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Crecimiento de coraies (Érntastriea dnmiarts y Yorites lobata) en gradiente dé prófundidad

T: E S I S Prasentadm como requisito purcjal para optar al grado de Maestría en Cien cías en Recursos Naturales y De^rrollo Rural

Tsiarla 'Elena A m ila t 'Bjih

i El Colegio de la Frontera Sur

ECOSUR

Crecimiento de corales (Montastraea annularis y lobata) en gradiente de profundidad.

TESIS Presentada como requisito parcial para optar al grado de Maestría en Ciencias en Recursos Naturales y Desarrollo Rural

por

María Elena Aguilar Ruiz

1999 Agradezco al Consejo Nacional de Ciencia y Tecnología (CONACyT), por el financiamiento otorgado dentro del programa de posgrado en el Colegio de la Frontera Sur (ECOSUR), Folio 114865 A Horacio e Ivan

A Mis Padres Agradezco

A mis Padres Ma. Elena Ruiz Q. y Lic. Andrés Aguilar M., por todo el apoyo que nne han brindado, y por ser ejennplo de fortaleza.

A Horacio por que es un buen connpañero.

A Max, Cesar, Andrés, Lupita y Lupitina, por que siennpre hay alguien con quien contar.

A Juan Pablo Carricart y Aurora Beltrán, por su apoyo, annistad y conocinniento compartido,

A todos los profesores, en especial a Sergio Solazar V.

A Beto Bohena, por lo bueno fotografía, y o Miguel A, Ruiz por el apoyo en campo.

A Mortha, Sereno y Toño por su apoyo siempre Incondicional, que facilitó nuestra estando en Chetumal.

A los organizadoras del Baby Shower,

A los amigos. René, Almo, Tere, Adrián, Adriano, Poty, Mortho, Gaby, y o todos los que de algún modo me brindaron su ayudo y amistad. Resumen Se midieron extensión esqueletal, densidad y tasa de calcificación en las bandas anuales de crecimiento en lajas obtenidas de 11 esqueletos de Porites lobata y 14 de

Montastraea annularis. Las colonias de P. lobata fueron recolectadas en un gradiente de profundidad de 12 a 35 m en el Atolón de Clipperton (Pacífico oriental) y las de M

annularis de 2 a 15 m de profiindidad en el arrecife de Majahual (sur del Caribe mexicano).

Ambas especies fueron elegidas dada su importancia ecológica, en cuanto a cobertura y densidad, en arrecifes del Pacífico este y el Atlántico occidental.

La extensión esqueletal de cada banda se midió utilizando la técnica radiográfica convencional y la densidad con el método de peso congelado. La calcificación de cada banda se calculó multiplicando los valores correspondientes de extensión y densidad. Para ambas

especies, se hicieron análisis de varianza de una vía entre los especímenes de cada profundidad, entre el tiempo (años) y entre las profundidades. Además, se realizaron pruebas de correlación entre las variables.

En ambas especies, los corales de cada profiindidad y el tiempo no resultaron una

fiiente importante de variabilidad en el crecimiento; así mismo no se observó ninguna tendencia en el período de tiempo representado por las lajas. Las variables a lo largo del gradiente de profundidad mostraron patrones distintos para cada especie. En P. lobata las tres variables tuvieron diferencias significativas; la extensión y la calcificación aumentaron con el incremento de la profundidad, mientras que la densidad presentó valores menores a profundidades intermedias (entre 15 y 27 m), aumentando posteriormente con la

profundidad. En M annularis únicamente la extensión y densidad fueron significativamente

diferentes, la extensión disminuyó con la profiandidad, mientras que la densidad presentó un patrón inverso. Al evaluar la relación entre las variables, se observó que las variaciones en

calcificación están mejor ligadas a las variaciones en extensión que con las variaciones en

densidad. Al comparar los resultados obtenidos con aquellos de trabajos previos, se vio que la respuesta en el crecimiento dentro de una misma especie tiene variaciones importantes en función de las diferencias en las condiciones ambientales encontradas a diferentes profundidades y/o localidades. , .s,...... iiu i. UJ.U ^UIIiLun-uamvet Bull M ar. ScL Submitted

