Breeding Patterns of Three Species of Caribbean Brittle Stars (Echinodermata: Ophiuroidea)

BULLETIN OF MARINE SCIENCE. 33(2): 363-372,1983 CORAL REEF PAPER

BREEDING PATTERNS OF THREE SPECIES OF CARIBBEAN BRITTLE STARS (ECHINODERMATA: OPHIUROIDEA)

Philip V Mladenov

ABSTRACT Reproductive periodicity of three species of brittle stars at Barbados, W.I. was studied for one year using a gonad index technique. Ophiothrix oerstedi has a synchronous annual reproductive cycle with a breeding season that extended from mid-July until early December. Ophiothrix suensoni reproduces continuously, but individual reproductive cycles are asynchronous and there was higher spawning activity in the late summer and early fall. Ophiocoma echinata has an asynchronous annual reproductive cycle with a prolonged breeding season. Males of O. oersledi and O. suensoni have significantly larger gonads than females at certain times during the breeding season; a large volume of spermatozoa may be required to com- pensate for sperm wastage during spawnings. Detailed information is presently available for reproductive periodicity of 19 species of tropical brittle stars. Contrary to earlier suggestions, prolonged breeding seasons and continuous reproduction are common in tropical brittle stars.

Brittle stars are an abundant and diverse component of invertebrate faunas associated with coral reefs, coral rubble and soft sediments of the tropics (Glynn, 1973; Bray, 1975; Clark, 1976; Singletary, 1980; Sloan, 1982). Until recently, inferences concerning reproductive periodicity of tropical brittle star species were based mainly on sporadic, qualitative observations made by Mortensen (1921; 1931; 1937; 1938) of gonad ripeness and laboratory spawnings. Stephenson (1934) was the first investigator to study the reproductive cycle of a tropical brittle star throughout a I-year period. Summarizing Mortensen's data, Boolootian (1966) concluded that tropical ophiuroids have a breeding season of only I to 2 months duration and are generally spring and summer spawners. In recent years, the reproductive cycles of 16 species of tropical brittle stars have been studied for a period of at least I year using various quantitative gonad index techniques (Hen- dler, 1973; 1979; Stancyk, 1974; Singletary, 1980). These studies show that some tropical brittle star species have lengthy breeding seasons of at least 4 months duration, while some species reproduce continuously throughout the year. In this paper, in an effort to supplement our present understanding of breeding patterns of tropical brittle stars, I present information on reproductive periodicity of three species of Caribbean brittle stars, Ophiothrix (Ophiothrix) oerstedi Ltitken, Ophiothrix (Acanthophiothrix) suensoni Ltitken, and Ophiocoma echinala (La- marck) studied at Barbados, West Indies. The reproductive cycle of the first two species has not previously been studied, whereas the reproductive cycles of several populations of O. echinata from the Atlantic coast of Panama have been studied by Hendler (1979). All three species treated in this study are widely distributed in Caribbean waters (Clark, 1933; Parslow and Clark, 1963). O. oerstedi, a member of the family Ophiothricidae, ranges from southern Florida southwards to Trinidad and the north coast of South America at depths from 0.5 m to 400 m. Both O. suensoni, also of the family Ophiothricidae, and O. echinala, which belongs to the family Ophiocomidae, range from Bermuda southwards to Brazil but have not been reported on the United States coast north of Florida; the bathymetric range of the former is 2 to 525 m, while the latter is found in water less than 5 m deep. O. oerstedi may attain a disc diameter of more than 14 mm, but adults are generally

363 364 BULLETIN OF MAR[NE SCIENCE, VOL. 33, NO.2, [983 less than about 10 mm in disc diameter; very large specimens of 0, suensoni can have a disc diameter of nearly 20 mm, although the disc diameter of adults is usually less than 12 mm; 0, echinata is a large brittle star with a disc diameter that may exceed 30 mm, but typical adults are less than 25 mm in disc diameter (Clark, 1933; Mladenov, 1976),

