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Abstract

Calogossa leprieurii (Montagne) J. Agardh was isolated from a freshwater, an estuarine and a marine locality. The responses of these isolates to a range of external salinity over time periods of 0-48 h was investigated in terms of internal ion concentrations (K+, Na+ and Cl-) and the organic solute mannitol. Changes in intracellular ions in response to hyposaline and hypersaline treatments were rapid with steady state 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 accumulation in hypersaline media was shown within 8 h, but in general a new steady state was not achieved until after 24 h. In hyposaline media mannitol concentration decreased markedly within 1 h. The extent and rate of the change in inorganic ions and mannitol varied between the three 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.