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SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 200

Variation in the Western Atlantic Clinid Fish Malacoctenus triangulatus with a Revised Key to the Atlantic Species of Malacoctenus

Victor G. Springer
and Martin F. Gomon

SMITHSONIAN INSTITUTION PRESS

City of Washington

1975

A B S T R A C T

Springer, Victor G., and Martin F. Gomon. Variation in the Western Atlantic Clinid Fish Malacoctenus triangulatus with a Revised Key to the Atlantic Species of Malacoctenus. Smithsonian Contributions to Zoology, number 200, 11 pages, 3 figures, 3 tables, 1975.—Malacoctenus triangulatus occurs along the shallow coastlines of the Caribbean Sea, southwestern Gulf of Mexico, southern Florida, Bahama Islands, Fernando de Noronja and Bahia, Brazil. Data on meristic characters and their variation are reported for many populations of M. triangulatus. The species is highly variable but shifts in means for various meristic characters tend to follow a geographic pattern; however, several of the means for the Trinidad and Venezuela populations stand out from those of nearby populations. A key is given to the Atlantic species of Malacoctenus, following Springer (1958), but employing additional characters.

OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution’s annual report, Smithsonian Year. SI PRESS NUMBER 5335. SERIES COVER DESIGN: The coral Montastrea cavernosa (Linnaeus).

Library of Congress Cataloging in Publication Data
Springer, Victor Gruschka, 1928–
Variation in the western Atlantic clinid fish.
(Smithsonian contributions to zoology, no 200)
Supt. of Docs, no.: SI 1.27:200

1. Saddled blenny. 2. Malacoctenus. 3. Marine fishes—Atlantic Ocean. I. Gomon, Martin F., joint author. II. Title. III. Series: Smithsonian Institution. Smithsonian contributions to zoology, no. 200.

QL1.S54 no. 200 [QL638.C63] 591'.08s [597'.58] 74–32385

Contents

Introduction

Methods

Distribution

Results

Discussion

Key to the Atlantic Species of Malacoctenus

Material Examined

Literature Cited

Publication in Smithsonian Contributions to Zoology

Variation in the
Western Atlantic Clinid Fish
Malacoctenus triangulatus with a
Revised Key to the
Atlantic Species of Malacoctenus

Victor G. Springer
and Martin F. Gomon

____________

Victor G. Springer, Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560. Martin F. Gomon, University of Miami, Rosenstiel School of Marine and Atmospheric Sciences, Miami, Florida 33149.

Introduction

Springer (1958)[1] described Malacoctenus triangulatus. He had too few specimens to permit analysis of geographic variation. Since 1958, numerous specimens of M. triangulatus from many localities have become available. Study of these specimens indicates that M. triangulatus is geographically variable. Reporting this variation is desirable, not only because it expands the description of the species, but also because it represents the most comprehensive account detailing meristic variation in a shorefish of the tropical western Atlantic. The description of this variation can serve as a basis for comparison with other, similarly distributed species.

Early in our study we believed that we were dealing with a complex of related, allopatric species, but as analysis of our data progressed, the differences separating the supposed species decreased. It may well be that other presently recognized, closely related, allopatric species of tropical western Atlantic shorefishes may be synonymized when more complete geographic representation of the species is available.

INSTITUTIONAL ABBREVIATIONS.—The following abbreviations denote the institutions that furnished the additional material for the present study: AMNH=American Museum of Natural History, New York City; ANSP=Academy of Natural Sciences of Philadelphia; FAU=Florida Atlantic University, Boca Raton; FMNH=Field Museum of Natural History, Chicago; FSM=Florida State Museum, Gainesville; GCRL=Gulf Coast Research Laboratory, Ocean Springs, Mississippi; LACM=Los Angeles County Museum of Natural History; UMML=Rosenstiel School of Marine and Atmospheric Sciences, University of Miami; USNM=National Museum of Natural History (formerly in United States National Museum), Smithsonian Institution.

ACKNOWLEDGMENTS.—For the loan or gift of specimens we extend our appreciation to C. L. Smith (AMNH), J. E. Böhlke (ANSP), W. R. Courtenay, Jr. (FAU), C. R. Gilbert (FSM), D. W. Greenfield (Northern Illinois University), C. E. Dawson (GCRL), R. J. Lavenberg (LACM), C R. Robins (UMML), and F. Cervigon (Universidad de Oriente, Porlamar, Venezuela).

