the littoral zone on rocky shores: a biological or physical entity?

23
Nordic Society Oikos The Littoral Zone on Rocky Shores: A Biological or Physical Entity? Author(s): J. R. Lewis Source: Oikos, Vol. 12, Fasc. 2 (1961), pp. 280-301 Published by: Wiley on behalf of Nordic Society Oikos Stable URL: http://www.jstor.org/stable/3564701 . Accessed: 01/07/2014 15:21 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. . Wiley and Nordic Society Oikos are collaborating with JSTOR to digitize, preserve and extend access to Oikos. http://www.jstor.org This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PM All use subject to JSTOR Terms and Conditions

Upload: j-r-lewis

Post on 27-Jan-2017

214 views

Category:

Documents


1 download

TRANSCRIPT

Nordic Society Oikos

The Littoral Zone on Rocky Shores: A Biological or Physical Entity?Author(s): J. R. LewisSource: Oikos, Vol. 12, Fasc. 2 (1961), pp. 280-301Published by: Wiley on behalf of Nordic Society OikosStable URL: http://www.jstor.org/stable/3564701 .

Accessed: 01/07/2014 15:21

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact [email protected].

.

Wiley and Nordic Society Oikos are collaborating with JSTOR to digitize, preserve and extend access to Oikos.

http://www.jstor.org

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

OIKOS 12:11 1961

THE LITTORAL ZONE ON ROCKY SHORES - A BIOLOGICAL OR PHYSICAL ENTITY?

BY

J. R. LEWIS

(Department of Zoology, University of Leeds)

Introduction

The present paper is a result of the emergence of new facts, and a reconsidera- tion of older data concerning the zonation of shore plants and animals. It arises also from the belief that although the system of littoral zonation at present in use with many English-speaking biologists is based upon biological reality and has served us well during the past decade, certain modifications of outlook which may necessitate changes of terminology ought now to be considered. In arriving at these conclusions I have had the advantage of very detailed discussion and argument with a number of people, and especially with Dr. E. M. BURROWS, Dr. R. G. EVANS, Mr. H. T. POWELL, Dr. A. J. SOUTHWARD, and Professor and Mrs. T. A. STEPHENSON1. In acknowledging their help with much gratitude I wish it to be understood that the opinions expressed in this paper do not necessarily represent their viewpoints.

The term littoral was used originally for the area between tidemarks, but has since been variously used to refer to part or the whole of the shelf area. It is, however, only with its original, if somewhat imprecise, meaning of the edge of the sea that this paper is concerned. In this sense the word was incorporated in new terminology, and European algologists accepted a system of three "regions", the "littoral", "sublittoral" and "elittoral", the last lying beyond the depths of algal growth (KJELLMAN 1877)2. It was also recognised at an early stage that certain marine algae could grow at levels above the theoretical high water mark as a result of the influence of waves and spray, and the levels thus occupied

1 Shortly before his death, Professor Stephenson discussed this paper with me very fully. It was, J believe, his intention to answer the points made, but now I think it should be stated that he did not believe the facts or arguments presented here necessitated any change in zonation terminology.

2 More extensive reviews of the literature than are required here are available in GISLtN (1930), SOUTHWARD (1958), DEN HARTOG (1959).

OIKOS 12: 11, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

The Littoral Zone on Rocky Shores 281

were designated "supralittoral" (LORENZ 1863). Such terms, or others which could be roughly equated with them (eulittoral, mesolittoral, midlittoral, infralittoral) have been, and still are, in constant use. But the precise limits of these zones or regions, and the criteria used to characterize them, have varied greatly from author to author, and although they were conceived and applied originally to tidal waters their use has been extended to tideless areas in which the margins of the land are periodically wetted by waves or subjected to irreg- ular fluctuations of sea level.

Both physical and biological criteria have been used but, inevitably, tidal levels have been well to the fore and "intertidal" is frequently used as a syno- nym or preferred alternative to "littoral". As a physical entity the latter has sometimes been regarded as extending from the highest to the lowest tide levels, but in other cases average values of spring tides have been suggested, so that parts of the sub- and supralittoral regions have fallen within the extreme range of tides. But from the beginning shores have also been divided by re- ference to dominant zone-forming organisms (AUDOUIN & MILNE-EDWARDS 1832), and in what is probably the first classification to refer to a "littoral zone" there are other zones named after the laminarians and corallines (FORBES 1846). As the uppermost laminarian algae in N.W. Europe generally extend up above the lowest tidal levels, and as later workers usually accepted the upper limit of these algae (or an equivalent organism) as the upper limit of the sublittoral region, the lower boundary of the littoral, in a biological sense, (or eulittoral as it is sometimes called) has usually lain within tidemarks. The precise levels of this boundary proposed by various authors have varied from below M.L.W.S. to M.L.W.N., a range which is now fully understandable when allowance is made for the many factors which can determine the upper limits of the lamina- rians.

The dividing line between the eulittoral and supralittoral has been a matter of greater controversy. In some cases it has simply been regarded as "high tide" level, or mean high water, while in others it has been placed at the upper limit of marine algae. The validity of the "supralittoral concept" was itself doubted (BORGESEN 1908; COTTON 1912) and it was suggested that algae occurred above the highest tide levels simply because the entire littoral had been widened by local wave action. However, the view persisted that a difference did exist, and ought to be recognized, between levels submerged regularly by tides and those wetted only or mostly by splash and spray. The practical difficulties of locating the exact boundary between these two areas are very great, and recourse was made to the easily recognizable limits of zone-forming species. But whereas the laminarians were available in the lower shore and were generally used, there is no ubiquitous and dominating alga in the upper shore. Thus several types of organism have been considered, and it appears to-day (DEN HARTOG 1959) OIKOS 12:11, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

282 J. R. Lewis

that those European algologists who accept the system of supra-, eu- and sublittoral regions place the upper dividing line at the upper margin of fucoid algae (Pelvetia) on sheltered shores, and at the junction of black lichens (Verru- caria spp.) with the uppermost barnacles where fucoids are absent'.

This widening of outlook from algae alone to all forms of shore life, and with it greater reliance upon biological rather than physical criteria, was carried much further in the scheme of classification proposed in 1949 by T. A. and A. STEPHENSON. This scheme, the first to consider the subject on a world-wide scale, rests on the contention that certain widely-occurring types of organisms characterize approximately the same levels of most rocky shores. These organ- isms, together with general but not rigidly defined tidal criteria, led to the postulation of three universally occurring zones. Broadly equivalent to the "supralittoral" of botanical thought is an upper marginal belt characterized by littorinid molluscs and by blackening organisms such as lichens and Myxophy- ceae. In cool temperate latitudes, Laminariales dominate the lower zone while equivalent organisms uncovered only between waves or at the lower tides, are seen in for example the corals or Rhodophyceae/ascidian populations of warmer areas. Between these two zones lies the most truly tidal zone of the shore, being covered and uncovered daily for the most part and dominated by acorn barnacles, limpets, limy tubeworms, short turf-forming algae and by fucoid algae (in the N. Atlantic) and showing a variety of locally occurring subzones.

