause-Jensen et al 2012; Olesen et al 2015) and Canadian coasts (Merzouk and Johnson 2011)

Methods

Results

Discussion

Conclusion