Environmental Variation in Skeletal Morphology Within the Caribbean Reef Corals Montastraea Annularis and Siderastrea Siderea

BULLETIN OF MARINE SCIENCE. 30(3): 678-709. 1980 CORAL REEF PAPER

ENVIRONMENTAL VARIATION IN SKELETAL MORPHOLOGY WITHIN THE CARIBBEAN REEF CORALS MONTASTRAEA ANNULARIS AND SIDERASTREA SIDEREA

Ann Budd Foster

ABSTRACT Environmental variation within the scleractinian species, Monlaslraea annularis and Sid- eraslrea siderea, has been described quantitatively between populations collected in a range of environments within a limited geographic area near Discovery Bay, Jamaica. Characters studied in each species consist of linear measurements on the dimensions and spacing of corallites, the thickness and arrangement of vertical and horizontal structures constructing corallites, and the size and shape of coenosteal voids. Highly variable characters in M. annalaris describe the size of corallites, the porosity of the coenosteum, and the thickness of columellae and endothecal dissepiments. Highly variable characters in S. siderea describe the size and arrangement of synapticulae, the thickness of columellae, and the spacing of dissepiments. In both species, the variation of each character is continuous. Different characters have different amounts and different patterns of variation. The magnitude of interpopulation variation is generally less than or equal to that of intracolony variation. Comparisons between species show that the same character often varies to differing degrees and has different patterns of interpopulation variation. Growth rate varies more in S. siderea. whereas corallite dimensions vary more in M. annu/aris. Vertical and horizontal corallite structures vary equally in the two species. In general, variation is correlated with light intensity and food supply in M. annuloris and with sedimentation rate in S. siderea. These results show that environmental variation is an important attribute of the species and suggest that variation is related to the magnitude and type of energy sources used by species. M. annllloris may be deriving energy largely from products of zooxanthellae photosynthesis while S. siderea may be deriving energy from organic particles in fine sediment.

Classic studies by Vaughan (1911, 1917a, 1918) and recent work (Veron and Pichon, 1976; Veron et aI., 1977; Wijsman-Best, 1972; 1974; Foster, 1977; 1978; 1979) in scleractinian taxonomy have shown that numerous reef-coral species have highly plastic phenotypes. The corallite morphology of species with a range of feeding strategies (in sensu Lewis and Price, 1975) from at least three scleractinian suborders varies significantly between environments. It appears that each species has a unique morphologic "response" to the environment. Some species show greater amounts of variation than others, and some alter their morphology in a characteristically distinct manner. In general, "inflexible" scleractinian species seem highly specialized for one specific environment, whereas phenotyp- ically plastic species inhabit many environments (Yonge, 1935a; b). These find- ings suggest that plasticity may allow many scleractinians to adapt readily to a variety of environments with minimal natural selection and genetic differentiation occurring within species. The purpose of this paper is to examine and compare plasticity in two common Caribbean species by describing populations from nearby localities. Previous work has suggested that the variation between these populations is caused largely by environmental factors and, therefore, may be considered a result of plasticity (Foster, 1978; 1979). The data presented in this paper document in detail the morphologic characters which vary and the patterns of variation which exist between characters in each species. Analysis of these patterns is used empirically to determine which specific environmental factor(s) may be causing the observed variation. Hypotheses are proposed explaining the morphologic response of scler- 678 FOSTER: ENVIRONMENTAL VARIATION IN REEF CORALS 679 actinian species to the environment and the differences in this response between species. Throughout the paper, the term "population" refers to all the colonies collected in one locality. No assumption is intended of a common gene pool within each population or of mutually exclusive gene pools between populations.

SPECIES STUDIED Two species, Montastraea annularis (Ellis and Solander, 1786), and Sideras- trea siderea (Ellis and Solander 1786), were selected for study because: (1) both species commonly occur in a range of reef-related habitats (Goreau, 1959), (2) both have massive colony shapes, and (3) corallites in both are non-polymorphic and are separated by discrete wall structures. The two species have similar trabecular fan systems, corallite diameters, and endothecal dissepiments. They differ in colony form, wall structure, and the development of the coenosteum (Vaughan, 1915; Wells, 1956). Montastraea annularis is a species of the suborder Faviina (superfamily Fa- viicae, family Faviidae, subfamily Montastreinae). Species of Montastraea form incrusting or subfoliaceous, plocoid colonies. The theca is septothecate with no synapticulae. The septa are laminate and exert, with rare perforations and dentate margins. The columella is trabecular. Montastraea annularis is distinguished pri- marily by having three cycles of septa and small calices (2-3 mm in diameter). It has subequal costae and an equal number of primary and secondary septa which extend to the columella (Vaughan, 1919). Siderastrea siderea is a species of the suborder Fungiina (superfamily Agari- ciicae, family Siderastreidae). Species of Siderastrea generally form cerioid colonies. Thecae are well developed and consist of several synapticular rings. The septa are porous with beaded margins. One or more papillary trabeculae form the columella (Wells, 1956). Siderastrea siderea is distinguished by a complete fourth cycle of septa, a deep columellar fossa, calices 3-5 mm in diameter, and 6-8 septal teeth per millimeter (Vaughan, 1919). Considerable variation has been reported between colonies within each species. In Montastraea annularis, colony shapes range from "round-bulbous" to "f1at- plated" with increased fore reef depth (Goreau, 1963; Barnes, 1973; Dustan, 1975), whereas numerous "varieties" have been distinguished on the basis of size and spacing of the calices, the number of septa, the elevation of the calices above the colony surface, the porosity of the exotheca, and the overall colony shape (Ver- rill, 1902; Vaughan, 1919). Intracolony variation has also been noted in corallite structures. Slowly extending portions of colonies have more widely spaced corallites, less exert calices, thicker but less prominent septa, and more massive thecal and coenosteal structures (Land et aI., 1975). In Siderastrea siderea, colony shapes range from hemispherical to flat (Roos, 1976). Little has been reported about variation between colonies in corallite structures. Verrill (1902) observed that "impoverished" varieties of S. siderea having smaller calices, shallower columellar fossae, and fewer septa strongly resemble S. radians. My preliminary comparisons between impoverished varieties of S. siderea and S. radians suggest that the following features are diagnostic of S. radians: (1) the solid, thick columella composed of three fused papillae; (2) the distinct sclerodermite margins; (3) the thick septa; (4) the reduced number of synapticular rings. Montastraea annularis and Siderastrea siderea differ in basic polyp morphology and in overall behavior. Polyps of M. annularis usually have two cycles of longer retractile tentacles and may expand as much as 3 mm over the colony 680 BULLETIN OF MARINE SCIENCE, VOL. 30, NO.3. 1980

A PR

LAG

RF sc

~-+-1 ~-<-1 ~-+-1 ~-+1-~ 4..0 5.0 6..0 7.0 mm

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RF 1 sc N ~+I __ ~.--+I ~_, ~.r--<-I~, __ 3..0 4,.0 5,.0 mm Figure I, (Left) Map .of Discavery Bay, Jamaica, shawing the lacatian .ofthe five callecting lacalities. (PR, patch reef lacality; LAG, lagoan lacality; RF, reef locality; SC, sand channellacality; ES, east forereef lacality,) Figure 2. (Right) Means and standard deviatians .of characters describing band thickness. The midpaint .of each harizantalline represents the mean. The length .of the line on either side .of the midpoint is .one standard deviatian. A, Montastraea alllllliaris; B. Siderastrea siderea,

surface. When the polyp retracts, the column wall is partially drawn over the oral disc covering the tentacles. Numerous continuous mesenteries and the gastro- coelomic cavity permit communication between polyps. Polyps of S. siderea have four cycles of short, widely separated tentacles and may expand minimally. When the polyp retracts, the column wall may not infold; consequently, the tentacles always remain exposed. Mesenteries are perforated by synapticulae, and no communication exists between polyps (Duerden, 1902). In feeding, both species use tentacles and mucus nets to capture and ingest food (Lewis and Price, 1975); however, M. annularis appears to be a more active carnivore whereas S. siderea seems to be a more efficient suspension feeder (Lewis, 1976; 1977). Colonies of both species expand fully only at night (Porter, 1974); however, some shallow M. annularis colonies have been found fully ex- panded during the day (Dustan, 1975). In sediment removal, both species remove a wide range of sediment sizes; however, S. siderea more readily removes fine particles (Hubbard and Pocock, 1972). Both species have geographic distributions ranging throughout the West Indies, Florida, and Bermuda (Vaughan, 1919); however, little is known about larval transport or settling behavior in either species. Genetic differentiation between shallow and deep populations of M. annularis has been suggested by Dustan (1975) but geographic variation has not been studied in either species. Similarly no information has been collected on recruitment patterns or population structures.

