Abstract
Until recently, Arctic kelp forests were so understudied that they did not even appear in global kelp forest maps. An increasing focus on Arctic coastal ecosystems has documented extended kelp forests along Arctic coastlines but the distribution of the forests is still not well documented and opens up for surprises. Here we report kelp depth limits deeper than 61 m (median: 38.4 m, 10-90% percentiles: 10.8-54.4 m) in the Disko Bay region, Greenland, at latitudes of 67-70°N. We compiled, for comparison, existing records of kelp depth limits in high latitude (50°N) regions (median: 17.7 m, 10-90% percentiles: 9.0-38.1 m), which underline that the Disko Bay kelps hold a depth-record for this region. The deepest kelps were located at offshore sites beyond the Disko Island and the main coast. The clear waters offshore with euphotic zones (1% of surface irradiance) extending to 67 m depth provide, along with deep rocky seafloors and low density of sea urchins, the basis for these deep kelps. The sites were ice-covered for 77-133 days yr-1, which is beyond the length of the polar night (30-60 days yr-1) in the region, suggesting a potential for further depth penetration of kelp forests in a future with longer open water periods and more light potentially reaching the seafloor.
Highlights
Kelp forests are widely distributed along coastlines where rocky substratum and cool, clear, and relatively nutrient-rich waters fulfill their growth requirements and where sea urchins do not overgraze them (e.g., Steneck et al, 2002)
The 33 observations of kelp depth limits from this study in the Disko Bay area represent a mean of 35.5 m and 10–90% percentiles of 10.8–54.4 m (Figure 2)
The Disko Bay depth limits are considerably deeper than depth limits earlier reported for the high latitudes, which represented a mean level of only 18.4 m and 10–90% percentiles of 9–31.8 m (Figure 2 and Supplementary Table S2)
Summary
Kelp forests are widely distributed along coastlines where rocky substratum and cool, clear, and relatively nutrient-rich waters fulfill their growth requirements and where sea urchins do not overgraze them (e.g., Steneck et al, 2002). In spite of their large ecological relevance in terms of habitat provision, productivity and carbon cycling (e.g., Teagle et al, 2017; Wernberg et al, 2019), kelp distribution is still widely unexplored, in Arctic regions, which are often ignored in global reviews and maps of kelp forest ecosystems (Steneck et al, 2002; Graham et al, 2007; Krumhansl et al, 2016). There is a need to balance available estimates with those derived from offshore, open coastal Arctic habitats, where the underwater light environment and deep rocky seafloors are expected to allow deeper penetration of kelp forests
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