BULLETIN OF MARINE SCIENCE, 52(2): 792-805, 1993 PAPER

ASPECTS OF THE REPRODUCTIVE BIOLOGY AND SOCIAL STRUCTURE OF THE STOPLIGHT VIRIDE, AT GRAND TURK, TURKS AND CAICOS ISLANDS, B.WJ.

Karen H. Koltes

ABSTRACT The reproductive biology and social structure of the protogynous stoplight parrotfish, Sparisoma viride, were investigated from 1985-1987 in shallow-water areas « 10m) at Grand Turk, Turks and Caicos Islands, B.W.I. Over 225 fish were speared, and size at maturation and sex reversal, number of eggs in ripe females, stage of sexual development and variation in reproductive condition were determined. Sex reversal occurred from 150 to 250 mm standard length (SL). Females matured between 170 and 270 mm SL, but ripe eggs were found only in females> 260 mm SL indicating a period of growth between maturation and reproduction. Gonadal indices for females> 260 mm SL varied among sites, with higher gonadal indices found at the more exposed sites. Eggcounts among ripe females varied widely (5,543-68,606 eggs' female-I) and showed no relationship to size. Visual surveys indicated that abundance and sex ratio varied according to habitat, with males predominating in the lagoon and females otfthe ends of the island. Overall, stoplight parrotfish were more abundant off the ends of the island where reproductively active individuals appeared to congregate. Results indicate that S. viride at Grand Turk maintains some sort of haremic mating system.

The stoplight parrotfish Sparisoma viride (Scaridae) is a large reef herbivore (> 500 mm; Randall, 1968) and a common member of the shallow water coral reef fish community in the Caribbean (Randall, 1968; Frydl and Stearn, 1978; Robertson and Warner, 1978; Alevizon and Landmeier, 1984; Lewis and Wain- wright, 1985). It is a relatively sedentary species, grazing on a limited number of substrates (Barlow, 1975; Frydl and Stearn, 1978; Hanley, 1984). Reproduction in the Scaridae is characterized by sequential hermaphroditism in which some individuals undergo protogynous sex reversal (Reinboth, 1968). Additionally, S. viride is one of at least three Sparisoma species examined in which some males are secondary gonochores-testes are derived from ovaries by changing sex without passing through a functional female stage (Robertson and Warner, 1978). Sex reversal is accompanied by color change, resulting in the drab- colored "initial-phase" of females and males in the early stages of sex reversal, the brightly colored "terminal-phase" males, and the "transitional" which ranges in color from the initial-phase ("female-like") to those which are "male-like" (terminal-phase) but lack fully-developed coloration. Despite the abundance and importance of the stoplight parrotfish in the reef fish community, relatively little is known about this species. The lability of scarid socio-sexual systems has been documented for a few species (Thresher, 1984), and existing studies of S. viride indicate that their behavior, distribution and social structure vary with habitat and location (Alevizon and Landmeier, 1984; Barlow, 1975; Gygi, 1975; Robertson and Warner, 1978). This has important implications for fisheries management, due to increased exploitation of this species. The pur- pose of this study was to investigate the social structure, distribution and repro- ductive biology of the stoplight parrotfish Sparisoma viride in shallow-water hab- itats in the northern part of its range.

