|Environment and development
in coastal regions and in small islands
Coastal region and small island papers 3
Parque Nacional Morrocoy, Venezuela
David Bone1,3, Daisy Perez1,3, Alicia Villamizar2, Pablo E. Penchaszadeh3,4, and Eduardo Klein3,4
|1||Departamento de Biología de Organismos|
|2||Instituto de Recursos Naturales Renovables|
|3||Instituto de Tecnología y Ciencias Marinas (INTECMAR)|
|4||Departamento de Estudios Ambientales, Universidad Simón Bolívar, PO Box 89000, Caracas, Venezuela|
The CARICOMP site in Parque Nacional Morrocoy is located on the northwestern coast of Golfo Triste, a large inlet on the west-central coast of Venezuela (10°52'N, 69°16'W). The 32,090 ha park includes continental, insular, and marine ecosystems, and two marine zones are distinguished within the park. The seaward zone is connected to the open ocean and is characterized by coraline communities, moderate swells, low turbidity, and 20 m water depths. The inshore zone is characterized by low wave activity, higher turbidity, and shallow waters with mangrove (mainly Rhizophora mangle) and sea grass (Thalassia testudinum) communities developed primarily along the lee sides of keys and on sandy bottoms of the internal lagoons. Since 1974, the park has been subject to intense tourism, which extensively stresses the coral reefs. At present, the park is still being used for recreational purposes, but efforts are underway to preserve it and to carry out scientific research with international cooperation. Our aim is to monitor Morrocoy ecosystems to allow comparison with other coastal sites in the Caribbean.
Golfo Triste (Fig. 1) is a large inlet on the west-central coast of Venezuela, in easternmost Falcón state between the villages of Tucacas and Chichiriviche. The gulf lies south of the Bonaire trench, the central region of the Venezuelan Basin, and is the submerged part of an extensive sedimentary deltaic-alluvial plain resulting from sediment dispersal by the Yaracuy and Aroa Rivers. The 32,090 ha Parque Nacional Morrocoy is located on the northwestern coast of the Golfo Triste and encompasses continental, insular, and marine areas.
|Fig. 1. Map of Golfo Triste showing
the locations of the Parque
Nacional Morrocoy, major towns (dots), and drainages of the Aroa
and Yaracuy Rivers.
The continental platform that extends from the southeast to the northwest to Golfo de la Vela is characterized by a gentle slope, except near Puerto Cabello and the keys off Tucacas and Chichiriviche, where bathymetric dropoffs occur. Such irregularities correspond to depressions, shallows, and coral islands keys partially covered by mangroves. The bottom consists of terrigenous and biogenic sediments: fine sand (80-100%), muddy sand (50-80%), sandy mud (20-50%) and mud (0-20%).
Golfo Triste is characterized by a relatively constant climate throughout the year (Fig. 2). The air temperature varies from 24.9 to 29.7°C during the dry season (December-April); maximum temperatures occur during the rainy season (May-October). The relative humidity is high, 83-90%, with the highest values recorded between May and August. Mean wind velocity ranges from 1.5 to 2.5 m s-1 (Pagán, 1992), the predominant wind direction is NE-SW during most of the year. Seasonal changes in physico-chemical parameters are closely related to variations in wind intensity, which is at maximum during the dry season (Pérez-Nieto, 1980). Water temperature ranges are 26-29°C at the surface and 18-20°C at 150 m depth. Salinities are consistently greater than 36 and, because of low runoff and high evaporation rates, often exceed 36.5 in the Venezuelan coastal fringe.
|Fig. 2a. Annual air temperature and
rainfall pattern at Punta
Morón, Morón, Golfo Triste.
|Fig. 2b. Annual water temperature and
salinity fluctuations at
Punta Morón, Morón, Golfo Triste.
The Parque Nacional Morrocoy has a total surface area of 32,090 ha (Fig. 3). The climate of the Morrocoy region is a savannah climate with seasonal influence. The diurnal temperature variation of surface waters fluctuates between 27°C and 32°C, where oceanic influence prevails; the salinity varies between 30 and 38 (Bitter, 1988), being more constant near the ocean. Mean annual precipitation is 1,213 mm and varies seasonally (Fig. 2a). Two marine zones are distinguished within the park. The seaward zone is connected to the open ocean and is characterized by coraline communities, moderate swells, low turbidity and depths to 20 m. The inshore zone is characterized by low wave activity, higher turbidity, and shallow waters with mangrove (mainly Rhizophora mangle) and seagrass (Thalassia testudinum) communities (Losada and La Schiazza, 1989). Such communities develop mainly along the lee shores of the keys and in sandy sediments near the mouths of ocean inlets to the internal lagoons.
|Fig. 3. Map of Parque Nacional
Morrocoy (southern portion) showing the
locations of the CARICOMP sampling sites. Small numbers represent
depth in fathoms.
