Sea of Cortez
Page 30
The fact is worth passing mention that competent collecting has turned out some of these southern animals as strays in the north. With increased collecting intensity, more and more ranges will be extended in both directions, so that the qualitative zoogeographical records of the future will read, almost literally: “everything—everywhere.” But the great numbers of given animals will still remain in their optimum areas, with differential distribution observable quantitatively only—which is in any case the way the competent field zoologist will see it. In the large picture, the rarities will be regarded as rarities only, and weight will be given chiefly to the common forms which comprise 99% of the scene.
II:C
WITH reference to faunal barriers in general, but particularly to Pt. Conception as a northern limit for Panamic forms, it will be argued that many species are common to areas both north and south of this alleged line of demarcation. But it can be shown equally that a greater number of commoner and more important shore animals are limited by this complex than by any similar stretch of coastline many times its length. Actually there is more divergence between the common shore animals fifty or a hundred miles north and south of this point than there is within the whole area between St. Sal (just to the north) and Cape Flattery (in the latitude of Victoria)—or, for that matter, clear up to Sitka, ecologic conditions being equal.
As attenuated extensions of the Panamic fauna can be traced all the way to southern California where Pt. Conception is thought to function as a last barrier to their farther northward migrations, so the more northern fauna fades out gradually and terminates finally somewhere in the almost unexplored stretch of coastline in northern or middle Lower California. (An unexplored area, incidentally, can be a very effective barrier in zoogeography!) This might aptly be termed the North Temperate Fauna, extending as it does almost throughout the entire temperate zone as far as to Sitka without any sudden breaks, as can be seen by any shore observer who is more concerned with common animals than with rarities (which most experienced collectors definitely are not). There is a fairly obvious break at Cape Flattery, but this seems to be ecological rather than geographic, since most of the littoral distribution records immediately north of there are based on quiet water collecting in the Straits of Juan de Fuca, in the Straits of Georgia, and in Puget Sound, as opposed to open coast conditions to the south. So marked is this uniformity in the distribution records, on the whole, that Fraser, noting not even a Pt. Conception break in his total records, writes (1938, “Hydroid Distribution in the North Eastern Pacific,” Trans. Roy. Soc. Canada, Sec. V: p. 42) : “There is nothing to indicate that there is any especially effective barrier to hydroid distribution at any point between Bering Sea and the boundary between United States and Mexico.”
But for these northern animals also, Pt. Conception is something of a real barrier, because, as has been noted above, such of those as have dispersed past this boundary to the south will be found there sparingly or stuntedly, as compared to their lush and healthy abundance in Monterey Bay and to the north. But Cedros Island, opposite the mainland Pt. San Eugenio complex, marks the extreme southern limit of such few as have come thus far all the way from Alaska: Strongylocentrotus franciscanus, S. purpuratus (Clark 1913, § K-5, p. 222) , and Parastichopus californicus (in 35-45 fathoms, Deichmann 1937, § L-5, p. 163, 1938, § L-6, p. 362) , to name a few. And Pisaster, Mitella, Mytilus , and other northern horizon markers will have disappeared somewhere in the poorly-known stretch between the Ensenada area, where they all occur sparingly, and Cedros Island which has finally barred their farther southward dispersings.
II:D
IF then the region between Pt. San Eugenio and Pt. Conception can be looked upon correctly as an overlap area, the Panamic Province can be defined as extending from about latitude 4° 30’ S., just below Ecuador, to about 28° N., opposite Cedros Island in Lower California, with an attenuating extension to the north, limited finally by Pt. Conception, 34° 30’ N. A north temperate fauna can be conceived as extending from an unknown point in the north (possibly around 57° at Icy Strait north of Sitka, but possibly not short of the passes into the Bering Sea between the Aleutian Islands) down to Pt. Conception, 34° 30’ N., with an overlap extension to Cedros Island at about 28° N.
Hence for purposes of zoogeographical evaluation and classification, we have adopted the following possibly arbitrary rules: north temperate forms are those which, having a southern limit at or north of Cedros Island, range materially north of Pt. Conception. Species restricted to the Cedros Island—Pt. Conception area are probably overlap forms, although they may be North Temperate or Panamic animals not yet discovered in their northern or southern extensions. Panamic animals have their northern limits at or south of Pt. Conception, but range materially south of Cedros Island. Animals known to occur in several provinces are rated as cosmopolitan, tropicopolitan, etc.