792 KOL TES: STOPLIGHT PARROTFISH BIOLOGY 793

MATERIALS AND METHODS

Field studies were conducted at the Smithsonian field station at Grand Turk, Turks and Caicos Islands, B.W.I. (21°90'N; 71°10'W) (Fig. I). Four shallow-water habitats were sampled (Fig. I). The eastern lagoon (Site I) is shallow (about 1-10 m) and sandy with scagrass beds (Thalassia sp.) and numerous patch reefs composed of small coral heads and a heavy growth of macroalgae (, Padina, Halimeda and Lobophilia). The lagoon is bounded to the east by a shallow (about I-IS m) barrier reef (Site 4) dominated by Acropora palmata, but composed mostly of eroded limestone with little live coral. Along the shelfedge extending north (Site 2) and south (Site 3) from Grand Turk are long, shallow (0-15 m) reef-lines consisting of finger-like platform reefs bisected by sand channels. Composed largely of eroded limestone blocks, these platform reefs are covered with turf and numerous small coral heads. Dense patches of A. cervicornis and some A. palmata occur along some margins of the limestone platforms at Site 3. These reef-lines experience strong tidal and wind-driven currents, heavy surge and upwelling from the Turks Island Passage. At the time of the study, fishing pressure on scarids at Grand Turk was light,. with most taken as incidental catch in a small-scale, subsistence trap fishery. To determine maturation/sex reversal and reproductive activity, stoplight parrotfish were collected approximately twice weekly from August 1985 through June 1986 and again in October 1986 by spearfishing in shallow «8 m) areas accessible by free diving. Most individuals were taken at random, but some of the fish :::;200 mm standard length (SL) were deliberately captured to determine the minimum size for sex reversal and/or maturation. Therefore, sampling was not always random. From August 1985 to January 1986, most of the fish were collected from Site I while all four sites were sampled more consistently from February 1986 to October 1986. Near-surface temperature and time of collection usually were recorded. Speared fish were returned to the laboratory within 3 h of collection where SL, total weight and gonad weight (GW) were recorded to the nearest 1.0 mm, 0.1 g and 0.00 I g, respectively. Body weight (BW) was calculated as total weight less GW. For each individual, a scraping of the gonadal tissues, mounted ona glass slide under a coverslip, was examined under a compound microscope equipped with an ocular grid. In males and transitionals, the presence/absence of viable sperm was noted. For females, ovarian development (stage) was determined by noting the diameter (to the nearest 50 /Lm) and stage of oocytes in the leading clutch (group of oocytes with the greatest diameter) (Clavijo, 1982; DeYlaming et aI., 1984). Four stages of oogenesis were noted. Ovaries of immature females (Stage I) contained undifferentiated oocytes < 100 /Lm. During Stage 2 (100-450 /Lm), multiple nucleoli appeared around the nucleus and vitellogenesis (yolk accumulation) began. In Stage 3 oocytes (450-650 /Lm), accumulating yolk spheres coalesced into a continuous mass and the cytoplasm became finely granular. Ripe females (Stage 4) were easily distinguished by the presence of1arge (700-1,200 /Lm), transparent (hydrated) oocytes which were free of the ovarian lamellae. Comparisons of reproductive activity among different-sized fish were made using a modification of the standard gonadal index (GW/BW x 100) because allometric growth of the gonads in some species of fish results in a non-linear relationship between gonad weight and body size (DeYlaming et aI., 1982; Rolf, 1983). The traditional allometric growth equation, y = ax" (where x and yare morphological dimensions and a and b are growth constraints), best describes this pattern of relative growth (De- Y]aming et aI., 1982; Rolf,. 1983). Transforming the allometric growth equation with a logarithm (In) linearizes the relationship to: ]n(GW) = b In(BW) + InCa). To determine whether gonadal stage affected the relationship between In(GW) and In(BW), the In(GW) of females in Stages ]-4 was compared using analysis of covariance (ANCOYA) with In(BW) as the covariate (DeYlaming et aI., 1982; Rolf, 1983). After least squares regression slopes for the four gonadal stages were found to be homogeneous (ANCOY A; P > 0.12), a modified gonadal index (MGI) of the form, In(GW x 1O)/]n(BW) for females and In(GW x 102)/ln(BW) for males, was computed for each individual. Because MGI depends ]argely on the number of eggs in the ovary and this number in tum depends at least partly on time of capture relative to spawning activity (C1avijo, 1982; Colin and Clavijo, 1988; Koltes, in prep.), I both mean MGI and oocyte size of females> 260 mm SL were compared among sites using analysis of variance (ANOYA; Duncan's Multiple Range test of means). The number of eggs in the ovaries was estimated in eight ripe females. Ovaries were dissected and the tissues teased apart with dissecting needles. Tissues were placed in I liter of seawater and bubbled vigorously for about 10 min which separated the ova from the ovarian lamellae. A 100 ml sample of the suspended ova was removed and the ripe eggs counted under a dissecting scope. The total number of eggs in the ovary was calculated by multiplying this number by 10. To describe egg and larval development, gametes were obtained from ripe females and males by teasing apart the gonadal tissues, placing eggs and sperm in approximately] liter of filtered (257 /Lm)

