THE LIVING EDGE

Joel Hedgpeth
1976

American Bald Eagle

American Bald Eagle with a littoral 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

THE LIVING EDGE
by
Joel W. Hedgpeth
Pacific Marine Station
University of the Pacific
Dillon Beach, California 94929
Geoscience and Man, Volume 14, June 1, 1976
Chapter

"...Before the land rose out of the ocean, and became dry land, chaos reigned; and between high and low water mark, where she is partially disrobed and rising, a sort of chaos reigns still, which only anomalous creatures can inhabit.
Henry Dvid Thoreau." (1864, p.71)

"... To primitive collector and modern naturalist alike, the borders of the sea are richly rewarding. Between hihg and low tide a wide assemblage of life forms useful to man is to be had for the taking. These differ from place to place according to the bottom, whether it is sand, silt or rock, according to the qualities and motions of the water, and by the extent of daily exposure above the water. In warm oceans sea turtles visit sandy beaches to deposit their eggs, From back beach to sea cliff a different and varied fauna and flora yield edible shoots, fruits, eggss, and nestlings. The shallow sea holds yet another assemblage.

"... We still like to beachcombing, returning for the moment to primitive act and mood. When all the lands, will be filled with people and machines, perhapss the last need and observance of man still will be, as it was at his beginning, to come down to experience the sea."
Carl O. Sauer (1962, p45,46).

ABSTRACT

This essay reviews the various approaches to the study of life on intertidal (rocky) seashores from the first summaries of zonation tot he present-day emphasis on interactions, especially between the more conspicuous organisms. Significant parts of long inaccessible work by Edward F. Ricketts are included and research on Antarctic and isolated island shores is reviewed in some detail. No one approach to the study of intertidal life can provide answers to all the questions that occur; while a multiphase approach may in the long run yield the most information, the essential component still remains time, the time to observe and contemplate-to think about this most complex of environments.

SOME GENERALITIES

The great ocean down to which Carl Sauer would have us go is not the poet's vast, untraversed deeps, but its edge, a minor phenomenon of the ocean's 300 million cubic miles of water. And this edge, the shore, is but the edge of the edge. All over the ocean of the world, life is controlled by the first and most basic phenomenon of all, the radient energy from the sun. More than 98% of energy is reflected back from the surface of the water, and what does penetrate reaches at best a few hundred feet on the high tropical seas far from land. Near land, the penetration is much less because of sediments and materials from the land. Where light reaches the bottom, and attached plants can grow, there is the beginning of the shore. This is the depth of the littoral zone, which reaches upward to the limit of the tide and dash and swash of spray against the beaches. The penetration of light makes possible the heavy growth of seaweeds, and the action of waves and surge breaks up these plants. The action of waves and tides against the land sets in motion concentrating and recirculating currents that bring together the fragmented seaweeds, the ground-up parts of animals once attached to rocks, adherent to the bottom, or living within it, larval stages and young of shore animals, and all the rest of the material to form the abundant supply of food upon which so many of the numerous creatures of the shallow seas and contiguous shores depend. Here is where the action is, in the shallow seas and the shore; the life in the deep waters may be abundant, but it goes at a slow pace and seems for the most part to live as passive but alert parishoners awaiting largesse from the more active regions of the sea.

The ultimate region of the sea is not this remote, lightless deep inhabited by zoological curiosities, but the narrow fringe where the sea impinges on the land. Here in this living edge, there are both plants and animals, crowding each other for space on which to reach out for the nutrients and food brought to them. It should not be surprising that the organisms of the shore are arranged according to their ability, not so much to withstand the lack of water associated with the periods of low tide, but to make the most of the time available at these different levels of the sea with respect to the land. And so we have the phenomenon of zonation, the more or less orderly arrangement of life along the seashore in bands that we associate with the fluctuating levels of the sea.

"One of the most vital of natural rhythums is the ebb and flow of the tides...........................................................We need not interpret this as meaning that all the seashore are one seashore and therefore boring; but in the sense that although the tapestry formed by the variations is kaleidoscopic in its permutations, there is a theme underlying the variations" (Stephenson and Stephenson, 1972, p.7).

This charming passage from the late Alan Stephenson's long-delayed book does indeed warn us that we are concerned with an environment "kaleidoscopic in its permutations," nevertheless having some basic order to it, related to the changing interfaces of air, water, and land and to the interactions of organisms to these interfaces and to each other. Our first impression of a visit to the rocky seashore may be that we are looking at a jumble of plants and animals, all crammed in between high and low tide. On the gentle slope of a bay shore, there does seem to be somewhat more order to things, from marsh grass to pickleweed, and to green seaweeds in the mud in season. On a sandy beach, tehre seems to be not much visible and only digging reveals much of anything, although what is there is in dynamic equilibrium with the movements of sand and water. However, a second look at a rocky seashore, at least in the the temperater zones, usually reveals to us that things are not haphazard as at first appears. Below the grasses and and shrubs of the land, there are lichens that seem to prefer situations not completely away from the sea and perhaps need an occasional splash of sea water. At the highest levels of tide and wave action, there are scattered barnacles and small snails; farther down, where the high tides reach everyday, the barnacles become more abundant, forming conspicuous white patches, and predacious snails that feed on the barnacles begin to appear. With these barnacles, tufts of brownish olive and reddish brown seaweeds begin to appear. At mid tide, this abundant life appears rather confused, but if we stand at a distance, we can observe that it tends to occur at certain levels, even where teh rocky surfaces are very irregular. At the lowest levels, not always exposed by every tide, there are brilliant splashes of color formed by such encrusting animals as sponges, bryozoa, and compound ascidians. At the highes levels, but sometimes surprisingly low into the intertidal zone, there are many small, specialized arthropods - insects, arachnids, and an occasional centipede (Schuster, 1962).


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