BULLETIN OF MARINE SCIENCE, 50(1): 186-204, 1992 CORAL REEF PAPER

POPULATION BIOLOGY OF THE REDLIP BLENNY, ATLANTICUS MACCLUREI (SYLVESTER) IN BARBADOS

M. Labelle and J. R. Nursall

ABSTRACT Information on the demographic traits of the redlip blenny was collected to characterize its life history cycle, and identify the major determinants of its abundance on shallow reefs. Adult Ophioblennius at/anticus collected in Barbados during the 1978-1986 period ranged in size from 56 to 126 mm. Females and males are approximately the same length, but females achieve a greater weight. Growth is described by the von BertalanffY model, with parameters Loo,K and To respectively estimated to be 110.039,0.061 and -6.24. Less than 10% of the population lives beyond the third year. Monthly fecundity ranges from 794 to 4,390 eggs per female. GSI is highest in spring (April-May). Males polygamously and sequentially; nests were found to contain between 1,638 and 11,490 eggs (mean = 5,799), in as many as four cohorts. There was a positive correlation between nest size and number of eggs. In general, mates were of the same size. Larvae are believed to have a pelagic life of 6 to 8 weeks, mostly spent over deep barrier reefs near shore. Settlement is at night, near the time of the new-moon period. Local hydrological conditions probably affect recruitment. There is marked annual variation in abundance. It could not be demonstrated that Hurricane Allen had a marked long term effect on the population of O. atlanticus.

In the western Caribbean, almost all the fishing effort is directed towards the exploitation of reef populations (Munro, 1976). After a close examination of the fisheries potential of coral reef environments, Stevenson and Marshall (1974) concluded that "Reference to suitable management regulations brings up the need for fundamental fishery biology information to accompany development efforts. First and foremost, we need such basic facts as harvest statistics, population estimates related to supporting environments, growth rate data, - recruitment data, etc." The objective of this paper is to provide some of those data for the redlip blenny, Ophioblennius atlanticus macclurei (Sylvester), a small primary consumer which holds permanent territories on coral reefs in shallow waters (Nursall, 1977). It has been characterized as being one of the most abundant fishes on West Indian reefs (Randall, 1968). Redlip blennies form an important link between coralline (and probably their bacterial associates) and a variety ofpiscivorous fishes in Caribbean coastal ecosystems. The environmental factors that affect its life history must also affect other reef fishes.

MATERIALS AND METHODS

Field and laboratory investigations were conducted intermittently between May 1975, and August 1986, at Bellairs Research Institute of McGill University, St. James, BaI'bados. O. at/anticus has been observed rarely to depths of 30 m, but the population is concentrated in the reef crest zone (Lewis, 1960). That is where observations and sampling of adults and recruits were carried out. Behavioral observations were made while snorkeling and recorded with pencil on a plastic slate. Direct observations totaled about 1,200 h. Censuses were conducted by means of transects. Transect AA, at Heron Bay, about I km north of Bellairs Research Institute, was 57 m long, by 1 m wide. It was located on the reefcrest at a depth of 0.5 to 2.5 m (at mean low tide), parallel to shore, approximately 40 m offshore. Transect BB, measuring 100 m by 1.0 m, was similarly located about 1.5 km north of transect AA. Transect AA was patrolled at least once a week from May to August 1980, and both

186 LABELLE AND NURSALL: REDLIP BLENNY BIOLOGY 187 transects were patrolled from January to August 1981. Counts were made by swimming slowly (0.5- 1.0 m-min-I) along the transect. During each reproductive period, pieces of coral with eggs attached were collected and taken to the laboratory in seawater. Such sampling was mostly done using SCUBA. At the same time, nest char- acteristics were recorded. Individual fishes were collected by spear. In the laboratory, the sex of each fish was verified, its total length (TL) measured to the nearest 0.1 mm, and the number of eggs per nest determined by visual inspection with a stereo microscope. The stage in development of egg batches was determined by reference to information obtained during previous rearing experiments (Labelle and Nursall, 1985). Female gonadal changes were monitored from April to August 1981. Six to 10 female blennies were collected ad lib every fourth day for examination. Body weight before removal of the gonads, and gonad weight were measured to the nearest 0.1 g, and TL to the nearest 0.1 mm. Gonads were preserved in 5% buffered formalin and dissected a few days later. Ovum diameter was measured to the nearest 0.0 I mm, using a stereo microscope and ocular micrometer. Ichthyoplankton tows were carried out over inshore and offshore waters in the lee (to the west) of Barbados, mostly during the periods of May to August 1980, and January to August 1981. Double oblique tows and step-oblique tows to a maximum depth of 60 m were made, using a 3.5 m long net, with a 1.0 m2 mouth and a mesh size of 1.1 mm2• Recruitment was investigated by means of rotenone collections. Two coral heads were used as experimental sites. These heads were located near the inner edge of the reef crest zone in front of the Bellairs Research Institute (Heads M and A in Nursall, 1981). The heads were completely rid of resident fish, then re-examined once or twice daily with rotenone, during periods in 1978, 1981, 1982, 1984 and 1986. Head M was about 1.0 m high, 1.0 m in diameter, and located in 2.0 m of water (at mean low tide). Head A was about 1.5 times the size ofM, and in 3.0 m of water.