, Kolles, K. H. Spawning behavior of the stoplight parrotfish, Sparisoma viride. In prep. 794 BULLETIN OF MARINE SCIENCE, VOL. 52, NO.2, 1993

~FIOrida)

STUDY AREA

'•.'''', / Grand Turk

Puerto Rico CJ~:

GRAND TURK TURKS AND CAICOS ISLANDS

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Figure 1. Top: Map of Caribbean showing location of Grand Turk. Bottom: Map of Grand Turk and vicinity; sampling sites are indicated. KOLTES: STOPLIGHT PARROTFISH BIOLOGY 795 seawater and gently aerating. Fertilization occurred after about 10 min, whereupon eggs were placed in a 50 liter flow-through kreisel at ambient temperature and salinity. Static systems (Houde, 1973) also were used. Fertilized eggs were stocked at densities of 20, 40 and 400 eggs·Iiter- J. Newly hatched larvae were offered cultured phytoplankton (Isochrysis and Dunaliel/a) and wild-caught plankton. Abundance and sex ratio of adults were determined for each site by visual census. While swimming at a constant speed, the number and phase of stoplight parrotfish greater than about 200 mm SL (the approximate size of sexual maturity) were recorded in a lane about 3 m wide for 10 5-min intervals. Surveys were conducted around noon to avoid the possibility of time-dependent differences among the four sites (Colin, 1978a). All initial-phase fish were assumed to be female since only a small percentage (about 5%) of initial-phase fish were found to be transitional in this study. Abundance and sex ratio were compared among sites (ANOY A; Bonferonni T test) after calculating the proportion of terminal-phase males in each interval and transforming it with an arcsine. The population sex ratio, estimated by pooling the observations from all sites, was tested (chi-square) against an expected ratio of I: I.

RESULTS Size, Sexual Development and Maturation. -Length-frequency distributions in- dicated that males and females achieve the same maximum size at Grand Turk (Fig. 2). Females, all with initial-phase coloration, ranged in size from 100 mm to 367 mm SL (31.5-1,615.2 g; N = 155) while terminal-phase males were 179 mm to 370 mm SL (172.5-1,549.6 g; N = 50). Transitionals measured 154-248 mm SL (110.6-462.9 g; N = 15) and ranged in color from initial-phase ("female- like") to appearing "male-like" but lacking complete color development. All tran- sitionals possessed fully-formed testes with viable sperm. Microscopic examination of the ovaries of 142 of the 155 females captured showed that they begin to mature between about 170-270 mm SL (Fig. 2). The ovaries of immature (Stage I) females were dark reddish-brown and appeared well vascularized. The ovaries of sexually mature females contained enlarging (> 100 J,Lm) oocytes and were pale pinkish-orange. Advanced oogenesis (Stages 3 and 4) was observed only in females larger than 260 mm SL. In females, gonad size was related to both body size and stage of sexual de- velopment (Fig. 3). Allometric growth of the gonads was indicated by the signif- icant positive correlation between log-transformations (In) ofGW and BW (AN- CaVA; df= 142; F = 674.7; P < 0.0001; R2 = 0.95). Gonad size also was affected by gonadal stage, with fish in advanced stages of oogenesis having proportionately larger ovaries (Fig. 3; Table 1). The pattern of sexual development in males (Fig. 4) appeared to be analogous to that of females (Fig. 3). After the development of terminal-phase coloration ("male-like transitional"), In(GW) appeared to increase linearly with In(BW) in males up to about 270 mm SL [In(BW) = 6.4]. As in large (>260 mm SL) females, gonad size was proportionately greater in males> 270 mm SL. No atretic follicles were observed in the testes of males or transitionals, consistent with secondary gonochorism (Robertson et aL, 1982).

