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Environment and development in coastal regions and in small islands |
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Environment and development in coastal regions and in small islands |
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Coastal region and small island papers 3
Cahuita and Laguna Gandoca, Costa Rica
Jorge Cortés
Centro de Investigación en Ciencias del Mar y Limnología, Escuela de Biología, Universidad de Costa Rica San Pedro, Costa Rica
The Costa Rican CARICOMP sites are located in two protected areas in the southern portion of the Caribbean coast near the border with Panama: the Refugio Nacional de Vida Silvestre Gandoca-Manzanillo (mangrove site) and the Parque Nacional Cahuita (seagrass and coral reef sites). This tectonically active area is characterized by rocky headlands, extensive wetlands, and beaches. The climate is hot and humid. This region hosts over 150,000 tourists per year. The mangrove swamp in Laguna Gandoca, which is about 250 ha in area, harbors the country’s only natural population of mangrove oysters, contains the largest patch of red mangrove, and is one of the main nursery grounds for the Atlantic tarpon. In the Parque Nacional Cahuita, the seagrass bed is one of the largest in the country, about 20 ha in area; the coral reef is the longest continuous coral reef in the country, with the outer crest extending 5 km, and contains the most number of species.
Introduction
The Costa Rican CARICOMP sites are located in two protected areas on the southern portion of the Caribbean coast of Costa Rica near the Panamanian border (Fig. 1). The mangrove site is located at Laguna Gandoca, within the Refugio Nacional de Vida Silvestre Gandoca-Manzanillo (9°35'N, 82° 36'W). The seagrass and coral reef sites are located in the Parque Nacional Cahuita (9°45'N, 82°48'W), about 30 km northwest of Gandoca-Manzanillo.
The extensive wetlands of this portion of Costa Rica consist mainly of freshwater Raphia palm swamps, known locally as "yolilalles." The coastal lagoon, Laguna Gandoca, harbors a mangrove forest. Land use in adjacent areas includes banana and forestry plantations. On the coast itself, sandy pocket beaches alternate with rocky headlands. These promontories are uplifted Pleistocene and Holocene fossil coral reefs and beach rocks. The present-day coral reefs grow on the bathymetric highs seaward of the promontories, as at the Parque Nacional Cahuita.
The town of Cahuita, from which the park was named, has a population of 3,000 (Bermúdez, 1992). Tourism has grown rapidly over the past decade and, together, Cahuita and Gandoca-Manzanillo host more than 150,000 tourists per year (Bermúdez, 1992).
Atmospheric and Oceanic Climates
The hot and humid climate of the Caribbean coast of Costa Rica consists of two rainy seasons, November-March and June-August. Average precipitation decreases from north to south along the coast, from about 5,000 mm near the Nicaraguan border to less than 2,500 mm near the Panamanian border (Coen, 1983). In the study area, average rainfall varies from 3,000 mm at Cahuita to 2,500 mm at Gandoca. Air temperature ranges from 24°C to 27°C (Herrera, 1984).
The main marine current along the coast is from northwest to southeast, with small eddies in the opposite direction. These eddies transport terrigenous sediments derived from the larger rivers along the coast into coral reef areas (Cortés, 1981, 1992a).
The tidal range is 30-50 cm, but the area is also greatly affected by local winds. Tides are mixed, mainly diurnal. Waves are mainly from the northeast January-June and from the east July-December, depending on the position of the Intertropical Convergence Zone.
Mangrove Forest
The mangrove site is located at Laguna Gandoca and covers an area of 250 ha. (Fig. 2). It is the least altered by human activities of any mangrove forest on the Caribbean coast of Costa Rica. The lagoon is a topographic depression at the land-sea interface created by fluvial-tidal interactions. Long-shore currents here built a sandy bar or spit across the confluence to create a coastal lagoon. Exchange between the lagoon and the ocean depends on precipitation and run-off. More freshwater exits the system than marine water enters. The outlet varies in size, from occasionally being closed to being several meters wide.
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| Fig. 2. Mangrove site at Laguna
Gandoca within the Refugio Nacional de Vida Silvestre, Gandoca-Manzanillo, Costa Rica. |
The lower section of the mangrove forest is dominated by large Rhizophora racemosa G.F.W.Meyer and Avicennia germinans (Linnaeus); other species include R. harrisonii Leechman, Conocarpus erecta Linnaeus, and R. mangle Linnaeus. The upper reaches of the forest are dominated by the fern Acrosticum aureum Linnaeus and the palm Raphia taedigera Martius.