COLLECTING LOCALITIES

Caral calanies were callected at five lacalities (Fig. I) near Discavery Bay, Jamaica which were selected t.o represent a maximum range .of environmental factars within a limited geagraphic area. These lacalities are: (I) a patch reef lacality at the sauth end .of Discavery Bay at a depth .of 3 m, (2) a laga.on l.ocality an the west side .of Discavery Bay at a depth .of 16 m, (3) a reef lacality narth- narthwest .of the laga.on l.ocality at a depth .of 20 m, (4) a sand channell.ocality 150 m west .of the reef FOSTER: ENVIRONMENTAL VARIATION IN REEF CORALS 681

Table I. Relative means of environmental factors at collecting localities (Descriptions in parentheses based on empirical evidence)

Suspended Particle Concentration Horizontal & Bacterial Water Velocity Sedimentation Content Locality ··water energy" Rate Light Intensity "food supply"

Patch Reef (PR) high*t moderatet high* (high) Lagoon (LAG) low*t hight low* (high) Reef (RF) high*t lowt low-moderate* (low) Sand Channel (SC) hight lowt (moderate) (low) East Forereef (ES) (very high) high§ (moderate-high) (low?)

SOllrces: • Brakel (1976): t Foster (1978). Appendix lb. c; * Foster (1978). Appendix Ie. f; § Moore & Shedd (1977).

locality at a depth of 20 m, (5) an east fore reef locality approximately I km east of the reef locality at a depth of 15 m. The patch reef locality is located on a small platform (approximately 50 m by 50 m in dimension) constructed of lithified skeletons of corals and coralline algae. The area surrounding the platform (8 m in depth) consists of the Tha/assia and bare sand environments described by Jackson (1972). Collections were made near a station located on the south central portion of the platform near its contact with the adjacent sand. Coral cover consisting largely of Montastraea, Agaricia, Favia, Porites, and Acropora is sparse in this area and colonies are usually less than 20 cm in diameter. Predation on corals by echinoids, gastropods, and fish was observed to be especially intense at this locality. The lagoon locality lies on the western edge of the "low energy," deep sediment basin described by Reiswig (1973) between the Porites and Madracis zones delineated by Bonem and Stanley (1977). Corals were collected on and below a ledge above a 30 m dropoff located approximately 200 m east of the Discovery Bay Marine Laboratory. Corals on the ledge consist of mounds (approximately 30 cm in diameter) of the genera Step/wnocoenia, Porites, Siderastrea, Montastraea, and Mussa sparse- ly scattered over a T/w/assia-covered area. The dropoff is populated by numerous sponges and by patches of Madracis decactis. The reef locality is located within a moderately sloping "lobe" of the fore reef terrace near its junction with the fore reef escarpment (Goreau and Land, 1974). A few small mounds of the collected species occur below extensive stands of Acropora cervicornis which cover and dominate the reef framework. However. most massive colonies (Montastraea, Siderastrea, Porites, Madracis. and Agaricia) are scattered over the barren reef framework between patches of dead Acropora cervicornis which are covered by algae (the "algal lawns" of Kaufman, 1977). The sand channel locality lies on a sandy tract on a flat ledge at the head of a steeply sloping, incised channel. Immediately south of the area, three smaller channels join to form this broad tract. Numerous collapse blocks called "coral islands" (Kinzie, 1973) are scattered across the tract. These are colonized by large (up to I m diameter) massive corals (Monta,~traea, Siderastrea, Dip/aria, Porites, Agaricia, Dichocoenia). The east forereef locality is located on a broadly sloping plain east of the Kaiser ship channel. The substrate consists of a patchy arrangement of sandy areas and reef framework covered by stands of Acropora cervicornis. The well-established zonation pattern west of the Kaiser channel (Goreau, 1959) is poorly developed and a diverse assemblage of corals is scattered randomly across the plain. Corals were collected on or adjacent to sandy areas. Quantitative studies of many environmental factors at or near each of the five localities have been attempted by numerous workers. Relative values of four environmental parameters at each locality are summarized in Table 1. In general, means of monthly measurements of temperature made on the forereef (Dustan, 1975) and in the bay (Jackson, 1972; Reiswig, 1971) as well as my summer measurements (Foster, 1978) suggest that annual patterns of temperature variation are approximately equivalent at the five localities. Similarly, though sporadically reduced salinities occur in the bay following winter storms, annual salinity variations are less than 2% in the bay (Jackson, 1972) and summer means appear equal in the bay and fore reef (Foster, 1978). Though surge activity is especially strong in all localities during winter storms, it is most intense at the patch reef locality (Foster, 1978). Zooplankton abundance is minimal in samples from waters near both the outer reef and bay bottom, however the particle concentration and volume of bacteria as well as particulate organic carbon content is greater in bay than in outer reef water samples (Reiswig, 1972). Similarly, bacterial content of sediments is generally higher in the bay than on the fore reef (Pigott, 1977). 682 BULLETIN OF MARINE SCIENCE. VOL. 30. NO.3. 1980

METHODS Sampling Design

As in other colonial animals, intraspecific morphologic variation occurs at four levels in scleractinians: (I) within an individual, (2) between individuals within a colony, (3) between colonies in a population, (4) between populations (Oliver, 1968; Boardman and Cheetham, 1969; Boardman et aI., 1970). Since this study is concerned only with environmental variation, attempts have been made to sample populations in a way that would eliminate or reduce any bias caused by non-environmental variation at each level. At level I, variation within an individual, the most significant non-environmental source of variation is ontogeny. Mori et al. (1977) and other earlier workers (Duerden, 1904; Boschma, 1929; Stephenson, 1931) have found that insertion of the third and fourth cycles of septa occurs in the final stage of corallite development prior to maturity. No further age-related changes in corallite morphology after maturity have been recorded. Consequently, in the colonies sampled in the present study, only individuals with well-developed tertiary septa were analyzed. At level 2, intracolony variation between individuals, the most significant sources of variation are: (a) astogeny and (b) polymorphism. Scleractinian colonies generally mature at an age of 7-10 years and often survive several centuries (Stephenson and Stephenson, 1933; Abe, 1937; Connell, 1973); however, no change in morphology or distinct astogenetic stages have been recorded during any period of colony growth. Nevertheless, colony growth is often described as sporadic (Wood-Jones, 1912; Mayor, 1924; Edmondson, 1929; Stephenson and Stephenson, 1933) and, in some species, growth rate reduces with age (Vaughan, 1915; Mayor, 1924; Abe, 1937; Motoda, 1940; Goreau and Goreau, 1960; Connell, 1973; Buddemeier and Kinzie, 1976). To avoid any possible bias caused by astogenetic variation, most colonies were between 10 and 20 years of age as shown by x-radiography. All colonies were probably mature but not old enough to experience senility. Polymorphism in the form of specialized feeding, reproductive, protective, or supportive individuals has never been documented in scieractinians; however, in branched species, apical polyps often assume a more important role in growth and reproduction than radial polyps (Wood-Jones, 1907; Goreau and Goreau, 1959). Therefore, the morphology of apical polyps differs from that of radial polyps (Duerden, 1902; Verrill, 1902). To avoid bias caused by polymorphism, two non-branching species were chosen for analysis. At level 3, the intercolony level, and at level 4, the interpopulation level, the most significant non- environmental source of variation is genetic. This source is especially important between populations where genetic differentiation may have occurred. To reduce any genetic bias, populations were collected from a limited geographic area. Quantitative estimates of variation were made at level 2 (the intracolony level), level 3 (the intercolony level), and level 4 (the interpopulation level). By nature of the sampling design, all variation at level 2 is caused by only environmental factors, whereas variation at levels 3 and 4 is caused by environmental and genetic factors. Estimates for level 2 approximate the minimal magnitude of po- tential environmental variation in a species.