The names proposed for these zones introduced certain new concepts. Thus the principal tidal zone called the "midlittoral" was flanked by two marginal zones or "fringes". The littorinid Verrucaria Myxophyceae belt became the "supralittoral fringe", above which lay the "supralittoral zone", a belt of maritime terrestrial organisms outside the sphere of marine biology. In the lower shore the upward extensions of laminarians (or their equivalent) were distinguished from the main sublittoral population as the "sublittoral fringe"2. Tidal criteria play only a minor part in this system, and the authors emphasized that although zones may be related to tidal levels they cannot be defined by them. The word littoral itself is deliberately excluded from the terminology but regarded as equivalent to intertidal, and in their Fig. 3, p. 299, is shown extending from E.H.W.S. to E.L.W.S. The former level lies within the supra- littoral fringe and the latter constitutes the boundary between the sublittoral zone and the sublittoral fringe.

1 The usefulness of this proposed dividing line rests on the assumption that the two boundaries stated are at approximately the same level. This is implied in DEN HARTOG'S Table XII, p. 86, but it is not a true picture of the vertical distribution of these organisms, for around much of N. W. Europe Pelvetia forms a well-defined belt within the Verrucaria zone several feet above an equally well-defined upper limit of barnacles (Balanus balanoides). For fuller discussion see LEWIS (1955).

2 In the original paper "infralittoral" was proposed instead of sublittoral, but in a later com- munication the latter term was accepted again (1954, p. 15).

OIKOS 12: I, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

The Littoral Zone on Rocky Shores 283

In the decade since this scheme was introduced it has been used widely, or in modified form, by English speaking authors, in various parts of the world. While criticism has not been lacking (WOMERSLEY & EDMONDS 1952; DEN HARTOG 1959) there has been wide recognition (in which I concur) of the three principal biological features which were postulated, and of the practical value of having a universal framework within which to describe the many locally occurring zones and communities (both plant and animal) without recourse to systems of nomenclature which would be of local significance only. Parallel with the development and use of this system many French authors have been using a somewhat similar scheme in which, although very similar biological zones are recognised, a slightly different terminology is used. Thus there is a supralittoral zone, and a mesolittoral zone which approximates to most of the midlittoral, but the infralittoral begins at a higher (biological) level and is not subdivided at E.L.W.S. Having found this terminology applicable to Medi- terranean as well as Atlantic shores, PE'REiS & PICARD (1955) specifically reject the use of the word intertidal ("intercotidale"). These systems with their deriva- tives or modifications represent the present end-points in a trend away from the use of tidal criteria, and to some extent are a return to the position existing before close correlations with tidal movements were sought. They differ however in avoiding the use of littoral, and in effect substitute mid- or meso- littoral for eulittoral, the principal intertidal zone, in which sense "littoral" is advocated by HEDGPETH (1957) and still actively championed by WOMERSLEY (1959). It is here proposed that this trend from tidal to biological criteria should be continued further and to the point of enquiring if the word "littoral" itself can be given a new biological meaning. Before expanding this proposal it will be of value to reconsider the merits and practicability of using physical or biological bases for zonation purposes.

The physical environment of the shore

Most authors agree that the primary cause of the observed patterns of zona- tion are fluctuations of the water level brought about by tides, seiches, changes in barometric pressures or by waves. Historically, the semi-diurnal tides of the North-east Atlantic attracted attention first, and it became usual to describe distribution limits in terms of, and to relate them to, the average tidal values such as M.H.W.S., M.L.W.N. etc. (PRUVOT 1897; BEAUCHAMP 1914; JOHNSON & YORK 1915), and such studies led to the recognition of "critical levels" (COLMAN 1933; EVANS 1947 a, b). More detailed analyses of tidal phenomena have revealed the apparent importance for both short and long-lived species, not only of average tide levels, but of tidal variations which may be regular and seasonal (LAWSON 1957), or of more intermittent occurrence (LEWIS & POWELL 1960). In the "tide factor hypothesis" (DOTY 1946, 1950) it has been possible OIKOS 12: 11, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

284 J. R. Lewis

to relate limits of vertical distribution to the abrupt increase in emergence time which characterises certain levels of shores experiencing "mixed tides". But although there are many instances of near or exact coincidence between distribution and theoretically significant tidal levels, there are many other cases in which this is not so. This results from the fact that although tidal or other changes of sea level are primarily responsible for the distinctive alternat- ing character of the shore environment, the complete physical environment is a balance of many additional factors. Moreover it is these latter, the so-called modifying factors, which determine the precise levels upon any shore at which the actual limiting factors (desiccation, light intensity, temperature, rain water, etc.) become operative.

Foremost among these modifying factors, and among the earliest to be recognised, is wave action, the effects of which are reported in almost every paper on shore ecology and which led to the concept of the "supralittoral". To allow for the difference between a theoretical, predicted high water mark and the actual effective height of a stormy sea the term "physiological high water line" was introduced (KYLIN 1918), and this to-day is regarded by some as the upper limit of the eulittoral zone. (It will be noted that this concession to the effects of waves and other factors is not enough to incorporate the supralittoral but merely to raise the boundary between the two zones.) This and similar concepts do not, however, provide us with practical demarcation lines in the environment. Moreover, they assume or imply that in the absence of wave action it would be possible to designate one particular level as "high water mark", the edge of the sea, a level having greater significance than any other. Where should this level be placed? At E.H.W.S., which is only reached once or twice in the year? A mean level - M.H.W.S. or M.H.W. - may appear more reasonable, but analyses of average emersion/submersion values at different levels (COLMAN 1933; EVANS 1947 a) show that these particular levels have values differing only slightly from those of levels slightly above or below them. In European waters there is no single level of the upper shore at which this value changes abruptly enough to constitute a major physical barrier - the edge of the sea. "Tide factor" analyses have recently been published for French Atlantic shores by EVANS (1957) and these (together with personal investigation) suggest that on this basis the most critical level is that at which daily emersion gives way to longer periods extending over consecutive tides, i. e. in the vicinity of M.H.W.N.1

1 Mean tide levels appear to have been sometimes accorded greater biological significance than may be warranted. M.H.W.S., for example, is not the mean of all "spring tides", but of the "heights of two successive high waters during those periods of 24 hrs., in each semi-lunation when the range of the tide is greatest" (A.T.T. 1960) - i. e. the mean of approximately 25 pairs of spring tides per year. Moreover no allowance is possible in tables for the often appreciable differences between predicted and actual values resulting from meteorological conditions.

