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The islands of the Revillagigedo Archipelago are oceanic islands of volcanic origin that emerge from a volcanic floor along the Clarion Fracture zone, west of the union between the Pacific, Ribera and Cocos geologic plates. The Insular Arch of the Revillagigedo Archipelago represents an authentic submarine mountain system, with some summits above sea level, such as the islands Roca Partida, Socorro and San Benedicto. The islands are characterized for being surrounded by cliffs, with mountainous areas and interior volcanoes as well as rugged sites, lava fields and soft crests. Its topographic forms are of endogenous, accumulative nature, while exogenous processes have modified the original volcanic physiognomy, mainly in the central and higher parts, which reach up to 1,040 m above sea level.
The regional climate is considered arid or desertic, with an average yearly temperature higher than 22ºC. Climate is regulated by tropical depressions and hurricanes that occur during the summer and which characterize the Western Pacific. Annual rainfall is scarce (313 mm) and takes places mainly during the months of August to October, with a predominant regime of summer rains. The average temperature of the islands´ surrounding waters fluctuates between 28ºC and 29ºC during the summer, while during the winter the average surface temperature of the adjacent oceanic water oscillates between 22ºC and 25ºC.
The islands biota presents a considerable degree of endemism, both on land and in its surrounding waters, particularly concerning birds. The Revillagigedo Archipelago is under the influence of the tropical zone of the Mexican Pacific and of the temperate-tropical zone of transition of the northeastern Pacific. Thus, its flora and fauna includes species from the coast of Tropical America, of the Indo-Pacific region and of circumtropical areas.
The marine fauna is characterized not only by its beauty but also for its high diversity of invertebrates (and in some groups also by the number of endemisms), particularly crustaceans and mollusks, as also equinoderms and corals. There are 133 species of birds registered for the islands, 25 of which are endemic to the archipelago. There are also 22 species of hermatypic corals, of which more than half are found only near oceanic islands of the Eastern Pacific, and near to one third is found only at the Archipelago of Revillagigedo. There are also 156 species of mollusks on the islands, 99 species of equinoderms, 92 species of crustaceans, three of which are endemic. The fish fauna of the archipelago also presents a high degree of species richness with at least 321 species, 25 of which belong to the elasmobranquia, with 20 species identified as sharks and five as rays. Also, the waters surrounding the Revillagigedo Archipelago represent an important feeding, breeding and transit area for cetaceans of the Mexican Pacific, and 16 species of whales and dolphins have been registered in the area.
(vii): The Revillagigedo Archipelago is located in the Eastern Pacific, on the northern end of the ridge of Los Matemáticos. This ridge is a submarine topographical feature that marks the site where, approximately 3.5 million years ago, there was an expansion of the ocean floor. Continuing volcanic activity makes the Reserve a geologically important site, as it allows for the study of volcanic, plate tectonic, and risk of earthquakes phenomena. Geologic evolution has made possible the formation of polimetallic nodules on the ocean floor, considered the largest in the world. Socorro Island is a unique example in the Pacific basin, as it constitutes a mountainous area in which the highest elevation is found on the Evermann Volcano, characterized by different stages of pre-caldera, syn-caldera and post-caldera formations, From its inception in the depths of the ocean, it reaches almost 4,000 m of height. Its base diameter measures 4.8 km and the cusp reaches an altitude of 1,040 m above sea level. In a radius of 3.5 Km, at an altitude of some 700 m, 12 adventitious volcanoes surround the Evermann, with another ten found in a radius of 4.5 Km without an apparent subordination to the Evermann, but also of adventitious origin, which date from the Tertiary. On the island of San Benedicto, the Bárcena volcano is the more prominent topographical feature. The island San Benedicto contains a series of Quaternary traquitic domes in its northern end. The origin of the San Benedicto Island resides in the distension movements associated to submarine fissures, canyons and mountains. The island is, in fact, the cusp of a submarine mountain, and its southeastern flank a lava-flow was discharged, reaching the ocean, and forming a delta that measures 700 x 1 200 m. The island Clarion was formed from materials produced by Miocene to Eocene volcanic eruptions. The islet Roca Partida is the tip of a submarine stratovolcano.
(viii): The Revillagigedo Archipelago is representative of an oceanic island ecosystem characterized by its volcanic origin, and as such it is considered a fragile ecosystem. The archipelago is composed of four islands separated of the continental mass by several hundreds of kilometers (382 km to the North and 661 km to the West), varying in size and geological and ecological characteristics. Its insular nature and factors prevailing in the reserve, adverse to colonization by terrestrial organisms, transform this emerged land into a natural laboratory, in which important progress can be made in the study of evolutionary processes, and mechanisms and strategies of dispersion, competition, population dynamics and control of species.
(ix): It possesses impressive terrestrial landscapes of diverse geomorphology, covered by scrub brush and deciduous forests, and surrounded by temperate crystalline waters of an outstanding transparency. Known for their abundance of marine life that includes the Giant Pacific Manta ray, dolphins, marine turtles and sharks, the islands also provide during the winter a courtship and pairing area for the spectacular Humpback whale.
