Ecology of Fucus vesiculosus (Phaeophyceae) at its southern distributional limit: growth and production of early developmental stages.

Growth and survival of two populations ofFucus vesiculosuswere studied at its southern limit of distribution on the eastern Atlantic coast. Experimentally denuded areas at an estuarine and a semi-exposed site in an upwelling area (NW Spain) were followed for 17 months. Three different cohorts were detected during the sampling period. Differences among the three cohorts in terms of growth, reproduction and survival were detected. These differences may be due to the different time of appearance of the different cohorts or the presence of the previously established individuals when the second and third cohorts were recruited. Although growth of the cohorts recruiting in autumn was faster than for the cohorts recruiting in spring and summer, individual growth was represented in all cases by a logistic function, as the fastest rates of increase in length occurred during the first 6 months of life, and maximum length was attained after the thallus reached 1 year in age. In the same way, production was maximum for the first cohort, recruiting in autumn, even when it had the lowest survival rate, because of the rapid growth of survivors during spring and summer. For both populations, reproduction was continuous through the year but it was maximal during spring and summer. Protection from waves might have been thought to favour higher production and standing stock biomass values at the estuarine site compared with the semi-exposed site, while turnover rates of biomass were higher at the latter. Contrary to expectations, most of the nutrients available for the studied populations were not related to upwelling. Despite the fast initial growth of new recruits, both populations appeared to be very sensitive to clearance. [ABSTRACT FROM PUBLISHER]