OIKOS 12: 11, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

The Littoral Zone on Rocky Shores 285

Thus it is difficult (and, I believe, impossible) to specify one high water level which on tidal evidence can sensibly be regarded as the edge of the sea, and where marine life ought to cease. If, nevertheless, one level is selected for this purpose there remains the great practical difficulty of evaluating wave action under all weather conditions throughout the year, and then identifying the equivalent level (in terms of wetting) on all other shores with their various exposure conditions. But in the absence of a well-defined "high tide level" or upper limit of the shore, there is, however, a definite gradient of conditions from shore to land. Along this gradient a number of organisms have their own "physiologically critical limits". The number and type of organisms differs locally and geographically, and their vertical limits may or may not coincide. The most we can do is to decide, for biological reasons, which species in this transitional area best indicate the limits of the marine province. Then fluctua- tions in their levels from one shore to another reveal the extent to which the effective sea level has changed.

The uplift of organisms as a result of wave-action is not, of course, restricted to the upper shore, but whereas the "physiological high water line" or the "law of Widar Brenner" (Du RIETZ 1940) made allowance for it here, there has been a lack of equivalent concepts for the lower shore where, if biological criteria are ignored, the "littoral" has remained firmly anchored to extreme low water or even the ebb between waves. The uplift of the laminarians is never as great as that of littorinids or Verrucaria (probably because of greater susceptibility to occasional periods of calm conditions), but differences of up to three or four feet may be seen in their upper limit between the more exposed and more sheltered positions of the same district, and in extreme cases they have risen upshore to the theoretical high tide level.

But the severity of wave action is not the only additional factor to influence the shore environment. While the relative importance of many factors has yet to be fully assessed, it is apparent from papers dealing with shores throughout the world that striking differences in zonation result from local variation in the aspect of a shore or of a particular rocky face, from the nature of the substratum, from the configuration of the shoreline in relation to prevailing winds and waves, from the shore profile and its bearing upon drainage or water retention, from the time of day or season of year when the lowest or highest tides occur, and so on; within the geographical range of a single species there may be appreciable climatic differences, either seasonally or from place to place. Such factors may act together to raise or lower the levels occupied, but often they have to be balanced against each other, and to assess their total effect one is obliged to accept the evidence of the organisms themselves. When, for example, the depth of the Verrucaria/Littorina belt increases fivefold, or the upper limit of barnacles rises from below theoretical M.H.W.S. to heights five to ten feet, or more, above this level, we are presented visually with a more OIKOS 12: II, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

286 J. R. Lewis

accurate indication of the balance of all environmental factors than can be obtained in any other way. The limits of certain species may, of course, have been determined during one critical period of the year (or of individual life- cycles) by a fortuitous combination of adverse or favourable conditions, while in other cases there may be seasonal variation, but nevertheless, the levels occupied provide the most reliable evidence we possess.

The physical environment is also influenced by the organisms themselves. Some will retard drainage, some will create shade and others may graze away the algae which could create shade. Such indirect effects may be supplemented by the direct action of competition. Yet the effectiveness of these biological factors and the extent to which they influence zonation may well have been determined initially by conditions regulating fecundity, survival of planktonic larvae or of spores, dispersal and settlement. Such conditions occurring at another season, on another shore, or in the sea may be sufficiently remote in time and space to warrant the title "chance factors" as far as the immediate problems of particular species upon particular shores are concerned.

To sum up, the distinctive alternating character of the shore environment results from regular or irregular changes in sea level. Then the conditions appropriate to a particular level are modified, often drastically, by a consider- able number of additional physical and biological factors. It is the balance of all these factors which determine at what level limits will be imposed upon the vertical distribution of organisms. With our present (and probably future) inability to measure the entire physical environment it is most inappropriate to delimit and define the zones by reference to one contributing factor - the tides - alone. There is no alternative but to use the dominant zone-forming organisms.

The use of indicator organisms

The last sentence of the previous section may suggest that the use of organ- isms is a second-best choice. This is not so. Out interest in the shore is biological, not physical, and indeed this viewpoint has already led to the previously mentioned rejection of "intercotidale" by PE'RtS & PICARD. There will inevitably be some agreement between physical and biological systems, but since shore populations are constantly being renewed, and the environment itself is the product of regularly and irregularly recurring phenomena, it seems unlikely that exact coincidence would ever occur. As it is, with such frequent disparity between tidal and biological levels, and with the organisms themselves affording the best way of assessing the entire physical environment, a biological system remains not only desirable but the only logical and practical one.

Reliance upon zone-forming organisms has some disadvantages. Essentially OIKOS 12: 11, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

The Littoral Zone on Rocky Shores 287

local patterns of zonation may intrude excessively, a point which will be appreciated by those whose early outlook was distorted by the emphasis which was so often placed upon the conspicuous patterns of fucoid zonation in N.W. Europe. Difficulties may be met where an important species is locally absent or behaves differently in one part of its geographical range, or where one key indicator species gives way to another of similar type, but which does not occupy precisely the same levels or proportion of the shore.

Such difficulties have to be seen in perspective and they appear minor problems when set against the universality of the three biological zones postu- lated by the Stephensons. These zones vary greatly in their proportions relative to each other, in the exact levels occupied, in the extent of their subdivision and so forth, according to tidal regime, climate, wave action, etc.; but they, or some recognisable variations, appear to persist on all types of rock shores. While individual species respond in different degree to changes in conditions influencing zonation, the dominant organisms characterizing the three major zones appear to respond largely in unison and the distinctive character of the zones in maintained. Thus, whereas in Britain some Rhodophyceae are re- stricted to the laminarian zone in one habitat but cover much of the barnacle zone in others, the dominant species do not overlap in this way. If conditions favour the uplift of the laminarians, the characteristic midshore population will rise too, although not necessarily to the same extent. If the Verrucaria/ Littorina belts are depressed in level the uppermost barnacles and associated species will also be lower, and the zones will remain distinct.

If, therefore, it is accepted that organisms provide the most desirable and practical means of defining the individual zones of the shore, is it not possible to redefine the littoral itself by similar means: to discard the unsatisfactory physical definitions - i. e. either the imprecise "intertidal", or the very precise tidal definitions which are not applicable everywhere - and to regard the littoral as a biological zone? It could perhaps be defined as the marginal belt of marine life characterized by organisms which are adapted to or require alternating periods of exposure to air and of wetting by submersion, splash or spray. A definition on these lines would then be applicable to any shore, with or without tides, with or without wave action, upon which there is sufficient fluctuation of water level for the junction between land and sea to take the form of an en- vironmental gradient rather than a sharp boundary line. It would also encom- pass seasonal and other fluctuations of level inherent in a dynamic biological system.

