Abstract.A tentative method is developed to determine the assimilative surface and the total and active photosynthetic volume in caespitose algal communities. The estimation of these variables and the analysis of photosynthetic pigments allow the description of structural adaptive responses in relation to light reception in two morphotypes ofCorallina elongata, i. e., those growing in sunny and shaded intertidal localities.A cross transplantation of both morphotypes demonstrates that one type rapidly converts to the other. This indicates an adaptivity of morphology and pigment composition.The results presented in this work as well as the comparison between intertidal and terrestrial communities suggest that both have a similar potential efficiency in harvesting the incident radiation, but that the degree of compactation of the photosynthetic apparatus (Leaf Area Index) is different.
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