Distribution and Ecology of Isopods (Crustacea: Peracarida: Isopoda) of the Pacific Coast of Mexico

Abstract

The Pacific coast of Mexico extends from 32° 27′ N to 14° 32′ N, including warm temperate, subtropical and tropical waters. Considering the 200 nautical miles limit, the Mexican Pacific covers approximately 2364200 km² of marine and oceanic environment from estuaries and intertidal to over 2000 m depth. An exhaustive review of published literature and intensive sampling along the coast of the Mexican Pacific and offshore allow us to report a total of 120 species of Isopoda for the area. These species belong to 8 of the 10 currently recognized suborders of Isopoda. Almost half of the species (54) are Flabellifera, while Microcerberidea and Gnathiidea are represented by only one known species each. As expected, there is a clear bathymetric segregation from one group of species to the other. Gnathiidea, Microcerberidea and Oniscidea (10 spp.) are found exclusively in the intertidal, among rocks and on sandy beaches, often associated with algae or decaying material. Anthuridea (10 spp.), Asellota (5 spp.) and Valvifera (20 spp.) occur from the intertidal to 200 m depth, in sandy, muddy or mixed habitats or as commensals. Flabellifera also occur from the intertidal but range to deeper water, with a maximum depth record of 2214 m (Rocinella belliceps (Stimpson, 1864)); these are either free-living or parasites and are found in a wide variety of habitats. Epicaridea (21 spp.) are all parasites. Without any doubt, the least studied suborders are Anthuridea (10 known species and at least 2 undescribed species) as well as Gnathiidea and Microcerberidea due to their small size, difficulty in sampling and complexity of available related literature. Contrary to what has been observed with other groups of crustaceans, the diversity of isopods appears to be much higher in Mexican temperate waters, where 59.1% of all known species occur (California Current area), than in the SW tropical coastal area (only 26.7% of the species are registered there). The Gulf of California, on the contrary, features an unusual (relative) richness with up to 73.3% of Mexican species recorded. It should be stressed, however, that most of the collecting effort of the last 30 years has been done in the Gulf of California and along the west coast of Baja California.