The practical application of this definition necessitates more than simply encompassing the present zones of the shore within this "littoral". It must be decided which organisms are "littoral" and which are not, decisions which can be as difficult and arbitrary as those concerning the position of "high water OIKOS 12: 11, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

288 J. R. Lewis

mark". The affinities and characteristics of the populations of the two marginal belts must therefore be considered, bearing in mind the previous discussion of the physical environment. The position on shores of Britain and N.W. Europe is considered first and in detail, and both the criteria and terminology of the Stephenson scheme are temporarily used.

The limits of the littoral zone (i) The Lower Limit

The upper limit of the laminarians is the outstanding biological horizon of the lower shore. Laminaria digitata is the principal species involved but under the appropriate conditions of wave action or substratum, or in certain geo- graphical areas it may be joined or completely replaced by Alaria esculenta, Saccorhiza polyschides, Laminaria saccharine, Halidrys siliquosa, Himanthalia elongate, Codium spp., or by a variety of distinctive types of Rhodophyceae- dominated communites (See LEWIS 1957; LEWIS & POWELL 1960). In most cases a marked contrast exists between the midshore and laminarian zones and the boundary is clearly defined. Its precise level varies slightly with the many species concerned and greatly according to the local conditions, but in all cases, except the Baltic sea and its approaches, it lies inside the tidal area and sometimes appreciably so. The E.L.W.S. mark below has no biological signif- icance, for although Laminaria digitata and Alaria usually form narrow belts above the principal laminarian population of L. hyperborea (which also extends slightly but regularly into the tidal area), both these and the other algae pass down into the permanently submerged levels, where all but these two have their most luxuriant and abundant growth. Thus in spite of the local subzones which may be seen on the lower shore the dominant species and the population as a whole are sublittoral, and only their uppermost representatives penetrate the tidal area to form the sublittoral fringe. Similarly with the fauna, many of the species found here are essentially members of the benthos of the continental shelf area, and how far they penetrate upshore is largely determined by the availability of pools, damp clefts, and shaded overhangs etc., where the dam- aging effects of exposure to air are absent or minimised. In my opinion the sublittoral affinities of this population as a whole outweight the fact that individual organisms or even species are exposed to air at certain tides, and therefore these species are not regarded as "littoral" in the sense proposed on p. 287.

Looked at from the other viewpoint this same boundary, at whatever tidal level it occurs, is approximately the lower limit of the principal midshore population. The coincidence is not exact: some species fail to reach the top- OIKOS 12: 11, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

The Littoral Zone on Rocky Shores 289

most laminarians, others overlap them to varying extents, and some species behave differently according to local conditions. In broad terms however, the lower limits of the principal midshore barnacles, gastropods and Fucaceae lie sufficiently close to the upper limit of the laminarians to enable us to recognise this boundary as the dividing line between truly shore-living organisms and the marginal upshore extensions of the sublittoral population.

It must be conceded, however, that the simple barnacle/laminarian division is complicated by the presence of subordinate (but locally important) species whose vertical range may lie astride this junction. Thus under certain circum- stances Corallina, Mytilus edulis and Patella aspera may extend from the midshore to E.L.W.S. (and possibly beyond?) while Himanthalia, Fucus serratus Gigartina, Laurenciapinnatifida and Rhodymenia may variously lie above, astride or below the boundary line. The more species and the greater the range of habitats considered, the greater will be the range of patterns of overlapping distributions of subordinate species astride the topmost laminarians. Thus a division into "littoral" and "sublittoral" may be regarded as an oversimpli- fication; even so and probably because most of this variation involves the subordinate species, most biologists (with the recent exception of adherents to the French concept of "mesolittoral") do in fact now accept a division at this level, whatever the system of nomenclature being used. This boundary, the upper limit of laminarians in cold temperate waters, provides the most natural lower limit of the littoral zone. What lies below is (biologically) part of the sublittoral, and it is immaterial that in some circumstances there is only slight penetration of the tidal area, while elsewhere in exposed situations in high latitudes the sublittoral reaches M.T.L. or above. The latter is no more incongruous than the readily accepted finding of marine algae and littorinids fifty to eighty feet above theoretical high water mark or "midshore" barnacles five feet above this level. They are all manifestations of the same phenomenon of uplift.

(ii) The Upper limit With the shore above the sublittoral boundary clearly divided into the bar-

nacle/fucoid midlittoral zone and the littorinid/ Verrucaria/Myxophyceae supralittoral fringe, the upper limit of the littoral could be provided by the top of either zone. The crucial question is how far the fringe is indeed supra littoral, and it is therefore appropriate to consider not only its affinities but also the levels at which it may occur in the full range of habitats between very sheltered and very exposed shores. The relationship to tide levels and to the reach of waves and of spray is illustrated diagrammatically in Fig. I, and at the outset it must be emphasized that the right-hand side of the figure (representing extremely sheltered shores) is not an atypical example but occurs widely over OIKOS 12:11, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

290 J. R. Lewis

Spray EX PC(SURE SHELTER line

liVerrucaria

X[Gus SkLittorina spp.

I okPelvetia

Other Fucaceae

Splash lI ne< C6d. < :: u de

E. H. W. S. . Barn aeHW. .

M u'sselIs, 44~1' M. H.W. N.

Fig. 1. Diagrammatic representation of the distribution of upper shore species on British coasts in relation to tide levels and the reach of waves and spray. The junction of the Verrucaria and barnacle zones may be higher or lower than shown here, or a relatively bare area may intervene

between the two zones.

many hundreds of miles along the sheltered bays, inlets and sea lochs of western Scotland and western Ireland, and more infrequently on the less suitable coasts of England and Wales.

On exposed shores the effective level of E.H.W.S. is raised by the wash and splash of waves to varying amounts above the predicted level. Above this again lies the spray zone which becomes increasingly arid towards it indefinable upper limit. Moving towards shelter and less wave action the effective and predicted levels of the tides become closer until in extreme shelter the two virtually coincide. Similarly the spray zone contracts markedly and disappears in extreme shelter, where the highest level of marine influence more or less coincides with the highest reach of tides. Thus on physical grounds those algologists (see p. 281) who regarded the "supralittoral" ( spray zone) as a wrongly named and local phenomenon found only on exposed shores appear to have been correct, but the actual distribution of species now regarded as "supralittoral" reveals a different picture.

