|Environment and development
in coastal regions and in small islands
Coastal region and small island papers 3
Cayo Coco, Sabana-Camagüey Archipelago, Cuba
Pedro M. Alcolado1, Grisel Menéndez1, Pedro García-Parrado1, Daily Zúñiga2, Beatriz Martínez-Darana1, Magalys Sosa1, and Raúl Gómez2
|1||Instituto de Oceanología, Ministerio de Ciencia, Tecnología y Medio Ambiente, Ave. 1ra. No. 18406, Rpto. Flores, Playa, CP 12100, Ciudad de La Habana, Cuba|
|2||Centro de Investigaciones de Ecosistemas Costeros, Ministerio de Ciencia, Tecnología y Medio Ambiente, Morón, Cayo Coco, CP 69400, Ciego de Avila, Cuba|
Cayo Coco is part of the Sabana-Camagüey Archipelago off the north coast of Cuba. The sampling site on the northern shore of the cay includes reefs, seagrass beds, and a permanently flooded red mangrove forest. Human influence on marine, coastal, and terrestrial environments is limited. Wave action and sedimentation are the most important large-scale physical stressors governing the marine ecology of the site. Freshwater runoff is limited and influences salinity only very close to the coast. The virtual absence of the black urchin Diadema antillarum probably accounts for the great proliferation of fleshy algae on rocky reef substrates. The marine and coastal ecosystems of this area remain almost pristine and are included in plans for biodiversity conservation and sustainable tourism development.
The Cuban CARICOMP Site is located on the northern shore of Cayo Coco, which lies north of Cuba in the Sabana-Camagüey Archipelago, at 22°33'N, 78°26'W (Fig. 1). The northern coast of Cayo Coco is open to the Old Channel of Bahamas; the southern coast is open to the very shallow and hypersaline Perros Bay. Cayo Coco occupies an area of 370 km2, making it the second largest cay within the archipelago (after Cayo Romano).
|Fig. 1. Geographic setting of Cayo
Coco, Cuba, and broad scale habitat
distribution; CERC is the Coastal Ecosystem Research Center.
Three institutions of the Cuban Ministry of Sciences, Technology and Environment (formerly the Academy of Sciences) participate in CARICOMP: the Institute of Oceanology (IO), the Institute of Ecology and Systematics (IES), and the Coastal Ecosystems Research Center (CERC). The excellent new research facility of CERC at Cayo Coco contains a well equipped Class A meteorological station.
Site mapping was done using black/white aerial photographs (scale 1:10,000). The three sampling sites are located in Ensenada Puerto Coco cove and comprise three habitats: reef, seagrass beds and a permanently flooded red mangrove forest. The marine and coastal ecosystems of this area remain almost pristine and are included in plans for biodiversity conservation and sustainable tourism development.
Human influence on marine, coastal, and terrestrial environments is limited. Wave action and sedimentation are the most important physical stressors governing the ecology of this offshore marine shelf. Freshwater runoff is limited and apparently influences salinity only very close to the coast. The virtual absence of the black urchin Diadema antillarum, since a massive die-off in the early 1980s, probably accounts for the great proliferation of fleshy algae on reef rocky substrates.
The relief of the Sabana-Camagüey Archipelago is due to the neotectonic transformation of ancient structures and formation of new tectonic disruptive features that fragmented the area into transverse and longitudinal blocks. Other factors include the trend of block movements during the Holocene (ascending and descending), its geographical location in the northern tropical belt, sea level oscillations during the Quaternary, and the predominance of carbonate lithological assemblages during the Quaternary (Magáz et al., 1990).
The archipelago was formed by elevation of the central northern margin of the shelf of Cuba, reaching down to the insular slope (northward). It is separated from the mainland by a longitudinal tectonic depression (southward), which is occupied by an ensemble of lagoons. A line of bordering cays on the north exists on the domes of the fragmented structural elevations (Magáz et al., 1990).