RESULTS Size and Abundance.- The redlip blenny, Ophioblennius atlanticus macclurei, is a common shallow water reef fish in the western central Atlantic from North Carolina to Venezuela. Greenfield and Johnson (1990) characterized this as a member of fish assemblages of various shallow water reef habitats, and particularly the forereefs, the rubble/algae zones, and the offshore rocky areas. Springer (1962) reviewed the genus Ophioblennius and described the morphology of adults. Nursall (1977) described color change and color variability in O. at- lanticus. In Barbados, there appear to be two color morphs. Our investigations focused almost exclusively on the darker morph in which coloration is charac- terized by a chocolate brown body with red lips, reddish translucent pectoral fins, and a reddish trim extending from the dorsal part of the caudal fin to the anterior part of the dorsal fin. In Barbados, redlip blennies found on shallow reefs range in size from 40 to 126 mm in total length (TL). Individuals exceeding 87 mm generally make up less than 10% of the total population. The largest female collected in Barbados was 107 mm, and the largest male, 126 mm. The smallest mature female was 61 mm, and the smallest mature male, 56 mm. Small populations on isolated coral heads are often characterized by relatively uniform length frequency distributions (Fig. 1). Coral heads covered extensively by a large colony of the corallimorpharian Ricordea florida, were occupied pre- dominantly by larger individuals (80-126 mm). Presumably, the presence of anemones and differences in the availability of crevices are strong determinants of population structure. Both habitat features undoubtedly offer some protection against benthic predators, which in tum influence the natural mortality rates and the ensuing life span of the residents. However, the exact mechanism by which this occurs remains to be investigated. Nursall (1981) observed that redlip blennies averaged 1.9individua1s·m-2 (range: 0.6-4.0) on suitable substrate along 14 transects. At such densities, the biomass ratio ofredlip blennies over other benthic species {excluding muraenids and large 188 BULLETIN OF MARINE SCIENCE, VOL. 50, NO.1, 1992

80 70 - - - - 60 - - - - TL - - - - (mm) 50 - - . 40 30 20 10 o 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Specimen number Figure 1. Body size distribution in a small population (22 individuals) of O. at/anticus from an isolated coral head. Specimens were sorted from smallest to largest. transient ones) ranged from 1.1 to 1.9, indicating that redlip blennies contribute on average at least as much and probably more biomass than the remainder of the benthic fish community in the surge zone. Growth. - For reasons of expediency and accuracy, size measurements made under field conditions were usually obtained in total length. However, the relationship between standard length (SL) and total length (TL) has been established: Females: TL = 1.22SL - 0.386 (N = 26; r2 = 0.98) (1) Males: TL = 1.21SL - 0.086 (N = 42; r2 = 0.98) (2) Based on a sample of 274 redlip blennies collected unsystematically in Barbados between June 1976 and April 1977, Marraro (1978) found no significant differ- ences between the weight/length ratios of males and females (ANCOVA, P > 0.05). Marraro (1978) estimated the functional relation between weight and total length for this species by means of a geometric mean regression (Ricker, 1975): Weight (g) = 5.5 .1O-6TL3·16 (N = 134; r2 = 0.92) (3) Growth in O. at/anticus was estimated in the present study by reference to length frequency histograms. This method was chosen because of the lack of scales in this species and the difficulty of determining the number of sagittal growth rings. Male and female length data collected by Marraro (1978) were grouped separately in 2-month intervals. Female growth was estimated by analysis of modal progressions in time series of length frequency distribution. Growth rate data derived in the above manner were analyzed according to the von Bertalanffy growth model. Vaugham and Kanciruk (1982) found a nonlinear least squares fit to be the preferred method for fitting this type of growth equation. Therefore, least squares estimates of the von Bertalanffy parameters were obtained using the nonlinear Simplex algorithm ofthe microcomputer statistical program SYSTAT. Beyond metamorphosis (>40 mm TL) female growth is represented by the fol- lowing equation:

LI = 110.039'1 - eO.061(I+ 6.24) (N = 159; adj. r2 = 0.996) (4) where: LI = Total length in mm at time t (in months). The pattern shown in Figure 2 indicates that for O. at/anticus, growth is high following metamorphosis (~4.0 mm per month) and gradually decreases for the LABELLE AND NURSALL: REDLIP BLENNY BIOLOGY 189

120

100

80 Total Length (mm) 60

40

20 o o 5 10 15 20 25 30 35 40 45 50 Relative age (months) Figure 2. Growth pattern offemale O. atlanticus following recruitment (reI. age I). remainder of an individual's life span. No such relationship is provided to account for growth in males since male samples were too small or irregularly spaced to produce coherent results. However, Marraro (1978) found no evidence to indicate that male growth rates were different than those of females. Furthermore, the estimated female growth rates appear to be consistent with results of tagging experiments carried out in October 1976 by Marraro (1978), who reported that an adult male grew 5.8 mm from 48.0 mm (TL) during 6 weeks. Since all fish > 107 mm collected by us and by Marraro (1978) were males, it is hypothesized that males can attain larger sizes than females. Reproductive Pattern. -Examination of oogenesis gives limits to the period of spawning of the female redlip blenny. As many as five distinct stages of devel- opment of ova, including atretic follicles, may be distinguished in a blenny ovary, both in fresh specimens and histologically. Asynchronous maturation of several groups of oocytes within an ovary is characteristic of fish species exhibiting it- eroparity (Warner, 1975). Ripe ova in fresh ovaries of O. at/anticus were opaque, contained an oil globule, and ranged from 0.56 to 0.65 mm in diameter. The presence of ripe ova and the corresponding degree of maturity of ovaries varied throughout the lunar cycle. Significant differences were detected between the mean size of the most advanced group of ova of females at different times of the lunar month (Kruskal- Wallis test, P < 0.05). Mean ova size was greatest during the 3 days before full moon (x = 0.52 mm), decreased significantly during the week following full moon (Newman-Keuls test, P < 0.05), and was lowest 9- 12 d after full moon (x = 0.35 mm). Thus one can predict that spawning would occur about the time offull moon. According to Cote (1987), the peak reproductive period (PRP) for O. at/anticus extends from 10 days before full moon until 6 days after. Our own field observations agreed with those of Cote (1987). Fecundity is usually defined as the number of mature eggs in a female just prior to spawning. In tropical species which are not seasonal spawners, batches of eggs follow one another continuously. According to Bagenal (1978), fecundity should be determined for single batches of eggs. Therefore, we determined female fecun- dity by visual count of mature ova in 34 females. Between April and August 1981, egg production was found to range from 794 to 4,390 eggs per female. Egg pro- duction in O. at/anticus increases exponentially with length and can be expressed by the equation: 190 BULLETIN OF MARINE SCIENCE, VOL. SO, NO. I, 1992