The Verrucaria belt (with littorinids in its lower two-thirds) occupies a wide, ill-defined area of the spray zone, overlapping into the levels reached by waves. As the spray zone contracts the supralittoral fringe contracts too, but it does not die out completely, and in extremely sheltered waters it persists as a narrow but distinct belt entirely within the reach of spring tides. Indeed, during the higher spring tides not only the black zone but all the orange and some of the lower grey lichens above may be submerged for an hour or so. Where rocks and OIKOS 12:II, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

The Littoral Zone on Rocky Shores 291

stones are absent and the upper lichens are replaced by salt marsh grasses and other flowering plants these too are regularly invaded by the higher tides, and the principal flotsam lines always lie in this vegetation. In the transition from exposure to shelter Littorina neritoides is replaced by L. saxatilis, and in extreme shelter the latter persists in only small numbers in the lower part of the Verru- caria belt. The boundary between the supralittoral fringe and the midlittoral zone is a vexed problem in British waters, (see LEWIS 1955) but whatever alter- native is used (the junction of Verrucaria and Balanus or the upper limits of Pel- vetia and Chthamalus) it will range from heights well inside the reach of tides to others near, or well above, the theoretical E.H.W.S. (The actual levels on any particular shore, of course, are determined by those many factors, local and climatic, outlined on p. 285, but precise, specific reference is not required here).

These facts demonstrate further the conclusion reached above, that definition of zones by tidal levels is impossible. More important, they also show that wetting by spray on exposed shores is apparently comparable to that caused by occasional spring tidal submersion in shelter. Populations which, with few exceptions, have always been regarded as supralittoral (primarily on the basis of their being above tide levels) are completely tidal in shelter, and their supra tidal position on open coasts results frcm the uplifting effect of spray and wave wash. Where then should the upper limit of the littoral lie? Regarding the littoral in its intertidal sense the highest tidal level in shelter must be used i. e. E.H.W.S.; then the biologically equivalent level on exposed shores will lie well above the Verrucaria belt, among the maritime lichens and flowering plants. This is not acceptable. If we seek a biological limit and use the top of the Verrucaria/Littorina belt (at present defined as "supralittoral") we have also to accept that our new littoral would not reach, in shelter, to the uppermost very occasional limits of marine influence. This is both reasonable and accept- able. In the previous discussion of factors influencing the environment and zonation the emphasis was mainly upon uplift, and indeed in most published accounts this is the aspect which is stressed. But throughout Britain it is appar- ent that in the absence of waves the normal limiting factors (desiccation, rain water) experienced in the upper shore are such that the uppermost tidal levels are not sufficiently subjected to marine influences to support marine life. The frequently made assumption that E.H.W.S. or "high water mark" in shelter coincides with the upper limit of marine organisms is incorrect, even if we accept the littorinid/ Verrucaria belt as part of the littoral. If the bottom of this belt, i. e. the variously occurring upper limits of barnacles and fucoids, is regarded as the top of the littoral the discrepancy between the biological and tidal boundaries becomes even greater. These facts and their significance for the theoretical and practical delimitation of zones do not appear to have been appreciated before; the positions ascribed (by the use of indicator species) to OIKOS 12: II, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

292 J. R. Lewis

the "physiological high water line" or the equivalent "litus line" by a number of authors (KYLIN 1918; SJ6STEDT 1928; LEVRING 1937; SANTESSON 1939) have approximated to the bottom of the present supralittoral fringe and (unless relationships are fundamentally different) have apparently been well within reach of the sea in sheltered waters.

Accepting that the supralittoral fringe is tidal (or subject to equivalent wetting) do the composition and affinities of its population justify its inclusion in the littoral, rather than in its present transitional category between sea and land? Here one meets the problem of an overlap between essentially marine organisms (littorinids, red and green algae), those with marked terrestrial affinities (lichens) and certain groups such as the isopods and Myxophyceae which are more difficult to categorise. But on British shores the bias is heavily towards inclusion of this population in the littoral, for the two littorinids which characterize and may dominate the belt and which rise to considerable heights above theoretical high tide levels, are equally (and sometimes more) abundant among the upper barnacles and may be found at much lower levels. Moreover, L. neritoides, which rises furthest upshore, has a planktonic larvae. Both L. neritoides and L. saxatilis characterize the upper shore not because they are peculiar to it, but because they alone can extend so far upshore beyond the upper limits of the dominating barnacles or algae of the middle shore. Among the algae of this belt are some (Porphyra especially) which in different localities or in some seasons are most luxuriant at much lower levels. The terrestrial element is represented mainly by lichens, but it must be noted that the genus Verrucaria occurs throughout the shore, and that V. maura itself is restricted to this fringe zone; its presence here does not therefore represent the lower end of the range of a terrestrial plant.

Above the Verrucaria and Lichina confines of this zone lie orange and grey lichens some of which may extend many miles inland where a suitable surface exists on rocky outcrops, walls and roofs. These are the supralittoral, the maritime, terrestrial organisms which provide the best counterpart to the sublittoral population, and which similarly just come within reach of tidal (or equivalent) influences. The junction of the black and orange/grey lichens may be a wide, spray-extended area or a distinct line; in either case it marks the greatest discontinuity of the shore and the point where the fewest organisms normally occur on the open rock surface. From the barnacle line upwards there is a fall in the number of species; first the overlapping midshore molluscs die out, then the Porphyra, Myxophyceae and other algae, and finally the loss of the littorinids leaves Verrucaria and Lichina alone. Within the deep clefts there may be a few Ligia, Petrobius and other terrestrial arthropods which emerge to roam over the surface at certain times, but on the open rock surface itself this level supports the least number of species. Then above this level first OIKOS 12: 11, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

The Littoral Zone on Rocky Shores 293

the few orange lichens and then the wide variety of grey lichens appear, together with the first mosses and flowering plants where ledges and clefts provide a root-hold. Thus on British shores the upper limit of the littorinid/Verrucaria belt is a more important biological horizon than the upper limit of the barnacle zone, though rarely is it such a striking visual landmark. There is no continuity of population astride this boundary (except for the highly mobile and crevice faunas), and no biological justification for uniting the populations on either side of it in one extensive supralittoral zone. Bearing in mind the relation of this supralittoral fringe to tides, waves and spray, and the composition and bias of its population this zone must be regarded as the uppermost part of the littoral.

There is one final but very important point. The shore may be regarded physically as the meeting place of sea and land, but when it is considered biologically the bias swings heavily towards the sea. Organisms with terrestrial affinities are certainly not absent from the shore, and phanerogams such as eel-grass may intermingle with rock and shingle populations in some sublittoral areas, but the overwhelming majority of shore species are marine. This alone goes far to counterbalance the terrestrial element in the upper shore and in my opinion provides the final justification for setting the upper boundary of the littoral at the upper limit of attached or slow-moving marine organisms.

In practice this means the littorinids first and foremost. Then because throughout the world the littorinids and the Verrucaria/Myxophyceae belts may coincide, or either may lie within the other, it seems acceptable to set the limit of the littoral zone at the top of whichever of these two belts is uppermost on any particular shore.