Weiss and Goddard (1977) reviewed damage to the northern reefs of the park up through 1973 and reported on a series of changes at Chichiriviche, a former fishing village that is now a tourist-centered town within the park. From 1957 to 1964, a cement plant, a water tank and pipeline, and an asphalt road connecting the town to the coastal highway were constructed. These brought about a population explosion in the area, as well as an increase in tourism and related activities that affected not only the mainland but also the keys off Chichiriviche. Towards the end of the 1960s, the reefs began to show signs of man-made disturbances, due to the construction of houses and docks and the disposal of garbage, sewage, and other materials. Weiss and Goddard (1977) considered that sewage caused the most damage.
The 1970s began with the construction of buildings on all existing keys and on many shoals, sand banks, and reef flats. In May 1974, the government of Venezuela declared the area a national park, ordered demolition of all construction on the keys and beaches, and prohibited further development of coastal towns within the park. Despite these and other protective measures, the damage suffered by the reefs has continued to increase. The reefs, reported healthy by Weiss and Goddard (1977) in 1973, were found to be greatly damaged when first studied in 1979 by Bone (1980) and Weil (1980). Other reefs, in the northern part of the park, had obvious symptoms of deterioration such as high dead coral coverage (>70%) and the stressing and burial of reef colonies by sediments (Bone, 1980). Man-made disturbances in this area include those resulting from bad management of mainland agriculture, with erosion products being carried into the gulf by river drainages and the action of marine coastal currents. Bone et al. (1993) suggested that the extent and degree of the damage was due mainly to high sedimentation rates, which began to increase around 1972 with land clearing and construction and have increased further since then.
Other disturbances, both natural and man-made, have impacted the southern portion of the park for several years. Before the park was officially established, elevated houses ("palafitos") were constructed over Thalassia testudinum beds. The loss of vegetation and their stabilizing rhizomes produced drastic changes in substrate granulometry such that, more than ten years since demolition, there has been no recolonization of denuded areas. The cutting of mangrove for wood is still a common activity by inhabitants of the area, as is cutting of mangrove roots to collect the oysters that grow on them.
The seagrass ecosystem is well represented in submerged areas of the park, where extensive monospecific prairies of Thalassia testudinum and associated algae are found. The sampling site is located in the northern portion of the bay known as Las Luisas (Fig. 3 and Fig. 4). The Thalassia prairie develops from shore for 80-100 linear meters seaward, where it reaches a depth of 3 m (Losada and La Schiazza, 1989). This prairie is characterized by long leaf plants (30 cm or more), an elevated number of rhizomes, and a leaf cover of more than 60%. Maximum productivity (3.30 ± 0.41 g m-2 d-1) and total biomass (862.41 ± 190.89 g m-2) are found in July and August, respectively. The contribution of each fraction of the plant to the total biomass is: green leaves 18.4%, non-green leaves and short stalks 30.1%, live rhizomes 30.2%, dead rhizomes 2.0%, live roots 13.9%, and dead roots 3.5%. Minimum productivity (1.69 ± 0.22 g m-2 d-1) and total biomass (385.18 ± 78.74 g m-2) are found in October and July, respectively (Guevara, 1993). The contribution of each fraction to the total biomass is: green leaves 12.5%, non-green leaves and short stalks 25.4%, live rhizomes 40.9%, dead rhizomes 3.4%, live roots 11.1%, and dead roots 5.8% (Guevara, 1993). The seagrass bed ends in a muddy-sand substrate (Losada and La Schiazza, 1989), where the depth is 3 m.
|Fig. 4. Detailed map showing the
CARICOMP seagrass study site at Las
Luisas. Small numbers represent depth in fathoms.
Mangroves are well represented in Morrocoy, where they dominate most of the inner emerged areas of the park. The mangrove station is located at Tumba Cuatro (Fig. 3 and Fig. 5), where the mangroves are a fringe type that are common throughout the park. The dominant tree species is Rhizophora mangle, which is found exclusively at the fringe and occurs mixed with Laguncularia racemosa farther inland. The trees are represented by 68% Rhizophora mangle, 29% Laguncularia racemosa, 8% Avicennia germinans (A. nitida, Jacq.), and less than 1% unidentified species. The density of the forest is approximately 348 trees/0.1 ha, a value within the range reported for other fringe forests in the Caribbean (densities varying between 100 and 500 trees/0.1 ha; Schaeffer-Novelli and Cintrón, 1986; Lugo and Snedaker, 1974; Snedaker, 1982; Lugo, 1980). According to the "value of importance index" (VI), R. mangle is the most valuable species of the area from a structural point of view, with a VI of 259.65; L. racemosa has a VI of 140.28; A. germinans has a VI of 54.35. The mean height of the trees is 8.0 m, with a maximum height of 15 m for trees with diameter breast height, dbh > 10 cm, and a minimum height of 5 m for trees with dbh < 2.5 cm. The mean dbh for the group of trees with dbh > 10 cm = 37.5 m, representing 45% of the total trees sampled; trees with dbh < 2.5 cm comprise the other 55%. In this area, the mangrove community has reached a high level of structural development i.e., a high density both of mature and juvenile trees.
|Fig. 5. Detailed map showing the
CARICOMP mangrove study site at
Tumba Cuatro. Small numbers represent depth in fathoms.