F = aLb (5)

I where: F = fecundity (eggs'month- ), L = total length offish (mm), a = constant and b = numerical exponent. The average fecundities estimated during 1981 were: F = 0.0871OU·39 (April-May, N = 7, r2 = 0.8281) (6) F = 0.00363L3.04 (June-July, N = 10, r2 = 0.578) (7) Since maximum monthly egg production in O. atlanticus occurs in the spring (see below), Eq. 6 can be used to estimate maximum monthly egg production. Owing to the lack of information on development rates of ova in redlip blennies, both fecundity estimates were based on the assumption that only ova in the largest group within the ovaries are shed every month. It is possible, although not prob- able, that ovum development is such that ova of different sizes are shed within the same monthly reproductive period, in which case the relationships suggested above would underestimate potential egg production. We observed one case where mature eggs apparently had not been shed. The egg mass was large, opaque and wrinkled. It probably obstructed the oviduct. Occasional atretic follicles are seen in histological sections of ovaries. In general, it seems that all mature eggs are shed. Since fecundity estimates were formulated for only two periods, reproductive seasonality was investigated by reference to female gonadosomatic state. Between April and August 1981, seven or more female gonads were collected every month on the day preceding the full moon. Female gonad weight was expressed as a percentage of total body weight to give the gonadosomatic index (GSI). By mon- itoring changes in GSI throughout the spawning period, it is possible to determine the proportion of body weight devoted to egg production each month. During the period from April to August, this fraction decreased from 4.0% to 2.2%. Peters (1981) showed similar trends in the Florida blenny Chasmodes saburrae, where monthly changes throughout the year ranged from 0.9 to 8.7% of body weight. Average pre-spawning GSI was highest in April (x = 5.63, s = 2.45) and lowest during July (x = 3.22, s = 0.63). Kruskal-Wallis tests revealed no significant differences in average GSI between the spring months (April, May), or among the summer months (June, July, August), suggesting that changes in reproductive output are small and gradual. However when monthly GSI estimates were pooled in their respective seasons, a t-test showed the average GSI spring figures to be significantly greater (P < 0.05) than summer ones, as concluded by analysis of fecundity estimates. Additional information on seasonal changes in female GSI collected by Marraro (1978) was used to produce a preliminary estimate of the annual reproductive cycle of O. atlanticus. These data indicated an apparent annual cycle of repro- duction in which female reproductive output peaks in the spring and is lowest in the fall (Table 1). In some fishes, fecundity has been shown to be density dependent (Bagenal, 1978), high densities being correlated with low fecundity. We found no evidence to indicate the existence of a relationship between average egg production (GSI) and population density ranges encountered. Mate Selection. - During the spawning period, females leave their to search for males that are ready for mating. Although several neighboring males may be ready to mate, females do not distribute their eggs randomly or uniformly among the nests. Rather they appear to be strongly attracted to certain males. Occasionally, females can be observed to visit a male nest before actually laying eggs inside it. We assume that such females are actually evaluating the 'quality' of the nests. These facts and the evidence provided in the previous section suggest LABELLE AND NURSALL: REDLIP BLENNY BIOLOGY 191

Table I. Reproductive pattern in female O. at/anticus based on monthly aSI figures. Figures were extracted from two independent studies

Survey date Mean GSI ('!til SDGSI Sample size Data source

Jan. 1981 n/a Feb. 1976 2.05 0.20 7 Marraro, 1978 Mar. 1971 3.15 0.60 7 Marraro, 1978 Apr. 1981 5.63 2.45 7 Labelle, 1982 May 1981 4.83 1.41 9 Labelle, 1982 Jun. 1981 3.75 0.99 11 Labelle, 1982 Jul. 1981 3.22 0.63 10 Labelle, 1982 luI. 1976 3.60 0.90 7 Marraro, 1978 Aug. 1981 3.24 1.47 10 Labelle, 1982 Aug. 1976 2.20 0.30 7 Marraro, 1978 Sep. 1976 1.90 1.25 7 Marraro, 1978 Oct. 1976 1.50 0.30 7 Marraro, 1978 Nov. 1976 2 0.32 7 Marraro, 1978 Dec. 1981 n/a

that biotic factors (male body size) and abiotic factors (nest volume and nest location) may playa significant role in determining female choice for certain nests. However, males make the final choice of female with which to mate. A definite relationship exists between the body sizes of a mating pair. The relationship is:

2 TLf = 25.43 + 0.6454TLm (N = 13; r = 0.865) (8) where: TLf = Total length offemale (mm) and TLm = Total length of male (mm). The above relationship indicates that on average, males select females which are slightly shorter (3%) than they are, but for all practical purposes, mates can be considered as being of similar sizes. This relationship, combined with infor- mation on fecundity estimates (Eqs. 6, 7), and on egg contents of each nest, can be used to estimate the potential number of mates a male can take. The results indicate that one nest guarding male might have spawned with as many as five females (Table 2). This confirms earlier observations that polygyny occurs in O. atlanticus (Marraro and Nursall, 1983). Recent work by Cote (1987) showed that individual males can guard as many as 21 batches of eggs per reproductive period. Sequential visitations by one female to two nests and mating there have been seen at least four times, confirming suspicions of polyandry. There is no evidence of hermaphroditism in this species. Nest Contents. -Information about the breeding pattern of O. at/anticus was also obtained through examination of nest contents. Between January and August 1981, 67 nests were examined. The presence of eggs inside the nests corresponded to the times predicted from the study of oogenesis. Typically, the nests contained eggs during a period of7 days following the day of full moon. However, it should be noted that occasionally eggs were found in nests a few days before or after this period. In 10 nests examined, the mean number of eggs was 5,799 (range: 1,638- 11,490). Most nests contained cohorts of eggs at different developmental stages; an early or young stage «30 h old), an intermediate stage (31-55 h old), and an advanced stage (56-80 h old). The age of eggs was determined in rearing exper- iments (Labelle and Nursall, 1985). The presence of several cohorts of eggs of different stages inside a nest can be explained by the fact that redlip blennies spawn repeatedly during the reproductive period. The pattern observed indicates that the majority of males will spawn with only one female per day. The number 192 BULLETIN OF MARINE SCIENCE, VOL. 50, NO.1, 1992

