The Islas Marías Biosphere Reserve is a UNESCO Biosphere Reserve located in the Islas Marías in the municipality (municipio) of San Blas, Nayarit, Mexico. The 641,284.73 hectares (2,476.0142 sq mi) reserve includes ecosystems with a great wealth of species of biological, economic, scientific and cultural relevance. Its biological wealth is to be found in the dry forests of its landscape, in the mangroves, the succulent rosette scrubland, the reefs, coasts and pelagic environments it harbors.