SEASONAL-VARIATION IN GROWTH, REPRODUCTION AND NITROGEN-CONTENT OF FUCUS-VESICULOSUS L IN THE ORESUND, SOUTHERN SWEDEN

The autecology of Fucus vesiculosus at Barseback, Oresund, southern Sweden, was studied from May to December 1984. The length, growth rate, biomass increase, reproduction and nitrogen content were followed. Fucus vesiculosus at Barseback exhibited an average growth rate of 0.54 cm/week with the highest growth rates of 0.7-0.8 cm/week observed during June and August. The mean length of the vegetative tips increased almost linearly with time during May to September. At the end of the year the new growth constituted over 80% of the total plant biomass. The mean total length increase was 15.6 cm during the period studied. Two reproductive periods were observed during 1984. Mature receptacles were found during May to July and new receptacles were initiated in July on the same plants and matured during September and October. The nitrogen content in F. vesiculosus varied both seasonally and between tissues of different ages within the plants. Variations were most pronounced in the new vegetative tips with the highest concentrations in winter; 1.71 mmol/g dw in December, and lowest during summer, about 0.5 mmol/g dw in July and August. Basal parts did not show any seasonal variation in nitrogen content. In November-December the vegetative tissue grown during the year contained almost 90% of the total nitrogen within the plant.