Table 2. Estimated mating success in male O. at/anticus. Female fecundity estimates are based on the assumption that males mate with females of similar body size

Eggs per nest Male size (TL, mm) Female fecundity Potential mates 1,638 64.0 1,124 1.46 3,374 72.6 1,649 2.05 8,313 79.9 2,206 3.77 2,490 69.0 1,413 1.76 11,490 88.3 2,990 3.84 4,994 81.1 2,309 1.73 5,218 82.3 2,414 2.16 9,794 76.2 1,910 5.13 6,780 79.9 2,206 3.07 3,900 83.5 2,523 1.55

of cohorts per nest commonly ranged from one to three. In two cases there were four egg cohorts found, but in both cases, two of the four cohorts were of the intermediate stage, suggesting that the eggs had been laid only a few hours apart. Nest characteristics such as height above the sand bottom, depth, volume and position in relation to the beach were recorded. Biotic factors recorded included male body size and nest emplacement in relation to neighboring occupied terri- tories. Of all nest characteristics monitored, only nest depth was observed to influence the number of egg cohorts per nest. Although nests are found from the surface to 3.0 m below the water level at mean low tide, nests containing three cohorts were always positioned approximately 1.0 to 2.5 m deep. No relationship was found between the number of egg cohorts per nest and male body size or nest emplacement. Only nests containing three cohorts of eggs ("full nests") were considered for further analysis, because nests with fewer cohorts were considered to have not yet achieved or had passed their full potential. Nests containing only one or two cohorts can be found at all times during the reproductive period. Thus, there is no reason to believe that all nests end up being "full." For the June and July periods of 1980 and 1981, the total number of eggs per "full" nest was correlated with nest volume (r2 = 0.774; N = 15), and male body size (r2 = 0.504; N = 15), though no strong correlation was shown to exist between male body size and nest volume (r2 = 0.33; N = 50). For some coral reef fishes, Shulman (1984) proposed a variable relationship between fish size and shelter size, presumably a function of predation pressures and population density. Our observations suggest that nest (or shelter) size also influences the reproductive success of individuals. Field observations and examination of nest contents, showed that some males guarded nests for up to 12 consecutive days, which implies replacement of hatching eggs by new cohorts. We have no estimate of the number of cohorts that may pass through a nest during one reproductive period. Since males continually remove dead or dying eggs, accurate data on egg mortality are difficult to obtain. However, in one case, egg mortality was seen to reach 60% during the incubation period. At the present time, we have no information on the average mortality or its main causal factors. Pelagic Phase,-O. at/anticus larvae (described by Labelle and Nursall, 1985) were collected during ichthyoplankton surveys over inshore and offshore waters of the west coast of Barbados. The distribution of the larvae is best described by reference to the sea bottom topography in coastal waters: the western (leeward) LABELLE AND NURSALL: REDLIP IlLENNY 1l10LOGY 193

6 - 5 - 4 Number - of 3 recruits - 2 -- - . -- - - o 1/1/81 2/1/81 3/1/81 4/1/81 5/1/81 6/1/81 7/1/81 8/1/81 9/1/81

Sampling date (mjdjy) Figure 3. Catches of O. at/anticus metalarvae obtained by sampling coral head M each week between January I and August 26, 1981. The dotted vertical lines represent the time of full moon.

side of Barbados is characterized by the presence of an incomplete fringing reef extending about ISO m offshore (Lewis, 1960). Beyond it is a wave-cut terrace of sand and coral, which declines gently at first, then more steeply to a trough some 40 m deep, from which rises a submerged barrier reef, 600 to 800 m offshore (Macintyre, 1967; 1968; Ott, 1975). The top of that First Ridge reef lies within about 20 m ofthe sea surface; it is less than 100 m wide, and covered with prolific coral growth. The Second Ridge is found about 1,200 to 1,500 m offshore at a depth of 70 m. It is about 10m higher than the trough from which it rises. Newly hatched larvae were found above the fringing reefs on the west coast of Barbados during full moon period all year. The distribution of larvae there is patchy because of nearshore currents. Larvae are caught further offshore in the days fOllowing this lunar period. A total of 79 larvae were collected from 29 ichthyop1ankton surveys conducted during 1980 and 1981. A single larva (2.1 mm TL) was caught approximately 1,500 m from shore, in a double oblique plankton tow to 40 m. All others were caught 500 to 1,000 m from shore, mostly beyond the First Ridge. They ranged in size from 2.9 to 6.7 mm TL. The larvae were most abundant 13-24 d after full moon, and during June of both years. The distribution by depth of larvae during June (N = 30) and August (N = 6), 1980, was contrasted by means ofa Kruskal-Wallis test. In neither month did we find any significant difference in numbers taken from 0-10 m, 11-30 m, or 31- 45 m (P > 0.05). No significant difference was detected in mean total length of larvae taken from different depths. This suggests that young O. at/anticus larvae are well mixed throughout the water column while in this region. Current velocities vary greatly around the First Ridge. They are strongest at the crest of the ridge and least on its inner slope (Ott, 1975). No O. at/anticus larvae exceeding 7.0 mm were caught by our plankton net. O. at/anticus larvae exceeding 40 mm TL eventually return to the reef as large predators of (metalarvae), and could easily avoid our plankton net. Thus, our sampling was not intensive enough to provide a complete picture of the larval distribution. Recruitment. -In Barbados, O. at/anticus metalarvae are easily collected after settlement on inshore reefs. Weekly sampling of an isolated coral head (M) between 194 BULLETIN OF MARINE SCIENCE, VOL. SO, NO. I, 1992

Table 3. Recruitment pattern of O. at/anticus larvae on two isolated coral heads during June 1982