The sectors of discontinuous emersion are manifested in the relief by the existence of several erosive and erosive-accumulative relict marine terraces, as well as in the formation of sand bar systems and consolidated dunes with crossbedding where the coast is elevated. The immersion sectors are represented by the predominance of cumulative and swampy marine biogenic flats with thick layers of sandy-argillaceous and peaty sediments. There also exists superposition of facies of coastal sand bars over peaty facies of sealed lagoons and swamps (Magáz et al., 1990).
Hydrogeology and Oceanography
Pooling data from Cayo Coco (1985-1990) and Cayo Paredón Grande (1946-1963), the monthly average minimum air temperature at the site is 20.0°C and the average maximum is 32.5°C. The monthly average mean air temperature varies from 23.3°C to 28.7°C. (Fig. 2). Average precipitation at Cayo Coco is 1,076 mm annually (1985-1990), whereas nearby Cayo Paredón Grande has only 733 mm (1946-1963). The recorded average number of rainy days per year at these two cays is 92 and 76 days, respectively. The rainy season is from May to October (maxima in September and October); the dry season is November to April (Pazos-Alberdi et al., 1990). Annual average evaporation is in the range 2,100-2,200 mm (IGEO/ICGC/IGN, 1989), resulting in a strongly negative hydrobalance. Eastward winds predominate at Cayo Coco. From May 1989 through April 1990, annual average wind speed was 4.4 m s-1; calm periods made up only 1.2% (Pazos-Alberdi et al., 1990). Horizontal Secchi disk measurements at the reef station on March 27 and 29, 1994, varied from 26.1 m (cloudy noon) to 32 m (sunny noon); at the seagrass stations, measurements on March 28, 1994, were in the range 11.5-11.6 m (sunny noon). Coastal currents are predominantly westward. Rodríguez-Portal and Rodríguez-Ramírez (1983) classified the tides at the site as mixed (two cycles daily with different ranges) and recorded a maximum range of 1.2 m. Cold fronts affect the site with a frequency of 14.6 times per year (data from 1916-1917 and 1987-1988), occurring between October and April, resulting in decreased air temperature and humidity and increased rainfall, cloudiness, wind speed, and wave height (Pazos-Alberdi et al., 1990). Synoptic cyclones and hurricanes rarely affect the site, with hurricanes occurring only once every 6.6 years, most commonly from August to October. Only one high-intensity hurricane has hit the site in the last 178 years, on the 9th of November, 1932 (Pazos-Alberdi et al., 1990).
|Fig. 2. Monthly variation of air
temperature and rainfall at the Cayo
Coco station, 1985-1990 (after Pazos-Alberdi et al., 1990).
Historically, Cayo Coco has been virtually devoid of human population. The social and economic assimilation of Cayo Coco and adjacent cays of the archipelago took place at the beginning of the 20th century, characterized mainly by forest exploitation and charcoal production. Cattle ranching was also tried, and some feral cattle still inhabit Cayo Coco. Many forest areas were cleared by timber harvesting or were burnt to clear land for pasture (Alcolado et. al., 1992). Most cleared areas are redeveloping as secondary forests.
A small airport was constructed and began to operate in Cayo Coco in 1995. Two villages provide accommodations for coastguard, construction, and tourism personnel. One hotel has 450 rooms, another with 500 rooms is under construction, and others are projected. There are plans for significant growth of the tourism industry, focused on the beach and nature. A GEF/UNDP Project (CUB/92/G31) is dealing with protection of biodiversity and establishment of sustainable development, mainly tourism, in the region. A system of marine and terrestrial protected areas, including Cayo Coco, is being proposed.
The greater part of the offshore marine environment north of Cayo Coco has been only slightly affected by human activities; it seems to be driven mainly by wave action, sea level fluctuations, and wind and precipitation regimes. Fishing in this area has been maintained at near maximun sustainable yield. It is still common to observe great quantities of snappers and groupers while diving on the reefs. However, tourism is modifying the ecology along some stretches of the northern coast. Inshore waters tend to be hypersaline, with large fluctuations in salinity, due in part to limited exchange with ocean waters and in part to human activities such as the construction of bermed roads and dams. Fisheries have been severely affected in some inshore areas, and saline-induced mangrove mortality has been noted in some places. Mitigation actions are being planned and undertaken for improving the ecological situation in the affected areas. These include increasing the number of culverts and bridges along the bermed roads, releasing dammed-up waters, and channeling runoff.
