EFFECTS OF SALINITY ON THE DISTRIBUTION OF FUCUS-CERANOIDES

The success of the brown seaweed Fucus ceranoides L. in estuaries and its absence from fully marine situations was investigated by means of culture experiments in the laboratory and transplantation experiments in the Silverburn Estuary, Isle of Man. The responses of F. ceranoides were compared with those of F. vesiculosus L. a potential competitor in marine conditions. Germlings of F. ceranoides developed from zygotes and grew at all salinities from 34‰ down to 8·5‰. Those of F. vesiculosus did not survive below 24‰ if settled directly at these low salinities, but grew over the same range of salinity as F. ceranoides if initially cultured at 34‰ for 48 h. Tips detached from young adult plants of F. ceranoides displayed a wider tolerance range than the germlings and grew slowly even at a salinity of only 1‰. Both the germlings and adult plants of F. ceranoides grew faster than those of F. vesiculosus at all salinities from 17‰ downwards, but F. vesiculosus was the faster grower at full salinity. p F. ceranoides plants eventually decayed if cultured at, or transplanted into full salinity, but not if at reduced salinity. In contrast, F. vesiculosus decayed in very brackish water but remained healthy at full salinity. Clearly the distribution of both species can be limited by extremes of salinity, but, whereas for F. vesiculosus low salinity is unfavourable, for F. ceranoides it is high salinity that presents the most stress. © 1979.