Reproduction. - Year-round spawning was indicated by the collection of ripe fe- males in 7 of the 10 months sampled (Table 2; Fig. 5) during which water tem- perature varied from 25°C to 28.5°C. One ripe female was collected as part of an incidental catch from the north reef (Site 2) during July 1986. No fish were collected during August or September. The greatest percentage of ripe females occurred in early spring (February-April; Table 2) when the MG! of both sexes reached a peak (Fig. 5). Mean MG! offemales > 260 mm SL was highest at Sites 2 and 3, and lowest at Site I (Table 3; ANOV A; dJ = 3; F = 26.4; P < 0.000 I). Oocyte diameter in the leading clutch varied correspondingly (Table 3; ANOV A; dJ= 3; F = 6.67; P < 0.0004). 796 BULLETIN OF MARINE SCIENCE, VOL. 52, NO.2, 1993

5 IMMATURE FEMALES tilnJ n=22 o -,-,-. ~I-I~I ,~,-, --, -, ,-,--

30

25 MATURE FEMALES n=120 20

J: 15 CJ) -u.. u.. 10 0 a: w en 5 :E ::J Z 0

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0 10 MALES n=48 5

o 100 150 200 250 300 350 400 LENGTH Imml

Figure 2. Size frequency distribution (mm SL) of immature (oocytes < 100 !tm) and mature (oocytes > 100 !tm) females, transitionals (both stages) and terminal-phase males. KOLTES: STOPLIGHT PARROTFISH BIOLOGY 797

8 FEMALES 6 • <100 IJm MALES a lOO-460um o TERMINAl PHASE 8 • 4&O-e60um -1'RAHSIT1ONAl.; MALE-LICE ·,...,... 5 • TRANSIllONAL: FEMAlE-ut

0 -; 0& o 'C 0 0 00000 i: Q9 ~ 0 0 I 0 0 5 1 • 00 ~ 0 -4 0 ..

-8 +---.,..---r----,-~-__,_--- -1 3 4 5 6 7 8 4 5 6 7 8 Ln BODY WEIGHT (Ill Ln BOIlY WEIGHT (Ill

Figure 3 (left). Relationship between In(GW x 10) (g) and In(BW) (g) for females; symbols indicate oocyte diameter (ILm) in leading clutch of ovaries of Stage I « 100 ILm), Stage 2 (100-450 ILm), Stage 3 (450-650 ILm), and Stage 4 (>650 ILm) females. Figure 4 (right). Relationship between In(GW x 10') (g)and In(BW) (g) for "female-like" transitionals, "male-like" transitionals and terminal-phase males.

The number of eggs per ripe female varied widely and showed no relationship to SL or GW (Table 4). The total number of eggs ranged from 5,540 in a large female (300 mm SL; 637.4 g) to 68,610 in a female measuring 292 mm SL (692.0 g). One of the highest egg counts (66,530) was noted in the second smallest female (279 mm SL). The testes of all males and transitionals examined, regardless of location or time of collection, contained viable sperm, indicating that they are capable of spawning at any time of the day or year. However, reproductive potential, as measured by MGI, varied among the stages of sexual development (Fig. 4). The MGI of "female-like" transitionals (x = 0.674; SD = 0.165; N = 6) was signifi- cantly higher (ANOV A; P < 0.0001; Bonferroni T test, P < 0.05) than compa- rably-sized «250 mm SL) terminal-phase males (x = 0.214; N = 9) or "male- like" transitionals (x = -0.0204; SD = 0.123; N = 8). Large terminal-phase males [> 270 mm SL; In(BW) > 6.4)] also had relatively higher MGIs (Fig. 4) and appeared to be the reproductive equivalents of ripe females (Fig. 3). All of these males (N = 11) were captured along the reef-lines (Sites 2 and 3), except for one