A. George, University of Maryland, assisted in the recording of data; F. J. McKinney and E. N. Gramblin (USNM) made many of the radiographs.

The manuscript benefited from critical reviews by J. E. Böhlke, C. R. Robins, and W. R. Smith-Vaniz, and from discussions with B. B. Collette, T. H. Fraser, and R. H. Gibbs, Jr. Some of these colleagues disagreed with certain of the speculations that appear in the text. The senior author takes full responsibility for all subjective matter that this study includes.

Methods

Fin-ray and scale counts based on specimens reported by Springer (1958) are incorporated with those taken from the new material (see “Material Examined”). Fin-ray and vertebral counts on the new material were taken from radiographs. Fin-rays were counted following the methods of Springer (1958) with the following exception: wherever a dorsal- or anal-fin pterygiophore appeared without a corresponding fin ray, the ray was counted as being present. Such “blank” pterygiophores occurred in only 11 of the approximately 500 specimens examined by radiograph. We do not believe, therefore, that combining Springer’s original counts, from approximately 150 specimens, with the new counts has affected the averages or our conclusions based on them.

Only caudal vertebrae are reported; the first caudal vertebra is the anteriormost vertebra bearing a hemal spine. There are consistently 10 precaudal vertebrae in M. triangulatus.

Cirri counts include the number of free cirri tips (the cirri are normally simple, but where branched each branch was counted). The number of cirri increases slightly with size but appears to stabilize at about 30 mm SL. For this reason we include counts of only those specimens 30 mm SL or larger.

In Tables 1–3 and Figure 2 the localities were arranged in a geographic sequence intended to reflect the essentially circular configuration of the coastline where M. triangulatus occurs. We began with Florida and the Bahamas in the north, progressed south, then east, south, west (along northern South America) and, finally, north along the Central American coast. Fernando de Noronja and Bahia, Brazil, followed at the end. Because of the coastline’s circularity we could have begun the sequence of localities with almost any locality. No arrangement was completely satisfactory in reflecting the trends of the means. Plotting the means for the various characters on maps (which we did) has some advantages that are helpful in interpreting the data, but also has disadvantages in presenting the data in publication. We have also presented the means of several characters graphically (Figure 2). This method enables one to compare at a glance how several characters correlate, and also how the means shift for each character.

Distribution

Malacoctenus triangulatus occurs in the clear, shallow (to about 10 meters), tropical-subtropical waters of the western Atlantic from the northern Bahamas south to Bahia, Brazil (Figure 1). Rocks and corals are almost always, if not always, a dominant feature of its habitat. The absences of the species on the northern coast of South America between Trinidad and Fernando de Noronja and from all but the southwestern portion of the Gulf of Mexico are undoubtedly real and probably result from a lack of suitable habitat in these areas. Many of the reef-fish species of the Caribbean region are also absent from these same areas. The apparent absence of M. triangulatus from other long expanses of Caribbean coast (for instance, between Cubagua, Venezuela, and Santa Marta, Columbia; from western Cuba to eastern Hispaniola) probably indicates lack of collecting.

There is little known about the life history of M. triangulatus that might contribute toward an understanding of its distribution, for instance, whether it has pelagic stages during its life history. Even if it does not, the adults might be wafted. If the species owes its distribution to the prevailing ocean currents, it probably entered the Caribbean from the Brazilian coast and spread west and northward. Fernando de Noronja lies in the path of the South Equatorial Current, which flows east to west. This current splits at the eastern hump of South America and sends branches flowing both south along the Brazilian coast and northwest into the Caribbean. Currents in the Caribbean generally flow westward from the Lesser Antillean chain. A gyre forms along the Panamanian coast, but the major flow passes north through the Yucatan channel and continues both northwestward into the Gulf of Mexico and northeastward through the Straits of Florida and up the coast of Florida (the Gulf Stream). There is also a prevailing northwestward flowing current, extending from the northern Lesser Antilles, that skirts the eastern coasts of the Bahama Islands. In this scheme there would be little chance for the northern populations to furnish colonizers to the south.

FIGURE 1.—Distribution of Malacoctenus triangulatus based on specimens examined.

Malacoctenus triangulatus, however, may have had a more continuous distribution along the northeastern coast of South America in past geologic periods. If so the Fernando de Noronja and Brazilian populations would represent relict populations. There is some divergence, particularly in color pattern, exhibited by both of these southernmost populations, and one or both may be expected to speciate ultimately. If, however, the prevailing currents do carry introductions of M. triangulates from these southern populations into the Caribbean, complete differentiation of the southern populations, as distinct from the northern populations, may never transpire.

