Location and General Description
Cocos Island in the central eastern Pacific Ocean (5º32’N-86º59’W) lies 523 km southwest of Cabo Blanco, in Costa Rica; the country to which it has belonged since 1869, and 665 km northeast of the Galapagos Islands, in Ecuador. This small island measures 7.6 km long and 4.4 km across with a surface area of approximately 24,000 ha. There are also small islets nearby such as Dos Amigos, Rafael and Juan Bautista (IUCN 1982; UNEP 1997).
The climate is strongly influenced by the equatorial counter-current, flowing in an easterly direction. It is warm, with an average annual temperature of 23.6 ºC, and extremely wet, with average annual rainfall higher than 6,000 mm. It rains throughout the year, although slightly less during the months of January, February and March and to a lesser extent in late September and October. The island represents the only submarine volcano that has emerged from the mountain range of the Cocos tectonic plate, which extends in a southwesterly direction from Costa Rica nearly to the Galapagos archipelago. It is primarily composed of strata of solid lava (basalts) in a well-defined columnar structure. The island probably formed from a hot spot some two million years ago, during the late Pliocene. The topography is irregular, with maximum elevations of 634 m in Cerro Iglesias and abundant waterways, cliffs, cataracts and caves. The largest rivers are the Genio and the Pittier, that empty into Wafer Bay. The soils can be classified as entisols that are highly acidic, fragile and easily eroded, particularly by high rainfall levels (Cortés 1986; UNEP 1997).
The island has dense vegetative cover classified as moist tropical forest; there are 235 known species of plants and 70 of these, or nearly 30%, are endemic. Predominant endemic tree species include the huriki Sacoglottis holdridgei, Ocotea insularis and Cecropia pittieri. There are three principal plant formations. The first is in the coastal zone (up to an elevation of 50 m.), with species such as Erythrina fusca, Cocos nucifera, Annona glabra and various ferns. In the undergrowth, shrubs in the Rubiaceae and Solanaceae families are common and the herbaceous vegetation includes Cyperaceae, Poaceae, Leguminosae and Malvaceae (Cortés 1986). The second formation is in the mountainous area, starting at an elevation of 50 m continuing to 500 m. The most common canopy species in this formation include "palo de hierro" (Sacoglottis holdridgei), avocado (Ocotea ira) and the endemic Cecropia pittieri. The undergrowth is characterized by the presence of sedges such as Hypolitrum amplum, and various species of arborescent ferns including Alophila armata. There are numerous epiphytic plants such as orchids, ferns, bromeliads and mosses growing throughout the forest strata. A palm that is abundant and endemic on the island is Rooseveltia frankliniana. At the highest elevations starting at 500 m, we find the third type of plant formation, the tropical cloud forest, where Melastoma spp. are frequently found (Cortés 1986).
The high percentage of endemic plants (nearly 30%), linked to their relatively low biodiversity (235 species), is due to phenomena associated with oceanic islands. The biodiversity of oceanic islands is generally poor with combined characteristics that are known as "disharmonious biota", usually simplified yet exceptional (Montoya 2001). In addition to the 235 plant species, 85 species of fungi, 74 species of ferns and other cryptogams (pteridophytes, psilophytes and lycopodiophytes) and 128 species of mosses and hepaticas (briophytes) have been identified, this latter group has exceptional diversity (Government of Costa Rica 1996). Some plant species have evolved adaptions that allow them to survive in a habitat devoid of a full faunal complement as that found in the mainland. An example is Mucuna urens, which has flowers that are clearly different from the continental plant because the island form is pollinated by an endemic finch rather than a bat, which do not exist on the island (Government of Costa Rica 1996).
The diversity of fauna is also low but at the same time there is a high percentage of endemism. There are 362 known species of insects, 65 of which are endemic to the island (18% of the total), although it is estimated that the total number of insects on the island could be as high as 800 species. The most diverse groups are the Lepidoptera and Formicidae. There are also spiders, centipedes, millipedes, isopods and miriapods. The endemic spider, Wendilgarda galapagensis is worth noting as it represents an example of niche expansion in an invertebrate, showing greater variation on the island in terms of its habitat selection and web design and construction than continental species of the same genus (Cortés 1986; Eberhard 1989). There is a total absence of amphibians on the island, as happens in other oceanic islands far from continental masses. The two existing species of land reptiles, the anolis lizard (Norops townsendii) and the gecko (Sphaerodactylus pacificus), are endemic. Of the seven species of land birds, the Cocos cuckoo (Coccyzus ferrugineus), the Cocos flycatcher (Nesotriccus ridgwayi) and the Cocos finch (Pinaroloxias inornata) are also endemic. This latter species belongs to a subfamily of finches that lives only on Cocos and the Galapagos Islands showing foraging specialization on the islands that may contribute to the high level of intra-species variation. Cocos Island is considered one of the 27 areas of avian endemism in Central America and the Caribbean because it has three species with limited range that are confined to this ecoregion alone (Wege et al. 1995; Harcourt et al. 1996). The five land mammals present on the island are introduced.
The entire island was declared a National Park and Biological Reserve by the government of Costa Rica in 1978 (IUCN management category II), a World Heritage Site by UNESCO in 1997 (criteria ii and iv) and a Wetland of International Importance (Ramsar 1998). Most of the island natural habitat can be considered intact, despite the negative influence of introduced plants and animals. The low relative biodiversity and isolation of this ecoregion make it particularly vulnerable to disturbances (UNEP 1997).
Types and Severity of Threats
After two failed attempts to settle the island, the island has remained free of permanent human intervention. The first settlers introduced different agricultural plant species as well as domestic animals and these continue to represent serious threats to the maintenance of the natural ecosystems. The crops introduced on the island include guava groves, coffee plantations and cocoa plantations. Their spread has adverse effects on the natural equilibrium of the park’s ecosystems. Most of these effects are caused by coffee plants (Coffea arabica) that have invaded certain areas of the undergrowth, particularly around Wafer Bay. Of the mammal species introduced, wild boars (Sus scrofa) have the worst impact because, more than other animals, boar alter plants in the undergrowth, affect the spread of many plants and destroy their root systems, accelerating soil erosion. In the long run, the affect could be as far reaching as damaging the coral reefs through siltation (UNEP 1997; Cortés 1986).
Justification of Ecoregion Delineation
This ecoregion was identified as unique and distinct from the mainland by the presence of numerous endemic species, including three endemic bird species (Stattersfield et al. 1998) and by its great distance and subsequent isolation from the mainland (Tosi 1969).
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Prepared by: Ugo Dambrosio
Reviewed by: In process