Head M Head A Survey date am pm am Jun. 14 0 Jun. 15 Jun. 16 1 0 Jun. 17 0 0 Jun. 18 0 0 Jun. 19 0 0 Jun. 20 1 0 Jun. 21 0 0 Jun. 22 0 0 Jun. 23 7 0 8 Jun. 24 8 0 6 Jun. 25 I 0 4 Jun. 26 5 0 6 Jun. 27 5 0 1 Jun. 28 0 0 o Jun. 29 0 0 o Jun. 30 0 o

January and September 1981 revealed that metalarvae settle on the reef each month (Fig. 3). Recruitment rates were relatively low between January and May (:::::0.I-O.3·m-2). Recruitment peaked during early summer with densities of 0.7 in June, and 1.1 in July. No recruitment was observed between 20 July and 30 August. Each time metalarvae were obtained from head M, other areas of the fringing reef were also sampled, within 24 h. On every occasion, metalarvae were captured at the other sites as well. Extensive trapping was also conducted on the reefs, near sand bottoms around the reefs, and in the reef grooves each week, but metalarvae were never caught there when they were absent from head M. Such results lend credence to the use of our isolated head for monitoring recruitment periodicity. The catch record indicates a peak in recruitment in the early summer, but our data set is too fragmentary to account for the annual pattern in recruitment. Additional sampling in 1982 indicated that settlement usually occurs at night between 1800 and 0600 (Table 3). Sampling data from 1982 to 1986 was used to describe the relationship between recruitment patterns of O. at/anticus and environmental factors such as daylight, tidal flow and moon phase (Fig. 4a-c). Recruitment takes place at night and during the periods oflow light, i.e., between the first and last quarters, which includes the period of new moon. An onshore current accompanying the flowing tide is also generally present at this time. The relationship between moon phase and onshore current in governing recruitment is not clear because of the variance shown. However, it must be remembered that another cue to recruitment may be the cessation offeeding by metalarvae (Labelle and Nursall, 1985). It is not known what controls the cessation of feeding, but a possible and prominent cue may be found in lunar periodicity. That is to say, light and currents may be intricately correlated to provide conditions of relatively safe and easy return to the adult habitat. Our sampling method showed that the presence of adults is not required for settlement to occur. Metalarvae were found in appropriate sites whether or not adults were present. Although the presence of adults itself is not required for settlement to a particular site, metalarvae were found exclusively where adults might have been expected to be found. None was ever found at depths exceeding LABELLE AND NURSALL: REDLIP BLENNY BIOLOGY 195

4 m, or in the sand. These facts suggest that redlip blennies do not migrate back to the reef by following the bottom and stopping in crevices along the way, but that they remain pelagic until they detect the proper habitat, to which they descend. Our observations also agree with those conducted on other coral reef species. Sale et al. (1980) noted that juvenile Pomacentrus wardi do not settle preferentially adjacent to adults or on previously occupied adult territory. Williams (1980) observed that for pomacentrid fishes, the presence or absence of adults did not affect the rate of settlement. Williams (1980) also suggested that the settlement pattern of juvenile pomacentrids is primarily the result of active habitat selection, which may be the case for O. at/anticus as well. It is difficult to establish the length of time the larvae remain pelagic before returning to the reef to establish a territory. According to Cote (1987), the peak reproductive period (PRP) for O. atlanticus extends from 10days before full moon until 6 days after. By comparing PRP with metalarval recruitment periods (MRP) as shown by sampling coral heads M and A, it is possible to arrive at a figure that suggests the length of time spent by O. atlanticus as a pelagic larva. Table 4 shows that there is considerable variance in the length of time of larval life, the range being 28 to 69 d, with a mean of 48.7 d. This represents a pelagic life of approx- imately 7 weeks, and is highly variable as for other species studied (Victor, 1982; Brothers et al., 1983). A size variance in recruits was also observed. A sample of 32 specimens, collected during 1984 and 1986, ranged from 42 to 58 mm TL, with a mean of 50.5 mm. Another sample of 27 specimens collected in 1981 ranged in size from 42 to 53 mm TL, with a mean of 45.6 mm. Newly settled metalarvae collected on the reef were subsequently used for ex- amination of otolith growth rings. E. B. Brothers (at our request) observed an average of 28-29 increments on the lapillus of six specimens, followed by a distinctive change in increment spacing, which we believe corresponds to phys- iological, ecological and behavioral changes associated with settlement and meta- morphosis. Our own examination of 26 specimens of sagittae of adults and larvae indicate the deposition of incremental rings averaged 36.7 (range: 26-48) before metamorphosis. Both figures are less than the length of pelagic existence suggested in Table 4. The relationship between otolith increments and pelagic existence, and between hatching and initial deposition of otolith rings are not yet clear (see also Brothers et al., 1983). Microscopic examination of 5-day-old larvae (::::::3mm) reared in an aquarium, showed no visible otoliths in the large otic capsules present then. Otoliths were present in 6 mm larvae caught over inshore waters. It is probable that incremental growth of otoliths does not begin until some time after hatching. We also note that comparison of all otoliths from 63 specimens showed that the sagittae display from 10-12% more rings premetamorphically than do either lapilli or asterisci. This seems to confirm the utility of the sagitta in at- tempting to determine the age of fishes and that not all of the otoliths begin incremental growth at the same time. We are satisfied that we are getting a conservative measure of larval life from the otoliths. Population Survey. - Results of our 1980-1981 population surveys on transect AA are given in Figure 5. The mean population density observed in 1980 was 1.7 blennies·m-2 (range: 1.7-2.2). During 1981, the population remained at rel- atively low levels from January to April (x = 0.5' m-2), and increased dramatically thereafter to reach a maximum density of 2.4·m-2 during July. Similar results were obtained in 1981 at transect BB where we observed average densities 0.8·m-2 between January and April, which increased linearly to 2.2·m-2 by the end of July. Such low densities followed by substantial increases through the 196 BULLETIN OF MARINE SCIENCE, YOLo 50, NO. I, 1992

