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: The deepest kelps were located at offshore sites beyond the Disko Island and the main coast. The sites were ice-covered for 77โ days year -1 , which is beyond the length of the polar night 30โ60 days year -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. 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.
In spite of their large ecological relevance in terms of habitat provision, productivity and carbon cycling e. Only very recently, Greenland kelp forests appear in maps of global kelp distribution Filbee-Dexter et al. While kelps are generally confined to temperate and Arctic regions, additional extended kelp forest habitats exist at 30โ m depth in tropical regions, where the shallow zones are too warm and nutrient-limited to support kelp growth but where the deeper zones fulfill the habitat requirements of kelps Graham et al.
Temperate and Arctic kelp forests typically extend down to maximum water depths of 30โ40 m Wernberg et al. In line with this, a recent compilation showed, e. Arctic kelp forests in Svalbard also grow down to 18โ20 m depth Bartsch et al. However, the vast majority of studies on Arctic kelps represents fjords and bays, which experience stronger light attenuation than offshore and open coastal stretches due to planktonic production in combination with turbidity caused by river and glacier runoff Murray et al.
Hence, 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.
