INTERNAL FACTORS CONTROLLING THE RATE OF EVAPORATION FROM FRONDS OF SOME INTER-TIDAL ALGAE

Factors controlling the rate of desiccation of single algal fronds were investigated using a diffusion porometer. Three species were compared—Laminaria digitata, Fucus serratus and Fucus spiralis. In all species the turgid thalli had a very high surface conductance (equivalent to a low resistance) to water loss. The rate of evaporation would therefore be controlled mainly by the environment, especially by the magnitude of the transfer resistance across the boundary layer. As the tissue of all species dried, the apparent surface conductance fell, though the conductance at any relative water content tended to be in the order Laminaria F. serratus F. spiralis. The more rapid the rate of desiccation, the lower was the surface conductance at any particular water content. This sensitivity to evaporation rate was much more pronounced in F. serratus than in the other two species and was less apparent in tissue stored for longer periods. An important factor contributing to water conservation in all three species was the shrinkage of tissue as water was lost, causing reduction of evaporating surface. The time taken for tissue of the three species to reach any given relative water content, when exposed to a particular environment, would be largely determined by the amount of water per unit area, which in saturated tissue, was highest in Laminaria, followed by F. serratus and then F. spiralis. The mechanism causing the lowered surface conductance was investigated using wet filter paper with or without the addition of mucilage or alginate gels. Copyright © 1979, Wiley Blackwell. All rights reserved