Biometrics in Laminaria digitata: A useful tool to assess biomass, carbon and nitrogen contents

Sporophytes of Laminaria digitata (Hudson) J.V. Lamouroux (Ochrophyta: Phaeophyceae) were haphazardly collected seasonally from September 1996 to March 1999 in the rocky shore of the eastern English Channel in order to conduct a biometrical study relating fresh weight (FW), dry weight (DW), carbon and nitrogen masses to the length of the thalli. The aim was to create a tool that allows estimation of the weight of the algae by a simple, rapid and non destructive morphological measurement of the total length of the sporophyte. The highly significant and lasting relationships obtained appeared very useful to express the standing biomass of L. digitata in terms of carbon or nitrogen. Variations in tissue carbon (C) and nitrogen (N) were examined over a complete seasonal cycle and showed clear patterns, ranged from 26.8 to 33.1% of the total dry weight for carbon and 1.87 to 3.20% for nitrogen. The seasonal variations in C/N ratio corresponded to a winter nitrogen uptake from the medium and to high spring carbon assimilation due to photosynthesis.