Laguna Gandoca has the only natural populations of the mangrove osyter, Crassostrea rhizophorae (Guilding) in Costa Rica, and the largest patch of red mangrove, R. mangle. This lagoon is one of the main nursery sites for the Atlantic tarpon, Megalops atlanticus Valenciennes, and other species of economic importance (Chacón, 1994).
Seagrass Beds
The seagrass site is located in a shallow (<1 m) lagoon in the Parque Nacional Cahuita (Fig. 3). The lagoon covers an area of 250 ha, and the seagrass beds cover 20 ha behind the reef crests. The predominant species is turtle grass, Thalassia testudinum Banks ex König, with intermixed manatee grass, Syringodium filiformis Kütz. Haloodule wrightii Ascherson is also found mixed with the other seagrasses or alone in protected areas. This seagrass site was affected by the 1991 Limón earthquake (7.5 on the Richter scale), as a result of co-seismic uplift of about 50 cm (Cortés et al., 1992). One year after the earthquake, Thalassia had completely overgrown the lagoon, but the populations of algae and seagrasses had returned to pre-earthquake levels two years after the quake.
At the site in the middle of the lagoon, the ratio of Thalassia to Syringodium is about three to four. Several coral species and many algae are present, especially Dictyota, Amphiroa, Laurencia, and Halimeda. In early 1995, the density of Thalassia was 1,035 ± 38 short shoots m-2, and the density of Syringodium was 771 ± 365 short shoots m-2. Between April and May 1995, the growth rate of Thalassia was 300 ± 320 mg m-2 d-1.
Coral Reefs
The coral reefs are the most studied marine ecosystems on the Caribbean coast of Costa Rica.Oof these, the one at the Parque Nacional Cahuita has been studied longer and in greater detail (Fig. 3). The reef was described first by Wellington (1974a); since then, high levels of siltation and turbidity have been investigated. Studies have suggested that the high levels of terrigenous sediments are responsible for the siltation and turbidity as well as being the main stressor on the reef (Risk et al., 1980; Cortés, 1981; Cortés and Risk, 1984, 1985; Cortés and Guzmán, 1985a). A study conducted 15 years after these initial observations indicates a continuous deterioration of the coral reef (Cortés, 1994).
Descriptions have been published of coral species (Cortés and Guzmán, 1985b; Cortés, 1992b), octocorals (Guzmán and Cortés, 1985), algae (Wellington, 1974b; Soto and Ballentine, 1986), microcrustaceans (Breedy, 1986; Breedy and Murillo, 1995), sponges (Loaiza, 1991), densities of Diadema (Valdez and Villalobos, 1978), and primary productivity (Silva, 1986). Pollution on the reef has been documented by Mata et al. (1987), Rojas (1990), Sandí (1990), and Guzmán and Jiménez (1992). The death of corals and other reef organisms due to high temperatures in 1983 was reported by Cortés et al. (1984), while that resulting from the 1991 earthquake was reported by Cortés et al. (1992). The massive 1983 die-off of Gorgonia was described by Guzmán and Cortés (1984), that of Diadema by Murillo and Cortés (1984).
The coral reef is characterized by an outer crest extending for 5 km around Punta Cahuita; the forereef base is at a depth of 15 m. The reef crest is dominated by Millepora complanata Lamarck and coralline algae. A smaller inner crest extends for 500 m around Puerto Vargas; the base of the forereef is at 5-6 m and is built mainly of Agaricia agaricites (Linnaeus) and Porites spp. on the eastern end, and of massive corals in other sections. The reef crest had Acropora palmata (Lamarck), but the species died off in 1983 (Cortés et al., 1984) with little recovery since then. The backreef has Diploria clivosa (Ellis & Solander) and Millepora complanata; the lagoon is mainly rubble, with a few seagrasses and algae.
The CARICOMP site is located on the inner crest at the base of the reef at a depth of 5 m. The main coral is Siderastrea siderea (Ellis & Solander), together with Diploria strigosa Dana and a few Montastraea franksi Gregory. Average live coral coverage is 28.8 ± 2.8% (n = 5 x 10-m-long transects).
Acknowledgments
I would like to acknowledge the support of the Vicerrectoría de Investigación of the Universidad de Costa Rica, CONICIT (Project 90-326 BID), and R. W. Parkinson.
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