GROWTH RESPONSES OF PORITES LOBATA AT CLIPPERTON ATOLL,

EASTERN PACIFIC, AND MONTASTRAEA ANNULARIS AT MAJAHUAL,

MEXICAN CARIBBEAN, ALONG A DEPTH GRADIENT

M. Elena Aguilar-Ruiz and Juan P. Carricart-Ganivet

ABSTRACT

Skeletal growth variables (extension, density and calcification) were determined fi-om annual

density bands in skeletal slabs of the reef building corals Porites lobata and Montastraea

annularis. Colonies of P. lobata were collected along a depth gradient fix)m 12 to 35 m at

Clipperton Atoll, eastem Pacific, and those of M. annularis fix)m 2 to 15 m at Majahual, southem

Mexican Caribbean. No significant trends in growth variables were evident for the period

represented by the slabs for either of the species. For both species, variations in calcification are

better linked with variations in extension than with variations in density. For P. lobata differences

among depths were significant for the three growth variables. For M annularis, only skeletal

extension and density were significantly different. No common patterns along the depth range for

the three growth variables were observed between the two species studied In P. lobata, extension

and calcification tended to increase with increasing depth, while the mean density was lowest at 15

and 27 m depths. ForM annularis, mean extension values were lowest and density the highest, at

the shallowest depths. Comparing our results witii those of previous authors, coral growth

responses seem to vaiy greatly within the same species as a fimction of the differences in

environmental conditions found at different depths and/or locations.

Growth in corals is achieved by an increase in the mass of the calcareous skeleton and the overlying living tissue (Goreau et al., 1979; Bames and Lough, 1993). Since the discovery of the annual density banding of massive coral skeletons (Knutson et al., 1972), a wealth of environmental information has become available (Dodge and Vaisnys, 1975; Flor AguUar-Ruil and Carricart-Ganivet Bull Mar. ScL Submitted

and Moore, 1977; Dodge et al, 1984; Tomascik and Sander, 1985). Coral growth variations reflect environmental conditions that force a change in growth variables. Nevertheless, which environmental conditions are the most important, and the particular responses of different species under the same environment, as well as a single species under different environments, is not clear at this moment. At least three major abiotic environmental factors are negatively correlated with depth: light availability, water motion and sedimentation rate. It has been shown that these factors have effects on both coral diversity (Jackson, 1991) and coral growth responses (i.e. Huston, 1985; Brown et al., 1986; Risk and Sammarco, 1991).

At the annual scale, growth of the deposited skeleton of coral can be described by the increment in length of the skeleton (extension in cm), the distribution of the calcium carbonate

(density in g-cm‘^) and the mass of calcium deposited over area and time (calcification in g-cm‘

^•yr‘^). These variables are not redundant and contain complementary information about coral growth (Dodge and Brass, 1984). Porites lobata (Dana, 1846) and Montastraea annularis

(Ellis and Solander, 1786) sensu Weil and Knowlton (1994) are two dominant reef building corals; the former in the eastem Pacific (Guzmán and Cortés, 1993; Reyes-Bonilla et al., in press) and the second in the Caribbean Sea (Goreau, 1959). In the present study, we used the three growth variables mentioned above to assess and contrast growth responses, along a depth gradient, of these two coral species in order to increase our understanding of coral growth.

M aterial and Methods

Specimens at least 10 cm high of the hermatypic corals Porites lobata and Montastraea annularis were collected at Clipperton Atoll, eastem Pacific, and at Majahual, southem coast of the Mexican Caribbean, respectively (Fig. 1). P. lobata was collected on November 1997, in the fore-reef at water depths from 12 to iguaar-KUK and Carricart-Ganivet Bull Mar ScL Submitted

35 m. Environmental conditions of strong cunents and winds at the time of the study precluded the collection of specimens at shallower depths. The specimens of M. annularis were collected on July 1998, in the reef lagoon at 2 m depth, and in the fore-reef from 5 to 15 m depth. This species does not inhabit higher depths in the Mexican Caribbean (Beltran-Torres and Carricart-Ganivet, in press).

