And this situation is true also of the work on sponges, holothurians, alcyonaria, and to a surprising extent of the work on conchology. It might be well at this point for zoological workers to recognize that specialization, although desirable and necessary, has, too, its hazards and that liaison writers are much needed here. Co-ordination of this type would not only benefit zoology, but would render its findings more intelligible to workers in other fields.
Setting aside any evaluations as to the thoroughness, integrity, or competence brought to a given task, there are several kinds of papers. In working up a collection of animals from a given region, the specialist has three choices. He may do the job in hand most simply by listing the species taken, with citations in the synonymy only, by suitable descriptions and by diagnostic illustrations especially of such species as appear to be new to science, and by repeating any collecting or natural history observations which may have been noted on the label by the collector. Or, he may find that with a little extra exertion he can also review all the published work on that particular group in that area, evaluating and collating the literature to date, and citing in a bibliography all the apropos items with short abstracts. By so doing, he will have made it unnecessary for future workers to dig back into scattered and often inaccessible literature; or, if they must do this, at least he will have simplified the task by having provided a foundation. The Nielsen 1932 ophiuran paper based on Dr. Mortensen’s expedition is a good example. As a third possibility, our hypothetical specialist may discover that with still more effort, he may be able to have suitable toto-illustrations prepared (as contrasted to figures of diagnostic details) of all the commoner forms, so that laymen using the paper may quickly familiarize themselves with that particular fauna without having to make a special study of the highly specialized subject matter. Miss Rathbun’s “Stalk-Eyed Crustacea of Peru,” but especially her four volume monograph on the Brachyura of North America, are cases in point.
But the “field eye” is as different from the “laboratory eye” and the “library eye” as these are from each other, and they all contribute to the whole and to each other. So the ideal situation would be for the specialist to have been a member of the expedition, or for him otherwise to have familiarized himself largely and at first hand with the living animals in the field. Opportunities of this sort must be rare, but they provide rich rewards in bringing together, for evaluation by a single mind, all the known logical factors in the specialist’s field. The subsequent report will be an expression of this co-ordination, and should prove an increasing joy to work with in the field, laboratory, or library. Darwin’s account of the barnacles is a classic example; in recent years Fisher’s monograph on the asteroids and Ashworth’s Arenicola paper are good illustrations, along with some of the Glassell decapod papers, among the shorter accounts. Even by the informed general public, expressions of this type are coming to be recognized as monuments to real achievement, to be contrasted with the annoyance and inconvenience of less thorough works as time shows up their inherent oversights and shortcomings. The British conchologist Philip P. Carpenter summarized this situation well for his day, by saying (p. vi, § S-8): “My principal object in the preparation of these works has been to make out and compare the writing of previous naturalists, so that it might be possible for succeeding students to begin where I left off, without being obliged to waste so large an amount of time as I have been compelled to do in analyzing the (often inaccurate) work of their predecessors.”
In these remarks—the complaint of one who unwittingly has been led through some pretty bad morasses of indifferent work and of poorer reporting of it—there may be sensed a frank propaganda for research and write-ups of the most thorough sort. Work of this type would seem to be, in its own right, a satisfying task and an honorable avocation not unconnected with what Keats would have termed pure “joy,” and, from the viewpoint of functionalism, a hearty and lasting contribution to the “increase and diffusion of knowledge” which is one of the fundamental aims of science.
I:C
IN connection with the phyletic catalogue, it should be emphasized that, although we seem to have collected a good representation of the littoral species, no general survey of the entire fauna has been attempted. Dredged animals will be lacking from our list unless it happens that they occur also along shore. Therefore any conclusions arrived at through the analyses and syntheses of these data must be regarded as valid for shore conditions only.
Experience elsewhere has indicated that depth is an important, although by no means the only, or even the most important, factor of distribution. A typical beach fauna, for instance, will consist in part only of true shore forms. The majority will derive obviously from the continuously submerged zones, as more or less successful shore colonizers, with migrations still going on, and with possibly a few motile stragglers from land—the whole welded into a fairly coherent, mutually interrelated society in a more or less stable state of equilibrium. Although this particular zone, centering around the line of lowest tides, is thought to be the richest area in the entire ocean, both for species and for individuals, there will be no attempt to suggest a delineation of the whole region from a study of the one part.
II:A
THERE has been mention of a Panamic Fauna. It may be well to characterize it at this point more clearly. A faunal province for mollusks has been defined by Schenck and Keen, (1936, p. 923) as a region “populated by a distinctive assemblage of species. Distinctiveness is not simply a matter of ecologic situation but of spatial extent or range. . . .” Just how distinctive the assemblage must be would seem to vary with the province. What is regarded as the Panamic Fauna seems to be pretty definite beside that which has been regarded traditionally as the Californian, the Oregonian, the Aleutian, the Sitkan, etc.
