Biomass, photosynthesis and growth of Laminaria saccharina in a high-arctic fjord, NE Greenland

Abstract

Biomass, photosynthesis and growth of the large, perennial brown alga Laminaria saccharina (L.) Lamour. were examined along a depth gradient in a high-arctic fjord, Young Sound, NE Greenland (74°18′N; 20°14′W), in order to evaluate how well the species is adapted to the extreme climatic conditions. The area is covered by up to 1.6-m-thick ice during 10 months of the year, and bottom water temperature is 4 m long and older than 4 years. In contrast to temperate stands of L. saccharina, old leaf blades (2–3 years old) remained attached to the new blades. The old tissues maintained their photosynthetic capacity thereby contributing importantly to algal carbon balance. The photosynthetic characteristics of new tissues reflected a high capacity for adaptation to different light regimes. At low light under ice, or in deep water, the chlorophyll a content and photosynthetic efficiency (α) were high, while light compensation (E c) and saturation (E k) points were low. An E c of 2.0 µmol photons m–2 s–1 under ice allowed photosynthesis to almost balance, and sometimes exceed, respiratory costs during the period with thick ice cover but high surface irradiance, from April through July. Rates of respiration were lower than usually found for macroalgae. Annual elongation rates of leaf blades (70–90 cm) were only slightly lower than for temperate L. saccharina, but specific growth rates (0.48–0.58 year–1) were substantially lower, because the old blades remained attached. L. saccharina comprised between 5% and 10% of total macroalgal biomass in the area, and the annual contribution to primary production was only between 0.1 and 1.6 g C m–2 year–1.