The littoral zone thus proposed would in effect combine the midlittoral zone and the supralittoral fringe of the Stephensons, the supralittoral zone and most of the mesolittoral of French workers, but would cut through the supra- littoral zone of those who unite the littorinid/Verrucaria belt with the lichens above. There could be no constant relationship to tidal levels for the limits, being biological, would vary according to the exposure, aspect, latitude, topography and so on, and in certain circumstances or localities could be expected to vary seasonally or over a few years. Expressed in tidal terms (for reference to tidal or other levels of the sea will remain the most useful way of describing as opposed to defining, the levels occupied) the littoral will range from heights which may lie several tens of feet above or several feet below E.H.W.S., to levels which are always above E.L.W.S. and which may even rise to M.T.L. or even higher. As a biological entity it would remain distinct from "the shore" or the "intertidal zone", which is the physical entity, and with which its- limits would rarely if ever coincide. Just as it would be possible to investigate the upper part of the littoral at heights well above E.H.W.S., so one could be in the sublittoral but still on the shore. 20 OIKOS 12: 11, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

294 J. R. Lewis

Terminology

Accepting the concept of such a littoral zone some reconsideration of terminology is necessary. Here it is worth emphasizing that the alternatives discussed below, and the alternatives to, or modifications of, the Stephenson system which are in use represent merely differing philosophical interpretations (doubtless influenced by local experience) of basic facts which are not in real dispute, i. e. the presence of three major biological zones on the shore.

The alternatives which now require consideration are as follows. The Stephenson terminology can be retained primarily to indicate the posi-

tion of the three zones, and in recognition of the fact that it was under this terminology that the present broad basis of the zones was established. In sup- port of this is the fact that a number of authors have been and still are using this system and any further radical change of terminology might cause con- fusion when increasing numbers of shores throughout the world are being compared. Again the fundamental simplicity of this scheme enables most shores so far described to be accomodated within it, without undue pre-occupa- tion over the precise affinities and exact limits of the many local, subordinate populations. (Such arguments can equally be used in support of some much older systems of terminology, even if their biological bases require amending). If the Stephenson system is retained it would be better, in view of the fact given on p. 290 to remove the relationship between the supralittoral fringe and E.H.W.S. implied in Fig. 3 of the 1949 paper. Then since their two upper zones make up the littoral as envisaged in this paper, one could accept that such a "littoral" exists but for the reasons advanced above persist with the same terminology.

This terminology conveys however more than the position of the three zones. The supralittoral fringe was seen as the lower fringe of the supralittoral zone, an invasion of the tidal area from above, and the sublittoral fringe as a corresponding invasion from below. This portrays a symmetrical situation which appears to be too great a reflection of the physical standpoint - the view from the middle of the shore only, with an upper, almost terrestrial margin balancing a lower, almost sublittoral margin. Such a view is not entirely in accord with my interpretation of the relationships of the zones (especially the supralittoral fringe) to each other and to marine or terrestrial life in general, and by which the limits of a biological littoral zone were decided. To convey these relationships and the overwhelming marine bias of the shore population, either of two alternative systems of terminology appears more suitable.

Both start with the division of coastal organisms into i) the principal marine population of the SUBLITTORAL ZONE1. ii) the marginal marine population of the LITTORAL ZONE.

1 It is perhaps illogical to name the principal marine population by reference to the special- ized and marginal littoral, but this is a result of the historical development of marine studies which it would now be difficult to reverse.

OIKOS 12:11, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

The Littoral Zone on Rocky Shores 295

Then it should be recognised that each zone may contain species able to occupy, and possibly restricted to, those upper parts of each zone in which conditions become increasingly difficult for their respective populations as a whole.

Thus some sublittoral species extend to levels where slight exposure to air is experienced; and if there is sufficient biological justification one can then distinguish a distinct SUBLITTORAL FRINGE, i. e. the upper marginal belt of the sublittoral zone. In this, as opposed to the solely positional sense, the term is applicable on many, but not all British shores, and where a fringe is present its lower limit usually lies above E.L.W.S. Elsewhere the term has been found applicable in some cases (CHAPMAN and TREVARTHEN 1953; GUILER 1953) and not, or only partly so in others (DEN HARTOG 1959; WOMERSLEY 1959, 1956 and earlier). These conflicting opinions support the contention that a biologically distinct fringe is not universal, and that it is best regarded as one of the possible sub-divisions of the sublittoral zone. The incorporation of these latter together with those of the littoral in a single biological system is a de- sirable aim, and while it has been attempted to some extent already (HEDGPETH 1957; PEIREs 1957), the practical difficulties of investigating the sublittoral on many open coasts may well prevent complete integration. In the meantime the "upper sublittoral" proposed by WOMERSLEY & EDMONDS (1952), appears the least objectionable interim term by which to refer to the sublittoral where a distinct fringe is lacking.

The littoral zone itself is obviously divisible into the principal belt of bar- nacles or equivalent organisms, and the marginal belt of littorinids, Verrucaria and Myxophyceae. "Lower" and "upper" littoral are adequate terms in one sense, but it seems preferable to indicate that the majority of littoral organisms occur in the lower zone and that only the hardier species extend into or are confined to the upper zone. With the word littoral already in use for the entire area there appears to be no more suitable term for the lower and principal zone than EULITTORAL - the term used originally in this sense by European algo- logists. Then LITTORAL FRINGE (suggested by Womersley & Edmonds but not used by them) would adequately convey that the upper belt is marginal and has greater affinities with the eulittoral than with the terrestrial levels above.

There remains the use of the term "supralittoral". If the present proposal is accepted this term could be restricted to the lowest maritime belt of the land, to levels which are strictly supra-littoral and indeed for which the term MARI- TIME seems even more appropriate; this usage will remove the long-accepted illogicality (recently repeated by WOMERSLEY 1959) of a supralittoral identified and delimited by marine organisms. The lowermost members of the maritime zone would be the orange and grey lichens and flowering plants which lie above the highest littorinids, Verrucaria or Myxophyceae and which in some cases extend far inland. In extreme shelter they will be submerged by the 20* OIKOS 12: 11, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

296 J. R. Lewis

highest tides, but this is immaterial for these are the situations where the littoral fringe fails to reach the highest tide levels.

The terminology proposed therefore envisages sublittoral and littoral zones, with the former probably and the latter invariably having upper marginal belts known as the fringes of their respective zones. The depth of the eulittoral zone will be controlled mainly by the tidal range and the exposure; but the depth and position of the littoral fringe and the extent to which the sublittoral zone (or fringe) penetrates upshore, will be controlled mainly by the exposure, but will be influenced also by the aspect, latitude and topography of the locality.

