SEASONAL LAMINA GROWTH IN 2 AGE-GROUPS OF LAMINARIA-SACCHARINA (L) LAMOUR IN WESTERN NORWAY

In this study of Laminaria saccharina the length-to-width ratio of newly grown lamina tissue was observed to vary throughout the year. The ratio was at its lowest during the period of slow growth and at its highest during the period of rapid growth. An increase in both length and width growth took place at mid-winter simultaneously with a decrease in carbon content of the lamina, indicating consumption of stored carbohydrates. Long laminae were more prone to distal erosion than short ones during the autumn. The distribution of more growth in the width direction during summer and autumn may therefore maximize the lamina area during autumn and winter and thus increase the amount of stored carbon available for the plants at this time. It may be interpreted as a morphological adaptation to a period of slow growth. A period of rapid lamina growth during late winter and spring was observed. Both length and width growth declined early in the summer, probably due to nitrate limitation. At the end of the investigation the plants were harvested and their age determined. The lamina elongation was found to be generally lower in third-year plants than in second-year ones, while width growth was similar in the two groups. This means a decreased length-to-width ratio of the new tissue produced with increasing age. Depopulation of the tagged plants was at its highest during the period of slow growth.