INORGANIC-IONS AND MANNITOL IN THE RED ALGA CALOGLOSSA-LEPRIEURII (CERAMIALES, RHODOPHYTA) - RESPONSE TO SALINITY CHANGE

Calogossa leprieurii (Montagne) J. Agardh was isolated from a freshwat er, an estuarine and a marine locality. The responses of these isolate s to a range of external salinity over time periods of 0-48 h was inve stigated in terms of internal ion concentrations (K+, Na+ and Cl-) and the organic solute mannitol. Changes in intracellular ions in respons e to hyposaline and hypersaline treatments were rapid with steady stat e conditions achieved within 1 h. Sodium ions appeared to be excluded from the cells in all salinities. The concentration of mannitol in all populations correlated positively, with salinity. Some mannitol accum ulation in hypersaline media was shown within 8 h, but in general a ne w steady state was not achieved until after 24 h. In hyposaline media mannitol concentration decreased markedly within 1 h. The extent and r ate of the change in inorganic ions and mannitol varied between the th ree populations. The relevance of mannitol as a compatible solute, as well as its potential to effect an osmotic role within a tidal cycle, is emphasized. A summary of the specific responses involved in osmotic adjustment in C. leprieurii is presented.