Laminaria hyperborea off the island of Helgoland (North Sea, Germany) was sampled along a depth gradient (0.5, 2, 4, 6 m) throughout summer 2014. Chlorophyll a content was measured. Discs were cut from three different blade regions (5, 25 and 50 cm above the stipe-blade transition zone) and normalized to either dry mass, fresh mass or disc area. The samples were freeze-dried for approximately 36 h (Beta 1–8 LDplus, Christ, Osterode am Harz, Germany), finely ground for several minutes using steel grinding balls (3 mm diameter) in a Mikro-Dismembrator U (Braun Biontech International, Melsungen, Germany), cooled centrifuged (Centrifuge 3K10, Sigma, Osterode, Germany), and measured in the spectrophotometer (U-3310, Hitachi High-Tech, Japan) at two wavelengths (347 and 664.5 nm).

Additional funding was provided by the Postdoctoral fellowship grant of the Fonds de recherche du Québec - Nature et technologies and the Weston Foundation.