BULLETIN OF MARINE SCIENCE, 44(3): 1186-1194, 1989 PAPER

GROWTH RATES OF EIGHT OF SCLERACTINIAN CORALS IN THE EASTERN PACIFIC (COSTA RICA)

Hector M. Guzman and Jorge Cortes

ABSTRACT The annual linear skeletal growth rates for the following hermatypic corals was studied at thc non-upwelling area of Caiio Island, Costa Rica: lobata Dana; Pavona varians Verrill; Pavona clavus Dana; Pavona gigantea Verrill; Gardineroseris planulata (Dana); Psam- mocora superficialis (Gardiner); elegans Dana; (Linnaeus). The seasonal growth rates of the main reef-building corals, P. lobata and P. damicornis, were measured and correlated with five environmental variables. Growth rates for P. varians and P. superficialis are presented for the first time. The species with growth rates similar to corals from non-upwelling areas, Porites lobata, Pocillopora damicornis, P. elegans, are the dominant species at Caiio Island, while the other species studied, Pavona clavus, P. gigantea and Gardineroseris planulata, have reduced growth rates compared to other areas. The results suggest that seasonal growth, which is greater during the dry season, may be affected by variations in available light, cloud cover, turbidity, salinity and reproductive time rather than temperature changes.

Coral reefs grow under a variety of oceanographic and climatic conditions (e.g., upwelling and non-upwelling areas) along the Tropical Eastern Pacific coast, from Ecuador to Costa Rica. Thus, the community structure (coral zonation, abun- dance, and dominance) of these reefs differs markedly among localities, and the growth rates and morphology of colonial corals vary greatly in response to different environmental factors (Dodge and Vaisnys, 1975; Chappell, 1980; Hudson, 1981). Several studies have investigated coral growth in the eastern Pacific: Panama (Glynn and Stewart, 1973; Glynn, 1977; Wellington and Glynn, 1983), Galapagos (Glynn et al., 1979; Glynn and Wellington, 1983) and Costa Rica (Glynn et al., 1983; Guzman, 1986). However, only the growth rates of the most important and abundant species at each reef have been studied. Here, we present the growth rates of eight species of hermatypic corals at Cafio Island reefs, a non-upwelling area on the Pacific coast of Costa Rica. The growth rates of two species, Pavona varians and Psammocora superficialis, are reported for the first time. We also examined the seasonal growth rates of the two dominant species, Porites lobata and Pocillopora damicornis, and related them to five en- vironmental variables.

METHODS

Twelve species of hermatypic corals occur at Caiio Island (8°43'N, 83°52'W), 15 km off the Osa Peninsula, Costa Rica (Fig. I). The reefs are dominated by pocilloporid species in the shoal platforms and by the massive coral Porites lobata from the upper slope to the base of the reef (15 m). A full description of the reef structure around the island is available in Guzman (1986) and Guzman and 'Cortes (1989). Rates of coral growth were determined by staining massive and non-massive species with Alizarin Red S, and measuring the skeleton deposited from the stain line to the tip of the branch or the colony (Barnes, 1970; Lamberts, 1978), and by measuring annual growth increments on X-rays of massive corals (Knutson et al., 1972). Whole colonies (6-8 cm in size) or fragments of colonies (15 to 25 cm in size, only for P. lobata and Pocillopora spp.) were used. The growth rates obtained probably apply to other colony sizes since it has been demonstrated that the linear extension rate is independent of colony size, at least for Pocil!opora damicornis (Kinzie and Sarmiento, 1986) and for the massive coral (Hudson, 1985).

1186 GUZMAN AND CORTEs: CORAL GROWTH RATES 1187 "C:,,,:'G~i~\t_ ',' S.a

COSTA 10.00' / RICA /1-

II

200-- 0 200 400 600 800 m. Figure 1. Map ofCano Island and its location in Costa Rica. Shallow station = I; deep station = II.