Extension was measured from X-radiographs as described by Baker and Weber (1975) and Hudson

(1981). Slabs were cut to a thickness of 0.5 ± 0.1 cm with a rock saw (4 mm kerQ. Slabs were then exposed to X- rays from CGR equipment (Trendix 525) with the following conditions of exposure: 44 KV, 6 MAS, 50 MA, 0.15 s, and 100 cm of focal distance; in all cases, Kodak InSight Diagnostic Fihn (14x17 in) was used. As suggested by

GuiQaume (1994), X-radiographs were made with the highest possible contrast so that density variations were more clearly revealed. On black and white contact prints of the X-radiographs, the distance from the younger edge of a high-density annual growth band to the yoimger edge of the next one was measured along the main axis of skeleton growth, as described by Carricart-Ganivet et al. (1994).

Density was measured using the freezing method of Carricart-Ganivet et al. (in press), a method based on the weight change of skeleton fragments after water invasion and freezing. Better than 1% precision was obtained using this method by these authors for Montastraea annularis. To verify the precision of the method for Porites lobata, 10 replicate measurements were made on 11 coral fragments of different densities (1.16-1.86 g-cm'^). The variation coefBcient for each set of measurements ranged 2.3 - 7.2 %, and averaged 4.5 %. Annual calcification was calculated by multiplying the density average of each annual growth band by its corresponding extension. The higher precision of the method observed forM annularis density determinations could be because

P. lobata is a more porous coral.

Our experimental design was unbalanced for both species because the number of corals collected from each depth (1 to 3 for P. lobata and 2 to 4 forM annularis) and the number of years recoided by each coral (7 to

27 and 7 to 22, respectively) were variable (Table 1). Therefore, empty cells (not just missing values) precluded the use of a multifactorial ANOVA and the calculation of interactions between factors. Hence, one-way ANOVA was used to assess the effects of corals collected at the same depth, time (years) and depth on growth variabihty for each species. Means were compared using Tukey's Honestly Significant Difference (HSD) Test, as suggested by Zar (1984). Aguüar-KulZ and Carricart-Ganivet. Bull Mar. ScL Submitted

Results and Discussion

Contact prints with clear, unambiguous banding, of 22 specimens were obtained

(Table 1); eight of Porites lobata, and fourteen o í Montastraea annularis. The contact prints

of both species showed a low-density annual growth band in their apex. This agrees with the

reported timing of formation of the high-density growth band of the former at Clipperton Atoll

(Glynn et al., 1996), and ofM annularis at the Mexican Caribbean (Carricart-Ganivet et al., in

press).

For Porites lobata, extension ranged from 0.52 to 1.53 cm-yr'^ and averaged 1.04 cm-yr’\ Mean density was 1.09 g-cm‘^ and ranged from 0.86 to 1.38 g-cm'^. Calcification

averaged 1.12 g-cm'^-yr'^ and ranged from 0.57 to 1.70 g-cm'^-yf^ for the 100 annual growth bands studied. The specimen collected at 15 m (PL5) depth had a bumpy outer surface and the lowest values of extension and calcification (Table 1). Bames and Lough (1989) pointed out that these kinds of specimens are characterized by slower growth, while the smooth outer surface specimens, like specimen PL7 of this study (Table 1), are fast-growing colonies. The values obtained here are within the range of values presented by other authors for P. lobata in reefs throughout the Pacific Ocean (Buddemeier, 1974; Buddemeier and Kinzie, 1976; Bames and Lough, 1989; Guzmán and Cortés, 1989; Risk and Sammarco, 1991; Glynn et al., 1996).

Yox Montastraea annularis, extension averaged 0.82 cm and ranged from 0.47 to 1.39 cm. Density ranged from 1.33 to 2.39 g cm'^ and averaged 2.01 g cm’^. Calcification ranged from 1.02 to 2.79 g-cm'^-yr'‘ and averaged 1.64 g cm’^ yr'^ for the 195 annual growth bands

studied. These values are within the range of values presented by other authors for M. annularis in reefs throughout the Atlantic Ocean (Baker and Weber, 1975; Dustaii, 1975;

Graus and Macintyre, 1982; Dodge and Brass, 1984; Carricart-Ganivet et al., in press). Aguilar-Kuiz and Carricart-Ganivet. Bull Mar. ScL Submitted

Extension, density and calcification averages for each coral specimen of both species are presented in Table 1. For both species, and for the three growth variables, few significant differences (P < 0.05, Tukey’s HSD test) were found between corals collected at the same depth. In P. lobata, the extension of PL7 specimen, the density of PL9 specimen and the calcification of PL8 specimen were significantly higher at 30 m depth, and density was significantly different between both specimens at 12 m depth. InM annularis, extension and density resulted significantly different between the two specimens of 2 m depth, and density in the MAS specimen was significantly higher than that of the other two specimens at 5 m depth.