MATERIALS AND METHODS

Approximately 20 adult individuals of each of the three species were collected on a regular basis from June 1975 to May 1976. The mean size of specimens sampled was 8.0 mm ± 1.1 mm (n = 305), 7,6 mm ± 1.7 mm (n = 314) and 18,7 mm ± 2.6 mm (n = 215) for Ophiothrix oerstedi, Ophiothrix suensoni and Ophiocoma echinata respectively. Animals with broken or regenerating arms were never collected. Sampling frequency for each species depended upon the observed state of reproductive activity at a particular time of the year; ifgonad size was changing rapidly, then collections were made at least twice monthly; when reproductive activity was low, collections were made only monthly until evidence of increased reproductive activity was noted. Ophiothrix oerstedi was collected by snorkeling from depths of 3 to 10m from a portion of the fringing reef just offshore from the Bellairs Research Institute of McGill University, which is located midway along the west coast of Barbados, West Indies (13°11'N, 59°38'W). O. oerstedi is particularly common within the interstices of the finger-coral Porites porites. Small chunks of P. porites were separated from a larger bed of this coral and returned to the laboratory in plastic buckets. Here the coral was broken into fragments and the brittle stars gently removed. Ophiothrix suensoni was collected by S.C.U.B.A. from depths of 15 to 25 m at a site on the offshore banking reef (which parallels the west coast of Barbados) approximately 1 km south of the Bellairs Research Institute. O. suensoni is epizoic on a variety of sponges, most notably Cal/yspongia spp., Xestospongia spp. and Verongia spp. During each collection, several sponges were placed in buckets and returned to the laboratory where the brittle stars were carefully removed from the sponge surface. Ophiocoma echinata was collected at low tide at depths of less than 1 m at a site on the southwest coast of Barbados known as Grave's End (13°4'N, 59°36'W). Specimens obtained by overturning coral rubble were transported to. the laboratory in insulated containers. All specimens were processed on the day of collection. The animals were first killed by a 2-min immersion in freshwater, and then transferred to a 10% formalin in seawater solution for 24 h. Killing in freshwater prevented arm autotomy, while the period in formalin hardened the gonadal tissue slightly, making its removal easier. The aboral covering of the disc of each specimen was removed to expose the gonads. The sex was noted, and all of the gonads were carefully removed from the disc with fine forceps and placed in a pre-weighed aluminum pan. The arms and disc remains were placed in another pre-weighed pan. The tissues were dried to constant weight at 75° to 80°C (2-3 days), cooled for 2 h in a desiccator (to minimize the amount of atmospheric moisture absorbed by the tissues during cooling), and then weighed to the nearest 10-5 g. Empty pans were pre-weighed following identical drying and cooling procedures. The gonad index (GI) was defined as:

GI = dry wt of gonads x 100 total dry wt of organism (including gonad weight) Gonad indices for each species at each sampling date were plotted as frequency distributions and a mean index value calculated. All three species are dioecious and male and female data were plotted separately and the mean index values of the two sexes at each sampling date tested for statistical conformity using Wilcoxon's signed-ranks non-parametric test (P = 0.025, two-tailed) (Sokal and Rohlf, 1969). Microscopic examination of smears made from the preserved gonads of selected specimens of all three species was carried out on most sampling dates, prior to gonad index calculations, in order to compare gonadal development with gonad index values. The gonadal tissue of the smears was returned to the appropriate pan before drying and weighing took place. In addition, testis smears were made from fresh tissue obtained from approximately five adult males of each species collected at roughly monthly intervals throughout the sampling period and examined microscopically for the presence or absence of active spermatozoa. Information obtained from gonad indices and gonad smears was supplemented, whenever possible, with records of spawnings occurring in the laboratory. In order to induce laboratory spawnings, individuals of all three species were held in finger bowls following the procedure described in Mladenov (1979). This method was routinely successful in inducing spawning only for Ophiothrix oerstedi. MLADENOV: BREEDING PATTERNS OF CARIBBEAN BRITTLE STARS 365

