Abstract
ON June 18 and July 9, the Linnean Society of London, under the chairmanship of the president, Dr. E. S. Russell, discussed the causes of the intertidal zonation of plants and Animals. The discussion was opened by Prof. T. A. Stephenson, who attempted to elucidate the reasons for both the vertical zonation and the horizontal distribution round the coast of the common intertidal organisms of South Africa, as observed by himself and his collaborators during the years 1931-40 (see NATURE, 143, 503 ; 1939). In his introductory remarks Prof. Stephenson stressed the importance of field observation, as well as that of laboratory and field experiment, for the interpretation of intertidal phenomena, and pointed out also that since much of what is observed between tidemarks is evidently due to the operation of complexes of factors, it is doubtful whether much is to be gained by too great insistence on the part played by each individual factor in a complex. After a review of a number of the factors which may be expected to be concerned in intertidal processes (nature of substratum, desiccation, temperature, wave-action, feeding-habits, competition for food and space, salinity, submergence and emergence, oxygen, carbon dioxide and hydrogen ion concentration, nutritive salts, light and taxes) the conclusion was reached that there is scarcely any factor the effect of which between tidemarks can be imagined which is unable to produce some effect on zonation, although certain factors are undoubtedly more important than others; and that the effect of some factors is much more local than that of others. It was further concluded that the principal agent responsible for the horizontal distribution of organisms around South Africa is sea temperature ; that for zonation on open rock the controllers of primary importance are degree of exposure to the desiccation-heat-light complex acting together with degree of exposure to wave action ; that for zonation in rock-pools the leading factors appear to be variations in temperature and salinity ; and that light is probably more generally effective in determining the segregation of shade-loving from surface species than in contributing to the actual zonation. In all cases there are subsidiary effects due to causes other than the major ones.
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STEPHENSON, T. CAUSES OF INTERTIDAL ZONATION. Nature 150, 158 (1942). https://doi.org/10.1038/150158a0
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DOI: https://doi.org/10.1038/150158a0