Carbon and nitrogen allocation patterns in two intertidal fucoids: Fucus serratus and Himanthalia elongata (Phaeophyta)

Carbon and nitrogen contents of two intertidal fucoid species, Fucus serrat us and Himanthalia elongata, were investigated with respect to variations i n seasonal resource availability, growth and reproductive requirements. The linear growth rate of F. serratus peaked in spring at 2 . 3 cm 28 d(-1), c ompared with < 0 . 1 cm 28 d(-1) in the winter. In H. elongate, the button diameter increased slowly throughout the year (< 0 . 22 cm 28 d(-1)); in co ntrast, the receptacle had an elongation rate of up to 7 . 8 an 28 d(-1) in the spring months. There was no difference in the nitrogen content (% dry weight, dwt) of the vegetative tissue of both non-reproductive and fertile thalli and receptacle tissue of F. serratus, but the nitrogen content of al l three tissue types varied seasonally. Reproductive development was initia ted in May when nitrogen content was at its peak (3 % dwt). Tissue nitrogen content decreased rapidly through reproductive development to a minimum of less than 1 . 5% dwt in August; this decrease also occurred in non-reprodu ctive thalli. Tissue nitrogen varied between 0 . 5 and 1 . 75% dwt in the v egetative buttons on both non-reproductive and fertile H. elongata, but not in a distinct seasonal manner. Receptacle development in H. elongata was i nitiated in October/November. The nitrogen content of the receptacle tissue increased rapidly in the first two months of reproductive development (up to 2 . 5 % dwt) then progressively decreased throughout the remaining perio d of reproductive development. There was no evidence of carbon storage in t he vegetative tissues of either F. serratus or H. elongata.