RESULTS Ophiothrix oerstedi The mean gonad indices attained their highest values of the sampling period in July, reaching 5.8 for males and 4.6 for females (Fig. 1). The mean indices for both sexes then declined gradually, with some fluctuations, throughout the interval from August until mid-December, indicating a gradual reduction in gonad size over this time, and thus a prolonged period of spawning. From mid-December until February, the mean gonad indices remained at a very low value and the population was reproductively inactive. In March the gonad index of some mem- bers of the population was increasing; by early May the gonad index of most individuals was increasing, suggesting that gametogenesis and gamete accumu- lation were well underway by this time. The preserved gonads of all individuals examined microscopically during the mid-December to February resting phase of the reproductive cycle were very small and lacked spermatozoa or contained only small (less than 30 /.tm in diameter) oocytes. From March to June gonads were larger but still lacked spermatozoa or oocytes larger than 150 /.tm in diameter. Microscopic observation of preserved gonads from specimens sampled during the period from mid-July to early December revealed that the gonads always contained large (greater than 200 /.tm in diameter) oocytes or a mass of tailed sperm, although the relative size of the gonads often varied distinctly from one individual to the next. The large range of gonad index values obtained during this period (Fig. 1) is thus an indication of relative differences in gonad size between ripe individuals and not asynchrony in the yearly reproductive cycle of individuals. Testis smears made from fresh material showed that active spermatozoa were present in all males sampled from mid-July until early December. Furthermore, specimens of O. oerstedi maintained in the laboratory began to spawn on 1August 1975 and continued to spawn on a regular basis until 2 December 1975 (Table 1). These results show that O. oerstedi at Barbados has an annual reproductive cycle with a prolonged breeding season that, in 1975, extended from about mid- July until early December. Individuals within the population were in reproductive synchrony throughout the year. In other words, the majority of the population was reproductively inactive, undergoing gametogenesis, or ripe and able to spawn at the same time. On many occasions during the breeding season, specimens were found with gonads in one or two interradii disproportionately smaller than the gonads in remaining interradii. Size differences between gonads within a single interradius were never noted. During the breeding season the mean gonad index for males and females differed significantly for samples collected on 18 August and 10 September (Fig. 1). Males thus had larger gonads than females towards the beginning of the breeding season. On the other hand, the mean gonad index for females was significantly higher than males throughout the period oflow gametogenic activity from mid-December to March (Fig. 1).

Ophiothrix suensoni The mean gonad indices for both males and females remained at a compara- tively low level throughout the sampling period with little seasonal fluctuation (Fig. 2). Most mean gonad indices were slightly higher during the summer and 366 BULLETIN OF MARINE SCIENCE, VOL. 33, NO.2, 1983

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Table 1. Summary of laboratory spawnings of Ophiolhrix oerstedi

Date Time (local) I August 1975 Evening 4 1545 h 5 Late morning or early afternoon 11 Evening 14 2415 h 15 Between 2200 hand 2300 h 18 Between 1800 hand 1930 h 21 2015 h and between 2230 hand 0015 h 11 September 0930 hand 2130 h 12 Evening 17 1220 21 ? 22 1600 h 26 ? 2 October Between 2200 hand 0200 h 4 1610 h 8 0700 hand 1330 h 9 1900 h 13 2030 h 23 2100 h 5 November ? 8 2200 h 9 0600 h 10 ? 17 1920 h 21 0600 h 26 0600 h 27 2200 h 29 0730 h 2 December 0600 h

early fall than at other times of the year and peak values of 2.9 and 2.3 were obtained for males and females respectively at the end of July. The mean gonad indices were very low on 4 November (0.65 for males and 0.47 for females), 19 December (0.54 for males and 0.46 for females), and 23 February (0.59 for males and 0.31 for females), but there were periods of higher reproductive activity between these dates. The frequency distributions (Fig. 2) indicate that on all sampling dates a majority of the population had low gonad index values, and only a few individuals had high values. Microscopic observation showed that specimens with low gonad indices had either small ovaries containing small (less than 30 ~m in diameter) oocytes or small testes completely devoid of spermatozoa. However, those individuals with high gonad indices possessed either large ovaries packed with large (greater than 100 ~m in diameter) orange oocytes or large white testes filled with spermatozoa. Testis smears made from fresh material revealed that some males with active spermatozoa could be found throughout the sampling period. These observations suggest that O. suensoni at Barbados reproduces continuously, with higher overall gametogenic activity in the summer and fall. Within the population, reproduction is asynchronous, with individuals at various stages of the gametogenic cycle at anyone time. The mean gonad index for males and females differed significantly for samples 368 BULLETIN OF MARINE SCIENCE, VOL. 33, NO.2, 1983

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collected on 2 February, 18 March, 12 April and 10 May (Fig. 2). It appears that males had larger gonads than females during winter and spring.