Sampling Technique and Sample Preparation

Ten specimens of Montastraea allllu/aris were collected within a 20 m radius of the lagoon, reef, and sand channel stations, and two specimens of M. allllll/aris were collected within a 20 m radius of the patch reef station. Specimens collected near the patch reef, reef, and lagoon stations consisted of whole colonies measuring 10-20 cm in maximum diameter. Specimens collected near the sand channel station consisted of living portions of healthy columns (10-20 cm diameter) of larger (1-2 m) "columnar lobate" colonies. Eight similar-sized whole colonies of M. allllll/aris from the patch reef (SUI 4542574) were provided by S. Ohlhorst. Ten specimens of Siderastrea siderea were also collected within a 20 m radius of the patch reef, lagoon, reef, and sand channel stations. These specimens consisted of whole colonies measuring 10- 20 cm in maximum diameter. On each colony, one slab with a uniform thickness (5-8 mm) was cut along the greatest colony length through the colony axis. Two longitudinal and one transverse thin sections were prepared from the colony center and from the colony edge. Longitudinal sections were cut within 2-3 cm of the colony surface and were oriented to exhibit the maximum corallite length along the maximum corallite diameter. This position was ascertained by observing the length and orientation of the trabecular axis and a columella distinct from the septa. Transverse sections were cut 2-5 mm from the colony surface and were oriented so that corallites have an approximate circular shape. Measurements of corallite structures were made on five corallites from the colony center and five from the colony edge in M. allllll/aris and on three corallites from colony center and colony edge in S. siderea. FOSTER: ENVIRONMENTAL VARIATION IN REEF CORALS 683

VARIATION IN COLONY SHAPE In M. annularis, the shape of colonies from the patch reef ranges from low incrusting mounds to bulbous forms with smooth to lumpy outer surfaces. Col- onies from the lagoon consist of rounded hemispheres with smooth surfaces. Their internal skeleton is altered by irregular growth during periods of partial colony death and subsequent overgrowth. Reef colonies have lumpy surfaces and one of three shapes: (1) an amorphous incrusting shape, (2) a skirted hemispherical shape, (3) a knobby, columnar-lobate shape. Sand channel colonies have knobby columnar-lobate shapes with irregular surfaces. Two shapes are common among colonies from the east forereef: (1) a knob or column with a smooth surface, (2) a flat plate with a lumpy surface. Statistical tests (analysis of variance and multiple t-tests) using variables describing the linear dimensions of colonies suggest that little difference exists in overall colony shape between these populations of M. annularis (Foster, 1978). In S. siderea, colonies from the patch reef have low, irregular, incrusting mound shapes and contain numerous bore structures. Lagoon colonies are hemispherical in shape with highly irregular surfaces caused by periods of death and subsequent overgrowth and by extensive boring. Reef colonies consist of distinctly layered columns with flat upper surfaces. Surface irregularities caused by interference of growth by Acropora cervicornis are common. Colonies from the sand channel are hemispherical in shape with smooth upper surfaces. Statistical tests (analysis of variance and multiple t-tests) using variables describing the linear dimensions of colonies suggest that only the reef population has a significantly distinct shape in S. siderea (Foster, 1978). Additional statistical tests (t-tests) suggest that the colony shapes of specimens from four environments (PR, LAG, RF, SC) are the same in the two species (Foster, 1978). Sand channel colonies of M. annularis have a slightly more columnar shape, whereas lagoon colonies of S. siderea grow at greater angles from the central vertical colony axis.

VARIATION IN GROWTH RATE To determine the growth rates of colonies from the five populations, the slabs were x-rayed and thicknesses of high and low density band couplets were measured on the x-radiographs using the techniques described by Buddemeier et al. (1974). The thickness of each density band couplet was measured to the nearest tenth of a millimeter along a line parallel to the direction of maximum colony growth. Since annual and "stress" bands (Hudson et aI., 1976) could not be distinguished, all clearly visible bands on each colony were measured. Data consisting of colony means are listed in Foster (1978). To increase the sample size, 10 colonies from a transplantation study (Foster, 1979) have been added to the patch reef, lagoon, reef, and sand channel samples. In M. annularis use of statistical tests (Table 2) (Foster, 1978) suggests that variances of the reef and sand channel samples are less than variances of other populations. Means of the lagoon, reef, sand channel, and east fore reef populations are less than the patch reef mean (Fig. 2A). In S. siderea, results of statistical tests (Table 2) (Foster, 1978) suggest that mean growth rate is highest in the lagoon, intermediate in the reef and patch reef, and lowest in the sand channel. Variances of the four populations are equal (Fig. 2B). In both species, estimates of intracolony variation are equal to estimates of intercolony variation (Foster, 1978). Results of t-tests indicate that the mean band thickness of M. annularis (5.28 mm) is significantly greater than the mean of S. siderea (3.90 mm) in the combined 684 BULLETIN OF MARINE SCIENCE, VOL. 30. NO, 3. 1980

Figure 3. MOlltastraea allllu/aris. SEM photographs of the upper surface of corallites (scale bar = 0.2 mm). A. Patch reef specimen (SUI 45427-2); B. Lagoon specimen (SUI 45439-2); C. Reef specimen (SUI 45448-2); D. Sand channel specimen (SUI 45462-2). sum of colonies from four environments (PR, LAG, RF, SC); however, magni- tudes of F-values in analyses of variance (Table 2) suggest that the degree of interpopulation variation is greater in S. siderea. The species have equal estimates of intracolony variation in the patch reef and lagoon populations, but intracolony variation in M. annularis is greater than intracolony variation in S. siderea in the reef and sand channel populations. Estimates of intercolony variation are generally equal but may be greater in M. annularis than in S. side rea in the lagoon environment (Foster, 1978).

Table 2. Statistical tests performed on bnd thickness (Bartlett's test determines whether sample variances are equal; the analysis of variance determines whether sample means are equal; values of C( > .05 suggest that the variances or means are equal)

Species Banlelt's Test ANOVA

M. alll/II/aris F 5.15 F 10.75 d.f. 4,8998 d.f. 4,85 C( 0.000 C( 0.000 S. siderea F 4.96 F 22.85* d.f. 3, ]0397 d.f. 3,76 C( 0.002 C( 0.000

,.. Log transformation of the data used. FOSTER: ENVIRONMENTAL VARIATION IN REEF CORALS 685