A more generalized definition would substitute the word “forms” for “species” so as to read: “populated by a distinctive assemblage of forms.” There are indications that the word “species” may have different connotations in conchology, in car cinology, and in echinodermology. Quite possibly the amount of differential which to Fisher indicates a subspecies or no more than a forma among the starfish would, on the basis of shell alone, constitute a full species or even a subgenus for the conchologist. The standards, the mean, may be different in different groups. The further advantage of using a more generalized term in attempting to evaluate provinces is illustrated by the following situation: In comparing lists of distinctive and abundant animals of the southern California area with those of similar exposure, depth, and type of bottom in the Monterey Bay area, it turns out that a sea pansy, Renilla, characterizes tidal sand flats of a certain sort in the south, and there is nothing comparable in the northern lists. Sea pansies which the veriest amateur would recognize as such, and which would be differentiated only by specialists, occur at Newport Bay in southern California, at Estero de Punta Banda in northern Lower California, at Cape San Lucas, at Panama, in northern Peru, and probably elsewhere between and beyond. The fact that the Renilla of southern California and northern Lower California is identified by specialists as R. köllikeri, and that of Panama Bay as R. amethystina, is secondary in a zoogeographical sense to the fact that there are abundant sea pansies—a readily recognizable “form” of animal—south of Pt. Conception, and none whatsoever to the north.
Transcending species differentiations, there is a deeply real distinctiveness which is valid both scientifically and in factual common sense, although difficult to state. There is a profound gulf between an assemblage which comprises, say, the sea pansies (which are obviously separated from their nearest relatives), the sea hare Navanax inermis, the tubed anemone Cerianthus—a distinctive form—the fiddler crab Uca (as distinguished from the related grapsoids), the swimming crabs Portunus or Callinectes (as distinguished from the Cancridae), the clams Chione spp. and Dolichoglossus, and an ecologically similar assemblage only a few hundred miles removed spatially, which comprises the more northern Hemigra
psus oregonensis, Schizothaerus, Cardium corbis, Zirfaea pilsbryi, Saxidomus spp. and Macoma spp., Callianassa, Upogebia, the large northern Tethys (p. 737, MacGinitie 1935, § Y-26), and the dog whelk, Nassarius fossatus. And that gulf persists even though it may be shown that Haminoea, Urechis, etc., and dozens of less abundant or less dominant species are common to both assemblages.
One’s personal criterion of a zoogeographical province is difficult to put into words. If a field zoologist fairly well acquainted with the communities of shore invertebrates in a given region, X, should find familiar animals in comparable communities and in about the same proportions (depth, type of bottom, and conditions of exposure to wave shock being equal), at the widely separated points X-3 and X-1, and if, by traveling only a little farther in a given direction, he should find at the point X-2, markedly different animals proportioned differently or in different communities (the above mentioned factors being equal), he will likely assume that in the first case he was working entirely in one province, and that in the second he has passed the bounds of that province into another.
So the Monterey Bay worker must include in one zoogeographical province all the exposed rocky shore fauna between Sitka, Alaska, and Boca de la Playa (some 40 miles south of Ensenada), at least. In this 2600 mile stretch, many animals will have disappeared gradually (except at Pt. Conception where the changes are fairly sudden) to be replaced by comparable forms often scarcely distinguishable as different species. The large picture is found to be the same, the chief constituents are the same, even their proportions are similar. Balanus glandula, Littorina scutulata, Acmaea digitalis, Mitella, Mytilus, Pisaster, Thais emarginata, the lined Lepidochiton, the large solitary green Cribrina, Katherina, the large and abundant forms of Nereis, Tegula funebrale, Pagurus samuelis in Tegula shells, Mopalia, Strongylocentrotus franciscanus and purpuratus, Pycnopodia, Patiria, Cryptochiton (north of Pt. Conception especially), and Parastichopus californicus (along shore only in quiet waters north of Pt. Conception), all occur unchanged from Alaska to northern Mexico, although most of them become notably scarcer south of Pt. Conception. If we add to this list Littorina planaxis (recorded range intermediate), and several shore crabs, sponges, and compound tunicates, we shall have considered most of the common shore forms which make up 95 % of the total production on exposed rocky shores. Some are commoner to the north, or to the south, or to the center of this great traverse, but on the whole our collector would find himself equally at home in either of the extremes or anywhere between, ecological conditions being the same. He would have to be experienced and discriminating indeed to remark any difference whatsoever down at least to Pt. Conception, in landscape, weather, summer water temperature, rocky shore topography, or in the animals themselves. Such an assemblage of distinctive forms would seem to constitute a zoogeographical province, or at least some sort of subdivision whatever the terminology, and regardless of whatever else might be indicated by the total records of all the species involved.
