What causes zonation?
At first glance, the natural and obvious assumption is tides. But the actual reasons are much more complex and, historically, have been the subject of controversy. The Stevensons’ rejected tides as a direct cause, saying that zonation results from the air-water interface and various gradients, such as light penetration, below the surface and other factors, such as spray, above the surface. Their premise was that zonation was caused by influences related to tides, but not the tides themselves. Doty and others, on the other hand, attributed zonation more directly to tides, emphasizing that of all the environmental factors such as temperature, wind, rain, and waves that may be important to zonation, only tides vary uniformly with the biological zones. More recently, Benson (2002) has discussed other historical perspectives on studies of zonation, and more up to date summaries of the causes of these biological stratifications are presented in books such as, Pacific Seashores (1977), Seasho