Results

Our findings can, for the most part, be derived by examination of Tables 1–3 and Figure 2, where the shifts and trends of the means for meristic characters are readily observable. The Trinidad and Venezuelan populations stand out for their high numbers of dorsal-fin spines, total dorsal-fin elements and caudal vertebrae, and relatively high numbers of nape cirri. These two populations misled us initially into believing that we were working with a complex of species. However, it can be noted that there is a slight trend toward higher mean numbers of the same meristic characters in the northern populations—particularly those of Barbados and Tobago, and to a much lesser degree, Grenada—that are nearest to Trinidad and Venezuela.

TABLE 1.—Frequency distributions for certain meristic characters of Malacoctenus triangulates

TABLE 2.—Frequency distributions for certain meristic characters of Malacoctenus triangulates

TABLE 3.—Total number of nape cirri (both sides) in specimens, 30 mm SL and larger, of Malacoctenus triangulates

Aside from the Trinidad and Venezuelan populations, the means, except for nape cirri, tend to be highest in the northernmost, lower in the north-westernmost, and lowest in the eastern (Lesser. Antilles) populations.

The means for the Fernando de Noronja and Bahia populations are not close for most characters, and there is no overlap in the ranges for lateral-line scales between these two populations. In no character, however, do these two populations stand out from the Caribbean populations.

Springer (1958) reported meristic variation in dorsal- and anal-fin rays in the Caribbean populations of Labrisomus nuchipinnis and Malacoctenus gilli. The shifts in averages for the various populations of these two species show little relationship to each other or to those of M. triangulatus. A re evaluation of variation in L. nuchipinnis and M. gilli, based on the greater amount of material now available, perhaps would provide a more meaningful basis for comparison with M. triangulatus.

COLOR PATTERN OF PRESERVED SPECIMENS.—Although there is much variation in color pattern within all populations of M. triangulatus, some populations exhibit differences in pigmentation that are shared by many or most individuals of the same population. For example, sexual dichromatism is usually marked in specimens from the northern and western portions of the species’ range (Florida south to northern Lesser Antilles; Central America). Males possess rather uniformly dark, triangular saddle markings on the body, which often have irregularly intensified anterior and posterior margins. The marginal intensifications may be present as poorly defined spots, which are never a prominent feature of the color pattern. In females (Figure 3a) the saddle markings may be less prominent and less well defined than in males, and often enclose small irregular, pale marks, which are rarely present in males. Marginal intensifications of the saddles are usually even less obvious in females than males. Both sexes usually possess indications of dusky to dark areas in the pale spaces between the ventral ends of the saddles, but dark markings more dorsally in the interspaces occur more often in females. Males often lack dark spots posteriorly in the dorsal, anal, and caudal fins, but when the spots are present they are usually not as well developed as they are in females. An obvious dark mark on the body at the base of the anterior dorsal-fin spines that extends onto the fin basally is usually present in all specimens but may be more prominent in females than in males. The ventrolateral sides of the head in both sexes are usually pale with few prominent markings, and transverse bands beneath the head, when present, are approximately uniform in width and dusky.

FIGURE 2.—Graphs of means for certain meristic characters in populations of Malacoctenus triangulatus based on information in Tables 1–3. (Stars represent counts for single specimens.)

FIGURE 3.—Malacoctenus triangulatus, females; a, ANSP 74341, 43.3 mm SL, Hog Island (vicinity of New Providence), Bahamas; b, USNM 198134, 53.4 mm SL, Chupara Pt., Trinidad (innermost pelvic-fin ray not visible externally); c, GCRL 1576, 36.1 mm SL, Bahia, Brazil. (Drawn by J. R. Schroeder.)

