Distribution of freshwater oligochaetes in the west and east coastal regions of the North Pacific Ocean

Abstract

Faunistic data available from 10 different regions were reviewed: Middle and South China (55 species of freshwater oligochaetes recorded); Amur Basin, Manchuria and Primor’e (86); Korean Peninsula (20); Japan, Sakhalin and Kuril Islands (77); Kamcatka Peninsula (42); Cukci Peninsula including the Anadyr Basin and Korjak Mountains (41); Alaska Peninsula (31); Southern Alaska and British Columbia (62); Washington, Oregon and California (119); Mexico (25). A total of 306 valid species of freshwater oligochaetes includes the branchiobdellidans, freshwater and amphibiotic enchytraeids and lumbricids, as well as some brackish-water representatives of freshwater genera. Among them, 61 species of Naididae (56 on the Asian, 35 on the American side; 30 species common for both coasts); 68 of Tubificidae (40, 45; 17); 2 of Propappidae (2, 0; 0); 43 of Enchytraeidae (16, 27; 0); 43 of Lumbriculidae (29, 17; 3); 4 of Haplotaxidae (3, 2; 1); 1 of Biwadrilidae (1, 0; 0); 5 of Lumbricidae (4, 1; 0); 79 of the five branchiobdellidan families (36, 43; 0). Endemicity at the species or even generic level on either side of the Pacific appears to occur in over 2/3 of the total number of species, being prevalent in Lumbriculidae, Enchytraeidae, Haplotaxidae, Biwadrilidae and Branchiobdellida, less expressed in Tubificidae and rare in Naididae. Most of the species common to both coasts of the North Pacific are widely distributed in the Holarctic, or appear cosmopolitan. A weak faunal exchange appears to have happened in the Bering Strait region (Alexandrovia ringulata, Tasserkidrilus americanus, Styloscolex opisthothecus, Lumbriculus olgae).