The Analysis of variance showed that time was not a significant source of variability for the three growth variables for both species (P > 0.05). Scatter-plots of extension, density and calcification versus time, did not show trends for either species (results not shown), supporting the results of the ANOVA. Contrary to the resuhs for Porites lobata reported here,

Glynn et al. (1996) observed an increase in skeletal extension for 1987 and related it with an anomaly in seawater temperatures registered that year in the eastem Pacific due to the 1987

ENSO event. Our resuhs iox Montastraea annularis, for the three growth variables, agree with the observations of Carricart-Ganivet et al. (in press) for this species fi-om other areas of the

Mexican Caribbean. Since differences between coral specimens and time were not a significant source of variation, analysis of the differences among depths for both species were conducted using the value of each growth variable obtained for each annual growth band as one observation. Table 4 shows the coefficients of correlation and their significance values between the three growth variables for Porites lobata and Montastraea annularis. Correlation of skeletal extension versus calcification rate is highly significant, with a high percentage of the variability explained for both species (85% and 74%, respectively). The low coefficients between density and extension, and density and calcification, and the scatter plots of the three 5 Aguilar-Ruiz and Carricart-Ganivet. Bull Mar ScL Submitted

combinations for both species (Fig. 2) indicate that, for both species, variations in calcification are better linked with variations in extension than with variations in density.

This agrees with the relationship among extension and calcification observed forM annularis in previous studies (Dodge and Brass, 1984; Carricart-Ganivet et al., in press).

No common patterns along the depth range were observed between the two species studied for the three growth variables (Fig. 3). For Porites lobata, the results of the ANOVA showed that the three growth variables were significantly different among depths (P < 0.001,

Table 2). In general, extension and calcification tended to increase with increasing depth, while density was lowest at 15 and 27 m depths, with higher values in shallower and deeper depths (Fig. 3). On the other hand, for Montastraea annularis, extension and density were significantly different among depths (P < 0.001, Table 3), while calcification was not significantly different (P > 0.05, Table 3). In general, mean extension and density had an inverse relationship: extension tended to decrease with increasing depth, while density tended to increase (Fig. 3). The extension rate of several species of reef-building corals has been reported to decrease with increasing depth, while density presents an inverse pattern, increasing with depth increase (Baker and Weber, 1975; Highsmith, 1979; Hudson, 1981,

Grauss and Macintyre, 1982; Hubbard and Scaturo, 1985; Huston, 1985; Logan and

Tomascik, 1991; Bosscher, 1993; Logan et al., 1994). Nevertheless, there are also reports of the opposite for extension (Glynn et al., 1996) and for both extension and density (Camcart-

Ganivet et al., in press), and studies that found no changes in density with depth (Buddemeier et al, 1974; Dustan, 1975).

To our knowledge, this is the first study in which the changes in extension, density and calcification of Porites lobata along a depth gradient are analyzed simultaneously. The increase of extension with depth reported here for P. lobata confirm the resuhs obtained by 6 Agudar-Ruiz and Carricart-Ganivet Bull Mar ScL Submitted

Glynn et al. (1996) at the same locality of this study. These authors obtained significantly

different mean values of 1.30 cm at 6-8 m depth and 1.50 cm at 16-17 m depth. However,

Klein et al. (1993), combining results for several species of the genus Porites, observed a

decrease in extension with increasing depth.

Earlier reports on coral growth of Montastraea annularis did not consider that this

species has more recently been determined to be a complex of three sibling species (Knowlton

et al., 1992; Weil and Knowlton, 1994). Significant differences in extension and density

between the three current recognized species {Montastraea annularis, M. faveolata and M franksi) have been reported (Van Veghel and Bosscher, 1995). Nevertheless, our results agree

with those of Baker and Weber (1975), Hudson (1981), Graus and Macintyre (1982), Hubbard

and Scaturo (1985) and Huston (1985), who reported a decrease of extension and/or an

increase of density with increasing depth for M annularis at localities throughout the

Caribbean. In contrast, Dustan (1975) did not observe changes in density with increasing

depth in this species at Jamaica. Our mean calcification values are similar to those reported by

Baker and Weber (1975) forM annularis at St. Croix (U.S. Virgin Islands) growing between

5 to 13 m depth (1.60 to 1.73 g-cm’^-yr'^). These authors observed that calcification rate was

highest between 5-13 m, and then decreased with increasing depth.