The Cuban CARICOMP site (Fig. 3) is dominated by sandy and rocky-sandy Holocene plains that extend from the shore to a depth of 30-40 m. The slope steepens at 50 m deep, where the dropoff begins. Sandy surfaces are predominantly covered mainly by sparse seagrass beds of Thalassia testudinum. Unvegetated sandy bottoms are also common along stretches close to the coast, in bar-shaped patches within seagrass beds, in the reef channels and depressions, and in extensive patches along the forereef slope (lower terrace). Significant patches of Syringodium filiforme are found on this forereef slope, and abundant Halimeda has also been observed. Reefs are represented by zones of erosive-accumulative rock pavements, which are conspicuously inhabited by gorgonians and a few scleractinians. Several actual and relict reef crests and some spur-and-groove areas are also found. The spur-and-groove systems occur only close to the reef crests, perhaps as a consequence of the protection of these structures against the sediment-loaded waters outflowing from the shallow sandy plains during days with high wave energy. This protection allows better development of scleractinian corals. Some discontinuous reef escarpments, dropping 12-15 m, extend almost parallel to the coast north of Guillermo, Coco, and Romano Cays. The shores are characterized mainly by sandy beaches, with mangroves on the leeward sides. Some rocky shores are also present. Behind the shore, shallow lagoons are fringed by mangroves. In some places, complex channels and lagoon systems extend into extensive, marshy, mangrove plains that are dominated by Rhizophora mangle, especially northwest of Cayo Coco. As with many other cays in this area, terrestrial vegetation is represented by four forest assemblages: (1) tropical evergreen microphyllous woods, (2) subcoastal forests, (3) seasonally and temporally flooded forests with patches of herb communities and dominant Conocarpus erecta and Bucida sp., and (4) mangrove systems in which Rhizophora mangle dominates. There are also areas of tropical thickets, halophyte vegetation, sandy and rocky vegetation assemblages, and herb communities. Vegetation is also represented by degraded and secondary forests (Menéndez et al., 1990).
|Fig. 3. Distribution of sampling stations and habitats.|
Coral Reef Stations
The coral reef transects are located at a depth of 10-12 m across a very poorly defined spur-and-groove bottom or a rather rocky-sandy bottom with coral mounds (Fig. 3: A, 22°33'49"N, 78°26'19"W; B, 22°33' 48"N, 78°26'42"W). This transect area is located in the forereef zone adjacent to an escarpment that drops from 12 to 15 m; the area is rich in corals, sponges, and gorgonians. The adjoining lower terrace on the forereef slope is a rocky plain that is covered by a sand layer of varying thickness and extensive patches of Syringodium filiforme (surveyed to a depth of 20 m). At both reef sites, bottoms exhibit irregular patterns of mounds, sand grooves, and patches. The relief is accentuated towards the 12 m contour, where the escarpment begins.
The reef data are averages from both transects from March 1994 to April 1995. At each transect, the mean coral cover, including sand patches, varies from 5.5 to 7%. The dominant scleractinians are Montastraea annularis, with 10-55% of cover among scleractinians, M. cavernosa (3-22%), Porites porites (3-26%), and Siderastrea siderea (3-17%). Gorgonians and sponges are fairly abundant and moderately developed; sponges cover 2-3% of the bottom. The most common sponges are Aplysina cauliformis, Ircinia felix, Iotrochota birotulata, and Niphates digitalis. Most common among the gorgonians are Pseudopterogorgia americana, Briareum asbestinum, and Plexaura homomalla f. kuekenthali. The rocky substrate is covered by a mat of fleshy algae, including Dictyota, Lobophora, and Microdictyon, that is covered by sand. Fleshy and turf algae cover 52-60% of the bottom. From a depth of 10 m to 2 m, the bottom grades from a poorly defined spur-and-groove system to plain rock pavement, dominated by gorgonians. A discontinuous reef crest consists of a line of rocky outcrops covered by abundant colonies of fire corals (Millepora complanata), sea fans (Gorgonia flabellum), and small, sparse colonies of elkhorn corals (Acropora palmata). At both ends of the reef crest, extensive low-relief sandy rock pavements with gorgonians penetrate deeply into the lagoonal area, showing the abrasive influence of open ocean waves and perhaps tidal currents. The bottom of the rear zone is homogeneously covered by abundant coral rubble, profusely colonized by brown algae (Dictyota and Stypopodium). In the reef lagoon, the rubble bottom is colonized by sparse short-leaved Thalassia. The bottom slopes from the shore to the sandy sparse Thalassia beds of the reef lagoon. Extensive sandy areas, without vegetation, occur among the grass beds. The nearshore bottom is void of macrophytes, although some, mainly Thalassia, occur in elongated patches.