During 28-30 November 1985, small whole colonies (6-8 em in size) of the following species (N indicates the number of colonies) were collected at 2-3 m depth: Gardineroseris planulata (Dana) (N = 15), Pavona clavus Dana (N = 15), Pavona giganlea Verrill (N = IS), Pavona varians Verrill (N = 15), and Psammocora superjicialis (Gardiner) (N = 10). Also, chiselled fragments of colonies (15-25 em in size) of the following species were collected at 2-3 m and 8-10 m depth: Porites lobata Dana (N = 20, at each depth), Dana (N = 15, at each depth), and Pocillopora damicornis (Linnaeus) (N = 15, at each depth). To determine seasonal growth, an additional 20 colonies of Porites lobata and 15 of Pocillopora damicornis were collected from 2-3 m depth. The collected corals were transferred to an outdoor tank that contained aerated seawater with Alizarin Red S (15 mg . liter-I). After staining for 4-6 h, the colonies were emplaced on the reef at their collection depth by attaching them with wire to ceramic plates or to stakes: station I at 2-3 m at the slope on the north-east of the island, and station II at 8-10 m depth at the base of the reef on the east side of the island (Fig. I). On 14 February 1987, all stained colonies and fragments were collected at both localities to determine total annual growth. Upon collection from both depths, the branching colonies were sprayed with fresh water to remove the tissue, thus exposing the Alizarin stain. The maximum linear extension, that is the maximum distance from the stain line to the tip of the branch, was measured. Massive species were cut along the growth axis (vertical growth) to measure the growth from the Alizarin line to the top of the colony. Horizontal growth by Porites lobata over the ceramic plates was also recorded. All corals were measured, to the nearest 0.5 mm, with a caliper. The growth recorded was for a 14- month period (if we consider that growth is depressed for a week or more after staining, see Dodge et aI., 1984), and corrected to a year. Not all of the corals stained properly and some were lost during the year, so measurements reported (Table I) are from less colonies than indicated above. The seasonal growth of the two main reef-building corals of Cano were determined by collecting on 21 May and 17 December 1986, fragments (approximately Ifl the size of the colony) of Porites /obata (N = 9) and Pocillopora damicornis (N = II) from station I. The dry season's growth extended from 28 November 1985 to 21 May 1986, and rainy season's growth from 21 May 1986to 17 December 1986. The growth during the dry season was measured directly from corals collected 21 May 1986, 1]88 BULLETIN OF MARINE SCIENCE, VOL. 44, NO.3, 1989

Table I. Annual growth rates (mm·yr-') of eight coral species at various depths (m), determined by the Alizarin Red staining technique. N is the number of colonies analyzed and in parenthesis is the number of colonies stained. Standard error (SE) in parenthesis. Corals were stained on 28-30 November 1985 and collected on 14 Feburary ]987

Species Growth form Depth N Mean (SE) Range Gardineroseris planulata massive 2-3 15 (15) 10.4 (0.74) 6.3-12.6 Porites lobata massive 2-3 ]7 (20) ] 1.7 (1.02) 8.3-13.2 Porites lobata massive 2* 5 (5) 15.3 (1.15) 13.9-19.3 Porites lobata massive 8-10 ] I (20) 10.5 (1.90) 6.5-]4.6 Pocillopora damicornis ramose 2-3 II (15) 34.6 (4.24) 21.3-43.7 Pocillopora damicornis ramose 8-10 13 (J 5) 29.8(3.11) 17.3-38.1 Pocillopora elegans ramose 2-3 10 (15) 34.8 (3.45) 24.5-38.6 Pocillopora elegans ramose 8-10 9 (J 5) 31.7 (2.72) 19.3-36.8 PaI'ona gigantea massive 2-3 II (15) 8.3 (0.91) 6.2-]2.8 Pal'ona clavus massive 2-3 12 (15) 9.6 (I. 77) 5.4-13.4 Pavona varians encrusting 2-3 7 (J 5) 3.5 (0.65) 1.9-4.4 Psammocora superficialis nodular 2-3 10 (10) 6.2 (0.93) 4.1-9.4

* Planar growth over ceramic plates (i.e.. cruslOSc grovlth).

