Clarion, Roca Partida, and Shimata

Galapagos of Mexico; hot spot volcanoes on the sea floor

I. Map boundaries: 10 to 20 degrees North; 112 to 120 degrees West

II. Country (State): Mexico (Colima)

III. Overview

Isolated islands are noted for endemic plants and animals. The four Revillagigedo Islands formed on the East Pacific Rise or just to the west of the plate boundary between the Pacific and Rivera plates. Clarion Island, shown on this map, is 700 km southwest of the tip of Baja Peninsula and 1,000 km west of the state of Colima in Mexico. On Clarion, 14 of the 16 bird species are endemic, and there are an endemic lizard and snake. Approximately 26 percent of the plants are endemic. This endemism has earned the Revillagigedo Island chain the nickname of the Galapagos of Mexico. The rich marine fauna has been protected by the establishment of a nature reserve, but several articles not illegal fishing, and introduced sheep, pig, and rabbit, all of which compete with endemic flora and fauna, are the subject of control efforts.

To the east of Clarion is Roca Partida, or Broken Rock, which is essentially a sea stack sticking out of the Pacific Ocean. No vegetation is present, but the rock is used by nesting seabirds. To the southwest of Clarion is Shimata Seamount, which does not surface. It is believed to be a hotspot volcano of a geologically young age (The seafloor from which it rises is less than 20 million years old).

IV. Terrestrial Ecoregions

Tropical and Subtropical Dry Broadleaf Forests of the Neotropic Biome

NT 216, Islas Revillagigedo dry forests. Sparse forests of Conocarpus, Hibiscus, Ficus, and Opuntia are interspersed with grasses. Found on Clarion Island.

V. Marine Ecoregions

Tropical Eastern Pacific Realm, Tropical East Pacific Province

164. Revillagigedos. Found in the seas around Clarion, Roca Partida, and Shimata Seamount.

VI. Ramsar Site

Reserva de la Biosfera Archipielago de Rivillagigedo. This area includes Clarion, Roca Partida and two other more easterly islands managed by the Ministry of Environment, Natural Resources and Fisheries, National Institute of Ecology, Mexico. Clarion Island consists of a large grass-covered plateau with low shrubs and trees on the cliffs. There are three mountains on Clarion, which was formed by volcanic eruptions in Miocene to Eocene times. Clarion contains 43 species of plants, 26 percent of which are endemic. All terrestrial animals, including a lizard and snake, are endemic. There are 16 species of birds, 14 of which are endemic. The area is an Important Bird Area for the Clarion burrowing owl, Clarion wren,Clarion mourning dove, and Townsend’s shearwater. The island is a nesting area for four species of sea turtles—leatherback, olive ridley, hawksbill, and green turtle. Offshore, the area was noted for hammerhead sharks, giant Pacific mantas, and yellowfin tuna; however, illegal fishing has depleted these resources. Roca Partida (Broken Rock) is part of the reserve and is a nesting area for seabirds such as the Nazca booby, brown booby, sooty tern, and brown noddy. Ecoregion NT 216 and marine ecoregion 164.

VII. Other Point of Interest

Shimata Seamount (Hurricane Bank). Located to the southwest of Clarion, this volcano rises to within 50 m of the surface. It is believed to be a hotspot volcano because it is not on a plate boundary and is 600 km to the west of the Mathematician seamounts, which represent a plate boundary along the East Pacific Ridge. The seamount is noted as a good tuna fishing area.

VIII. References

Commission for Environmental Conservation. 1999. North American Important Bird Areas. CEC, Montreal. www.cec.org/storage/41/3373-iba-ang-EN.pdf (accessed February 1, 2011).

Engel, A.E.J. and Celeste G. Engel. 1964. Igneous Rocks of the East Pacific Rise. Science 146:477-485.

Graham, David W. et al. 1988. He, Pb, Sr, and Nd Isotope Constraints on Magma Genesis and Mantle Heterogeneity Beneath Young Pacific Seamounts. Contributions to Mineralogy and Petrology 99:446-463.

Ministry of Environment, Natural Resources and Fisheries, National Institute of Ecology, Mexico. http://www2.ine.gob.mx/publicaciones/libros/2/revill.html (accessed January 30, 2011).

Olson, David M., et al., 2001. Terrestrial Ecoregions of the World: A New Map of Life on Earth. BioScience 51:933-938.

Ramsar Site List. http://www.ramsar.wetlands.org/ (accessed February 1, 2011).

Seamounts Online. Seamounts.sdsc.edu (accessed February 1, 2011).

Revillagigedo Islands Overview. www.seawatch.org/reports/revillagigedoislands.php (accessed February 1, 2011).

Spalding, Mark D. and 14 others. 2007. Marine Ecoregions of the World: A Bioregionalization of Coastal and Shelf Areas. BioScience 57:573-583.

Vidal, R.M. et al. 2009. Mexico. Pp. 269-280 in C. Devenish et al., eds. Important Bird Areas Americas—Priority Sites for Biodiversity Conservation. BirdLife International, Quito, Ecuador (BirdLife Conservation Series No. 16).

World Heritage List. http://whc.unesco.org/en/list (accessed 11/6/10).