The position adopted here regarding the limits of the littoral zone, and the consequent rejection of "supralittoral", is based initially upon British and European coasts, and rests upon

i) the realization that the littoral fringe is sufficiently influenced by tides, waves or spray to no longer warrant inclusion in a supralittoral (- supratidal) area.

ii) the sharpness of the natural boundary provided by the upper limit of the zone, and the marine bias of its population.

If these bases should prove to be peculiarly British or European some modification of the terminology proposed might be required, if one is seeking for a system of wide application. Without quoting a great number of papers dealing with specific points on other shores, it nevertheless ap- pears that the conclusions reached here and the proposals made will apply elsewhere, but the opinions of other workers are awaited. Where very shel- tered shores have been investigated the Verrucaria/Myxophyceae belt (lit- torinids tend to be scarce in extreme shelter) is completely tidal, but further information is required, especially where a full range of exposed and shel- tered, but fully marine, habitats is available in the same district. Regarding the affinities of the population all authors regard the littorinids as marine organisms, but there are undoubtedly areas in which their zoning is more rigid than in Britain, and some are restricted to the very highest levels, e. g. Nodilittorina in Australia, Tectarius in Florida. If the terrestrial element is also strongly represented in the vegetation, or if isopods or land crabs pre- dominate, it might then be felt that this population was sufficiently distinct, or its littoral affinities so weak, that it should be placed above the limits of a biologically defined littoral zone. Here it must be emphasized that invasion of these levels by flowering plants represents an intermingling of two discrete types of habitat and population: rocky surfaces suitable for algae and lichens, and sand or soil which suit flowering plants and burrowing animals. While some authors believe that zonation terminology should apply equally to rock, sand and mud shores, others believe that the division between hard and soft substrata is too great to bridge in one system, and this view is taken OIKOS 12: 11, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

The Littoral Zone on Rocky Shores 297

EXPOSURE SHELTER

LITTORAL Xf ZONE

E.H.W.S. - - -- ---E.H.W.S. EULITTrORA ZOELTRL

-....zzSUBLITTORAL ZONE --------- .L.W.S.

Fig. 2. The proportions and positions of the zones proposed as they may occur around British coasts. Greater variation does- exist however, for on sheltered shores with a large tide range the eulittoral zone may be several times deeper than the littoral fringe, while on exposed shores with a very small tide range or under conditions of greater exposure on mild, northern coasts, the littoral fringe may be several times deeper than the eulittoral zone. Under special, local conditions the

upper limit of the sublittoral zone may rise more steeply than that of the eulittoral.

here. Therefore the presence of flowering plants and shrubs in clefts and de- pressions among lichens and littorinids should be ignored in assessing the character of the rock population, even if the juxtaposition permits snails to climb on land plants, for this vegetation is but the counterpart of the saltmarsh or sand dune flora. The littoral or maritime bias of the flora must be decided by reference to lichens and algae, and that of this zone as a whole by whether its upper limit constitutes as natural a break as it does on British shores. If, when the higher plants are discounted it is still felt that the terrestrial bias is strong it might then be necessary to restrict "littoral" to the principal shore population, i. e. to the eulittoral of the proposed scheme. If opinion eventually favours the inclusion of all types of substrata in one system, such a usage of littoral may be essential, for salt marsh vegetation undoubtedly extends further downshore than the maritime lichens, and intermingling of algae, phanerogans and littorinids is there more common. Even so, "littoral fringe" in the sense of a "marginal upshore extension of littoral organisms" is preferable to a return to "supralittoral" for a belt which contains marine species and is subject to submersion or equivalent wetting by spray. "Supralittoral" should be replaced by "maritime" and this term applied to those levels which are largely, if not entirely, beyond the sphere of marine biology.

Thus depending partly upon data yet to be obtained, and partly upon one's OIKOS 12:11, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

298 J. R. Lewis

interpretation of the status of the littorinid/ Verrucaria/Myxophyceae belt it would seem that the terminology best suited to rocky coasts, tidal or otherwise, would be either:-

(Maritime Zone.) 1. Littoral Zone.

i. Littoral Fringe. ii. Eulittoral Zone.

2. Sublittoral Zone (with a possible Sublittoral Fringe). or:-

(Maritime Zone.) 1. Littoral Fringe. 2. Littoral Zone. 3. Sublittoral Zone (with a possible Sublittoral Fringe).

One final topic remains. "Littoral" has had many meanings and yet another is proposed here. The biological interpretation outlined here is fundamentally different from previous meanings, but it is a logical result of the increasing reliance upon biological criteria. Can "littoral" bear another new meaning or should a new term be created? There would be little difficulty in doing the latter, but bearing in mind how thoroughly, if confusedly, "littoral" is now rooted in thought and literature, and the lack of support for the recently proposed terms of DU RIETZ (1940), one concludes that it may be best to cling to "littoral", but hope that it can be accepted and used in the sense proposed here.

Summary

1. The complete physical environment of the shore (resulting from tidal or other fluctuations of sea level and influenced greatly by the effects of exposure, aspect, latitude, topography, and the existing population), cannot be measured and it is therefore inappropriate to define and delimit zones by reference to one factor - the tides - alone. Organisms must be used, and then it is found that the principal biological horizons of the shore do not coincide with the limits of the intertidal zone.

2. In the lower shore the upper limit of sublittoral organisms (laminarians in N.W. Europe) lies variously above E.L.W.S., while in the upper shore the upper limits of the barnacle/fucoid and the littorinid!Verrucaria belts both lie within tidal limits in shelter, but may rise to small and considerable heights respectively above E.H.W.S. on exposed shores.

3. It is proposed to recognize a biologically defined littoral zone which is distinct from the physically defined intertidal or littoral zone: it is bounded

0IKOS 12: 11, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

The Littoral Zone on Rocky Shores 299

below by the upper limit of sublittoral organisms, and above by the upper limit of marine organisms. The latter is set at the top of the littorinid/ Verrucaria/Myxophyceae belt because i) the affinities of this population as a whole are judged on balance to be

more marine than terrestrial; and its upper limit constitutes the sharpest natural break in the population of the upper shore.

ii) this population, originally considered to be supralittoral because of its supratidal position on exposed shores, lies well within the reach of tides where waves are absent.

iii) the overwhelming majority of shore species are marine, and this bias ought to be reflected in delimiting the littoral and naming its zones.

4. It is proposed to recognize i) a sublittoral zone in which there may be local biological justification for

an upper sublittoral fringe. ii) a littoral zone divided into

a) eulittoral zone - the principal belt of littoral organisms, equivalent to the mid-, meso- and eulittoral of various previous schemes.

b) littoralfringe - the marginal belt of littoral organisms, equivalent to the supralittoral zone or fringe of previous schemes.

iii) a maritime zone to refer to the lowest belt of terrestrial life above the littoral fringe.

