Echinoderms of the National Park Isla Isabel, Nayarit, Mexico [Equinodermos del Parque Nacional Isla Isabel, Nayarit, México]

This study describes the species composition of echinoderms from Isla Isabel National Park, in the central Mexican Pacific. The samplings and collection transects band were made in October 2004, March and July 2005 by direct search on several rocky beaches, and on rocky and sandy substrates in subtidal areas to 19 m depth. The specimens collected with a trawling net from the shrimp vessel "America" in adjacent waters were also included. A total of 299 organisms belonging to 31 species and 19 families of echinoderms were registered. The greatest abundance was recorded in the nothern (43%) and eastern (39%) regions of the island where there is greater substrate heterogeneity, and the lowest was in the western region (3%). The highest richness of species was recorded in the eastern (36%), northern (31%) and southern (29%) zones of the island. The holothuroids were the most diverse with 10 species. The most important species according the biological value index are: Diadema mexicanum, Toxopneustes roseus, Phataria unifascialis, Pharia pyramidatus, Ophiocoma alexandri, Holothuria lubrica, Isostichopus fuscus and Eucidaris thouarsii representing the 60% of all individuals. The species affinity is greater with the Gulf of California than the Pacific center-south region