The physiology of zonation of coastal algae
Attention is confined to the longer and more complex benthic algae. Littoral zonation is defined as the regular horizontal arrangement of algae on coastal substrata.
Environmental Factors are divided into aerial and submarine. Complexity of the situation is emphasized. Aerial factors include water loss (connected with air humidity, temperature and movement), light and precipitation. Important among marine influences are spectral and intensity variations in light (in turn dependent upon water transparency and turbulence), hydrostatic pressure, temperature, salinity, pH, oxygen and carbon dioxide. Both these factor complexes are affected by tidal movement, which results in a vertical gradient of submersion and emersion conditions.
Many higher algae exhibit adaptations to improve photosynthetic activity and to reduce loss of water. With no conducting system metabolic substances simply diffuse over the plant surface. Mucilage and hard cuticles (e.g., Hormosira) are common. Water is necessary for reproduction. Algae are not fundamentally different from other plants biochemicially speaking, but are essentially aquatic, with a high degree of "protoplasmic resistance.