VARIATION IN CORALLITE STRUCTURES Qualitative Observations In both species, variation between colonies collected in different reef habitats can be readily observed in corallite structures. In M. annularis, corallite diameters tend to be greater in the patch reef and lagoon populations and septa are thicker in the reef and sand channel populations (Fig. 3). Septal ornamentation is best developed in patch reef specimens. The columella fills a large portion of intracorallite area in the reef and sand channel populations and only a small portion in the patch reef population. The thickness of trabeculae forming the columella appears greatest in the reef and sand channel populations, intermediate in the patch reef population, and lowest in the lagoon population. The endotheca is especially thin in the lagoon population and more widely spaced in the patch reef population (Fig. 4). The coenosteum is more porous in colonies from the patch reef and lagoon. Exothecal dissepiments are shorter and thicker in the reef and sand channel populations and more widely spaced in the patch reef population. Coenosteal voids in the lagoon population have a more rectangular shape (Fig. 5). In S. siderea. corallite diameters are smaller in the patch reef population and septa are thicker in the reef and sand channel populations (Fig. 6). Trabeculae forming the columellae appear thinner in the lagoon population. The amount of intracorallite area filled by thecal material is greatest in the reef and sand channel populations, intermediate in the lagoon population, and least in the patch reef population. Synapticulae are longer and thinner in lagoon specimens and more widely spaced in specimens from the patch reef and lagoon. Fewer synapticular rings form the theca in specimens from the patch reef. Dissepiments are thicker in the patch reef and lagoon populations and less widely spaced in the lagoon population (Fig. 7). Measurement Techniques The characters which were measured are listed and described in Tables 3 and 4 and illustrated in diagrams in Figures 8 and 9. Throughout the paper, the term "vertical" corallite structures refers to skeletal structures such as the septa and columellae which are oriented vertically within a corallite. The term "horizontal" corallite structures refers to skeletal structures such as the synapticulae and endothecal dissepiments which are oriented horizontally within a corallite. Because of the difference in construction of the theca between the two species, the theca is considered a vertical corallite structure in M. annularis and a horizontal corallite structure in S. siderea. The term "dimensions" of corallites refers to the height of the portions of corallites most recently occupied by polyps and to the diameter of the corallites. In M. annularis, five corallites were measured from the center and edge of each colony. In S. siderea. three corallites were measured from the center and edge of each colony. The data used in the following analyses (Foster, 1978)consist of means of each character: (I) for each corallite within each colony and (2) for each colony within each population. Because of non-normality in some of the characters in the lagoon and reef populations in M. annularis (Table 3), one colony was deleted from the M. annularis lagoon and reef populations in the discriminant analysis and in all univariate analyses. Similarly, because of the non- normality of two characters in the S. siderea lagoon population (Table 10), one colony was deleted from the S. siderea lagoon population in the discriminant analysis and in all univariate analyses. In univariate and multivariate variance 686 BULLETIN OF MARINE SCIENCE. VOL. 30. NO.3, 1980

Figure 4. Montastraea annu/oris. SEM photographs of broken longitudinal sections of corallites (left scale bar = 0.2 mm, right scale bar = 0.05 mm). A, B. Patch reef specimen (SUI 45427-1); C, D. Lagoon specimen (SUI 45439-1); E, F. Reef specimen (SUI 45448-1); G, H. Sand channel specimen (SUI 45462-1). FOSTER: ENVIRONMENTAL VARIATION IN REEF CORALS 687

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's.

Figure 5. Montastraea annl//aris. SEM photographs of broken longitudinal sections of coenosteum (scale bar = 0.1 mm). A. Patch reef specimen (SUI 45427-1); B. Lagoon specimen (SUI 45439-1); C. Reef specimen (SUI 45448-1); D. Sand channel specimen (SUr 45462-1).

component analyses, all the collected data were used. In M. annularis, three characters (% extratheca, % theca, % intratheca) were not included in multivariate analyses. The computer programs used in each analysis are listed in Foster (1978).

Multivariate Analyses Two types of multivariate tests have been used to quantify the previous observations: (1) multivariate analysis of variance, and (2) discriminant analysis. Since the assumptions of multivariate normal distributions and equal covariance structures cannot be tested with currently available computer programs, the power of the tests may be reduced (Huberty, 1975). In each species, multivariate analyses of variance have been performed separately on three groups of characters using a fixed model nested design. The results (Foster, 1978) suggest: (I) the colonies within each population have different morphologies, (2) the morphology characteristic of each population is significantly distinct, (3) amounts of variation at intracolony, intercolony, and interpopulation levels are roughly equivalent. Comparisons between species (Foster, 1978) suggest that amounts of variation at the intracolony, intercolony, and interpopulation levels are equal in the two species. 692 BULLETIN OF MARINE SCIENCE, VOL. 30. NO.3. 1980

Figure 6. Siderastrea siderea. SEM photographs of the upper surface of corallites (scale bar = 0.2 mm). A. Patch reef specimen (SUI 45481-2); B. Lagoon specimen (SUI 45492-2); C. Reef specimen (SUI 45497-2); D. Sand channel specimen (SUI 45509-2),

Discriminant analysis was performed using a total score formulation. Selection of characters was based on a stepwise method which minimized Wilks' lambda. In M. annularis three functions had significant discriminating power at ex = .05. The first function accounts for 68.35% of the variance explained by the populations, the second for 18.67%, and the third for 10.13%. In S. siderea, two functions had significant discriminating power. The first function accounts for 77.51% of the variance and the second for 18.32%. Plots of scores (Fig. 10) of colonies calculated using the first and second functions (Foster, 1978) show that colonies from each locality form a distinct group in both species. In M. annularis, slight overlap occurs between the reef and sand channel populations. The first discriminant function separates the patch reef group from the east fore reef and lagoon groups, and the east forereef and lagoon groups from the reef and sand channel groups. The second discriminant function separates the lagoon group from the east forereef group and the reef group from the sand channel group. In S. siderea, slight overlap occurs between the lagoon and patch reef groups and between the reef and sand channel groups. In all other cases, no overlap occurs. The first function separates the lagoon and patch reef groups from the sand channel and reef groups. The second function separates the lagoon group from the patch reef group and the sand channel group from the reef group. FOSTER: ENVIRONMENTAL VARIATION IN REEF CORALS 693

Figure 7. Siderastrea siderea. SEM photographs of broken longitudinal sections of corallites (left scale bar = 0.2 mm, right scale bar = 0.1 mm). A, B. Patch reef specimen (SUI 45481-1); C, D. Lagoon specimen (SUI 45492-1); E, F. Reef specimen (SUI 45497-1); G, H. Sand channel specimen (SUI 45509-1). 694 BULLETIN OF MARINE SCIENCE, VOL. 30, NO.3, 1980

A d I £lOO () .000 e tl . O.st Q oe~1 (] o2t 0

00 0 000 000 000 o 00 000 o 0 0 o 00

Figure 8. (Left A, B, C) Montastrea anna/aris. Line diagrams illustrating the locations of measurements, A. Longitudinal section; B. Transverse section; C. Slab. Figure 9. (Right A, B, C) Siderastrea siderea. Line diagrams illustrating the locations of measurements. A. Longitudinal section; B. Transverse section; C. Slab.

The relative importance of characters in the two analyses was determined using standardized discriminant function coefficients and correlations between variables and functions (Tables 5, 6). The standardized discriminant function coefficients are weights estimating the relative unique contribution of each character in an analysis. The correlations estimate the relative common contribution between characters (Mulaik, 1972). In M. annularis, the columella thickness/diameter ratio (cI/d 1) and fossa depth (t) are most heavily weighted in the first function. Corallite diameter (dl), coenosteal void shape (exl/exs), and endotheca thickness (ent) contribute highly to the second function. Corallite diameter (dl), endotheca thickness (ent), and the columella thickness/diameter ratio (c1/dl) are most significant in the third function. In S. siderea, the theca thickness/diameter ratio (t2/d2) and synapticula spacing (ss]) contribute highly to the first function, FOSTER: ENVIRONMENTAL VARIATION IN REEF CORALS 695

A B 2.0 L L L 2.0 , L R LL p S Ss p p 5 5 5 , f . pp E S 5 R R S R R' S 0,0 p R RS, E E RS~. S R R P 0,0 R S S S , P P R P L P P L .L L -2,0 p -2.0 L L J -2.0 0.0 2.0 -2.0 0.0 2.0

Figure 10. Results of discriminant analyses: Plots of first discriminant scores (x-axis) vs. second discriminant scores (y-axis). (P, colonies from patch reef; L, colonies from lagoon; R, colonies from reef; S, colonies from sand channel.) A. Montastraea annu/aris; B. Siderastrea siderea.