Figure 4a-c. The relationship of recruitment of Ophioblennius at/anticus to daylight, tidal flow and moon phase, at Barbados, during 1982 (top), 1984 (middle) and 1986 (bottom). Light rectangles represent daylight periods; dark rectangles represent night time. The dates of sampling are recorded beneath the daylight periods. M and A are two isolated coral heads sampled (see text for description). The numbers following M and A represent the catches of metalarval recruits sampled early in the LABELLE AND NURSALL: REDLlP BLENNY BIOLOGY 197

Table 4. The relationship of peak reproductive period (PRP) to metalarval recruitment period (MRP) as measured for Ophiob/ennius at/anticus at particular times in Barbados. PRP extends from 10 d before full moon to 6 d after (Cote, 1987). The mean pelagic life is given by subtracting time periods (5-3). The potential range oflarval pelagic life is calculated from the extreme dates ofPRP and MRP (4-2).· From Tables of Moon phase (American Ephemeris and Nautical Almanac. 1973. U.S. Gov- ernment Printing Office).•• Only one collection, so the date falls within MRP, but may not be its mid-point

Survey year Period 1978 1981 ]982 ]984 1986 I. Full moon· 20 July 19 April 8 May 13 July 24 April 2. PRP 10-26 July 9-25 April 28 Apr.-14 May 3-19 July 14-30 April 3. Mid-PRP 18 July 17 April 6 May II July 22 April 4. MRP 16-27 June 16-27 August 11-21 June 5. Mid-MRP 4 Sept.·· 13 June·· 21 June 21 August 16 June 6. Mean pelagic life 48 d 57 d 46 d 41 d 55 d 7. Pelagic life (range) 33-60 d 28-55 d 41-69 d

summer were also observed throughout the reef habitat occupied by O. at/anticus. These results suggest that the numerical response of the transect AA population to environmental conditions was repres~ntative of the reef population in general. They also indicate that pronounced seasonal changes occur in the redlip blenny population, with minimal numbers being found during the winter. The high sum- mer densities observed in 1980 and 1981 are in agreement with those observed by us during the 1978, 1985 and 1986 spring surveys of fringing reef populations. We do not believe the marked decline in abundance noted in January 1981 to be a normal feature of this population. This decline is undoubtedly part of a seasonal cycle attributable to changes in recruitment rates. However, we cannot discount the possible influence Hurricane Allen, which struck Barbados on 3 August 1980. At that time, exceptionally strong currents were generated, causing extensive damage to the reefs and shorelines, as well as redistributing vast quan- tities of sediments. Woodley et al. (1981) reported that Hurricane Allen disrupted algal beds in shallow waters of Discovery Bay, Jamaica, which was seen in Bar- bados as well. Following Hurricane Allen, Kaufman (1983) and Walsh (1983) noted differences in the behavior and distribution of benthic, territorial, herbiv- orous fishes in Jamaican waters. Abnormal fish activity was also seen in Barbados following the hurricane. Much territorial adjustment took place; fish of many species were seen to be injured, with cuts from the reef and wounds caused by spines of Diadema antillarum. Large numbers of predators were active, presum- ably attracted by injured fish and abnormal behavior. Since the densities did not decrease dramatically immediately after the hurricane (Fig. 5), it is assumed that the population was affected indirectly by the storm.

l- morning each day. The numbers marked with asterisks represent specimens that are metamorphonts rather than recruits, i.e., they are in situ for more than one day and were collected in different stages of metamorphosis. A dash indicates that no sampling was conducted that day. The oblique lines extend across the period oftlowing (i.e., onshore) tide, and intersect the margins at time intervals corresponding roughly to the periods of high and low tides respectively. Tidal data provided by the Barbados Port Authority. The symbols used were: 0 full moon, () first quarter moon, ct last quarter moon, • new moon. Black triangles indicate the night period during which metalarvae recruited to the reef. 198 BULLETIN OF MARINE SCIENCE, VOL. 50, NO. I, 1992

180 Hurricane Allen 160 140 120 Visual 100 . . counls . 80 .- 60 .. 40 .-.--.. 20 .- --.. o 21/05 02/07 13/08 24/09 05/11 19/12 29/01 12/03 23/04 05/06 17/07

Survey Date (1980-1981)

Figure 5. Average number of fishes counted each week along transect AA during the 1980-1981 season. No censuses were conducted during the period of Sept.-Dec., 1980.