Ophiocoma echinata Mean gonad indices for O. echinata were generally low throughout the year (Fig. 3). Values were lowest, however, in late fall and early winter and higher during the period from March to late September. The frequency distributions show that, during the latter period, individual gonad index values were spread over a large range. Microscopic observations of preserved gonads made over this interval showed that those specimens with high gonad indices possessed either large white testes filled with spermatozoa or large dark-red ovaries filled with large (greater than 70 /lm in diameter) reddish oocytes; those individuals with intermediate gonad indices had moderately sized white testes containing small amounts of spermatozoa, or moderately sized ovaries containing both white and red oocytes of various diameters; those with low gonad indices had very tiny gonads and were difficult to sex. Testis smears made from fresh material showed that throughout the year, with the exception of the period from late October to early February, some males could always be found with active tailed spermatozoa. O. echinata at Barbados has an annual breeding pattern with a prolonged breeding season that extended throughout the spring, summer and early fall. During the breeding season reproduction among individuals is asynchronous, and animals in various phases of the gametogenic cycle are found in the population. Only during the late fall did the population become synchronously unripe. At no time during the year were the mean gonad indices for males and females significantly different.

DISCUSSION The three brittle star species treated in this study display three different breeding patterns at Barbados, W.I. Ophiothrix oerstedi has an annual breeding cycle with a relatively long breeding season and with individual reproductive cycles in close synchrony throughout the year. Ophiothrix suensoni reproduces continuously, but individual reproductive cycles are asynchronous. Ophiocoma echinata has an annual breeding cycle with a prolonged breeding season, but individual reproductive cycles are asynchronous during the breeding season. There are no published data on reproductive periodicity for O. oerstedi and O. suensoni in other parts of the Caribbean. However, individuals of both these species collected from the north coast of Jamaica spawned on several occasions at the Discovery Bay Marine Laboratory in July 1981 and July 1982 (Mladenov, unpublished observations). The spawnings of O. oerstedi at Jamaica thus began somewhat earlier than what occurred at Barbados in 1975. It is not presently known if O. suensoni reproduces continuously at Jamaica. Spawning of O. echinata was observed in July at both Bermuda (Mortensen, 1931) and Jamaica (Grave, 1898). Hendler (1979) found that several populations of O. echinata from the Atlantic coast of Panama attained peak gonad index values in September 1974, with a major spawning period in September to November. The breeding season of these populations was thus considerably shorter than that of O. echinata at Barbados in 1975-76. Hendler (1979) did find, however, that one intertidal population of O. echinata at Panama showed evidence of spawning in January and April 1975, as well as during September to November. Thus, some intertidal populations at Panama do have a relatively prolonged breeding season. 370 BULLETIN OF MARINE SCIENCE, VOL. 33, NO.2, 1983

It was noted that gonad size often varies between interradii within specimens of Ophiothrix oerstedi during the breeding season. This suggests that this particular species can release gametes from the gonads of just one or two interradii during a spawning. Indeed, specimens of O. oerstedi were frequently observed to release gametes from the bursae of only one or two interradii during spawning in the laboratory (Mladenov, 1979). Individuals of this species probably spawn repeat- edly during the breeding season, releasing only a portion of their store of ripe gametes at each spawning. This would help explain the large range of gonad index values found among ripe specimens sampled during the breeding season. It is not known whether mass spawnings take place in the field since spawning was never observed during numerous snorkeling surveys of the fringing reef made during the day and at night throughout the breeding season. Nothing can yet be said about the reproductive pattern of individual specimens of O. suensoni and O. echinata. For instance, it is not known if individuals of O. suensoni breed annually, semi-annually, or frequently each year. As for O. echinata, it is not known if individuals undergo several gametogenic cycles during the prolonged breeding season. In the future, attempts should be made to monitor the reproductive cycles of individual brittle stars within populations that reproduce continuously or have prolonged breeding seasons. Males of O. oerstedi had larger gonads than females towards the start of the breeding season while, for O. suensoni, males had larger gonads than females on a number of occasions during the winter and spring. This may be an adaptation compensating for differences in the amount of gamete wastage between sexes. During spawning of O. oerstedi and O. suensoni in the laboratory, males spawn first, followed by females and more males (Mladenov, 1976; 1979). If such be- havior occurs in the field as well, then eggs would be emitted into seawater with high sperm densities and fertilization success would be enhanced. This strategy would be associated with considerable sperm wastage, however, and thus larger testes would be of adaptive significance. An examination of Hendler's (1973) gonad index data for the northwest Atlantic brittle star Amphioplus abditus also suggests that the mean gonad indices for males were consistently higher than those for females, except during spawning and post-spawning periods, but these differences were not tested statistically. The present study also shows that females of O. oerstedi had significantly larger gonads than males during the December to March post-spawning period. In this species, ovaries thus appear to have more residual mass than testes following the breeding season. Table 2 summarizes available information on the breeding seasons of tropical ophiuroids. This table includes only those studies employing a gonad index or other suitable monitoring technique for a period of at least I year. All of the 19 species so far studied have a breeding season exceeding the I to 2 months duration which Boolootian (1966) considered characteristic of tropical brittle stars. The shortest breeding seasons are at least 3 months long with a number of species having breeding seasons which are considerably longer than this. Furthermore, those species with discrete breeding seasons generally spawn in the fall which is in disagreement with Boolootian's (1966) suggestion that tropical ophiuroids generally spawn in the spring and summer. It should be noted, however, that Am- phioplus sp. is a winter breeder, Ophioderma brevispinum breeds in the summer and early fall, and Ophiothrix longipeda breeds in the austral summer. Table 2 also shows that continuous reproduction is common in tropical brittle stars with 6 of 19 species displaying this strategy. Four species of continuous MLADENOV: BREEDING PATTERNS OF CARIBBEAN BRITTLE STARS 371