Table 5. Montastraea annu/aris: Standardized discriminant function coefficients (SOFC) and correlations between discriminant functions and original variables (COR)

Discriminant Discriminant Discriminant Character Statistic Function I Function 2 Function 3

cl/d I SOFe 0.458** 1.371* 3.018* COR 0.844** 0.040 0.334* exl/exs SOFe -0.206 -0.402 0.495 COR -0.433 -0.668** 0.283 dl SOFC -0.073 1.93]** 3.583** COR -0.798* -0.030 -0.118 t1 SDFC -0.064 -0.088 0.471 COR 0.723 0.275 0.226 cl SOFe -0.005 -1.395* -2.740 COR -0.397 -0.040 0.130 ent SOFe -0.057 0.289 -0.012 COR 0.148 0.633** 0.369** ens SOFe -0.053 0.252 -0.416 COR -0.465 0.385 -0.291 ext SOFe 0.132 0.002 0.212 COR 0.582 0.321 -0.094 d2 SOFe 0.076 -0.295 1.076 COR -0.667 -0.001 0.316 SOFe 0.144 0.299 -0.082 COR 0.347 0.537* 0.125 n SOFe -0.033 -0,227 -0.567 COR 0.546 -0.325 -0.001 f SOFe -0.422* 0.364 0.002 COR -0.752* 0.440 0.101 end SOFe -0.199 0.194 0.258 COR -0.585 0.141 0.345*

• Variables contributing most heavily to the discriminant function. 696 BULLETIN OF MARINE SCIENCE. VOL. 30. NO.3. 1980

Table 6. Siderastrea siderea: Standardized discriminant function coefficients (SOFC) and correlations between discriminant functions and original variables (COR)

Discriminant Discriminant Character Statistic Function I Function 2

cl/dl SOFC 0.108 -0.223 COR 0.447 -0.377 c2/d2 SDFC -0.052 -0.668** COR -0.165 -0.839** t2/d2 SOFC -0.459** 0.051 COR -0.679* 0.053 dt SOFC 0.299* -0.358* COR 0.704* 0.046 ds SOFC 0.235 -0.378* COR -0.009 -0.688* ss 1 SOFC 0.291* 0.209 COR 0.802** 0.253 512 SDFC -0.148 -0.132 COR -0.482 -0.287 ss2 SDFC 0.227 0.080 COR 0.517 0.235

• Variables contributing most heavily to the discriminant function.

whereas the columella thickness/diameter ratio (c2/d2) and dissepiment spacing (ds) are most heavily weighted in the second function. In general, heavily weighted characters in M. annularis describe the dimensions of corallites and coenosteal voids, whereas heavily weighted characters in S. siderea describe thecal material. In both species, the size of the columella and the thickness and arrangement of internal dissepiments contribute significantly to the analysis.

Univariate Analyses Description of Variation.-Three types of statistical tests have been used to compare populations within each species: (I) tests comparing population variances, (2) tests comparing population means, (3) tests comparing amounts of variation at the intracolony, intercolony, and interpopulation levels. Tests used to compare population variances include Bartlett's tests (Appen- dices A, B) and F-tests (Foster, 1978). In M. annularis, the results suggest that the variances of the five populations are equal in most of the characters analyzed (Table 7). Seven characters, however, do not have equal population variances. Of these seven, variances are significantly higher in the patch reef, lagoon, and east forereef populations in % thecal surface area (%T) and % extrathecal surface area (%E). They are higher in the patch reef and lagoon populations in trabecula thickness (tr) and lower in the patch reef and lagoon populations in exotheca thickness (ext). Endotheca depth (end) has a lower variance in the lagoon population. In all seven characters, no one population has a consistently high variance. In S. siderea, the results of tests testing the equality of population variances also suggest that the variances of the four populatians are equal in most of the characters analyzed (Table 7). Five characters do not have equal population variances. Of these, corallite diameter (d!) has a higher variance in the lagoon population, columella thickness (c I, c2) has higher variances in the lagoon and patch FOSTER: ENVIRONMENTAL VARIATION IN REEF CORALS 697

Table 7. Results of Bartlett's tests teting univariate equality of population variances and of analyses of variance testing equality of population means

Types of Variances Variances Means Species Characters Equal not Equal Means Equal not Equal

MO/ltastraea Dimension n,dl,d2,f, end n, dl, d2, end, 1II11l1liaris and spacing %1 f,%1 of corallites Vertical #s, s, cl, c2, tr, t2, %T cl #s, tr, s, c2, corallite cl/dl, c2/d2, tl c lId I, c2/d2, structures tl, t2, %T Horizontal ens ent ens, ent corallite structures Coenosteal exl, exs, exl/exs ext, %E ext, exl, exs, structures exl/exs, %E

Siderastrea Dimensions of f, d2? dl, dd dd,f dl, d2 siderea corallites Vertical T#s, #s, s, cl, c2 T#s, #s, s, c lid I, c2/d2 corallite c lId I, c2/d2 cl, c2 structures Horizontal t2, t lId I, t2/d2, tl tl/dl t I, t2, t2/d2, corallite #sr, st, sll, s12, #sr,st,sll, structures ss I, ss2, dt, ds s12, ssl, ss2, dt, ds

reef populations, and dissepiment depth (dd) has a lower variance in the sand channel population. In all five characters, the lagoon population has a high variance. Tests used to compare population means include analyses of variance (Appen- dices A, B) and t-tests (Foster, 1978). In M. annularis, the results suggest that population means are not equal in all characters except columella thickness (c\). The variation of means is especially pronounced in characters having high F- values in the analysis of variance (Appendix A). These include: fossa depth (t), the columella thickness/diameter ratio (el/dl), theca thickness (t2), % thecal surface area (%T), exotheca length (exl), and % extrathecal surface area (%E). Study of variance components computed for the intracolony, intercolony, and interpopulation levels (Appendix A) and trends of variation in components (Table 8) suggest that: (1) amounts of intracolony variation are equal in all characters, (2) amounts of intracolony variation are greater than or equal to amounts of intercolony variation in all characters, and (3) the amount of interpopulation variation is greater than or equal to the amount of intercolony variation in highly variable characters. In S. siderea, the results of tests testing the equality of means suggest that population means are not equal in most characters. Seven of the 23 characters analyzed did, however, have equal population means. These include: dissepiment depth (dd), fossa depth (t), total number of septa (T#s), number of major septa (#s), columella thickness (cl, c2), and the theca thickness/diameter ratio (t1/dl). Exceptionally high F-values in the analysis of variance (Appendix B) occur only in synapticula spacing (ss I). Study of variance components (Appendix B) and their trends of variation (Table 8) suggest that: (1) in all characters, amounts of intracolony variation are equal, amounts of intercolony variation are equal, and 698 BULLETIN OF MARINE SCIENCE. VOL. 30, NO.3. 1980

Table 8. Suggested patterns of variation in variance components (POP = interpopulation component, INTER = intercolony component, INTRA = intracolony component)

pop < IN· POP = POP < POP> POP ~ TER < Types of INTER ~ INTER ~ INTER < INTER IN· Species Characters INTRA INTRA INTRA

MOil/as/mea Dimensions and n, dl, d2 f end alllluillris spacing of corallites Vertical t I, t2 #s, tr, s, c lid I, c2ld2 corallite ct, c2 structures Horizontal ent, ens corallite structures Coenosteal exl, exs ext exl/exs structures

