Abstract
We studied the depth distribution and production of kelp along the Greenland coast spanning Arctic to sub-Arctic conditions from 78 °N to 64 °N. This covers a wide range of sea ice conditions and water temperatures, with those presently realized in the south likely to move northwards in a warmer future. Kelp forests occurred along the entire latitudinal range, and their depth extension and production increased southwards presumably in response to longer annual ice-free periods and higher water temperature. The depth limit of 10% kelp cover was 9–14 m at the northernmost sites (77–78 °N) with only 94–133 ice-free days per year, but extended to depths of 21–33 m further south (73 °N–64 °N) where >160 days per year were ice-free, and annual production of Saccharina longicruris and S. latissima, measured as the size of the annual blade, ranged up to sevenfold among sites. The duration of the open-water period, which integrates light and temperature conditions on an annual basis, was the best predictor (relative to summer water temperature) of kelp production along the latitude gradient, explaining up to 92% of the variation in depth extension and 80% of the variation in kelp production. In a decadal time series from a high Arctic site (74 °N), inter-annual variation in sea ice cover also explained a major part (up to 47%) of the variation in kelp production. Both spatial and temporal data sets thereby support the prediction that northern kelps will play a larger role in the coastal marine ecosystem in a warmer future as the length of the open-water period increases. As kelps increase carbon-flow and habitat diversity, an expansion of kelp forests may exert cascading effects on the coastal Arctic ecosystem.
Highlights
The Arctic is the fastest warming region of the globe and temperatures are projected to increase during the 21st century at twice the global average rate (IPCC, 2007)
The length of the ice-free period ranged from 2 months (68 days) at Dundas (77 oN) to almost the entire year at Nuuk (64 oN) in 2009, and the combined effect of winter darkness and sea ice cover led to a wide range of the open-water period with light from 2 months in the north to almost an entire year in the south (Fig. 2a)
August surface water temperatures at the kelp sampling sites ranged from 1.4 °C (Eqip Sermia 70 oN) to 7.4 °C (Upernavik 73 oN), generally coldest in the north and near glaciers (Eqip Sermia and Ilulissat at 69–70 oN) (Fig. 2b)
Summary
The Arctic is the fastest warming region of the globe and temperatures are projected to increase during the 21st century at twice the global average rate (IPCC, 2007). The primary production of kelps and other benthic macroalgae can contribute over 20% of the total primary production (dominated by phytoplankton and at much less extent, sea ice algae and benthic microalgae) in a near-shore high-Arctic area, and even exceed pelagic primary production at water depths shallower than 20 m (Glud & Rysgaard, 2007; Krause-Jensen et al, 2007). This primary production enters the food web through grazing, exudation of dissolved organic carbon and as detritus (Mann, 1973; Duggins et al, 1989). Only very limited information exists on the in situ growth, abundance and depth extension of kelp forests along the Greenland coast and the physical factors responsible
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