while the growth during the rainy season was determined by subtracting the dry season's growth from the total growth (28 November] 985 to 17 December 1986). Eight control colonies of Porites lobata remained untouched during the whole study period. Measurements of growth were done as described above, i.e., by measuring from the stain line to the tip of the colony. To obtain the mean growth rate oflarger colonies of Porites lobata, Pavona clavus, and P. gigantea, density band widths (linear measurements along the growth axis, one couplet per year) were analyzed by X-radiographs. Fourteen fragments of Porites lobata and 10 of each of the Pavona species were broken and collected from healthy colonies located between 4-8 m depth at the east reef of the island on 28 January 1986. Of these, only six specimens of P. lobata and seven of each Pavona species were adequate for X-ray analysis because of bioerosion damage in some specimens and bad definition of growth bands in others. The colonies were placed in 5% solution of sodium hypochlorite for 24 h to remove the tissues and then sun dried. Coral slabs 5-8 mm thick were cut longitudinally and were X-rayed on a Funk (model RX-IO) odontological radiography machine, using Kodak Ektaspeed film; exposures were made at 110 V, 15 A for 6 s. Linear skeletal extension (i.e., band width) was measured using contact prints made from the X-ray negatives. Mean values for salinity and suspended particulate matter were taken from Guzman (1986). Mean sea surface temperature from Renner (1963). Rainfall and sunlight information was provided by the Instituto Meteorol6gico Nacional for the Palmar Sur meteorological station (8°57'N, 83°28'W), the nearest station to the island. Statistical assumptions were tested (normality, homocedasticity) and, where necessary, the data were transformed to conform to those assumptions.

RESULTS AND DISCUSSION Annual Growth Rates. - The mean annual growth rates observed for Cano Island, using the Alizarin method, ranged from 3.5 mm·yr-I for Pavona varians to 34.8 mm ·yeI for Pocillopora elegans (Table 1). Although P. varians is a widely dis- tributed species (Wells, 1983), this is the first time its growth rate is reported. Pavona varians is common but not abundant at Cano Island and its growth morphology is laminar-like or encrusting. The mean growth reported here (3.5 I mm 'yr- ) was based on lateral growth on an artificial surface (Table 1), in the absence of competition with other organisms (e.g., bryozoans, sponges, crustose coralline algae). Competition, together with a heavy predation pressure by the corallivore sea star Acanthaster planci (Linnaeus), may be important factors that regulate the abundance, growth and size of the species. Colonies up to lOO cm2 were seldom found, and recruited colonies were attacked by A. planci (pers. obs.). In Panama, where Acanthaster is present, the colonies are smaller and there is a GUZMAN AND CORTEs: CORAL GROWTH RATES 1189

Table 2. Reported growth rates in the literature of the same species used in the present study

Species Locality Growth rate Reference

Gardineroseris Panama mean 13.2 mm'yr-I 4 planulata range 12-14 mm·yr-' Pocillopora spp. Galapagos 28 mm·yel 7 Hawaii 13 mm'yr-' 11 Panama 31-39 mm·ye' 3, 5 Porites lobata Hawaii and Central Pacific 6-13 mm·yr-' 1,2 Enewetak 13.5 mm·yr-I 10 Australia 4-13 mm'yr-I 9 Galapagos 8.1 mm·yr-I 6 Philippines 13.0 mm'yr-' 12 Pavona clavus Galapagos 8.4-17.4 mm·yr-' 6 Panama 9.3-13.7 mm·yr-I 6,8 Pavona gigantea Galapagos 6.8-10.5 mm'yr-I 6 Panama 8.5-9.2 mm·yr-' 6,8 Papagayo, Costa Rica 7.0 mm·yr-I 8 References: I. Buddemeier el al.. 1974: 2. Buddemeier and Kinzie, 1976; 3. Glynn, 1977; 4. Glynn, 1985; 5. Glynn and Slewan, 1973; 6. Glynn and Welling.on. 1983; 7. Glynn el aI., 1979; 8. Glynn et aI., 1983; 9. lsdale, 1977; 10. Knulson el aI., 1972; II. Maragos, 1972; 12. Ptilzold. 1984. higher proportion of dead colonies, than in areas were Acanthaster is absent (Glynn, 1987). Another species with a previously unknown growth rate was Psammocora su- perficia/is. At Cano Island distribution and possibly growth were limited by com- petition with other benthic organisms, and by predation from the sea star A. planci and the corallivore puffer fish (Bloch and Schneider) (Guzman, 1986). Psammocora superficia/is at Cano Island had a mean growth rate of 6.2 mm·yr-I and a maximum of 9.4 mm'yr-I (Table 1). Gardineroseris planulata, a common species in the eastern Pacific, forms mas- sive colonies (> I m in diameter) in Galapagos, Gorgona Island, Malpelo Island and Panama (Glynn et aI., 1972; Birkeland et al., 1975; Glynn et al., 1982; Glynn and Wellington, 1983). At Caiio Island, however, colonies more than 20 cm in diameter were seldom found. The species normally occurs as a crust or in small nodules about 5 cm in diameter. Mean growth of G, planulata was 10.4 mm· l yr--I, with a maximum of 12.6 mm 'yc (Table 1). These values are lower than those reported by Glynn (1985) for this species in Panama (Table 2). At Cano Island, this species is also a preferred prey of Acanthaster planci (Guzman, 1988), which might limit its growth. Glynn (1985) observed that large colonies of G. planulata, in Panama, were eaten by Acanthaster planci after the death of Pocil- lopora barriers. These types of protection barriers are absent at Cano. The ramose, pocilloporid species Pocillopora damicornis and P. elegans, showed the highest growth rate of all the species at Cano Island (Table I). The annual mean growth rates of P. damicornis and of P. elegans were 34.6 and 34.8 mm' yr-I, respectively, in shallow waters, and 29.8 and 31. 7, respectively, in deep water (Table 1). In neither species were the growth rates significantly different between the two depths (P > 0.05, t-test). The growth rates of Pocillopora elegans are slightly higher than those of p, damicornis at both depths, but the differences are not significant (P > 0.05, t-test). The pocilloporid corals' mean growth of 30-35 mm ·yr-I for Cano Island are higher than the values reported for the Galapagos Islands and Hawaii, but similar to Panama (Table 2). Massive corals predominated in all the reefs around Cano Island, including 1190 BULLETIN OF MARINE SCIENCE, VOL. 44, NO.3. 1989

