ECOLOGY OF SARGASSUM-MUTICUM ON THE NORTH COAST OF SPAIN .2. PHYSIOLOGICAL DIFFERENCES BETWEEN SARGASSUM-MUTICUM AND CYSTOSEIRA-NODICAULIS

The variations of photosynthesis and C, N and mannitol content were an alyzed in the co-existing invasive species Sargassum muticum and the n ative Cystoseira nodicaulis. Both species exhibited similar seasonal p atterns of photosynthesis, with a significant decay in P-max in summer , which can be attributed to nutrient limitation. Nitrogen content was the lowest in summer (< 1.5%) and this decrease was simultaneous with a significant increase in mannitol, to a value of over 15% of the org anic weight, in both species. Cystoseira nodicaulis showed higher C/N values, typical of N-limited growth, both in February and June, while in Sargassum muticum high C/N values where found only in June. The var iations in N content and C/N ratio in C. nodicaulis were very similar to those in protein content, while in S. muticum there was a striking similarity between the variation in C content and that of mannitol. Al though the photosynthetic pattern may be similar in both species, thes e differences in biochemical status are interpreted as a consequence o f different growth strategies. While Sargassum shows a response to the environment, with growth confined to a short period during the favour able season, Cystoseira must have some storage ability that allows it to 'anticipate' favourable conditions and to exhibit two growth period s during the year.