The Panamic area so defined is then the subject of this bibliography, and, as illustrated by the Gulf of California as a typical and fairly virginal collecting ground representing its north extension, the subject also of the phyletic catalogue and of the book proper. A previous account, Ricketts and Calvin 1939, has been concerned with the common littoral animals of the temperate province, there considered to extend from Sitka to San Quentin Bay. The overlap animals are treated biblio graphically in both books. There are references herein to apropos parts of Between Pacific Tides, and cross references are considered desirable there, and are projected for possible future editions.
III
ALTHOUGH our purpose was, primarily, to get an understanding of the region as a whole, and to achieve a toto-picture of the animals in relation to it and to each other, rather than to amass a great collection of specimens, we nevertheless procured more than 550 different species in the pursuit of this objective, and almost 10% of these will prove to have been undescribed at the time of capture. And we merely scratched the surface.
Even this comprises a considerable amount of material. It would have been best—since a more or less intuitive feeling of familiarity with the bulk of the animals in their surroundings was a desideratum—if we could have kept track of every one of these. But the whole elaborate process detailed here, of which collecting and final write-up are merely first and last steps, comprises a labyrinth in which even the finest memory may falter. Hence, right at the start we deliberately restricted our attention to the obviously common forms, while still in the field. In this way we shall probably have missed most of the obscure, minute, or subtly differentiated species, even where common. And conversely we shall have remarked any spectacular animals we may have found, however rare.
Any random group of collected materials will consist 95 to 99% of common items, with a sprinkling of rarities, and there is no way of determining at the time of collection whether a given form is rare or common. There it is. It may never have been seen before. It may never be found again. But there, at that time, it looks ordinary enough. This difficulty can never be surmounted in a short survey. All one can do is to operate on the assumption that the bulk of the total number seen will be prevalent and characteristic forms. Human nature being what it is, the big plum-blue starfish at Puerto Escondido is far more likely to stand out in one’s mind, even though it may turn out to be one of the three known examples of its type on record, than the nondescript sponges which cover the rocks at every suitable location.
The plan of procedure followed these lines: After the preliminary field discrimination, we tried to differentiate our species, loosely at least, until a decently correct name could be found by which to handle them, to list them in the collecting report for the day, noting their position and abundance, and to follow this information through the specialist’s determination. Then, having a definitive name, to search out the original description of the animal, if important and accessible, and to trace its history through the literature so as to determine where it may have been found, by whom, and under what circumstances. In fact, generally to become famil
iar with the separate species, even in the field with its multitude of diverse individuals, without at the same time losing sight of the whole picture.
The achievement of this objective was fortunately not impossible, thanks to a unique and very favorable set-up. Most expeditions have been so large that there could be no summing up for many years, if at all. Or, at best, the report was merely a rehash of field notes, with determinations which were almost wholly tentative, or written by experts who had had only secondary contact with the actual field work. In our case, everything from the original planning to the final write-up was closely co-ordinated. One or the other of us has been able to keep a finger on the pulse of the whole situation, having had a hand in the direction of the trip; in the collecting, anesthetizing, and preserving of the specimens; in the recording of field notes; in the sorting, labeling, and packaging of the material, with the later examining, departmentalizing, and re-labeling attendant upon our retaining duplicates and records of examples dispatched to specialists; through the subsequent allocation of final names to the withheld specimens, through the bibliographic research, and finally in erecting an accurate conceptual and verbal structure of the published report. And all this, through intense concentration and directionalism, has fortunately been accomplished in less than two years, before the original freshness shall have dimmed.
Although more than 500 species have been determined, the work is still far from complete. Scarcely any information is available on the anemones and little more on the Alcyonaria. These two important groups have been omitted in the phyletic catalogue and bibliography which follow. Only a fraction of the fishes have been determined, and the information on flatworms and naked opisthobranchs is incomplete.