Coral reef formations dominate the entire coast along the east-northeast shores of the Morrocoy keys, including some shallows in inlets to the park. The reef sites are located at Playa Caimán, in front of Boca Grande, and at Cayo Sombrero, an exposed key in the eastern portion of the park (Fig. 3 and Fig. 6).
|Fig. 6. Detailed map showing the
CARICOMP coral reef study sites at
Playa Caimán and Cayo Sombrero. Small numbers represent depth in
Playa Caimán is a fringing reef with a channel that breaks with the continuity of the reef and separates the area in two zones: northern and southern. The northern zone has been more affected by man-made disturbances (until 1974, there were three elevated houses located on a small inlet on the leeward side of the reef). The southern zone is more secluded and less disturbed; the reef platform is only 50 m wide and the reef slope reaches to a maximum depth of 12 m. The anterior zone of the platform borders the mangrove forest and a poorly developed Thalassia testudinum prairie. The mean depth of the platform is 0.3 m. The algal species reported for the platform are Halimeda spp., Dyctiota cervicornis, Caulerpa spp., Panicilum capitatus, Jama capillosa, among others (Weil, 1980). The coral species reported are Diploria spp., Millepora alcicornis, Siderastrea radians, and Porites astrecides. Extensive formations of the zoanthids Palithoa mamillosa and Zoanthus sociatus are found toward the reef front. Several species of sponges as well as soft corals of the Plexaura sp. are found in crevices in the reef. The reef front (0.20-3.0 m depth) is dominated by formations of Acropora palmata, which give rise to high morphological heterogeneity. Other colonies found here are Millepora alcicornis, Millepora complanata, and Montastraea annularis, which grow in columns. This zone continues with an extensive fringe dominated by Montastraea annularis (2.5-7 m in depth). There are also colonies of Colpophyllia natans, Diploria spp., Agaricia spp., and some colonies of Solenastrea bornuoni in this zone, the most homogeneous coral zone. The deepest zone of the reef (7.0-11 m depth) or slope is mainly dominated by large colonies of Colpophyllia natans and also by Montastraea cavernosa. There are also several well developed colonies of soft coral such as Pseudopterogorgia sp., Plexaura homomalla, P. dichotoma, and Eunicea sp. among the most abundant. This zone ends in a sandy bottom with a soft slope that continues down to 15 m depth, with dispersed patches of coral colonies of variable sizes (Bone, 1980).
Cayo Sombrero is a sandy key surrounded by coral reefs. The CARICOMP station, established in June 1996, is located on the lee side of the key; however, the reef is influenced by strong lateral currents due to the bottleneck configuration of the key system. The main reef is separated from shore by a shallow sandy channel 80 m wide. There is not a genuine reef front. The shallow reef (3 m depth) is covered mainly by soft corals such as Pseudoplexaura sp., Plexaura homomalla, P. flexuosa, and Pseudopterogorgia americana. The predominant hard coral at this depth is Madracis mirabilis. The slope begins at a depth of 4 m; it reaches 15 m on the southern side and 6 m on the northern side. The CARICOMP station is located in the southern zone characterized by the deeper slope. Between 3 and 5 m deep, the community is represented by Millepora alcicornis and Madracis mirabilis. Down to 12 m, large colonies of M. annularis dominate the reef, with some conspicuous colonies of C. natans. There are also some colonies of M. cavernosa, D. strigosa, P. porites, and A. agaricites. The reef ends at a depth of 15 m with a gently sloped sandy bottom. In general, this station is structurally more complex than Playa Caimán, although M. annularis does not have large vertical formations.
In January 1996, a mass mortality event affected many reefs in the park and left less than 1% of live massive coral cover at Playa Caimán. At this site, only P. porites, S. sidera, and Millepora alcicornis survived. An uncommon upwelling event combined with large river outputs enriched waters with nutrients, leading to an anomalous planktonic bloom. Huge amounts of macroaggregates were produced by dinoflagellates and diatoms, forming a mucous layer that covered the reefs. Very calm seas and low wind speeds kept the bloom within the park. This condition persisted for a week, inducing mortality among fishes, crustaceans, mollusks, equinoderms, annelids, sipunculids, sponges, and cnidarians by either mechanical asphyxiation (obstruction of respiratory mechanisms by a thick layer of mucus) or anoxia (reduction of dissolved oxygen by decomposition of organic matter). The station at Cayo Sombrero was slightly affected, as it was one of the few sites in the park still presenting an important live coral cover.
The CARICOMP program at Parque Nacional Morrocoy is partially funded by the Instituto de Tecnología y Ciencias Marinas (INTECMAR) and Decanato de Investigaciones, Universidad Simón Bolívar (grant DI-CB-205-94).
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