A comparative analysis of biodiversity and distribution of shallow-water marine isopods (Crustacea : Isopoda) from polar and temperate waters in the East Pacific

Checklists of isopods currently reported for the polar and temperate waters of the East Pacific, in depths of 200 in or less, are presented, and compared with an updated list of species known to the eastern tropical pacific (ETP). A total of 213 species are recorded for the northern subregion (Arctic, Aleutian, and Oregonian Provinces), 133 for the southern subregion (Peru-Chile, Temperate Transitional, and Magellan Provinces) and 134 for the ETP. In total, 420 species are known to occur in the East Pacific. Considering the entire East Pacific region, the isopods fauna is dominated by the Cymothoida (36.4\% of total), followed by the Asellota (21.9\%), the Valvifera (17.3\%), the Sphaeromatidea (16.2\%), the Oniscidea (6.2\%), the Limnoriidea (1.4\%) and the Microcerberidea (0.5\%). The northern and southern polar-temperate faunae include a total of 340 species, with only seven species in common. The northern and southern subregions share only 34 out of 160 genera; of these, 103 occur in the nor-them subregion, 76 in the ETP and 65 in the southern subregion. The southern and northern subregions share 34 genera and 21 genera are shared by the three subregions, of which 12 belong to the Cymothoida. Forty-three families are registered in the East Pacific, 41 in the northern subregion and only 22 in the southern subregion, of which 18 are common to both. Comparatively, the ETP contains 25 families and 12 families are found in all three subregions. An analysis by provinces indicates that, according to our present knowledge, the highest number of species in the East Pacific is recorded in the Oregonian Province (140 species), followed by the Californian (128), Cortes (95), Magellan (75), Temperate-Transitional (61), Aleutian (61), Mexican (53), Panamic (52), Peru-Chile (43), and Arctic (15) provinces. Sixteen species are reported for the Galapagos, 10 each for the Juan Fernandez and Guadalupe Islands. A cluster analysis based on presence-absence of species revealed four major groups among the 10 previously recognized provinces, both when species and genera were used. The grouping of provinces into southern, ETP and northern subregions appears well defined and with comparable values of the similarity index, with the exception of the Arctic Province.