Table 3. Annual growth rates (mm ·yr-I) of hemispherical colonies of the massive corals Porites lobata. Pavona gigantea and P. clavus, based on the thickness of the density bands from X-radiographs (one couplet per year) (N is the number of colonies analyzed and in parenthesis is the number of colonies collected)

Species DCPlh N Period Mean (SE) Ran8e Porites lobata 4-8 6 (14) 1981-1984 8.4 (0.66) 7-11.5 Pavona gigantea 4-8 7 (10) 1980-1985 7.0 (0.57) 5-12 Pavona clavus 4-8 7 (10) 1980-1985 7.6 (0.52) 5-11 some platforms that were dominated by microatolls of Porites lobata (Guzman, 1986). Other massive species included Pavona clavus and Pavona gigantea. Av- erage annual growth rates of Porites lobata determined from X-radiographs (Table 3), is significantly lower (P < 0.0 1, t-test) than the rates determined by staining (Table 1). However, the difference between the two methods was not significant (P > 0.05, t-test) for the two pavonids. The discrepancy between the X-ray and the staining method in the case of Porites lobata may be due to two compounding effects: first, the X-rays represent several years of growth, and it has been dem- onstrated that variability in coral growth is high (Dodge and Thomson, 1974; Isdale, 1977; Dodge, 1987). The ranges given in Table 3 give an idea of the variability encountered at Caiio. Second: the growth reported by the staining technique was for 1986, while the X-rays were for the period from 1980 to 1985. During 1986, the dry season was almost 1 month longer than normal and the rainy season was not as intense as in previous years (a total of 2,606.0 mm of rain in 1986, as compared to the average yearly precipitation between 1980 and 1985 of 3,766.7 ± 480 mm, Instituto Meteorol6gico Nacional, 1986). This could cause increased growth during 1986, which is what we observed when comparing the X-ray and staining data. The growth rate of Porites lobata found at different depths (excluding the planar growth value) were not significantly different (P > 0.05, t-test) (Table 1). The growth rates reported here are similar to values from Hawaii, the central Pacific, Australia and Galapagos (Table 2). The highest mean value found for P. lobata of 15.3 mm 'yr-1 with a maximum of 19.3 mm ·ye1 (Table 1) represents horizontal growth over the ceramic plates. This fast growing ability may suggest how the species can spread to compete for space immediately after settling or to recover from wounds and partial mortality. The other two massive species, Pavona clavus and P. gigantea, showed mean annual rates of7.6-9.6 mm and 7.0-8.3 mm, respectively (Tables 1 and 3). There is no significant difference between the two pavonid species (P > 0.05, t-test). These values are comparable to the lower part of the growth range of the two species in Galapagos and Panama, and are higher than the values reported for Papagayo, Costa Rica, an upwelling zone (Table 2). The dominant species at Caiio Island, Porites lobata, Pocillopora damicornis and P. elegans, have growth rates similar to these species in other non-upwelling areas. The growth rates of the other species are lower than in other areas, probably due to the intense corallivorous activity at Caiio. It has been shown that coral- livores may cause partial or complete mortality of corals. In the first case, the growth rates of the colonies are reduced during recovery (Macintyre and Smith, 1974; Hughes and Jackson, 1980; Jackson, 1983). Seasonal Growth Patterns. - Table 4 contains the seasonal growth of Porites lobata and Poci!lopora damicornis, the two main reef-building corals at Caiio Island and GUZMAN AND CORTEs: CORAL GROWTH RATES 1191