In summary, the relationships between the growth variables were similar for Porites

lobata and Montastraea annularis, with variations in calcification better linked with

variations in extension than with variations in density. However, it seems that coral growth

responses can vary significantly within the same species as a function of the differences in

environmental conditions found at different depths and/or locations. This could explain the

fact that no common patterns along depth gradients exist for coral species, demonstrated by Águilar-Ruiz and Carricart-Ganivet Bull Mar. ScL Submitted

our results and those of previous authors.

Acbcnowledgments

We thank V. Solis-Weiss, researcher of the Instituto de Ciencias del Mar y Limnología of the

Universidad Nacional Autónoma de México, who invited J.P.C.G. to participate in the SURPACLIP-I cruise, which visited Clipperton Atoll from November 23 to 25, 1997. We also thank M.A. Garcia, A. Granados-

Barba, R. Herrera, A. Medina, L. Ortiz, H. Reyes-Bonilla and M.A. Ruiz-Zárate for the field assistance on coral collection. H. Jiménez del Angel provided facilities and use of the radiographic equipment of the

ISSSTE-Chetumal, E. González assisted us with radiographic work and H. Baena-Basave made the contact prints. During this research M.E.A.R. had a scholarship from CONACyT for the Postgraduate Program of

ECOSUR. The manuscript was notably improved by the comments of A. de Jesús-Navarrete, M. Merino and S.

Monks. Research was supported by the “Arrecifes Coralinos” project of ECOSUR and by funds from CONACyT for project number 4120P-N9607.

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D ate SuBMiTED: June 14,1999

Ad d r ess: Departamento de Ecología Acuática, ECOSUR, Apdo. Postal 424, Chetumal,

Quintana Roo. 77000. MEXICO. E-mail: ipcarri(á.ecosur-qroo.mx

11 Aguilar-Ruiz and Carricart-Ganivet Bull Mar. ScL Submitted

Table 1. Data sununary for each of the coral specimens of Porites lobata and Montastraea annularis studied: depth, period of time covered, nimiber of armual bands found in the slabs and extension (cm), density (g-cm'^) and calcification (g-cm'^) averages

Species Specimens Depth Period of Number of Extension Density Calcification time annual (m) covered bands

Porites lobata PLl 12 1990-1996 7 0.90 1.12 1.02 PL2 12 1990-1996 7 0.96 1.28 1.22 PL5 15 1991-1996 6 0.78 1.03 0.81 PL6 27 1980-1996 17 1.05 1.00 1.06 PL7 30 1984-1996 13 1.29 1.03 1.33 PL8 30 1970-1996 27 0.92 1.03 0.95 PL9 30 1987-1996 10 0.95 1.17 1.10 PLll 35 1984-1996 13 1.25 1.15 1.43

Montastraea MAI 2 1990-1997 8 1.08 1.54 1.65 annularis MA2 2 1985-1997 13 0.71 2.07 1.48 MA4 5 1979-1997 1,9 0.91 1.82 1.66 MA5 5 1983-1987 15 0.91 2.09 1.91 MA6 5 1983-1997 15 0.94 1,80 1.70 MA7 10 1985-1997 13 0.72 2.11 1.51 MA8 10 1988-1997 10 0.88 2.14 1.88 MA9 10 1991-1997 7 0.70 2.16 1.51 MAIO 12 1984-1997 14 0.68 2.23 1.52 MAH 12 1984-1997 14 0.78 2.11 1.65 MA12 15 1976-1997 22 0.77 2.13 1.63 MA13 15 1980-1997 18 0.84 1.94 1.63 MA14 15 1981-1997 17 0.78 1.95 1.51 MA15 15 1988-1997 10 0.84 2.05 1.72

12 Aguilar-Ruiz and Carricart-Ganivet Bull Mar ScL Submitted

Table 2. Average and standard deviation of density (g-cm'^), skeletal extension (cm) and calcification rate (g-cm'^-yr ') of Porites lobata at each of the depths sampled, and results of Tukey’s HSD test between the depths. Asterisks indicate significant differences (P<0.001).

