PHYSIOLOGICAL-RESPONSES OF THE EULITTORAL MACROALGA STICTOSIPHONIA-HOOKERI (RHODOMELACEAE, RHODOPHYTA) FROM ARGENTINA AND CHILE - SALINITY,LIGHT AND TEMPERATURE-ACCLIMATION

The marine red alga Stictosiphonia hookeri was isolated from three loc ations in cold-temperate Chile and Argentina, and the comparative ecop hysiology of the isolates was studied. The growth response in relation to various salinity, light and temperature conditions was investigate d and photosynthesis-irradiance curves were determined. The effect of increasing salinity on the intracellular concentration of the sugar al cohol sorbitol, and the accumulation/degradation kinetics of this comp ound, were studied. All isolates are characterized as euryhaline, eury thermal and low-light-adapted organisms because of the growth and phot osynthesis response patterns. With increasing salinities the macroalga e accumulated high concentrations of sorbitol, which acts as an organi c osmolyte and compatible solute. However, this process requires more than 24 h, and hence is too slow to contribute to osmotic acclimation within a tidal cycle. The geographic distribution and the growth versu s temperature data indicate infraspecific differences which are interp reted as a stage in the development of different (physiological) ecoty pes.