Table 2. Summ.ry of breeding seasons of tropical ophiuro1ds. Information derived from studies involving at least one year of continuous monitoring

Breeding Seasons Species Location Method JFMA~IJJASOf'lD Source

~!£I!J.!J_~ ~iortodes Biscayne Bay. Florida Gonad Index Singletary (19BO) ~~E.?.sp. - Hendler (1£l73l r~C_'=9..P.!!.9ll~gracill ima - - Sfngletary (19BO) .O.£!!i.oS!~_~a~th~ Pacific coast, Panama Hendler (1979) OE-hJ~o~~~.l.ey~.5!.!:.! Pacific coast, Panama - Q£.h~.9_r.}!ech1nata Atlantic coast. Panama _1- 9phiocorna echinata Barbados, 1-1.1. This study

Ophlocoma.~11!. Atlantic coast. Panama Hendler (1979)

QpMOCON l'4end.!!

Cedar Key. Levy County, Stancyk (1974) Flori da

Ophiodl"..!:!!!!cinereum Atlantic coast. Panama Hendler (1979)

Oph;odf'~ ~blcundum Ophione~ l1m1cola Biscayne Bay. Florfda - Singletary (198.0) Oph1ophraQn:us filograneus Cedar Key, levy County, 5tancyk (1974) Florida -

Great Barrier Reef Gonad smears and Stephenson (1934) visual inspection • of qonads on month- to-month basis - 9.E-~rix ~rstedi Barbados, W.I. Gonad Index Thfs study Ophiothrix !!!enson1 Thfs stUdy

1. An intertidal population showed evidence of a more prolonged breeding season than indicated here. 2. Variability among populations from different sites was noted. 3. Higher spawn1n9 activity from October to May. 4. Higher spawning activity in spring and early sUlIIller. 5. Higher spa••••·ning activity in late SUl!Illerand early fall. breeders, Ophioderma cinereum, Ophiophragmus filograneus, Ophiothrix angu- lata and O. suensoni, have periods of higher spawning activity during certain times of the year. Other tropical species of invertebrates with continuous breeding seasons have been found to have periods of more intense reproductive activity as well (Giese and Pearse, 1974). An indication of the various patterns of reproductive periodicity in tropical brittle stars is now emerging. The next step is to attempt to understand the proximate and ultimate factors underlying these patterns. This may prove to be a formidable task as pointed out by Hendler (1979). Whenever possible, future studies should be accompanied by precise measurements of as many physical and biological parameters as possible including temperature, salinity, precipitation, currents and phytoplankton and zooplankton densities. Simultaneous studies of the reproductive cycle ofa few key species over a wide portion of their geographical range, accompanied by the measurement of suitable physical and biological parameters, may provide for a better understanding of patterns of reproductive periodicity in brittle stars. In addition, experimental work using animals held in carefully controlled artificial environments might be a rewarding, although difficult, undertaking. 372 BULLETINOFMARINESCIENCE,VOL.33, NO.2, 1983

ACKNOWLEDGMENTS

I wish to thank Dr. C. M. Lalli for her advice and encouragement offered throughout this study. I also thank Dr. F. Sander for making available the facilities of the Bellairs Research Institute of McGill University. Dr. G. Hendler and an anonymous reviewer provided a number of useful criticisms of the original manuscript. Financial support was provided by NSERC Grant No. A5248 to Dr. Lalli, NSERC Grant No, A7604 to the author, and also by an NSERC Postgraduate Scholarship to the author.

