Factors Controlling the Delimitation of Littoral Benthic Marine Algal Zonation

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Abstract
SYNOPSIS. The physiological and morphological responses of various littoral algal species to the stresses imposed upon the adults and sporelings by a number of interrelated factors in different latitudes are discussed in so far as there is experimental evidence that they delimit the vertical range of a species. The upper limits of algal zones in the eulittoral region are primarily determined by the resistance of the species to loss of water during midday exposure, by the effects of desiccation upon metabolism, by the ability to adjust their osmoregulatory processes during the periods of exposure to the rapid changes of salinity, and by the degree of tolerance to diurnal and seasonal changes of air temperatures. Low intensity of light reduces the metabolic efficiency and affects the resistance to desiccation and to variations in temperature and salinity. The lower limits of the eulittoral algal zones are primarily controlled by the intensity of light, by the competition with algae and invertebrates for space and light, and by grazing animals. The primary factors controlling the upper limits of the sublittoral algae are the depth of the wave base; the ability to utilize the submarine illumination as affected by turbidity and wave action in the layers of surface water; and the resistance to hydrostatic pressure. The lower limits of the sublittoral algae and both the upper and lower limits of theelittoral algal zones are controlled by the illumination and its effect upon the compensation-depth, the hydrostatic pressure, and the availability of nutrients.

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