BULLETIN OF MARINE SCIENCE, 44(3): 1186-1194, 1989 CORAL REEF PAPER GROWTH RATES OF EIGHT SPECIES 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: Porites lobata Dana; Pavona varians Verrill; Pavona clavus Dana; Pavona gigantea Verrill; Gardineroseris planulata (Dana); Psam- mocora superficialis (Gardiner); Pocillopora elegans Dana; Pocillopora damicornis (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 Porites lutea (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), Pocillopora elegans 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.