Table I. Exponential relationship of ovarian weight to body weight []n(GW) = b ]n(BW)+ In(a)] for females in Stages 1-4; data plotted in Figure 3

Stage of ovarian development (oocyte diameter) b ± SEe In a ± SEt R'

< 100 ILm (N = 24) 1.92±0.15 -9.91 ± 0.76t 0.88 100-450 ILm (N = 73) 1.77 ± 0.11 -8.80 ± 0.66t 0.80 450-650 ILm (N = 29) 1.09 ± 0.24 -2.94 ± 1.6] 0.4] >650 ILm (N = ]9) 1.27 ± 0.44 -3.54 ± 2.85 0.30 • Regression slopes are homogeneous; ANCQVA; df= 3; F = 1.94; P > 0.12; R' = 0.95. t Intercepts are significantly different; ANCQVA; df- 3; F - 130.4; P < 0.0001. * P < 0.0001. 798 BULLETIN OF MARINE SCIENCE, VOL. 52, NO.2, 1993

32

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24 I A S o N o J F M A M J J A S o 1985 MONTH 1986 0.8

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I @ 0] @ @ I I~'@,- A S o N o J F M A M J J A S 0 1985 MONTH 1986 Figure 5. Relationship between modified gonadal index (MOl) and Julian day for mature females (oocytes > 100 /lm; N = 120) and terminal-phase males (N = 43); symbols indicate sample site: • = Site I; • = Site 2; 0 = Site 3; • = Site 4; females < 260 mm SL (spawning size) are also circled (0); daily temperature (0C) is indicated, KOLTES: STOPLIGHT PARROTFISH BIOLOGY 799

Table 2. Collections of spawning-size (> 260 mm SL) females by month: the total number collected (N), number ripe, percent ripe (%) and average temp COC). Site refers to the area in which the majority of the fish were captured: I = lagoon; 2 = north reef; 3 = south reef; 4 = barrier reef

Month N # Ripe % Site T'C

Aug. 1985 I 0 0 Sept. 1985 0 Oct. 1985 4 0 0 I Nov. 1985 7 I 14.3 I 26.0 Dec. 1985 6 0 0 I Jan. 1986 10 0 0 I 25.0 Feb. 1986 10 5 50.0 I 26.0 Mar. 1986 12 7 58.3 3 27.0 Apr. 1986 6 2 33.3 3 27.0 May 1986 10 I 10.0 3 27.5 June 1986 9 I 11.1 2 28.0 Oct. 1986 13 2 6.5 1,2,3 28.5

male taken with a ripe female at Site 4 and two males captured with ripe females from the southern end of the lagoon (Site 1) near Site 3. Egg Development and Hatching. -Egg development following fertilization pro- ceeded rapidly and was similar to that described by Randall and Randall (1963) for S. rubripinne and Clavijo (1982) for S. aurofrenatum. Eggs were spherical, negatively buoyant and measured approximately 1,000 J.tm (700-1,200 J.tm). At approximately 26°C and 350/00,eggs hatched in about 26 h (Fig. 6). Newly hatched larvae measured approximately 1.4 mm SL. As in other sparisomatine species, a large oil droplet, located anteriorly, caused larvae to float in a head-up position. No eggs were successfully reared beyond 3 d when the oil droplet and yolk dis- appeared. Abundance, Sex Ratio and Behavior. -SO viride > 200 mm SL occupied all four sites (Fig. 7) but abundance and sex ratio were highly variable. Differences in population abundance resulted from significantly more females at Sites 2 and 3 compared to Sites 1 and 4 (ANOV A; P < 0.0001; Bonferroni T test, P < 0.05).