Table 4. Seasonal growth rates (mm for 5 months during the dry season and 7 months during the rainy season) of the two main reef-building corals at Caii.o Island, Porites lobara (N = 9) and Pocillopora damicornis (N = I I), and mean values (standard error in parenthesis) of environmental variables: rainfall (mm· month-I), sunlight (h ·day-I), salinity (0/00), surface water temperature ("C), and suspended particulate matter (SPM, mg'liter-')

Growth period Dry season Rainy season December-April May-November 28 Nov 1985-21 May 1986 21 May 1986-17 Dec 1986 Species P.lobara 7.5 (0.27) mm 4.5 (0.52) mm P. damicornis 21.3 (1.23)mm 13.8 (0.85) mm Environmental variables Rainfall (1941-] 984) 110.34 (51.44) 453.31 (86.48) mm'month-I Sunlight (1973-1985) 7.92 (0.67) 4.74 (0.19) h·day-' Salinity (1984-] 985) 33.6 (0.70) 29.5 (0.49) 0/00 Temperature (]947-l958) 28.44 (0.24) 28.28 (0.19) DC SPM (1984-1985) 2.3 (0.34) 4.9 (2.01) mg'liter-' the eastern Pacific. The seasons (i.e., dry and rainy) were divided according to Gramzow and Henry (1971) and Coen (1983). The rainy season is longer and starts about mid May, ending sometime in late November (Gramzow and Henry, 1971), with the heaviest rainfalls during September and November (Coen, 1983). Growth rates of undisturbed corals and of the fragments used for seasonal growth determinations were not significantly different (P > 0.05, t-test); in other words, breaking the corals did not affect growth rates significantly. Both species studied presented significantly higher growth rates (P < 0.05, t-test) during the dry season (Porites lobata, 7.5 ± 0.27 mm· 5 month-I; Pocillopora damicornis, 21.3 ± 1.23' 5 month-I), than during the rainy season (P. lobata, 4.5 ± 0.52 mm· 7 month-I; p. damicornis, 13.8 ± 0.85 mm·7 month-I). During the dry season the mean rainfall per month was 110.34 ± 51.44 mm and an average of 7.92 ± 0.67 h of sunlight per day, while in the rainy season was 453.31 ± 86.48 mm 'month-l and 4.74 ± 0.19 h ofsunlight·day-l. Increased precipitation during the rainy season resulted in depressed salinity and increased suspended particulate matter product of the river runoff, while water temperature remained practically unchanged (Table 4). Seasonal growth rate changes may represent the response of the organism to cyclic changes in environmental factors such as light and temperature, or they may result from a genetically derived metabolic rhythm or internal clock that is entrained by external factors (Buddemeier, 1974). The environmental factors that are most frequently suggested to control coral growth rates are: water temperature (Highsmith, 1979; Grigg, 1981), available sunlight or cloud cover (Buddemeier, 1974; Glynn and Wellington, 1983; Wellington and Glynn, 1983), a combination of both variables (Grigg, 1981; Schneider and Smith, 1982), rainfall (Buddemeier, 1974; Buddemeier et a1., 1974) and suspended particulate matter (Dodge et a1., 1974; Cortes and Risk, 1985; Tomascik and Sanders, 1985). Salinity changes may affect coral growth, but the growth-salinity relationship has not been studied in detail (Buddemeier and Kinzie, 1976; Dodge and Lang, 1983; Muthiga and Szmant, 1192 BULLETIN OF MARINE SCIENCE, VOL. 44, NO.3, 1989