DISCUSSION The results of the present study indicate that the reproductive behavior of the redlip blenny resembles that of other tropical blenniids, and is similar to that of other shelter-spawners, as reported by Keenleyside (1979). The reef crest zone occupied by O. at/anticus is characterized by fluctuations in salinity, temperature, current velocity and turbidity. Selective mate choice, parental care, short incu- bation period, and the periodicity of spawning and hatching probably arose to counteract the harshness of the habitat and to ensure maximal survival of the progeny. It is generally assumed that the fitness of offspring increases in relation to the energy invested in them (Pianka, 1970). Redlip blenny eggs are guarded by the male for the short period before hatching (Labelle and Nursall, 1985), but like many other tropical fishes, they produce a large number of progeny, perhaps owing to the intense predation, the competition pressures that operate in tropical reef communities (Johannes, 1978), or the low probability of successful recruitment of larvae to the reef. The fecundity of O. at/anticus appears to be higher, on average, than that of many blenniids, although eggs of similar sizes are produced (Stephens et aI., 1970; Balbontin and Perez, 1979; Peters, 1981). It is recognized that spawning seasons of marine fishes are characteristically longer at lower latitudes (Qasim, 1955; Munro et aI., 1973). In this respect, O. at/anticus conforms to the pattern by spawning regularly throughout the year. If recolonization of living space on tropical reefs is on a "first come, first served basis" as suggested by Sale (1974), Russell et ai. (1974), and Sale and Dybdahl (1975), then spreading reproductive activity over the entire year constitutes an effective means of competing for the available space. Year to year differences in fecundities of temperate species, resulting from environmental effects, are well-established. Thus, it is reasonable to expect similar processes to occur on a monthly basis in tropical communities, at least for mem- bers which spawn throughout the year. Erdman (1976), in a review of the spawning patterns of Caribbean fishes, found many marine species to spawn year-round, with seasonal peaks occurring once or twice a year, while fewer species showed limited and well-defined spawning periods. Munro et ai. (1973) investigated the spawning patterns of Jamaican reef fish and determined that there was a general spawning peak from February to April, although members of some families showed evidence of spawning throughout the year. It would thus appear that the spawning LABELLE AND NURSALL: REDLIP BLENNY BIOLOGY 199 pattern of the redlip blenny is similar but not identical to that of other tropical fishes. The spring peak in gonadosomatic index cannot be attributed directly to any biotic factors such as those generally considered to have some effect on spawning patterns to temperate zone fishes. Steven (1971) found no seasonal variation in the rate of primary production near Barbados. Moore and Sander (1977) showed that no seasonal variation occurred in either biomass or zooplankton in offshore waters of Barbados. Although some seasonal variation in surface water temper- ature and salinity occurred, Sander and Steven (1973) observed no concomitant variation in production rate or standing crop of plankton and nutrient concen- tration inshore, but noted an increase in productivity, measured in various ways, from offshore (150 m depth) to inshore (10 m depth). We found no significant correlation between water temperature or salinity with egg production in O. at- /anticus. nor any indication to suggest that maximum reproductive activity is adjusted to capitalize on greater abundance of larval food at Barbados. Wourms and Bayne (1973) noted that the fall peak in reproductive activity of the Indian Ocean brotulid Dinematichthys ilucoeteoides. corresponds to a period of calm between monsoon seasons. Johannes (1978) noted that throughout the tropics, shallow-water marine fishes have adapted reproductive patterns that re- duce the transport oflarvae far offshore, which improves their chances of returning to shallow water. Hydrographic and atmospheric conditions at Barbados are most calm during early summer, closely following major spawning activity by O. at- [anticus. The redlip blenny may be adapted to maximize recruitment by having a spawning pattern which reduces the chance of drift mortality. It is difficult to interpret with certainty our observations on the distribution of the pelagic phases of O. at/anticus owing to our lack of information of the dis- tribution of the older stages. In general, the biology of tropical marine fish larvae, particularly reef species, is poorly understood (Leis and Miller, 1976). However, there is some information in the literature which helps us tentatively to account for our observations. Constant current regimes around islands such as Barbados have the potential to carry young larvae away from the island. The fact that the inshore fish fauna of Barbados is no less diverse than that of other Caribbean islands indicates that larval transport between islands does occur. However, given the low quantity of food available in offshore waters of low latitudes (Raymont, 1963; Johannes, 1978), it seems unlikely that most fish larvae undergo successful lengthy pelagic migrations. Johannes et al. (1981) argued from varied evidence that the larvae of many reef fishes remain close to natal reefs, despite a pelagic existence. Thus, it appears reasonable to look for a set of conditions that would return a significant number of larvae to the island from which they came. A number of offshore, eddy-like current patterns have been proposed as mech- anisms responsible for the retention of planktonic larvae (Emery, 1964; 1972; Sale, 1970; Powles, 1975; 1976; Lobel and Robinson, 1986; 1988; Lobel, 1989). With respect to such mechanism, Peck (1978) concluded: "Instead of conjecturing as to how the larvae are brought back to the west coast [of Barbados], it may be better to assume that most of the stock is not swept down in the first place. Larval stocks are maintained off the west coast because of a reduction in surface wind stress in the lee of the island, and because Barbados disrupts surface drift." Powles (1975) observed that catches of larvae of inshore fishes was high in the lee of Barbados, and nearly non-existent at windward locations. He also found blenniid larvae in greater abundance at nearshore stations (45 m depth), than at offshore stations (> 180 m depth). Our conclusions are in agreement with those of Peck (1978) and Powles (1975; 1976). A mechanism similar to that proposed by Miller 200 BULLETIN OF MARINE SCIENCE, VOL. SO, NO. I, 1992

