Revillagigedo Archipelago (2017)

The Revillagigedo Archipelago comprises four islands of volcanic origin in the Pacific Ocean, lying 400 to 700 miles southwest of Cabo San Lucas, Baja California Sur, Mexico. From west to east, the islands are Isla Clarión, Isla Roca Partida, Isla Socorro, and Isla San Benedicto.

Known for their unique ecosystem, the islands are uninhabited with the exception of a small number of Mexican military personnel assigned to garrisons on Isla Clarión and Isla Socorro. The four islands and surrounding waters were declared a Biosphere Reserve by the Mexican government in 1994, and in 2016, the archipelago was named a UNESCO World Heritage Site.

One of the most notable aspects of the archipelago’s biodiversity is the high level of endemism found there (meaning, organisms that are native and restricted to a certain place). These species are found nowhere else in the world and are priorities for conservation due to their limited distribution.

In February 2017, a team of international scientists and associates explored these remote islands to document the wealth of terrestrial diversity and evaluate the conservation status of the plants and animals found there. Museum curators and research associates joined colleagues from Mexico on a 21-day expedition aboard the 98-foot vessel Shogun, visiting each of the remote islands. They made brief stops on other islands to break up the long journey from San Diego.

One of the expedition’s most significant results is the documentation of numerous additions to the biodiversity known from the Revillagigedo Archipelago. The team collected vouchers—or preserved specimens—of plants, invertebrates, and mollusks, and photo vouchers of birds and reptiles. The new records from this expedition alone total more than 76 taxa (40 plants; 11 birds; 13 spiders; nine ants; two mollusks; and one lizard). In many cases, these new records bring to light the global distribution patterns of these species and provide opportunities to learn more about their abundance and behavior.

In a few cases, the team discovered species we believe are new to science, which may add to the already impressive number of species that are endemic this archipelago. These seemingly new species include the Dutchman’s Pipe vine on Clarión and the new record of a tobacco plant on San Benedicto, which may indeed be a new subspecies or variety.

In addition to species documentation, we used historical references to assess change over time when possible. One example is the changes in the vegetation documented on Isla Clarión, which has transformed from the cactus thickets of 1931 to the more recent Buffelgrass invasion of 2017.

The research findings are now documented in the Proceedings of the San Diego Society of Natural History #48 (link forthcoming), which includes detailed accounts of the biodiversity encountered on the islands, from a variety of disciplines. This will serve as a baseline of information for stewards of what is now a national park (Parque Nacional Archipielago de Revillagigedo).

This special issue documents at least 50 plants, two birds, and four reptiles that are known from nowhere else on earth but these remote islands. In spite of the impressive recovery of the islands, there was concern about the expansion of non-native species like the Common House Gecko on Isla Socorro and the Spiny Iguana and domestic rabbits on Isla Clarión.

The rich biodiversity of the archipelago, despite a history of significant human impacts in many areas, speaks to its incredible resilience under changing conditions. While there is still much to learned about the archipelago, research on the terrestrial biota of the island will be invaluable to future management.