The Tide as an Environmental Factor Chiefly with Reference to
Ecological Zonation on the California Coast

Edward F. Ricketts
Unpublished Essay Excerpts From Joel Hedgpeth Sources: Living Edge & The Outer Shores

Compiled by
Robert 'Roy' J. van de Hoek
Field Biologist & Geographer
Sierra Club, Wetlands Action Network, National Audubon Society

Ed Ricketts' 1934 Essay Excerpts:
"At least the most obvious regulatory factor in the vertical distribution of littoral life is the tide. By substituting the uniform oceanic environment obtain at flood, for the varying temperatures, salinity, desiccation, wave shock and light conditions obtainable during intervals of ebb, the alternating tide effects all littoral organisms. Zonation on rocky shores . . ..............................."

This study was originally the outcome of primitive attempts some years ago on the part of the writer to determine the shape of the tidal wave with reference to fixed heights on the shore, ...........

The tide as an environmental factor in the remote past, while the main evolutionary trends were developing, merits biological consideration. In important theory of cosmogeny, developed by G.H. Darwin, son of the biologist, postulates that tides were powerful earth-forming factors. ...............................

According to this hypothesis, interesting in itself but only of incidental import here, ........................

Since even now the tide establishes a measurable tho minute weight differential ........................

It appears that the physical evidence for this theory of Darwin's is more or less hypothetical, not in fact, .............................

Conclusions and derived discussions.
The rather obvious conclusion is reached that the tide must be even now a profound important regulatory factor for littoral organisms. There are a dozen or more minor, .........................................

A comparison of the environmental effects of Atlantic and Pacific tides.......................................

New informations derives chiefly from analysis of the exposure-submergence curves based on actual tidal records for a period of slightly more than half a lunar year at San Francisco, where the extreme amplitude is slightly under 9.0', the mean range is 3.9', the diurnal range 5.7' and the spring range 4.6. Hypothetically, on the basis of this strictly physical evidence, there at least three critical horizons for the local littoral organisms. These occur at mean lower low water, 0' (the datum for Pacific coast tide tables), at plus 3.5' and plu 5'. Mean sea level is about 3.0' above mean lower low water at San Francisco; these horizons therefore read-3.0', plus 0.5', and plus 2.0' on the mean sea level scale. Two are based on sudden breaks, at mean lower low water and at plus 5.0', in the six months graph of the exposure-duration factor. ...............................

These critical horizons would divide the ideal California shore into four fairly limited zones, everything else being equal and granting at the same time that such widely divergent factors as physical and biological environmental factors cannot possibly be equal, wave shock, type of bottom, internecine and interracial competition for food, attachment, shelter, etc., being what they are. The index of vertical distribution may lie very possibly not in the sum total of these analyzable factors, but in their integration, since even a slight change in one factor may have considerable balance repercussions on the others by changing their mutual relations. So a sudden and abiding vertical shift of .1' in the tidal mean may be relatively unimportant-altho it involves supposedly the most important single factor, or it may affect the whole very profoundly thru upset equilibrium, especially if it impinges some critical threshhold. As in the hawk-ptarmigan relation mentioned by Elton (Ency. Brit. XIV Ed., Vol. 7, p. 916) there is no possible way of evaluating this situation a priori, each separate occasion being unique due to the multitudinous and interrelated factors involved, and the situation properly ought to be examined as a whole, as indeed must inevitably be done by the field man.

The chiefly sublittoral life occurring in the lowest habitat is thought to be limited in its upper range by the sudden increase in exposure total duration at 0.0', conditions from below the littoral to about this point being almost the same. As a matter of fact, from -1.9' to 0.0' the exposure conditions aer almost identical, organisms stationed here being exposed to air only occasionally, more or less accidentally, and for short periods, with long intervals of submergence before and after. This zone has literally the whole ocean to draw from, animals need not in any particular way be highly specialized in order to do well here, and it cannot seem surprising that this zone supports a number of species greater than anywhere else-altho the number of individuals per species need not be high.

Sessile organisms above 0.0' start suddendly to be exposed to greater total amounts of air, still in small doses, but occurring more frequently..................

Above 3.5', the populations are suddenly subjected to larger doses of air and terrestrial conditions, at first frequently, then with fewer and fewer immersions and longer dry periods between, ................

"Above this point any persisting communities must be pretty well adapted to terrestrial life, since the conditions even at 5.0' are only 16% marine. From thence to the line marking 100% exposure at about 7.0' to 7.5' (surf for the moment not considered; this is a highly variable factor) animals are wetted only occasionally, and then for periods increasingly brief. The paucity of animals in this zone emphasizes again the fact that with littoral associations we are dealing with marine animals pushing up toward land, rather than with land animals colonizing downward. Some of the plants however (the tropical mangroves, and seed plants of local salt marshes) suggest that some at least of the land forms are migrating seaward, as well as vice versa."

In these concepts may lie one explanation of the confirmable fact that hosts of different animals inhabit the lowest zone with few individuals per species, while higher up there are more individuals of fewer species. The lowest zone has the whole ocean to draw from, and within this belt great numbers of animals unspecialized as to tidal rhythm may be competing. But in order to succeed higher up, animals must be specialized with regard to this factor, adaptations to other factors must be subordinated to this all-important one. They must be able to tolerate semi-terrestrial conditions, in this one thing at least having come a long way evolutionarily from the generalized situation. There cannot be nearly as many species that have succeeded in this adaptation as there are truly marine species, and what few there are can, and do exist in tremendous numbers. Applying similar ideas to plant distribution, we should expect to find vertical distribution a function of sunlight needs times adaptation to tidal rhythm. Realizing that the dispersal point for marine plants, which are at best comparatively few in species, cannot be below the shallow shore or upper pelagic zone - due to photosynthesis requirements - one would expect to see a balance struck in the mid-tidal, where actually the greatest plant production occurs, at least on this coast."

Some Notes and Reflections by
Robert Roy van de Hoek
July 4, 2002
Reference sources for Ed Ricketts' unpublished essays can be found in three places, two of which are in the writings of Joel Hedgpeth. Joel Hedgpeth has done his best to keep alive the spirit, philosophical, and scientific views of Edward Ricketts, and I hope to continue the tradition at least in small measure through the presentation for educational and scientific purposes here on the web pages, both the published and unpublished writings about "doc" Ricketts. Henceforth, these web pages are a fourth source of information for the writings of Edward Ricketts:

1. Hedgpeth, Joel. 1976. The Living Edge. Geoscience and Man, Volume 14, June 1, 1976, Page 17-51, 20 Figures.

2. Hedgpeth, Joel. 1978. The Outer Shores.Volumes 2, page 63-68. Mad River Press. 182 p.

3. Stanford University Library Archives. Unpublished Papers and Essays of Edward Ricketts.

Joel Hedgpeth had two title quotes that prefaced his article, The Living Edge. One quote was by Henry David Thoreau (1864) and the other by Carl O. Sauer (1962). They are presented here as background information for undertanding the linkages of Ricketts, Hedgpeth, Thoreau, and Sauer.

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 David Thoreau (1864,p.71)
Cape Cod
1951 Edition
W.W. Norton, New York

To primitive collector and modern naturalist alike, the borders of the sea are richly rewarding. Between high 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 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, eggs, and nestlings. The shallow sea holds yet another assemblage.
. . . We still like to go beachcombing, returning for the moment to primitive act and mood. When all the lands will be filled with people and machines, perhaps 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, p.45,46),
Seashore-primitive home of man?
American Philosophical Society Proceedings,
Volume 106, page 41-47