Supralittoral is rejected as unsuitable for a zone defined or characterized by marine organisms.

5. Recognizing that the grounds on which the position of the upper limit of the littoral was decided might apply less forcefully outside N.W. Europe, and they would undoubtedly do so if it was felt that schemes of zonation should apply to sand and mud shores as well as to rock, a slightly modified ter- minology is proposed pending comment and opinion from other areas.

References ADMIRALTY, HYDROGRAPHIC DEPARTMENT, 1959. The Admiralty Tide Tables, Vol. 1, European

Waters, 1960. London. AUDOUIN, J. W. et MILNE-EDWARDS, H., 1832. Recherches pour servir a l'histoire naturelle du

littoral de la France. I. Paris. DE BEAUCHAMP, P., 1914. Les Groves de Roscoff. Paris. B0RGESEN, F., 1908. The Algae-vegetation of the Faeroese coasts. Botany of the Faeroes, Vol. 3.

Copenhagen. CHAPMAN, V. J. & TREVARTHEN, C. B., 1953. General schemes of classification in relation to

marine coastal zonation. J. Ecol., 41, 198-204. COLMAN, J., 1933. The nature of the intertidal zonation of plants and animals. J. mar. biol. Ass.

U.K. 18, 435-476.

OIKOS 12:11, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

300 J. R. Lewis

COTTON, A. D., 1912. Marine Algae. Clare Island Survey. Proc. R. Irish Acad. 31 (15), 1-178. DOTY, M. S., 1946. Critical tide factors that are correlated with the vertical distribution of marine

algae and other organisms along the Pacific coast. Ecology, 27, 315-328. DOTY, M. S. & ARCHER, J. G., 1950. An experimental test of the tide factor hypothesis. Amer. J.

Bot. 37, 458-464. EVANS, R. G., 1947 a. The intertidal ecology of Cardigan Bay. J. Ecol. 34, 273-309. - 1947 b. The intertidal ecology of selected localities in the Plymouth neighbourhood. J. mar.

biol. Ass. U.K. 17, 173-218. - 1957. The intertidal ecology of some localities on the Atlantic coast of France. J. Ecol. 45,

245-271. FORBES, E., 1846. On the connection between the distribution of the existing fauna and flora of

the British Isles, and the geological changes which have affected their area, especially during the epoch of the northern drift. Mem. geol. Surv. U.K. 1, 336-432.

GISLtN, T., 1930. Epibioses of the Gullmar Fjord. II. Kristinebergs zoologiska Station, 1877-1927. Uppsala, 4, 1-380.

GUILER, E. R., 1953. Intertidal classification in Tasmania. J. Ecol. 41, 381-384. DEN HARTOG, C., 1959. The epilithic algal communities occurring along the coast of the Nether-

lands. Amsterdam. HEDGPETH, W. J., 1957. Classification of marine environments. Geol. Soc. Amer., Mem. 67,

Vol. 1, 17-27. JOHNSON, D. S. & YORK, H. H., 1915. The relation of plants to tide-levels. A study of factors

affecting the distribution of marine plants. Publ. Carneg. Instn. 206, 1-162. KJELLMAN, F. R., 1877. Sober die Algenvegetation des Murmanschen Meeres an der Ktiste Nowaja

Semlja und Waigatsch. Nova Acta Reg. Soc. Upsal. 3, 1-86. KYLIN, H., 1918. Svenska vistkustens algregioner. Svensk. Bot. Tidskr. 12, 65-90. LAWSON, G. W., 1957. Seasonal variation of intertidal zonation on the coast of Ghana in relation

to tidal factors. J. Ecol. 45, 831-841. LEVRING, T., 1937. Zur Kenntnis der Algenflora der norwegischen Westktiste. Lunds Univ. Arsskr.

33, 1-148. LEWIS, J. R., 1955. The mode of occurrence of the universal intertidal zones in Great Britain.

J. Ecol. 43, 270-290. 1957. Intertidal communities of the northern and western coasts of Scotland. Trans. roy. Soc., Edinb. 63, 185-220.

LEWIS, J. R. & POWELL, H. T., 1960. Aspects of the intertidal ecology of rocky shores in Argyll, Scotland. Pts. I and II. Trans. roy. Soc. Edinb. 64, 45-74, 75-100.

LORENZ, J. R., 1863. Physikalische Verhaltnisse und Vertheilung der Organismen im Quarnerischen Golfe. Vienna.

PtRtS, J., 1957. Le probleme de l'6tagement des formations benthiques. Rec. Trav. Sta. mar. Endoume, 21, 4-21.

PtRtS, J. & PICARD, J., 1955. Biotopes et biocoenoses de la M6diteran6e occidentale compares A ceux de la Manche et de l'Atlantique nord-oriental. Arch. Zool. exp. g~n. 92, 1-71.

PRUVOT, G., 1897. Essai sur les fonds et la faune de la Manche occidental compares A ceux du Golfe du Lion. Arch. Zool. exp. g6n. s6r. 3, 5, 511-662.

DU RIETZ, G. E., 1947. Wellengrenzen als okologische Xquivalente der Wasserstandslinien. Zool. Bidr. Uppsala, 25, 534-550.

SANTESSON, R., 1939. Amphibious Pyrenolichens. I. Ark. Bot. 29, No. 10, 1-67. SJOSTEDT, L. G., 1928. Littoral and Supralittoral studies on the Scanian shores. Lunds Univ.

Arsskr. 24, 1-36. SOUTHWARD, A. J., 1958. The zonation of plants and animals on rocky shores. Biol. Rev. 33, 137-177.

OIKOS 12:11, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions

The Littoral Zone on Rocky Shores 301

STEPHENSON, T. A. & STEPHENSON, A., 1949. The universal features of zonation between tidemarks on rocky coasts. J. Ecol. 37, 289-305.

-1954. Life between tidemarks in North America. IIIA, B. Nova Scotia and Prince Edward Island. J. Ecol. 42, 46-70.

WOMERSLEY, H. B. S., 1956. The marine algae of Kangaroo Island. IV. The algal ecology of American River inlet. Austr. Jour. Mar. Freshw. Res. 7, 64-87.

-1959. The marine algae of Australia. Bot. Rev. 25, 545-614. WOMERSLEY, H. B. S. & EDMONDS, S. J., 1952. Marine coastal zonation in southern Australia in

relation to a general scheme of classification. J. Ecol. 40, 84-90.

OIKOS 12:11, Copenhagen 1961

This content downloaded from 83.99.244.162 on Tue, 1 Jul 2014 15:21:06 PMAll use subject to JSTOR Terms and Conditions