SANDY BEACHES

Joel Hedgpeth
1957

American Bald Eagle with fish kleptoparasitized from an American Osprey

Compiled by
Robert Roy van de Hoek
December 21, 2000
Winter Solstice - at the lowest Low Tides & Highest High Tides
Malibu, California

A great part of the shores of the ocean are bordered by beaches of sand, subject to the full force of the ocean waves. On the open sandy beach physical factors interact to produce an environment which is in many ways less favorable to life than any other part of the ocean shore except gravel and cobble beaches, yet some organisms have been remarkably successful in colonizing it. Few macroscopic plants can survive on the beach, except as epiphytes on the hard substratum provided by an occasional stone or some animal, so the sand beach is essentially an environment occupied by animals and some microscopic plants. The sand flats of shallow bays and estuaries constitute another type of environment. (See Chapter 23.)

Many years ago Shaler, in a popular treatise on coastal geomorphology (1894), described the sand beach as a highly organized structure in which the various physical forces are in adjustment. For example, the height of the berm, or nearly level upper part of the beach, is 1.3 times (measured above mean sea level of the time of formation) that of the deep-water height of the waves that formed it, where the waves are nto subject to refraction by topographical features (Bagnold, 1940; Bascom, 1954).........Boomer Beach, La Jolla, where winter conditions, especially increased wave action and change of directions of waves, may move most of the sand, leaving a beach of cobblestones, or they may affect the width or slope of a beach to a degree not perceived by the casual visitor......

MacGinitie (1938) found that the males of [sand crab]Emerita analoga were concentrated somewhat higher up the beach than the ripe females. There is a general distribution of Pismo Clams according to size, ranging from the smallest to the largest, up the beach, except that the largest, adult individuals occur at the lowest part of the beach; this, however, may be an effect of human predation (Weymouth, 1923). ...

....Nevertheless, some ecologists (MacGinitie 1935; Pearse 1950) have been of the opinion that the open, surf-swept beach is the most favorable environment route for landward migration. Thie may be true in the region studies by MacGinitie (central California) where humidity is high during the summer months (at least during periods of morning fog), and plant cover on the shores of estuaries is comparatively sparse as compared with the tropics, but the sand beach remains a formidable barrier to most soft-bodied organisms, and it seems unlikely that it has been an important avenue in terms of geologic time on a world-wide basis.