LITERATURE CITED

Boolootian, R, A. 1966. Reproductive physiology. Pages 561-613 in R. A. Boolootian, ed, Physiology of Echinodermata. Interscience, New York, Bray, R. D. 1975, Community structure of shallow-water ophiuroids of Barbados, West Indies. M.Sc. Thesis, McGill University, 91 pp, Clark, A, M. 1976. Echinoderms of coral reefs. Pages 95-123 in O. A. Jones and R. Endean, eds. Biology and geology of coral reefs, Yol. 3, Biology II. Academic Press, New York, Clark, H. L. 1933. A handbook of the littoral echinoderms of Porto Rico and other West Indian islands, Scient, Surv. p, Rico 16: 1-60. Giese, A. C. and J. S. Pearse. 1974. Introduction: general principles. Pages 1-49 in A. C. Giese and J. S. Pearse, eds. Reproduction of marine invertebrates, Vol. 1. Acoelomate and pseudocoelomate metazoans. Academic Press, New York. Glynn, P. W. 1973. Aspects of the ecology of coral reefs in the Western Atlantic region. Pages 271- 324 in O. A, Jones and R, Endean, eds. Biology and geology of coral reefs, Yol. 2. Biology I. Academic Press, New York. Grave, e. 1898. Embryology of Ophiocoma echinata, Agassiz. Preliminary note. Johns Hopkins Univ. Circ. 18: 6-7. Hendler, G. 1973. Northwest Atlantic amphiurid brittle stars, Amphioplus abditus (Verrill), Am- phioplus maci/entus (Verrill), and Amphioplus sepu/tus, n, sp. (Ophiuroidea:Echinodermata): contributions on their systematics, zoogeography, annual periodicity, and larval adaptations. Ph.D. Thesis, University of Connecticut. 255 pp. ---. 1979. Reproductive periodicity of ophiuroids (Echinodermata: Ophiuroidea) on the Atlantic and Pacific coasts of Panama, Pages 145-156 in S. E. Stancyk, ed. Reproductive ecology of marine invertebrates. The Belle W. Baruch Library in Marine Science Number 9. University of South Carolina Press, Columbia. Mladenov, P. V. 1976. Reproduction and larval development in ophiuroids (Echinodermata) of Barbados, West Indies. M.Sc. Thesis, McGill University. 136 pp. ---. 1979. Unusuallecithotrophic development of the Caribbean brittle star Ophiothrix oerstedi. Mar. BioI. 55: 55-62. Mortensen, T. 1921. Studies on the development and larval forms of echinoderms. G.E.e. Gad., Copenhagen. 261 pp. --. 1931. Contributions to the study of the development and larval forms of echinoderms, I- II. K. Danske Vidensk. Selsk. Skr, (Naturv. Math. Afd.) 4: 1-39. ---. 1937. Contributions to the study of the development and larval forms of echinoderms. III. K. Danske Vidensk, Selsk, Skr. (Naturv. Math. Afd,) 6: 1-65. ---. 1938, Contributions to the study of the development and larval forms of echinoderms. IV. K. Danske Vidensk. Selsk. Skr. (Naturv. Math. Afd,) 7: I-59. Parslow, R. E. and A. M. Clark. 1963. Ophiuroids of the Lesser Antilles. Stud. Fauna Cura~o 15: 24-50, Singletary, R. 1980. The biology and ecology of Amphioplus coniortodes, Ophionepthys /imicola, and Micropho/is graci//ima (Ophiuroidea: Amphiuridae). Carib. J. Sci, 16: 39-55. Sloan, N. A. 1982. Size and structure of echinoderm populations associated with different coexisting coral species at Aldabra Atoll, Seychelles. Mar. BioI. 66: 67-75. Sokal, R. R. and F. J. Rohlf. 1969. Biometry, The principles and practice of statistics of biological research. W. H. Freeman, San Francisco. 776 pp. Stancyk, S. E. 1974. Life history patterns of three estuarine brittle stars (Ophiuroidea) at Cedar Key, Florida. Ph.D. Thesis, University of Florida. 78 pp. Stephenson, A. 1934. The breeding of reef animals. Part II. Invertebrates other than corals. Great Barrier Reef Exped. 1928-1929. Sci. Rpts. 3: 247-272.

DATEACCEPTED: August 23, 1982.

ADDRESS: Biology Department, Mount Allison University, Sackvi//e, New Brunswick EOA 3CO, Can- ada.