These total records, on which zoogeographical provinces have been based, include both rare and common forms, from shore to several hundred fathoms. There are reasons for believing that total records of all the species provide a distorted picture. Distribution records of this sort give equal weight to such dominant forms as Mytilus californianus and Pisaster ochraceus (which for every linear mile of rocky coastline in the temperate zone will produce hundreds of pounds of animal tissue and shell per year), and to such rarities as certain minute snails or worms which have never been seen by any save a few specialists and museum attendants. Records of deep water animals are included also, although obviously the zoogeographical provinces of the ocean floor, if any exist, must differ from those along shore. The deeper an animal lives, the more it is subjected to oceanic conditions which are more uniform than anything else on earth, so that abyssal animals are cosmopolitan. In deep water there is little differential geographic distribution, the only measurable differential is bathymetric. In the Monterey Bay area at least, and probably throughout the Pacific coastline with its great depths close offshore, identical and similar animals will be found indiscriminately at depths varying from 20 to several hundred fathoms, so that any attempt to limit the shore fauna by imposing the 100 fathom limit, generally presumed to mark the continental shelf, is seen to be highly artificial. Monterey divers insist there is a sharp threshold at 12 fathoms—72 feet—and it may be that somewhere around this level the limit of true littoral animals will be found, but documenting such a statement would require much work. However there can be no doubt that the only animals not subjected to uniform oceanic conditions are those restricted to the shore. And the only way to be certain of that, since here again no definite line of demarcation can be set at present, is to take animals from between the tides and from the few feet just below the line of low water. These surely can be considered as subject to shore conditions and not to the uniform conditions of ocean bottoms. Littoral zoogeographical provinces can be based only on such conditions (which are largely a function of ocean currents in controlling air temperatures and humidities), and on the ocean currents themselves which have not yet been adequately plotted. And, just as surely, the animals important in the marine sociology of an area arc not museum rarities, but the common and obvious forms which make up the bulk of the population.
II:B
TRAVELING only a few hundred miles farther south, our Monterey Bay observer, at Cape San Lucas, for instance (where the rocks are similar in type and exposure to those at Boca de la Playa below Ensenada, at Pt. Lobos south of Monterey, or at the Sitka outer islands) , would find himself in a territory wholly unfamiliar zoologically. He would be unlikely to see at first glance even one single familiar form. Unfamiliar animals would be found inhabiting familiar ecological niches. Pisaster would be replaced by the many rayed Heliaster which clings equally tightly; Strongylocentrotus spp. by Echinometra van brunti. There would be littorines, and Thais-like forms, all adapted to withstand heavy surf as are those in the north, but of different species, usually of entirely different groups. The limpets, the barnacles, the few chitons would be obviously different. Pendent gorgonians and (in more quiet waters) stony corals would occupy the overhangs and ledges inhabitated in the north by a complex of varied sponges, anemones, hydroids, and encrusting Bryozoa and tunicates. Unfamiliar crabs would scuttle about in the uppermost zone, just as hard to catch—harder in fact—than those in the north, but utterly different. All this would be evidence, even to the untrained observer, of an entirely new fauna.
The fact of the matter is that these different animals of the exposed rocky shore, and Renilla and others of the estuarine soft bottoms, characterize what has been called the Panamic Fauna, which in distinctiveness would seem to fulfill even the strictest definition of a zoogeographical province. Even its boundaries may be drawn with some degree of sharpness. The southern limits seem to be pretty well marked at latitude 4° 30’ S., bisecting the bulge in northern Peru near Paita, north of Sechura Bay. A short overlap area thereabout is formed by the variation in the limits of the cold Humboldt current.
The northern limit has been set generally at Cape San Lucas, latitude 23° N. However, there can be no doubt that the Panamic Province in its entirety extends at least to Magdalena Bay, and quite probably to the Pt. San Eugenio complex inshore from Cedros Island, latitude 28° N. In reporting on hydroid distribution of the 1934 Hancock Expedition, Fraser, 1938 (§ B-2) p. 5, states: “In passing northward along the west coast of Lower California, the most decided break in continuity of distribution in both fauna and flora appears to be in the vicinity of Thurloe Point. There the large kelps so characteristic of the coasts of United States and Canada make their first striking appearance, and other species appear, coincidentally with these.” Thurloe Head is about 25 miles south of Pt. San Eugenio. Also the northward limit of such important horizon-marking tropical shore forms as the Sally Lightfoot crab is known to be at Cedros Island, and many of the northern animals make their last stand there. T
he whole coastline between San Diego and Magdalena Bay has been very little worked over, and it can be expected confidently that future collecting will establish many northern limits of Panamic animals in that area.
Actually, a considerable number of Panamic invertebrates, especially the quiet water forms, reach their extreme frontier in southern California. A few of these have already become extinct there within our own experience, coincident with changes due to commerce, dredging, and the construction of breakwaters. The following come to mind as both common and representative of present or immediately past conditions: the pendent gorgonians Muricea spp., Renilla, the burrowing anemones Cerianthus and Harenactis; the starfish, Astropecten armatus, Linckia, and Astrometis; two of the three commonest shore ophiurans south of Pt. Conception, Ophioderma and Ophionereis (Ophiothrix occurs occasionally at Pacific Grove), the urchins Lovenia and Lytechinus; Sipunculus nudus, the spiny lobster Panulirus, Synalpheus spp., Callianassa affinis, Penaeus brevirostris (slightly sublittoral; the record for San Francisco must be the result either of downright error, or of the finding of strays), Pilumnus, Paraxanthias taylori, Uca crenulata, Amphioxus, the cockles Chione spp., most of the cowries and the murices and the cones, etc. None of these extend importantly north of Pt. Conception, which seems to be a barrier more effective for southern than for northern forms, although many of the rocky shore inhabitants are fairly common at Santa Barbara which is just a few miles to the south.
Sea of Cortez Page 29