Table 3. Mean, SD and range of SL (mm), MGI and oocyte size (to the nearest 50 JLm) in the leading clutch for females > 260 mm SL (the minimum size of spawning individuals) by site. N = number of fish sampled at each site. Sites as in Table 2. Subsets with different letters are significantly different (Duncan's multiple range; df= 3; P < 0.05)

Mean SL Mean MGI Mean oocyte size (SO) (SO) (SO) Sile N [range] [range] [range]

34 285 0.45 (A) 375 (A) (21.3) (0.13) (252.7) [262-365] [0.29-0.75] [50-1,000] 2 10 306 0.69 (B) 612 (B) (14.8) (0.05) (242.6) [279-323] [0.60-0.79] [450-1,200] 3 35 292 0.66 (B) 636 (B) (]9.0) (0.08) (255.2) [263-346] [0.49-0.82] [250-],200] 4 6 3]2 0.56 (C) 455 (A B) (40.4) (0.] 7) (273.]) [268-367] [0.39-0.84] [250-] ,000] 800 BULLETIN OF MARINE SCIENCE, VOL. ;2, NO.2, 1993

Table 4. Standard length (SL), body weight (BW), gonad weight (GW), total number of eggs, # eggs' g' ovary- I, and capture site of eight ripe females

SL BW ow Total eggs # Eggs.g.ovary I (mm) (g) (g) (x 10') (x 10') Site 269 572.2 5.78 16.95 2,93 3 279 706,3 16.99 66,53 3,92 3 281 702.7 15.04 44.2 32.94 3 285 588.7 11.93 33.55 2.81 2 292 692.0 20.62 68.61 3.33 3 296* 834.3 12.67 26.78 2.11 I 300 637.4 5.31 5.54 1.04 3 329 963.8 7.95 13.53 1.70 3 Mean 291.4 712.2 12.04 34.47 6.35 (SO) (18.2) (5.46) (23.70) (0.93) (10.78)

• Eggs were not fully mature but sufficiently developed to count. However, the somewhat smaller slze may bias the # eggs-g' ovary I estimate.

The number of males and transitionals did not differ among the sites (ANOYA; P > 0.20). Sex ratio varied accordingly; males outnumbered females at Sites I and 4 (by as much as 17.0: I in one survey at Site 4) while females outnumbered males at Sites 2 arid 3 (ANOV A; P < 0.000 I; Bonferroni T test, P < 0.05). Overall, females outnumbered males by 1.8: 1.0 (X2dJ= I = 56.5; P < 0.00 I). Qualitative observations indicated that stoplight parrotfish generally formed loosely knit foraging groups (2-30) which moved slowly about the reef. Along the north and south reef-lines, groups consisted of several initial-phase fish with one to a few terminal-phase males. At Site 2, large schools consisting of about 3-6 males and 15-30 females were almost always present. These schools were com- posed almost entirely of S. viride and were observed moving in the channels between the platform reefs or foraging in the shallow water above the reef. Along the south reef-line (Site 3), schools were less well organized, with one or two males loosely associated with four to ten females. Often, however, males foraged alone or in small (2-10) groups along the top of the reef, frequently congregating around isolated patches of A. palmata on the exposed surfaces. By contrast, females appeared to rely on crypsis, foraging within the dense patches of A. cervicornis along the lower reef margins. A similar pattern was observed along the barrier reef. In the lagoon, groups were smaller and all-male groups were common. On at least four occasions, a group of males was observed in an organized school moving between patch reefs at both the south reef and in the lagoon. These all- male groups appeared to be "bachelor" or "excess" (Robertson and Warner, 1978) males.

DISCUSSION In S. viride at Grand Turk, prematurational sex change (secondary gonochorism) resulted in similarities in the sexual development of males and females. Onset of maturation in females and sex reversal in males occurred over a broad but similar size range (approximately 170 to 270 mm SL). Size at sex reversal of S. viride at Grand Turk was slightly greater than that reported for the population at San Bias, Panama (130-200 mm SL; Robertson and Warner, 1978). Additionally, both males and females appeared to undergo a period of growth of up to 100 mm SL between the onset of maturation and reproduction, after which females became ripe and the MGI of terminal-phase males increased sharply. In transitionals, sperm production preceded color change and regression in KOLTES: STOPLIGHT PARROTFISH BIOLOGY 801