But despite incompleteness, some generalizations emerge. Now it can be affirmed positively that, except for a few scattered exceptions, such as sponges and tunicates, the color of the Gulf littoral as a whole is distinctly tropical. With these few exceptions, the entire fauna represents an extreme northerly extension of the Panamic Province. Also, though this may be untrue of certain separate groups, there is little distinctiveness to the fauna of the Gulf. For the Panamic Faunal Province, however, as exemplified by its northerly extension in the Gulf, considerable distinctiveness can be claimed. There are but slight affiliations with animals of the north temperate zones, again excepting the sponges and tunicates, and comparatively few species are identical with those inhabiting the West Indian or Indo-Pacific areas. A good many, however, are tropicopolitan or cosmopolitan. The faunal differences between the northern and southern portions of the Gulf are well marked in most groups. For analytical purposes, we divide the region into two halves by means of a line drawn from Guaymas to Santa Rosalia. Actually, there is evidence that the line should be drawn farther south, and that a quantitative investigation might disclose that this southern fauna ranges south from La Paz and Espiritu Santo Island to Panama and northern Peru. There are even some species which occur only from Cape San Lucas south.
Of the 507 to 520 plus species treated herein, geographic ranges have been compiled for 415, not always completely. 72 seem to be limited to the Gulf. This division ordinarily includes the area contained within a line drawn from Mazatlan to Cape San Lucas but, in some of the group totals, Magdalena Bay has been included. 160 species not reported from north of the Gulf (or in some cases, Magdalena Bay) range only to the south. 42 range northwardly, 68 both north and south. The range to the northward is usually limited by Magdalena Bay or Cedros Island, and rarely extends beyond southern California, although some species may occur at Monterey, and a few extend even to Puget Sound or Alaska. 39 are tropicopolitan or cosmopolitan. 20 are West Indian. Only 14 are Indo-Pacific.
These figures are thought to be fairly significant. They probably reflect a representative cross section of the common littoral species, whereas studies of a single group in this region ordinarily include all species recorded from the area—rare and common, littoral and dredged. They point to a high degree of distinctiveness, not of the Gulf fauna, but of the Panamic fauna as represented by its most northerly extension.
Although only 18 of these common species occur identically in the West Indies and 14 in the Indo-Pacific, this must not be construed as reflecting slight affiliations with these districts. The generic relationships may be very close, many genera being common to both, sometimes to all three areas. And in many cases analogous species are related so closely that only an expert can determine whether a given animal belongs to the West Indian or to the Panamic species. In this connection, the § S-413 remarks are applicable. Conchologists have, in the past, arranged lists to show up to 50 species of mollusks alone, common to the Panamic and West Indies regions, and half that many to the Panamic and Indo-Pacific, but modern differentials have become so delicate that the species in question are now generally considered distinct.
Zoogeographically significant information would accrue from the compiling of percentages to show how large a portion of the Gulf fauna is limited in northward extension by Magdalena Bay, how much by the Pt. San Eugenio complex, how much by Cape San Quentin, and, finally, how much by Pt. Conception. Percentages should be adduced to indicate what proportion of the common littoral species are restricted to the northern, and what to the southern half of the Gulf. We should determine how many of the extra-limital and tropicopolitan species have been able to migrate beyond the zoogeographical barriers which restrict Panamic forms, so as to populate North Temperate or Peruvian waters. All this must await a more favorable opportunity.