Siderlls/rea Dimensions of dd dl, d2, f siderea corallites Vertical c2/d2 T#s, s, ct, #s corallite c2, clld] structures Horizontal tl, t2, tlldl, ss I dt corallite t2/d2, #sr, st, structures s] I, s12, ss2, ds amounts of interpopulation variation are equal; (2) amounts of intracolony variation are greater than or equal to amounts of intercolony variation in all characters; (3) the amount of interpopulation variation is less than or equal to the amount of interpopulation variation in all characters except synapticula spacing (ss I). When comparing these results between the two species, a greater number of characters appear to have equal population means and equal population variances in S. siderea. Amounts of interpopulation variation are especially high in characters describing corallite dimensions in M. annularis. Vertical and horizontal structures measured in both species have equal amounts of interpopulation variation. In both species, amounts of variation are always high at the intracolony level. In most characters, amounts of intracolony, intercolony, and interpopulation variation are equal; or the intracolony and intercolony amounts are equal and greater than the interpopulation amount. Patterns of Mean Variation between Populations.-In all characters in both species, plots of interpopulation variation (Figs. 11, 12, 13) suggest that the populations overlap and interpopulation variation is continuous or gradational. Pop- ulation means of the characters analyzed follow one of three basic patterns of variation (Table 9): (I) the patch reef mean differs from other population means, (2) the patch reef and lagoon means differ from the reef and sand channel means, (3) the lagoon mean differs from other population means. Each pattern can then be further subdivided; however, for purposes of comparison and discussion, only the three basic patterns will be considered. In M. annularis, band thickness (Fig. 2A), all characters describing the dimensions and spacing of corallites (Fig. IIA-E), trabecula thickness (tr) (Fig. FOSTER: ENVIRONMENTAL VARIATION IN REEF CORALS 699

A B PR PR

LAG LAG

RF RF

SC SC

ES ES

I I I I I I I I 0.6 0.8 1.0 1.2 l.4mm 0.6 0.8 1.0 mm

c 0 PR PR

LAG LAG

RF RF

SC SC

ES ES

I I I I I I I I 32 40 48 1.8 2.0 2.2 2.4 2.6mm

E F PR PR

LAG LAG

RF RF

SC SC

ES ES

I I I I I I I 2.6 3.0 3.4 mm 0.032 0.036 0.040 mm

G H PR PR

LAG LAG

RF RF

SC SC

ES ES

I I I I I I . . I . . I . 0.25 0.30 0.35 0.40 0.45 mm 0.30 0.35 0.40 mm

Figure II. Montastrea anllularis. Means and standard deviations of characters following the first pattern of variation. The midpoint of each horizontal line represents the mean. The length of the line on either side of the midpoint is one standard deviation. A. Fossa depth (f); B. Minimum distance between coral lites (n); C. % intrathecal surface area (%1); D. Corallite diameter (d I); E. Endotheca depth (end); F. Trabecula thickness (tr); G. Endotheca spacing (ens); H. Exotheca spacing (exs). 700 BULLETIN OF MARINE SCIENCE, VOL. 30, NO.3, 1980

A B PR PR

LAG LAG -----

RF RF

SC SC

ES ES

I I I I I I I 0.40 0.44 O.4B 0.2 0,3 0.4 0.5mm

c 0 PR PR

LAG LAG

RF RF

SC SC

ES ES

I I I I I I I I I 20 30 40 50 60 0,1 0.2 0,3 0.4 mm

E F PR PR

LAG LAG

RF RF

SC SC

ES ES

I I I I I , 0.4 0,6 O,B mm O,OB 0,10 0,12 mm

G H PR PR

LAG LAG

RF RF

SC SC

ES ---+-- ES

I , , I , I ... I • I I I 0,015 0,020 0,025 mm 1.2 1.6 2.0 2.4 Figure 12. MO/ltastraea a/l/lularis. Means and standard deviations of characters following the second (A-E) and third (F-H) patterns of variation. The midpoint of each horizontal line represents the mean, The length of the line on either side of the midpoint is one standard deviation. A. Columella thicknessldiameter ratio (cl/d I); 8. Theca thickness (t\); C. % thecal surface area (%T); D. Exotheca thickness (ext); E. Exotheca length (exl); F, Septum thickness (s); G. Endotheca thickness (ent); H. Coenosteal void shape (exl/exs). FaSTER: ENVIRaNMENTAL VARIATIaN IN REEF caRALS 701

A B PR PR

LAG LAG

RF RF

sc sc

I I I I I I I I 3.2 3.6 4.0 4.2 mm 3.5 4.0 4.5 5,0

c o PR PR

LAG LAG

RF RF sc sc

, I , I 1 I 1 I ,. I I I I I 0..26 0..28 0..30. 0.32 0.012 0.014 0.016 0.018mm

PR PR

LAG LAG

RF RF sc sc

I I I 1 , I . I . I 0.12 0.14 0.16 0,18 0.\0 0.12 0,14 mm

G H PR PR

LAG LAG

RF RF sc sc

I I I I I 1 I 0.32 0.36 0.40 mm 0.05 0,06 0,07 0.08 mm

Figure 13. Siderasrrea siderea. Means and standard deviatians af characters fallawing the first (A, B). secand (C, D), and third (E-H) patterns af variatian. The midpaint af each harizontalline represents the mean. The length af the line an either side af the midpaint is ane standard deviatian. A. Carallite diameter (dl); B. # synapticula rings (#sr); C. Theca thickness/diameter ratio. (t2/d2); D, Dissepiment thickness (dt); E. Calumella thickness/diameter ratio. (c2/d2); F. Synapticula length (s 12); G. Dissepiment spacing (ds); H. Synapticula spacing (55 I).

IIF), and two characters describing the spacing of horizontal dissepiments (ens, exs) (Fig. II G ,H) follow the first pattern. Characters describing columella thickness (cl/dl, c2/d2) (Fig. 12A), theca thickness (tI, t2, %T) (Fig. 12B,C), and coenosteum development (ext, exl, %E) (Fig. 12D,E) follow the second pattern. Only septum thickness (s) (Fig . .\2F), endotheca thickness (ent) (Fig. 12G), and coenosteal void shape (exl/exs) (Fig. 12H) follow the third pattern. In S. siderea, means of most characters follow the third pattern (Table 9). Corallite diameter (d I, d2) (Fig. 13A) and a few correlated characters (tl, t2, #sr) (Fig. 13B) may follow the first pattern. Theca thickness (t2/d2) (Fig. 13C) and dissepiment thickness (dt) (Fig. 130) follow the second pattern. Band thickness 702 BULLETIN OF MARINE SCIENCE. VOL. 30, NO, 3, 1980

Table 9. Patterns of interpopulation variation. (-) signifies that the pattern followed by the character is inversely related to the suggested pattern (Populations not indicated in column headings have intermediate mean values)

Patch Reef .Dod PATal REEF KEAN !lIGH LAGOON MEAN HIGH Lagoon Means Lagoon Ree.f I Reef, lIigh, Reef and Patch Reef. Reef, Reef, Types of Sand Channel Sand Channel Sand Channel Sand Channel Sand Channel Sand Channel SBnd Channl'l Species Characters Means Low Mean Low Mean!l Low Means Low Helms Low Mean Loy Means Low

Mcntast files Corallites annutor1s 01Iaenlillonlil (-)n. :n di, d2, end and Spacing Cora111te (-)c1/dl, Vertical {-)c2/d2. (-)e Structures (-}ti, (-)t27 (-)%T

Coralllte Hori~ontal ens? (-) en' Structures Coenostcal (-)ext, oxl exl/axH Structures %E

Slderaatrea Corallitea (-)dI?, (-)d2? aiderea Dimensions Corallite Ve.~tlcal (-) d/dl? (-) c2/d2 (-)a'/' StructuTes Coralllte Horizontal (-) (-) tl1, (-) (-) t2/d2 (-) de (-)st, (-)a11, !J51, ,,' " (-)s12 Structures ." "

Environmental Factors light light light food 01' nu- (-) vater energy sedimentation sC!dlmcnt.:nion intensity intensity intensity, trlent supply Tate (1(-) Tate (Hood or nu- food or nu- water anergy) trlent 9upply) tTient supply

(Fig. 2B), columella thickness (c2/d2) (Fig. 13E), septum thickness (s), characters describing the size of synapticulae (st, s 11, s 12) (Fig. 13F) , and characters describing the spacing of horizontal structures (ds, ss 1, ss2) (Fig. I3G ,H) follow the third pattern.