There appears to be a change, perhaps gradual, from the northern type color pattern to another type that is found in the Lesser Antilles as far south as Trinidad and Venezuela. In specimens from Grenada, Trinidad, and Venezuela, for instance, sexual dichromatism, although present, is not always as obvious as in the more northern specimens, but is manifested by a generally darker overall coloration of males. Females (Figure 3b) have a much paler background color and, consequently, appear to have a more contrasting saddle pattern. The dark marginal spots of the saddles of females are more obvious than are those of males, and females have considerable numbers of irregular, dark spots along the ventral portion of the body, which are reduced or absent in males. Females often have darkly spotted, narrow, transverse bands on the underside of the head, which are faint and diffuse, at best, in males. The dorsal fin of females is marked with continuations of the body saddles basally along its anterior half, and the base of the fin is mostly free of pigment posteriorly. The dorsal fin of males is almost without pigment anteriorly and exhibits a diagonal banding posteriorly. Conversely, females possess banded anal and caudal fins, whereas those of males are overall dusky, although the caudal of males may be faintly banded. The dark mark anteriorly on the base of the dorsal fin is present in many of the Grenada specimens but is much less developed or absent in the Trinidad and Venezuelan specimens. Some females we have seen from Florida are indistinguishable from the southern females, but we have not found similar overlap with males from the two areas.

The body color pattern of both sexes from Fernando de Noronja approaches that of males from the northern areas, but the intensified spots on the margins of the body saddles are, in contrast, prominent. In addition, the intensified dark blotches between the ventral tips of the body saddles, together with the tips of the saddles, form a distinct horizontal row of large, irregular spots. There is little or no development of the dark mark anteriorly at the base of the dorsal fin. The anal fin is transparent to dusky. The underside of the head is traversed by several rows of small, dark spots or narrow, faint to dark lines. Males have no spots, or only faint spots, in the dorsal fin, whereas all females have prominent spots in this fin.

In specimens from Bahia, Brazil, sexual dichromatism appears as a reverse bicoloration or intensification of pigment on the dorsal and ventral halves of the body: males are darkest ventrally and females (Figure 3c) dorsally. Although the dorsal one-third of the body is usually darker than the ventral two-thirds in all populations of M. triangulatus, this intensification appears to be slightly more evident in females from Bahia. The body saddles stand out less in the Bahia specimens due to the complex dark, irregular spotting within the saddles and in the pale spaces between the saddles, particularly on the ventral half of the body. Spotting is less distinct and fainter on males despite the ventral intensification. Fine, dark spots anteriorly on the dorsal fin and banding posteriorly on the dorsal and anal fins are better developed in females than males. Both sexes have only faint development of the dark mark anteriorly on the dorsal fin. The ventral half of the head is often traversed by narrow, dark bands in females, whereas that of males is faintly marked at best.

Discussion

We are unable to explain fully the variation we note among the populations of M. triangulatus. Most probably the variations are the result of the varying degrees of reproductive isolation exhibited by the populations as influenced by complex ecological factors: temperature, light, water currents, physiography. Hence consistent trends in meristic characters should not be expected.

Often in fishes, high vertebral, scale and vertical fin-ray counts are correlated with the higher or lower latitudes as one progresses away from the equator (Barlow, 1961, gives an illuminating review of this subject). These correlations are also a reflection, but not necessarily a result, of decreasing average annual water temperatures. The generally high means for meristic characters of the northernmost populations of M. triangulatus conform with the temperature-mean relationship, but the appearance of the highest means for some characters in the Trinidad and Venezuelan populations, where water temperatures average higher than at the northern limits of the species’ distribution (Bahamas), and the low means of the population at Bahia, Brazil, where water temperatures are similar to those of the northernmost populations, do not.[2]

The fairly good correlation between high numbers of nape cirri and low numbers of lateral-line scales in the various populations is readily apparent on Figure 2. Inasmuch as both cirri and lateral-line scales have sensory functions,[3] one could infer that the species is compensating for reduction in one structure by increase in the other. We have no information that would permit expanding on this intriguing idea.

Springer (1958) reported that the prepectoral area of M. triangulatus was scaled, with rare exceptions, and that there was at least one scale in the midline before the first dorsal-fin spine. We now find these characters to be more variable than Springer reported. The absence or degree of scaling in the prepectoral and predorsal areas is quite variable within a population and can only be used with qualification as key characters. Several colleagues have mentioned to us difficulties in identifying specimens of M. triangulatus using Springer’s earlier key, which employed scalation. We, therefore, present a new key to the Atlantic species of Malacoctenus, which takes advantage of several characters not employed in the earlier key.