A few of the more general observations might be summarized here. Both the sponge affiliations and the tunicate affiliations, curiously, are with more northern (Californian) waters, although each has species in common with the West Indies, and among the sponges, the most spectacular, large, and common forms are West Indian; smaller species are cosmopolitan or southern Californian. The Panamic affiliations of both groups are entirely nil so far as known. There are few shore hydroids; their scarcity, beside the lushness reported from the Galapagos and easily observable in southern California, is all the more remarkable. These few have mostly northern Pacific affiliations, with faint Caribbean and cosmopolitan tinges. So far as can be seen from cursory observation, except for a single Stylatula, there are no Alcyonarian relationships with California or even with southern California. No Renilla are in the collection. There is one fleshy sea-pen, a Ptilosarcus or Leioptilus, but surely not quadrangularis of the north Pacific. A purple pendent gorgonian, a brown fleshy gorgonian, and a sea-fan are all common. Some of the commonest anemones are 2 species of Epizoanthus superficially indistinguishable from West Indian forms. Bunodid anemones similar to the aggregated north Pacific Cribrina are very common, and there are Cerianthus and Harenactis not separable from southern California species in appearance. Corals are very abundant, and it would seem that at Pulmo we have one of the few true reefs reported from the American Pacific. The polyclad fauna is abundant and varied, there are highly colored Cotyleans in the south, and mostly nondescript Leptoplanids in the north. One Nemertean, the Panamic Basiodiscus mexicanus, was widely obtained. Both sipunculids and echiurids are common—commoner on the whole than they are on the California coast, and one species, Physcosoma agassizii, occurs in both areas. Annelids are abundant, varied, and obvious, the tropicopolitan stinging worm Eurythoë being one of the commonest invertebrates of the region. Encrusting Bryozoa are abundant, especially in the north, and the purple Bugula neretina is widespread. A many-rayed starfish, Heliaster, is, with the club urchin Eucidaris, and the cucumber Holothuria lubrica, and several species of ophiurans including the giant Ophiocoma, among the commonest of shore animals. Among the 60 species of Echinoderms, holothurians are most abundant, including some giant creeping forms and a great worm-like synaptid, with 15 species of Echinoids next in importance. Sand flats are paved with huge cake urchins and keyhole urchins. The poisonous Centrechinus mexicanus, fortunately, occurs sparingly. Starfish are ubiquitous and abundant. The acorn barnacle
fauna is varied and abundant, mostly with cosmopolitan, northern, and unique species. 107 species of decapods were taken. Sally Lightfoot is everywhere on high rocks. Sand bugs, Xanthids, Majids, hermits, the large swimming crab Callinectes bellicosus, and many small decapods are abundant, although in its crab fauna the Gulf fulfills the proverbial tropical formula: many species, few individuals per species. Sand flats have hordes of fiddlers and some Ocypode. Spiny lobsters are occasional, the Panamic P. inflatus in the south, the southern Californian P. interruptus in the north. An important shrimp industry involving Penaeus stylirostris centers at Guaymas. Snapping shrimps are very abundant. The sand flats near La Paz constitute one of the few known regions where Dentalium can be taken intertidally. The Pelecypod fauna, with its pearl oysters and edible oysters, its huge Pinna, with its commensal shrimp, Pontonia, its great pearly and ornamented Spondylus and its edible clams, Chione and Macrocallista, is world famous. Among its 40 common species, the garbanzo clam Fossularca, the paper-shell clam, Isogno mon anomonioides, the heavy ribbed Carditamera affinis, and the small mussel, Brachidontes multiformis, the two last especially in the north, are very common. Among the naked Gastropods, a marine pulmonate, Onchidium, is characteristic of the northern part, occurring in overlapping hordes high on the rocky shore. Pleurobranchids and sea-hares are spotty; a large Dolabella may be found. Among other nudibranchs, a highly colored swimming species, with its undulating margins resembling a Cotylean flatworm, occurs commonly in the south. More than 90 species of shelled Gastropods are common enough to have been taken along shore in our short survey. It is to this group, especially in the south, that the Gulf’s more spectacular inhabitants belong. Some of the conches and murices are very large and highly colored. Olives, cones, cowries, limpets, and keyhole limpets are abundant. Pulmonate limpets were taken at several stations. A rather handsome hairy chiton, and the large Chiton virgulatus represent the Amphineura, along with 8 or 10 less common species. Octopi, said to be abundant, we found only occasionally. There is an important Pro-chordate fauna, all three groups being well represented. A huge Balanoglossus covers the sand flats with its castings. Although we collected only a few, Amphioxus confidently can be expected in the sublittoral sand bars. Tunicates are common, mostly compound. Fishes are very noticeable. Several hundred species are known to inhabit these waters, from the swordfish, tuna, and huge manta rays, down to the sardines and to minute Fierasfer living in the cloaca of holothurians. We took more than 40 species without being interested in the group, and while attempting to avoid the temptation of collecting them. Botete, the poison-liver fish, and the puffer Diodon, are common especially in the south. There are important associations of pelagic animals, attracted to the boat especially at night if a light is hung over side. Under these circumstances, assemblages of worms, minute crustaceans, ribbon fish, and snake eels are likely to collect, with occasional squid, Sguilla larvae, etc. Hordes of Pleuroncodes may be swept into the Gulf by currents from the open Pacific. Whales, porpoises, sharks, and great sea turtles are likely to be encountered. On one occasion, although this is outside our scope, we were visited by a great swarm of bats, a quarter of a mile or more offshore.