Table 10. Rough correlations between patterns of variation in environmental factors and characters analyzed in both species

Type of Character Character Montastraea annularis Siderustrea sh/erea

Dimensions of dl, d2 PATTERN I PATTERN I corallites (+) Light intensity & ( -) Light intensity Food or nutrient (?Food or nutrient supply supply)

Vertical s PATTERN III PATTERN III corallite ( -) Sedimentation rate (-) Sedimentation rate structures (?[ -] Water energy) (?[ -] Water energy) c lid I, c2/d2 PATTERN II PATTERN III (-) Food or nutrient ? (+) Water energy supply

Horizontal ent or dt PATTERN III PATTERN II corallite (+) Water energy (+) Food or nutrient structures supply ens or ds PATTERN I PATTERN III ?( +) Light intensity ( +) Water energy (?Food or nutrient supply)

Growth rate Band PATTERN I PATTERN III thickness (+) Light intensity (+) Sedimentation rate (?[ -] Water energy) FOSTER: ENVIRONMENTAL VARIATION IN REEF CORALS 703

Results obtained by comparing the patterns followed by the same character between species (Table 10) suggest: (1) only septum thickness follows the same pattern in both species; (2) diameter and possibly dissepiment (or endotheca) thickness follow similar patterns in the two species, however the patterns appear inversely related between species; (3) as in band thickness, the spacing of horizontal structures follows the first pattern in M. annularis and the third pattern in S. siderea; (4) endothecal dissepiments thicken following the third pattern in M. annularis, whereas the columella and synapticula thicken following the third pattern in S. siderea.

DISCUSSION Environmental Variation and Taxonomic Implications This study shows that considerable morphologic variation occurs within scleractinian species. Numerous characters in M. annularis and S. siderea exhibit significant variation at the intracolony, intercolony, and interpopulation levels. Since variation at the intracolony level was caused by environment alone and intracolony variation is always high, the data suggest that both species are capable of responding morphologically to the environment. Genetic sources may be responsible for some variation at the intercolony level; however, the higher values of intracolony variation relative to intercolony variation suggest that the environment influences morphologic variation to a greater degree than genetic factors at the intercolony level. Similarly, the equivalent values of intracolony and interpopulation variation in many highly variable characters indicate that interpopulation variation can be largely explained by environmental sources. These hypotheses are supported by results of transplantation experiments (Foster, 1979). On a larger scale, they suggest that the magnitude of intracolony variation can be used to predict the amount of interpopulation environmental variation occurring within species. Many characters used in the differentiation of species and even genera in the classification system of Vaughan (1919), Vaughan and Wells (1943), and Wells (1956) are highly variable. For example, the characters used in discriminating species of Montastraea consist of: corallite diameter, porosity of the coenosteum, number of septa per corallite, septum thickness, and the shape and arrangement of costae (Vaughan, 1919). Characters used in discriminating Solenastrea from Montastraea include: the size, shape, and arrangement of coenosteal structures and the shape and arrangement of costae (Vaughan, 1917b). Of these, characters shown to be plastic in this study include: the dimensions of corallites, septum thickness, the development of the coenosteum. Environmental variation in these characters within both species studied is continuous or, in other words, the populations overlap. These results suggest that scleractinian species must be differ- entiated on the basis of non-overlapping variation in corallite structures and support the approach in scleractinian taxonomy used by Wijsman-Best (1972, 1974), Veron and Pichon (1976), and Veron et al. (1977) which describes species on the basis of suites of specimens collected in a range of reef environments. Also, in the two species analyzed, different characters vary and the same character often varies to differing degrees and follows distinctly different patterns of variation. This suggests that each scleractinian species may have a unique morphologic response to the environment. Patterns of environmental variation in a particular morphologic feature of one species cannot be used to predict the amount or patterns of environmental variation of the same feature in another species. Similarly, the ability to vary the size or arrangement of a specific mor- 704 BULLETIN OF MARINE SCIENCE, VOL. 30, NO.3, 1980 phologic feature appears just as important as the presence or absence of that feature in scleractinian taxonomy.

Patterns of Variation In each species, many characters have distinctly different patterns of variation, suggesting that they are responding to different environmental factors. To determine which environmental factor(s) each character is responding to, patterns of variation in four environmental factors (Table \) have been qualitatively correlated with patterns of variation in characters measured in each species (Table 9). Of the three basic patterns followed by morphologic characters in the two species, light intensity follows the first pattern in which the patch reef mean is high. Food or nutrient supply follows the second pattern in which both the patch reef and lagoon means are high, Sedimentation rate follows the third pattern in which the lagoon mean is high. Water energy also appears to follow the third pattern. This correspondence suggests that characters following the first pattern may be responding to light intensity, characters following the second pattern may be responding to food supply, and characters following the third pattern may be responding to sedimentation rate or possibly water energy, Patterns of variation in the same character are compared between species in Table 10. These relationships suggest that the environmental response of the same character in the two species is commonly different. The function of each of these skeletal features in polypal activity is not clearly understood, However, some tentative explanations for the differences in growth rate, dimensions of corallites, and thickness of horizontal structures are discussed below. Growth Rate .-Growth rate appears to be responding positively to light intensity in M. annularis and to sedimentation rate in S. siderea (Table 10). This suggests that M. annularis may be deriving energy used in growth from light, whereas S. siderea may be deriving energy used in growth from sediment. In other words, M. annularis may be deriving energy largely from products of zooxanthellae photosynthesis and S. siderea may be deriving energy from feeding on suspended organic particles. Therefore, the different patterns of variation in the two species may be caused by differences in diet and energy sources. "Nutrition" has been observed to affect morphology within other colonial animals (Winston, 1976; Crowell, 1957). In general, most characters in M. annu/aris appear to be responding similarly to light intensity or food supply, while most characters in S. siderea are responding to sedimentation rate. This result suggests that nutrition is important in es- tablishing the patterns of variation characteristic of species. Notable exceptions occur in characters describing the porosity of the coenosteum in M. annularis and the dimensions of corallites in S. siderea. Since decreased photosynthesis by zooxanthellae causes decreased calcification (Vandermeulen and Muscatine, 1974), the derivation of energy largely from feeding rather than from assimilation of zooxanthellae products may cause increased coenosteal porosity in M. annularis in environments with low light intensities and high food supplies. Dimensions of Corallites.- The dimensions of corallites appear to be responding positively to light intensity and possibly food supply in M. annu/aris and negatively to light intensity in S. siderea (Table 10). In M. annu/aris, because corallites are separated by coenosteum, increase in corallite diameter permits greater space for tissue. In S. siderea, because the corallites are juxtaposed, increase in corallite diameter does not create space. It merely signifies decreased rates of FOSTER: ENVIRONMENTAL VARIATION IN REEF CORALS 705 budding. Therefore, M. annularis may be increasing space for tissue in high light environments, while S. siderea is increasing its rate of budding. The character most affected by budding in M. annularis is distance between corallites (n). It decreases in high light environments (Table 9) suggesting that budding rate is increasing. Consequently, budding rates may be increased by light intensity in both species. Thickness of Horizontal Structures.-Dissepiment thickness in M. annularis is positively correlated with water energy and negatively correlated with sedimentation rate, whereas dissepiment thickness in S. siderea is positively correlated with food supply (Table 10). This result suggests that dissepiments in M. annularis provide overall skeletal support in environments with increased water activity, whereas dissepiments in S. siderea may indirectly support muscles in environments with increased polypal activity. In S. siderea, the thickness of synapticulae and the columella are correlated with water activity (Tables 9, 10) suggesting that these elements are providing overall skeletal support in high energy environments in S. siderea. These conclusions imply that the synapticulae in S. siderea may be serving the same function as the dissepiments in M. annularis.