(x): Given their condition as oceanic islands, they represent a unique ensemble of species, habitats and ecosystems. The types of habitats found on these islands are very peculiar, from the smallest island (Roca Partida), that is only a rocky outcrop denuded of vegetation on which exclusively marine birds are found, to the vegetation of arid zones, halophytes, brush, grasslands and deciduous forests on the largest island (Socorro Island) Due to these characteristics, the islands of the Revillagigedo Archipelago constitute a separate biogeographical province within the Neotropical region and, in agreement with the world biogeography regionalization of the World-Wide Fund for Nature (WWF), it belongs to the Dry Forest of the Revillagigedo islands Eco-region (Revillagigedo islands dry forests -NT0216).
As already stated, the Revillagigedo Archipelago possesses very high levels of endemism, both on land as in the surrounding waters, particularly of birds. The archipelago is located in the ecological confluence of the tropical region of the Mexican Pacific and the temperate-tropical transition of the northeastern Pacific; its life forms include species of the Indo-Pacific Region, of the coast of Tropical America and circumtropical areas. In this area, four species of marine turtles feed, nest and develop, namely the Leatherback turtle (Dermochelys coriacea), Olive Ridley turtle (Lepidochelys olivacea), Hawksbill turtle (Eretmochelys imbricata), and Green turtle (Chelonia mydas). Another animal that breeds and nourishes its young in the waters surrounding the Revillagigedo Archipelago islands is the Humpback Whale (Megaptera novaeangliae). Several species of endemic birds and reptiles complement the fauna of the reserve. In relation to its flora, 202 plant species have been registered, 55 of them are endemic to the archipelago.
 Traquítico in the Spanish original. A type of volcanic rock.
Its distance from the mainland and the lack of fresh water represent limiting factors to the establishment of human population centers on the islands. Since their discovery (Socorro Island was discovered in 1533; San Benedicto in 1542; Clarion and Roca Partida Island in 1779), explorers, fishermen, and researchers have inhabited the islands occasionally and, since 1957, personnel of the Ministry of the Navy (Secretaría de Marina) have a permanent base. However, at present there are no civil population or indigenous group settlements on these islands.
The Revillagigedo Archipelago was decreed in the year of 1994 as a Nature Protected Area under the denomination of Biosphere Reserve. The guidelines and regulations applicable in environmental and conservation matters are those established by the General Law for Ecological Balance and Environmental Protection (Ley General de Equilibrio Ecológico y Protección al Ambiente- LEGEEPA).
The Official Mexican Norm´s (NOM-059-SEMARNAT-2001) purpose is to identify the species or populations of wild flora and fauna at risk in the Republic of Mexico, as well as to establish the criteria for inclusion or change of category of risk for species or populations by means of an method evaluating their risk of extinction. A series of species considered at risk are protected under this norm, such as marine mammals and marine turtles.
Furthermore, these islands have their own Conservation and Management Program, published in 2004, which considers the criteria and strategies to assure the conservation of the insular and marine ecosystems of the archipelago.
The Revillagigedo Archipelago is a Ramsar Site since 2004, and is thus considered a wetland of international importance. The World Conservation Union (UICN) includes this archipelago in its World Conservation Strategy, as a priority area for conservation within the terrestrial biogeographical provinces, and the International Council for Bird Protection (ICBP) consigns it as an endemic bird area of primary importance.
The Biosphere Reserve Revillagigedo Archipelago shows a great similarity with the World Heritage sites of the Galapagos National Park of Ecuador and the Marine and Terrestrial Conservation Area of Coco´s Island in Costa Rica. These three island systems are of volcanic origin, and are situated on top of submarine cordilleras. Furthermore, given their size, isolation and degree of conservation, they present high levels of endemism, a product of their evolution in isolated territories and under the absence of external genetic flows, reason by which they are cataloged as natural laboratories, ideal for research studies on the ecological and evolutionary processes being undergone by the species present, and for long term environmental monitoring. The Revillagigedo Archipelago shares some similarities with other properties inscribed on the World Heritage list.
Henderson Island, United Kingdom: inscribed given its almost unaltered state, for preserving numerous bird species and possesing mineral deposits formed by submarine volcanoes.
Gough and Inaccesible Islands, United Kingdom: inscribed due to the presence of little altered island and marine ecosystems and harboring marine bird colonies. It also possesses adjacent marine areas with a high faunistic diversity.
Islands and Protected Areas of the Gulf of California, Mexico: for having an arid or dessert climate, arid and abrupt mountainous areas with irregular formations and cliffs of varying heights. It also presents high levels of endemisms.
Lord Howe Islands, Australia: inscribed as an example of oceanic islands originated by volcanic activity over 2,000m below sea level. With a spectacular topography and habitat of numerous species, particularly birds.
Atlantic Islands of Brazil, Brazil: inscribed for the presence of important marine ecosystems serving as feeding and breeding areas for species of fish, sharks, turtles and marine mammals. There are also large concentrations of marine birds.