Chemical composition and physiological properties of fucoids under conditions of reduced salinity

Abstract

Thallus segments of Fucus serratus L. and F. vesiculosus L. (Phaeophyceae, Fucales) were transferred into seawater media with a salinity range from 32.65 to 2.25‰ and maintained for at least 2 weeks. Several parameters of chemical composition as well as rates of photosynthetic and respiratory oxygen exchange, 14C-assimilate patterns, and release of 14C-assimilates into the culture medium have been investigated. Compared to controls, in both species dry weight, ash, chloride, and mannitol contents distinctly decline proportionally to reduction of salinity in the incubation media, whereas content of total N (in terms of protein content) remarkably increase. Respiratory O2-consumption is markedly increased at lower salinities, whereas rate of photosynthetic O2-evolution shows some depression. Relatively little effects of salinity changes are observed in distribution of photosynthetically assimilated 14C among the major groups of photosynthates. Release of 14C-assimilates into the incubation medium never exceeds 2% of total 14C-uptake, but is stimulated in media of reduced salt content. The results are discussed with emphasis on phenomena of long-term adaptation and osmoregulation in the marine fucoid species.