1987). The increase in growth observed during the dry period may be correlated to more hours of sunlight, together with a decrease in suspended matter, that will permit more light reaching the bottom. Because abundance is at its peak of abundance during the dry period and decreases toward the rainy period (Guzman and Obando, 1988), this additional source of energy could be available to corals during the dry period. Wellington (1982), however, provided evidence that pavonids and pocilloporids are largely phototrophic organisms which suggest that zooplankton as a food supply may be relatively unimportant. Sea surface temperature at Callo Island varies very little during the year, being higher, but not statistically significant (P > 0.5, t-test), during the dry season (28.44 ± 0.24°C) than during the rainy season (28.28 ± 0.19°C). This indicates that temperature is not influencing the seasonal growth rates, but that light, salinity and perhaps productivity (zooplankton) may be responsible for the seasonal vari- ations found. Reallocation of energy from growth to reproduction could also explain decreased growth rate (Wellington and Glynn, 1983; Loya, 1985). At Callo Island and Panama, both Porites lobata and Pocil!opora damicornis have been found with ripe gonads from March through May (P. W. Glynn, pers. comm.) and P. lobata was observed spawning at Callo Island in June 1986. This suggests that the production of gametes takes place at the beginning of the rainy period. Wellington and Glynn (1983), proposed that coral growth is a complex phenomenon governed by endogenous processes which may be mediated by exogenous factors. At Callo Island the deposition of a high density band in Porites lobata coincides with the rainy season (May-November), when hours of sunlight are fewer and salinity lower than during the dry season (December-April), though temperatures are similar (Table 4). The low density band is deposited during the dry period, when growth rate is higher. Wellington and Glynn (1983) also observed in Panama that Pavona clavus has a high linear skeletal extension during the period of greater sunlight, when the low density band is formed. Contrasting to this, Patzold (1984) found in a Porites lobata from the Philippines, that the high density band is deposited during the summer, when temperatures, cloud cover and growth rates are higher. The low density band is formed during the winter, when temperatures, cloud cover and extension rates are lower. In all three areas, high density bands were deposited during the period of higher cloud cover, independent of growth rate during that period. Light levels may be a better predictor of skeletal density than temperature or extension rates (Wellington and Glynn, 1983). In conclusion, the main reef formers at Callo Island, Porites lobata and the pocilloporids, have growth rates comparable to the same species in other non- upwelling areas. The other species studied, Pavona clavus, p, gigantea, and Gar- dineroseris planulata, have lower growth rates than other areas, probably due to corallivores. For Porites lobata the growth rate is higher and the low density band is formed during the dry season (December to April) when the number of hours of sunlight is higher, turbidity is low, salinity close to normal sea water and the corals are not reproducing. The seasonal differences in growth rates may be related to available light (cloud cover, turbidity), salinity (precipitation) and time of reproduction.

ACKNOWLEDGMENTS

We thank the rangers of the National Park Service (Isla del Caito) for their cooperation and hos- pitality. C. E. Jimenez for the help in the field, Dr. J, B. Carvajal for the use of his X-ray equipment, and Dr. R. E. Dodge and J. Snyder for cutting and X-raying some of the corals. Comments on earlier drafts by M. Eakin, R. E. Dodge, H. Sweatman and two anonymous reviewers are greatly appreciated. GUZMAN AND CORTES: CORAL GROWTH RATES 1193

This work was supported by a grant from the U.S. National Science Foundation (OCE-8415615) to Dr. P. W. Glynn.

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DATEACCEPTED: May 24, 1988.

ADDRESSES: (H.M.G.) Smithsonian Tropical Research Institute, P.O. Box 2072, Balboa, Panama; (J.C) Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Cnvy., Miami, Florida 33149-1098. PERMANENTADDRESS:Escuela de Biologfa and CIMAR, Univer- sidad de Costa Rica, San Pedro, Costa Rica.