Jean-Sébastien Lauzon-Guay 1, Alison Feibel1, Malcolm Gibson2, Michéal MacMonagail3, Bryan L. Morse1, Collette A. Robertson1, Raúl A. Ugarte1
1Acadian Seaplants Ltd, 30 Brown Ave, Dartmouth, Nova Scotia, B3B 1X8, Canada
2Uist Asco, A865, Isle of North Uist HS6 5AY, United Kingdom
3Arramara Teoranta, Oyster Bay, Kilkieran, Co. Galway, Ireland
Ascophyllum nodosum (L.) Le Jolis (Fucales, Fucaceae) is an intertidal brown alga that is commercially harvested in several countries. Productivity estimates are sparse and for the most parts are calculated based on apical growth only. We carried out a broad-scale survey at twenty-three sites from both sides of the North Atlantic to measure growth, reproductive output, loss of tissue over winter, and productivity of A. nodosum. We assessed the length and mass of successive internodal segments and established that, contrary to previous findings, internodal segments continue accumulating mass for one to five years and increase in length for one to three years at most sites. Segments can almost triple their mass during their second year and more than double their length. In some populations, annual growth in older parts of the frond can represent as much as 36% of the biomass and be greater than the growth at the tip of the frond. When accounting for the growth at the tip and in older parts of the fronds, total annual growth can represent up to 55% of the frond biomass. These results indicate that previous productivity and growth estimates for A. nodosum based on apical growth alone greatly underestimated the productivity of the species and its role in coastal carbon cycling. Furthermore, because they grow over a period of several years, internodal segments should not be used to infer past environmental conditions or to reconstruct growth patterns over time.