BIOMASS, ENERGY CONTENTS AND MAJOR ORGANIC-COMPOUNDS IN THE BROWN ALGA LESSONIA-NIGRESCENS (LAMINARIALES, PHAEOPHYCEAE) FROM MEHUIN, SOUTH CHILE

Determinations of biomass, energy content and major organic constituen ts (proteins, lipids and soluble carbohydrates) were carried out on th e brown alga Lessonia nigrescens Bory from Mehuin, south Chile. Energy contents measured directly by bomb calorimetry did not show seasonal variation (values between 13.8 and 19.7 KJ g(-1) DW). In the case of t he organic compounds, the soluble carbohydrates were the only componen ts exhibiting seasonal changes. However, proteins, lipids and carbohyd rates varied significantly along the thallus: maximal contents of prot eins (25% DW), lipids (0.4% DW) and soluble carbohydrates (4.8% DW) we re measured in the fronds. Although energy contents expressed on a wei ght basis (KJ g(-1) DW) were similar along the thallus, the relative e nergy allocation in holdfast, stipes and fronds varied with plant size . In general, stipes accounted for more than 50% of the total biomass and/or energy in large plants, whereas in small individuals this propo rtion decreased to 30%. The increased allocation of biomass and energy in the stipes, which suffer less erosion processes compared to the fr onds, is favoured by morpho-functional adaptations allowing plants to withstand the constant mechanical stress on the rocky shore. Size stru cture strongly determined standing stock within the population: mainte nance of large long-living individuals rather than juvenile recruitmen t governed the seasonal patterns of biomass.