1000u

1.4 mm

Figure 6. Stages of egg development following fertilization; Temp = 26°C; Salinity = 350/00; A = 22 h; B = 26 h; C = 46 h; and D = 69 h post-fertilization. gonad size, a pattern consistent with other scarids (Choat and Robertson, 1975). MGI attained its maximum value in "female-like" transitionals, a high repro- ductive potential they have been observed to use to "streak" (Robertson and Warner, 1978) or "interference spawn" (release sperm over the freshly spawned gametes of a mating pair; Koltes, in prep.).] After the development of terminal- phase coloration, the gonads shrink dramatically, resulting in a drop in MGI by two orders of magnitude. When males reach about 270 mm SL, MGI increases sharply, suggesting that males have become reproductively active; almost all males >270 mm SL were captured in association with ripe females. Seasonality of spawning at Grand Turk could not be determined because of 802 BULLETIN OF MARINE SCIENCE, VOL. 52, NO.2, 1993

• MALES A FEMALES 40 • TRANSITIONALS

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II III IV SITE Figure 7. Results of visual survey; mean ± I SD of males, females and transitionals by site. Site I = lagoon; 2 = north reef; 3 = south reef; 4 = barrier reef. small sample size and the shift in sampling effort during spring 1986. However, spawning at Grand Turk appeared to occur year-round, with a peak in early spring, This pattern is similar to that observed in stoplight parrotfish in Panama (Rob- ertson and Warner, 1978) and Jamaica (Munro et aI., 1973) and consistent with that of other scarids (Robertson and Warner, 1978; Clavijo, 1982; Munro et aI., 1973; Colin and Clavijo, 1988; Colin, 1978a, 1978b; Randall and Randall, 1963). Ripe females varied widely in the number of mature eggs contained in the ovaries. This may reflect either actual individual variation in egg production, or more likely, that the females that were counted already had partially spawned (Clavijo, 1982). Spawning rushes in scarids are brief (Randall and Randall, 1963; Dubin, 1981; Clavijo, 1982; Koltes, in prep.)' and eggs are probably shed over several spawns. Therefore, time of capture relative to spawning and the number of spawns would affect the egg count of individual females. Variability in the relative number of ripe eggs also was noted in S. aurofrenatum (Clavijo, 1982), although sample sizes were small. KOLTES: STOPLIGHT PARROTFISH BIOLOGY 803