Depths (m) and mean differences Depths 12 15 27 30 35 (m) Mean SD «=14 n = 6 n= 17 n = 50 13

Skeletal extension 12 0.93 0.13 0.16 0.12 0.11 0.32* 15 0.78 0.08 0.21 0.27* 0.47* 27 1.05 0.22 0.01 0.20 30 1.04 0.25 0.21* 35 1.25 0.16 Density 12 1.20 0.11 0.17* 0.19* 0.14* 0.05 15 1.03 0.06 0.03 0.03 0.11 27 1.00 0.07 0.05 0.14* 30 1.06 0.09 0.09* 35 1.15 0.07 Calcification rate 12 1.12 0.21 0.31 0.06 0.02 0.31* 15 0.81 ■ 0.12 0.25 0.29* 0.62* 27 1.06 0.23 0.04 0.37* 30 1.10 0.27 0.33* 35 1.43 0.19

13 figuuar-nuiz ana i^arricart-Uanivet Bull Mar. ScL Submitted

Table 3. Average and standard deviation of density (g-cm'^), skeletal extension (cm) and calcification rate (g cm'^-yr ') of Montastraea annularis at each of the depths sampled, and results of Tukey’s HSD test between the depths. Asterisks indicate significant differences (P<0.001).

Depths (m) and mean differences Depths 2 5 10 12 15 (m) Mean SD n = 21 « = 49 « = 30 « = 28 « = 67

Skeletal extension 2 0.85 0.21 0.07 0.09 0.12 0.05 5 0.92 0.17 0.15* 0.18* 0.12* 10 0.77 0.16 0.03 0.03 12 0.73 0.12 0.07 15 0.80 0.14 Density 2 1.87 0.29 I, 0.03 0.26* 0.30* 0.15* 5 1.90 0.17 0.23* 0.27* 0.12* 10 2.13 0.10 0.04 0.11* 12 2.17 0.10 0.15* 15 2.02 0.12 Calcification rate 2 1.55 0.23 0.20 0.08 0.04 0.07 5 1.75 0.36 0.11 0.16 0.13 10 1.63 0.34 0.04 0.02 12 1.59 0.23 0.02 15 1.61 0.28

14 Aguilar-Ruiz and Carricart-Ganivet. Bull Mar. ScL Submitted

Table 4. CoeflBcients of correlation (r) between the three growth variables in Porites lobata and Montastraea annularis using all the data set (n = 100 and 195, respectively). The asterisks indicate significant correlation (P <

0.001).

Relation

Species Extension vs Density Density vs Calcification Extension vi Calcification

Porites lobata -0.04 0.35* 0.92* Montastraea annularis -0.46* 0.03 0.86*

15 AguUar-Kuiz and Carricart-Ganivet. BulL Mar. ScL Submitted

F ig u r e c a p t io n s

Figure 1. Location sampling sites at Clipperton Atoll, eastem Pacific, and Majahual, southem Mexican

Caribbean.

Figure 2. The relationships among the three growth variables for all the data plotted together for Porites lobata (n = 100) md Montastraea annularis (n = 195). Regression lines are y = 1.05X + 0.24 (r = 0.92, P < 0.001), for P. lobata, and y = 1.54X + 0.37 (r = 0.86, P < 0.001), forM annularis.

Figure 3. Mean skeletal extension, density and calcification rate of Porites lobata and Montastraea annularis plotted against each of the sampled depths. Vertical bars indicate the standard errors of the means.

16 E

s Oo

o 00

o o

o 00

o o fo o OOs

o o 5o o Aguilar-Ruiz and Carricart-Ganivet. BuU. Mar. ScL Submitted

Porites lobata Montastraea annularis 1.40-

1.20-

3

1.0 0 -

0.80 - |—I—I—I—I—I—I—I—I—I—I—I—I 0.60 0.93 1.26 1.59 Skeletal extension (cm)

1.59-

^ 1.26- i I •

1 0.93 13 U

0.60 T— I— I—I— I— I— r— I— I— I— I— I 0.80 1.00 1.20 1.40 Density (g-cm'^)

Skeletal extension (cm) 18

Fig. 2 AguUar-Ruiz and Carricart-Ganivet BulL Mar. ScL Submitted

Porites lobata Montastraea annularis

Depth (m)

19

Fig. 3