Dominant fishes, at depths between 3 and 15 m, belong to the families Haemulidae (Haemulon plumieri, H. flavolineatum and H. sciurus), Labridae (Thalassoma bifasciatum and Halichoeres bivittatus), Pomacentridae (Stegastes spp.), and Scaridae (Sparisoma spp. and Scarus spp.). At depths of 15 to 25 m, specifically on the deep slopes, the predominant families are Labridae (T. bifasciatum and Clepticus parrai), Pomacentridae (Chromis cyanea and S. partitus), Inermiidae (Inermia vittata), and Scaridae (Sparisoma spp. and Scarus spp.).
The most important physical stressors on this reef are wave action and natural sedimentation. Freshwater sources are limited. Human impacts on these reefs are negligible so far, limited to lobster fisheries and some tourism. The virtual absence of the herbivorous black urchin, Diadema antillarum, may account for the great proliferation of algae on the rocky substrates of this reef.
Seagrass Bed Stations
At depths greater than 1.5 m, luxuriant seagress beds are rare at the sampling sites (22°31'N; 78°32'W; Fig. 3: A, C2 and C3). A seagrass bed with a moderate standing crop of green leaves of Thalassia testudinum (mean dry weight = 60-116 g m-2, from samples at the two stations in March and October 1994) was monitored north of the mangrove station, north of Canalizo Genebra, at a depth of 1.40 m (Station A) and 1.75 m (Station B). Leaves are longer and less epiphytized than in the reef lagoon seagrass bed. Total Thalassia biomass, including roots and rhyzomes, varied from 931 to 2,396 g m-2 (data from March 1994 to September 1995). Some algae, e.g., Halimeda, Penicillus, Rhipocephalus, as well as many small sponges, anemones, gastropods, and holothurians, were observed. The bottom sediment is sandy. The water is transparent but greenish, suggesting nutrient enrichment from the neighboring mangrove swamp. Some influence of freshwater runoff during rainy days has been observed at this location.
Mangrove Forest Station
The mangrove sampling station is located in a permanently inundated forest of red mangrove, Rhizophora mangle. This is a basin forest occupying a depositional marshy plain with covered karst topography. A dendritic system of channels and lagoons of varying sizes irrigates the mangrove basin. A large, poorly irrigated marshy lagoon extends toward the southeast to Canalizo Ginebra, where flooding is continuous (Fig. 3, A: P3 and C1). Rhizophora mangle trees reach up to 7 m high at the sampling site. Tree height tends to decrease towards the highest high-water mark; thus, the distribution pattern of tree height is heterogeneous. Mangrove roots are poorly colonized by animals and algae. They are predominantly covered by some barnacles and biogenous silt. A few fire sponges (Tedania ignis) were observed. Fishes are apparently scarce and are represented primarily by Clupeidae (Jenkinsia lamprotaenia) and some Atherinidae (Atherinomorus stipes). Some black mangrove (Avicennia germinans) and buttonwood mangrove (Conocarpus erectus) trees are distributed near the eastern side of the entrance channel, also bordering the open coast, and in the band of contact between the mangrove swamp and the surrounding evergreen secondary microphyllous forest. An important influence of the freshwater runoff through this frontier during rainy days is expected. Until now, this mangrove ecosystem has not been impacted by human activity.
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