Eggs of S. viride were similar to those described for other sparisomatines (Clavi- jo, 1982; Winn and Bardach, 1960; Randall and Randall, 1963). Development and hatching of laboratory-reared eggs also was similar to that of related species (Clavijo, 1982). Although offered wild-caught and cultured plankton in flow- through and static systems, newly hatched larvae did not appear to feed and none survived beyond three days. Newly hatched larvae of S. aurofrenatum also did not survive beyond a few hours apparently due to starvation (Clavijo, 1982). It is also possible that organisms small enough to pass through the 257 Mm mesh screen preyed on the eggs and/or larvae resulting in the high mortality rates. Population structure and density of Sparisoma viride varied considerably among the four shallow-water sites at Grand Turk and appeared to be related to sex, reproductive condition, substrate characteristics and water conditions. Repro- ductively inactive individuals of both sexes formed loose social groups of mixed sex and size in the lagoon and other low-energy areas. Solitary individuals were common, but small foraging groups were more typical. It is not known whether these individuals select these areas or end up there because they are excluded from "more desirable" areas such as the reef-lines. In all areas, stoplight parrotfish formed mixed-species schools with other scarids, particularly Scarus vetula. acan- thurids, mulids and haemulids. Stoplight parrotfish were more abundant in the exposed reef areas, particularly off the ends of the island, where agitated water conditions produce an abundant standing crop of turf algae capable of supporting denser populations of scarids (Gygi, 1975; Barlow, 1975; Bouchon-Navaro and Harmelin- Vivien, 1981; Clavi- jo, 1982; Alevizon and Landmeier, 1984; Lewis and Wainwright, 1985). Here, females outnumbered males, forming groups of from three to as many as thirty. Sites 2 and 3 also contained reproductively active individuals. Almost all females in advanced stages of oogenesis (Stages 3 and 4) and terminal-phase males with proportionately higher MGIs were captured in these areas. An abundance of ripe females in association with a few large, reproductively active males suggests that S. viride maintains a harem-like mating system in the shallow-water reefs surrounding Grand Turk. This is further supported by qual- itative observations made during the study of frequent male-male aggression at Sites 2 and 3 in which a male associated with a group offemales drove off single males. Conversely, well-organized, all-male schools were frequently observed in both the high energy areas and in the lagoon. As in the Panama population (Robertson and Warner, 1978), the all-male schools appeared to be composed of "excess" males excluded from the more productive areas and/or spawning females. These excess males appear to be analogs of "foragers" in S. croicensis (Ogden and Buckman, 1973; Buckman and Ogden, 1973) or "wanderers" in S. aurofrenatum (Clavijo, 1982). Foragers have been interpreted as males channeling their resources to growth rather than reproduction until of sufficient size to compete for territories (Warner and Downs, 1977). Wanderers are terminal-phase males who assume territorial status as soon as a territory becomes available (Clavijo, 1982). Since mating appears to be limited to a few larger males in the stoplight par- rotfish, one should expect relatively fewer males than females in the adult pop- ulation. This appears to be the case since there were nearly twice as many females as males in the adult population. A bias toward females in the adult population also was observed in Panama (Robertson and Warner, 1978). Results from this study are consistent with other investigations which have suggested that the haremic mode of life common among scarids arises from the combined effects of social behavior and environment (Alevizon and Landmeier, 1984; Bouchon-Navaro and Harmelin- Vivien, 1981; Warner and Hoffman, 1980). 804 BULLETIN OF MARINE SCIENCE, VOL. 52, NO.2, 1993

The fact that S. viride is a gonochorist species in which males are derived from females that have not passed through a functional stage is interesting in light of suggestions that protogyny is an adaptation to mating systems in which older, larger males accrue more mating success than smaller younger males (Ghiselin, 1969; Warner, 1975; Warner et aI., 1975; Hoffman et aI., 1985). According to this theory, an individual would have higher fitness ifit functioned first as a female while small and as a male when large enough to compete successfully for mates. Since an S. viride male never functions as a female, the system of sex reversal in these fish must have evolved for other reasons. One possibility suggested by Smith (1975) and Robertson and Warner (1978) is that primary males may have been lost in the evolutionary past in monandric species and their position in the social structure has been filled by secondary gonochores. Another possibility suggested by the pattern of MGI values and field observations of S. viride (Robertson and Warner, 1978; Koltes, in prep.)' is that small size may be advantageous in reducing the conspicuousness of "female-like" transitionals, thereby increasing their ability to gain access to breeding females (interference spawn). In this way, individuals would increase their fitness by reproducing when young, exploiting the high re- productive potential of the transitional phase.

ACKNOWLEDGMENTS

The author gratefully acknowledges the assistance of D. Baudler and E. Simms who helped with all aspects of the field collections at Grand Turk. I am grateful to the citizens and officials of the Turks and Caicos Islands, especially His Excellency the Governor Mr. Christopher Turner, who allowed me to conduct my research at Grand Turk. I would also like to thank J. Felley for statistical advice and C. Page, C. Roland and J. Dietterle for assistance with the illustrations. This work was supported by USAID grant LAC-0605-G-SS-3070 to the Marine Systems Laboratory and I thank W. H. Adey for support and assistance during this study.

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DATEACCEPTED: July 27, ]992.

ADDRESS: Marine Systems Laboratory, NHB W-3/0, Smithsonian Institution, Washington, D.C. 20560; PRESENTADDRESS: U.S. Fish and Wildlife Service, Office of Research Support. 1849 C Street NW. MS 725-ARLSQ, Washington, D.C. 20240.