(1979) to account for the abundance of tuna larvae in nearshore Hawaiian waters may be appropriate to explain what we know about the distribution of the larvae of O. at/anticus. Miller (1979) suggested that larvae migrate from the wind-driven surface waters to deeper waters, perhaps near the thermocline, where their chance of dispersal away from the island is less, and their chance of returning to adult habitat is greater. Behavioral observations of O. at/anticus larvae (Labelle and Nursall, 1985) and field survey results showed that the larvae remain in surface waters two to four days after hatching, following which they move to deeper water. Strong surface currents at the time of hatching would sweep them away, but at Barbados, modest surface currents and winds in the lee of the island allow some larvae to congregate near the First Ridge, where we found them in greatest abun- dance. From that location, shoreward migration could proceed gradually or abruptly, taking advantage, at the end, of the onshore current of the flowing tide. Given that O. at/anticus hatches near the time offull moon, and that recruitment takes place during a dim-light, night-time period, i.e., sometime near new moon, we hypothesize that the larva have a pelagic existence of 6 to 8 weeks. That is to say, the larvae become recruits to the reef near the time ofthe second new moon following hatching. Most fishes of the Caribbean are thought to have relatively short larval lives, in the order of 3 to 4 weeks (Powles, 1975; Luckhurst and Luckhurst, 1977). The latter authors showed that many such fishes (Grammidae, Apogonidae, Sciaenidae, Pomacentridae, Gobiidae and Canthigasteridae) return to the reef while still small «20-25 mm TL). On the other hand, O. at/anticus returns to the adult habitat as relatively large metalarvae (~50 mm TL). Not only does that represent a huge volume increase, but each fish has stored a mass of as a reserve to carry it through metamorphosis (Nursall and Turner, 1985; Nursall, 1989). Leis and Miller (1976) seemed to suggest that larval size is the best correlate of larval lifetime. That relationship is only weakly supported by examination of the data in Brothers et al. (1983); a regression of standard length on mean age gives a coefficient of determination (r2) of 0.25. Nonetheless, the large size reached by O. at/anticus larvae supports suggestions of a longer larval life and metabolic preparation for metamorphosis and territorial adult life. Brothers et al. (1983), by means of otolith analysis, showed larval lifetimes of 38 species and five un- identified taxa in 12 families of coral reef fish to range from 16 d for an apogonid, to 84 d for an acanthurid. Commonly, the range found was from 3 to 6 weeks. The blenniids examined (two Petroscirtes spp.) had larvalli"es of 21-25 d, but wide ranges within families were apparent, e.g., gobiids (22-47 d), chaetodontids (25-39 d), labrids (26-56 d). Thus, it is not surprising to find a range of sizes and variance in time of recruitment in a species such as O. at/anticus that has a 2-week spawning period followed by larval growth to a large size. Assuming a pelagic existence of 6-8 weeks, the mean growth rate of O. at/anticus larvae will range from about 0.7 to 1.0 mm· d-1• It is similar to that of tropical clupeids (Houde and Palko, 1970; Saksena and Houde, 1972). Tropical fish species exhibit higher growth rates during the early stages of development than temperate species (Randall, 1962; Allen, 1972). Presumably, the nearshore distribution of O. at/anticus larvae allows them to capitalize on the high productivity of coastal waters associated with the island mass effect (Raymont, 1966; Sander and Steven, 1973). Although recruitment in O. at/anticus appears associated with lunar cycles, as shown for other tropical fish (Johannes, 1978; Shulman et al., 1983), variability in the timing of recruitment suggest that other factors may affect it. Williams (1983) suggested that recruitment timing might be related to tidal patterns, though LABELLE AND NURSALL: REDLIP BLENNY BIOLOGY 201 he could not demonstrate it for pomacentrids. Our observations suggests a rela- tionship between recruitment and physical conditions, namely onshore currents at night owing to flowing tide and the period of dim light around new moon. The dim light would provide a measure of protection against some predators; the onshore current would assist the return to the reef. Additional factors undoubtedly influence recruitment rates on a seasonal and annual basis. These include the spawning stock biomass, spawning cycle and oceanographic conditions. The relative importance of each factor can be tenta- tively accounted for based on our censuses. It has been established that spawning occurs year-round and peaks during April and May. Given a pelagic existence of 6-8 weeks, one would expect year round recruitment to occur, with a peak near the new moon period of June and July, just as observed during our study, though the rates are inconsistent throughout the year. In an attempt to account for vari- ation in recruitment in several tropical fishes, Johannes (1978) concluded that it might be revealing to compare the relative strengths of prevailing winds during years of high and low recruitment. Such physical factors were not monitored during our study, but there is some information on the oceanographic conditions which may provide some insight into this process. Hydrographic conditions around Barbados are profoundly affected by the Amazon and Orinoco river outflows between February and September. Steven and Brooks (1972) showed that series of separate, short-lived eddies are formed north ofthe Amazon mouth during the first half of each year. These drift northwest as far as the Lesser Antilles, having their greatest effect on surface (0-25 m) salinity near Barbados from about mid- July until September. Ryther et al. (1967) found nitrate, phosphate and phyto- plankton concentrations to be lower in these low salinity lenses than in surrounding waters. Lewis and Fish (1969) correlated zooplankton changes with local hydro- graphic conditions, rather than with seasonal changes in productivity. Changes in surface waters are also accompanied by changes in the position of the ther- mocline. Steven et al. (1970) showed the thermocline to migrate upward from > 150 m to 15-35 m between January and August, and then migrate downward from August to January. We hypothesize that larval fishes may respond to such environmental changes in such a way that recruitment rates are affected. Our experience with Hurricane Allen in 1980 showed that habitat and behav- ioral changes follow such a disturbance. While the adult population of O. at/anticus was not to be affected markedly immediately afterwards, the storm did occur shortly before the spawning period and must have influenced its success. The possibility also exists that pools of larvae available for recruitment were swept away during the storm. The combination of both processes may have contributed to the large fluctuation in density observed during this study. Sale (1980) reported that tropical fish populations fluctuated by as much as 2.3 times from year to year, which is rather less than we report. While we have not been able to show it directly, we hypothesize that the redlip blenny population of Barbados maintains itself through recruitment of larvae from its own community rather than from distant islands. It remains to be seen if blenniid populations of other islands have similar life history traits. Each of the islands will have important effects on its own oceanic environment by mod- ifying currents, vertical water movement, wave height, primary productivity and zooplankton composition. Little information is available on the effects of the geographical attributes of islands upon the retention of larval stocks. It may be that geographical attributes of the islands are major determinants of the stability of populations of primary consumers, such as O. at/anticus, and ultimately, of the piscivorous fish community as well. Munro et al. (1973) noted that manage- 202 BULLETIN OF MARINE SCIENCE. VOL. 50. NO. I, 1992 ment strategies for fish populations of Caribbean islands and banks will depend on knowledge of the recruitment mechanisms of these populations, and in par- ticular, on whether recruitment is from local populations or from those further upcurrent.

ACKNOWLEDGMENTS

This research was supported by NSERC Operating grants (A-2071 and A-3150) to J. R. Nursall. We are grateful to N. Kawaguchi and N. Newhouse for assisting with otolith collection, S. Stewart and S. Eng for assisting with otolith examination, and L. Turner Chapman for her support during the 1980 field season, and preparation of otoliths. The senior author is most grateful to W. Nixon, whose field assistance proved to be invaluable. The use of facilities at the Bellairs Research Institute of McGill University was appreciated.

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DATEACCEPTED: July 10, 1991.

ADDRESSES:(M.L.) South Pacific Commission. Tuna and Bil/fish Assessment Program. B. P. D5. Noumea CEDEX, New-Caledonia; (J.R.N.) Department of Zoology, University of Alberta, Edmonton, Alberta T6G 239, Canada.