|y/|QZ TRANSACTIONS LIBRARY OF THE SAN DIEGO SOCIETY OF JAN 29 1990 NATURAL HISTORY HARVARD UNIVERSITY Volume 21 Number 19 pp. 291-316 15 October 1989 Ranges of offshore decapod crustaceans in the eastern Pacific Ocean Mary K. Wicksten Department of Biology, Texas A&M University, College Station, Texas 77843, USA Abstract. Distributions of offshore decapods in the eastern Pacific fall into a pattern of at least five clusters: the Aleutian Islands to Washington, Washington or Oregon to southern California, Baja California and the Gulf of California to central America, Panama or Colombia to Peru, and Chile to Cape Horn. These clusters are supported by distributional data at all depths considered, although there is more blurring of provincial boundaries at depths greater than 1500 m than at lesser depths. There is a sharp break in faunal distributions between that of northern Baja California and all areas to the south, largely due to the replacement of species of Pandalus to the north by species of Heterocarpits to the south. The northeastern Pacific is particularly rich in species of hippolytid shrimps and lithodid crabs and contains endemic genera of the families Crangonidae and Majidae. Species in these and other groups probably underwent extensive radiation in the late Cenozoic and dispersed from the northern Pacific into the northern Atlantic and less readily into the southern hemisphere. Compared to the northeastern Pacific, the western coast of South America is poor in the total number of species and the degree of endemism in decapods. Except for a few cosmopolitan species of the lower continental slopes, North and South America have no species in common. Introduction The coast of the Americas constitutes the longest continuous north-south ocean margin in the world. In shallow and intertidal regions, the distributions of co-occuring invertebrate species have been used to define at least six zoogeographic provinces. From north to south, these are the Aleutian (the Bering Sea to Puget Sound), the Oregonian (Puget Sound to Point Conception, California), the Califomian (Point Conception to approximately Bahia Magdalena, Baja California, Mexico), the Panamic (Bahia Magdalena to the Gulf of Guayaquil, including the Gulf of California), the Peru-Chilean (northern Peru to approximately Isla Chiloe, Chile), and the Magellanic (Isla Chiloe to Cape Horn) (Dana 1853, Keen 1937, Ekman 1967, Valentine 1966, Briggs 1974). Different interpretations have been offered for designations of provinces. For example, Brusca and Wallerstein (1979) referred to all of the coastal warm-water (subtropical/tropical) area as the Eastern Pacific Zoogeographic Region, noting Briggs' subdivisions of four provinces: the Cortez, Mexican, Panamic, and Galapagos. They also recognized the west coast of Baja California between Punta Eugenia and Bahia Magdalena as a broad transition zone between the Califomian and Cortez provinces. Keen (1937) designated subprovinces of the Oregonian province. Garth (1955) considered the fauna of the outer coast of Baja California to belong to a province separate from that of the Gulf of California, but Briggs (1974) included both faunas in a common province. All of these interpretations were based on species living no deeper than the continental shelf. There are very few studies of wide-scale distributional patterns of invertebrates of offshore areas, at depths of 50 m or more. Menzies et al. ( 1 973) defined offshore provinces by depth, sorting invertebrate species into a Shelf Province (about 246 m or less), an Archibenthal Zone of transition (to 1000 m), and a deeper Abyssal Province. Their study did not consider distributions by latitude. However, Cutler (1975) noted that the region of Cape Lookout, North Carolina, constitutes a zoogeographical barrier to sipunculid and pogonophoran worms not only of shallow waters, but also to species living on the continental slope. Parker (1963) reported the distributions of decapods of the eastern Pacific by latitude.