Key to the Atlantic Species of Malacoctenus

(Couplets 4–8 refer only to specimens 25 mm SL or larger)

Material Examined

(for additional material incorported in this study, see Malacoctenus triangulatus in Springer, 1958)

FLORIDA: Broward County, FAU 71–21 (2), 71–22 (7), 71–63 (18), 72–19(1);Monroe County, USNM 186168 (1). BAHAMAS: Green Turtle Cay, UMML 5845 (5), 6508 (10); Bimini, UMML 10035 (3); Eleuthera, ANSP 100731 (5), 111904 (5); Andros: Pigeon Cays, UMML 1601 (12); Mastic Cay, ANSP 100730 (6); Cay Sal Bank, ANSP 100733 (2); Great Inagua, AMNH 21372 (5), 27193 (8); Little Inagua, AMNH 21297 (24), 21324 (6), 27663 (8). MISTERIOSA BANK: USNM 198599 (1). GRAND CAYMAN: FSM 10744 (25). JAMAICA: LACM 6383 (1), 6384 (1), 6385 (4). PUERTO RICO: ANSP 118488 (1), LACM 6721–15 (1). ST. THOMAS: LACM 7789 (5). ANGUILLA: ANSP 114362 (1). ST. BARTHELEMY: ANSP 127052 (2), 127057 (4), 127131 (12), 127574 (1), 127595 (1). ANTIGUA: ANSP 127597 (22). DOMINICA: USNM 198281 (6), 198282 (9), 201022 (1), 205074 (1), 212023 (1). MARTINIQUE: ANSP 112972 (2), 113003 (2). ST. LUCIA: ANSP 127057 (2), 127095 (1), 127116 (9), 127130 (27). BEQUIA: ANSP 124601 (1), 126958 (1). LITTLE ST. VINCENT: ANSP 114329 (1), 127092 (1), 127098 (1). GRENADA: ANSP 113241 (5), 114381 (3), 124599 (5), 127053 (1), 127129 (8). TOBAGO: ANSP 102189 (6), 102191 (10), 102193 (1), 102196 (3), 102197 (1), 102199 (2). TRINIDAD: USNM 198134 (22), 199159 (4). VENEZUELA: Charagato (Cubagua), USNM 212241 (6), 212242 (2), 212244 (8); Laguna Grande, USNM 212243 (2). COLOMBIA: Santa Marta, USNM 212108 (1). PANAMA: vicinity of Colon, GCRL V69:3153 (1), V69:3486 (1), V69:S488 (1), V72:9183 (6), V72:9795 (1), V72:9866 (1); San Bias Islands, GCRL V73:11O73 (1), V73:11152 (2). ALBUQUERQUE CAY: UMML 23327 (1). COURTOWN CAY: UMML 23364 (13), 24023 (1). BELIZE (British Honduras): FMNH 78689 (1), 78690 (10), 78691 (1), 78692 (1), 78693 (15), 78694 (16), UMML 9472 (3), 9543 (2), 9824 (9), 10314 (2). YUCATAN: Banco Chinchorro, UMML 9368 (1), 9754 (1), 9770 (1). FERNANDO DE NORONJA: USNM 212024 (77). BRAZIL: Bahia, GCRL 1576 (17), 1579 (2).

While this study was in press, additional specimens representing northern range extensions of M. triangulatus came to our attention: Florida Department of Natural Resources Marine Laboratory 4304 (2) and 4305 (16), St. Lucie Inlet, Martin County, Florida. We were also informed of specimens from Indian River County, Florida, at FSM.

Literature Cited

Barlow, G. W.

1961. Causes and Significance of Morphological Variation in Fishes. Systematic Zoology, 10(3): 105–117.

Ford, R. F.

1959. A Study of the Major Classification of Blennioid Fishes Based upon Cranial Nerve Evidence. 51 pages. MA Thesis, Stanford University.

Springer, V. G.

1958. Systcmatics and Zoogeography of the Clinid Fishes of the Subtribe Labrisomini. Publications of the Institute of Marine Science, University of Texas, 5:417–492.

Sverdrup, H. U., M. W. Johnson, and R. H. Fleming

1942. The Oceans, x + 1087 pages, 7 charts. Prentice-Hall, Inc.

____________

[1] The date of publication on the serial is December 1958, but the journal was not actually mailed until sometime in June 1959.

[2] Average surface water temperatures were inferred from data presented in U. S. Naval Oceanographic Publication 700 and Charts II and III in Sverdrup, Johnson and Fleming (1942).

[3] Ford (1959) reported that the cirri of Malacoctenus hubbsi are variously supplied by branches of the fifth, seventh, and tenth cranial nerves. On the basis of Ford’s findings, a sensory function for these cirri can be inferred.

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