CONCLUSION This study has shown that the magnitude of morphologic variation in corals is high and that environmental factors appear largely responsible at the intracolony, intercolony, and interpopulation levels. The variation is expressed by numerous characters within species. Each character varies to a differing degree and follows one of many patterns of variation. The amount and type of variation differs between species. Within species, the patterns of variation displayed by different characters appear related to the type of energy sources characteristically used in growth, reproduction, and metabolism.

ACKNOWLEDGMENTS This paper is based on part ofa Ph.D. dissertation to the Johns Hopkins University. I am grateful to my advisors Drs. S. M. Stanley and J. B. C. Jackson for many useful discussions and critical reviews of preliminary versions of the manuscript and to the Discovery Bay Marine Laboratory, the University of California at Los Angeles, and the University of Iowa for use of facilities. Discussions with A. G. Coates, J. C. Lang, D. M. Lorenz, L. A. Hardie, and C. T. Foster, Jr., were also especially helpful. Thanks go to R. Alkaly, T. E. Ronan, Jr., A. R. Loeblich, Jr., D. A. Pyne, J. Ketuola, C. T. Foster, Jr., and S. Twombly for invaluable technical assistance and to S. Ohlhorst for contributing additional specimens. The work was supported by grants from Sigma Xi and the Robert Balk Fund of the Johns Hopkins University. The specimens are deposited in the repository of the Department of Geology, University of Iowa. This is Contribution No. 185 of the Discovery Bay Marine Laboratory.

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DATE ACCEPTED: August 15, 1979.

ADDRESS: Department of Geology, The University of Iowa, Iowa City, IA 52242. 708 BULLETIN OF MARINE SCIENCE, VOL. 30,NO.3, 1980

Appendix A, Univariate statistical tests performed on M, annl/laris, Bartlett's test determines whether sample variances are equal. The analysis of variance (ANOVA) tests whether sample means are equal. Values of a: > ,05 suggest that the variances or means are equal. Variance components (VAR CaMP) estimate the relative amount of variation at the interpopulation, intercolony and intracolony levels,

character BARTLETT'S ANOVA VAR CO>IP d,f, : 4,2754 d.f. : 4,43 interpopulation intercolony intraco]ony

dl F 0,40 F 6.30 0,44464 0.30158 0.48015 0.805a 0.000 cl 0.68 2.50 0.00926 0.04074 0.10335 0.605a 0.56b cl/dl F 1.51 F 28.89 0.00096 0.00025 0.00110 a .196a 0.000 tl 0.77 F 15.62 0.05277 0.03055 0.07383 0.544a 0.000 ent 3.53 7.78 0.01364 0.01932 0.01879 0.007 0.000 ens F 7.18 F 6.30 0.00732 0.01364 0.01805 0.144a 0.000 ext 9.90 F 7.06 0.14168 0.49262 I.08439 0.000 ~ 0.000 exl J. 25 F 24.21 0.25630 0.08632 0.16922 0.288a 0.000 exs 0.48 15.23 0.03001 0.02042 0.03708 0.748a 0.000 exl/exs 0.79 F 14.65 0.11027 0.05623 0.14381 0.533a 0.000 d2 F 1.77 F 9.91 0.29415 0.41277 0.23299 0.132a ~ 0.000 n F 0.61 F 6.28 0.13856 0.25191 0.47189 0.652a 0.000 #s F 0.58c 1.62 0.00634 0.01729 0.19087 0.446a 0.000 tr 2.69 5.51 0.00227 0.00886 0.00703 0.030 0.001 F 1.92 F 6.98 0.00098 0.00208 0.00291 0.104a 0.000 c2 F 1.32 F 2.95 0.01046 0.05242 0.09907 0.261a 0.031 c2/d2 F 0.80 F 12.41 0.00036 0.00018 0.00124 0.522a 0.000 t2 F 2.60 F 19.17 0.33842 0.17585 0.22945 0.034 0.000 96E F 4.642d 24.92e 0.002 0.000 %T F 4.28d 36.34e 0.002 0.000 %1 2.44d 11.23e 0.045 0.000 end F 3.12 F 7.54 0.05063 0.05434 0.19786 0.014 0.000 f 1.45 F 23.02 0.04499 0.01508 0.06513 ~ 0.214a 0.000

Uhypothesis of equal variances supported at ~:.05; bhypothesis of equal means supported at ~ :.05; c d.f. : 1,768; d d.f : 4,2891; e d.f. : 4,45. FOSTER: ENVIRONMENTAL VARIATION IN REEF CORALS 709

Appendix B. Univariate statistical tests performed on S. siderea. Bartlett's test determines whether sample variances are equal. The analysis of variance (ANOVA) determines whether sample means are equal. Values of 0:: > .05 suggest that the variances or means are equal. Variance components (VAR COMP) estimate the relative amount of variation at the interpopulation, intercolony and intracolony levels.

character BARTLETT'S ANOVA VAR COMP d. f. = 3,2193 d.f = 3,35 interpopulation intercolony intracolony dl F 3.39 3.24 0.44584 1.31788 3.59833 tt 0.017 tt 0.034 cl F 3.37 F 0.18 -0.00327 0.04209 0.04612 tt 0.018 tt 0.905b cl/dl 0.89 F 5.64 0.00000 0.00019 0.00066 tt 0.445a tt 0.003 tJ F 6.27 F 3.96 0.05958 0.13304 0.41120 tt 0.000 tt 0.016 tl/dl F I.86 F I.52 0.00014 0.00018 0.00071 tt 0.6208 tt 0.225b st 0.45 F 4.84 0.01720 0.03083 0.02609 tt 0.720a tt 0.006 sll F I.44 F 5.49 0.00980 0.01615 0.01391 tt 0.230a tt 0.003 ssl F I.81 21.06 0.01122 0.00315 0.01713 tt 0.143a tt 0.000 dt 1.44 F 9.24 0.00573 0.00416 0.01264 tt 0.229a tt 0.000 ds F J. 23 F 5.18 0.02430 0.02593 0.14089 tt 0.2998 tt 0.005 d2 2.43 F 3.24 0.29498 0.94306 I.40197 a 0.063a a 0.034 Hs I.51 2.33 2.28364 12.72765 12.45995 tt 0.2108 0.091b #s F I.29 F 0.22 -0.00912 0.04315 0.47165 a 0.275a 0.884b F 1.64 F 3.77 0.00361 0.00931 0.01233 a O.I77a tt 0.019 c2 3.35 F 2.61 -0.00278 0.04916 0.08533 0.018 tt 0.067b c2/d2 2.17 F 10.89 0.00012 0.00022 0.00054 a 0.090a tt 0.000 t2 F 1.24 6.09 0.09100 0.14983 0.20369 tt 0.292a tt 0.002 t2/d2 F 0.31 F 9.64 0.00039 0.00032 0.00067 tt 0.820· a 0.000 #sr F 2.21 3.94 0.09543 0.26292 0.37521 tt 0.085a tt 0.016 s12 F 0.73 F 5.98 0.00993 0.01386 0.01424 tt 0.535a tt 0.002 ss2 F I.62 F 4.55 0.00626 0.01119 0.02719 tt o .182a tt 0.008 dd 3.44 F 2.96 0.12823 0.49070 0.17986 tt 0.016 tt 0.046 f 1.00 F 2.60 0.02352 0.08186 0.10630 tt 0.391a 0.067b ahypothesis of equal variances supported at tt=.05; bhypothesis of equal means supported at tt=.05.