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The Mexican Pacific Ocean (MPO) includes the oceanic area from the northernmost region of the West coast of the Baja California Peninsula to the southern portion of Chiapas at the border with Guatemala. The Gulf of California and the Gulf of Tehuantepec are located in this region. Surface ocean circulation in MPO is seasonal and varies with alternation in intensity and area occupation of the California Current, the Equatorial Countercurrent, the North Equatorial Current, and the Costa Rica Coastal Current System, which together determine the presence of marine fauna of different biogeographic affinities. The collection of cephalopod paralarvae (PL) with plankton nets has proven to be one of the best tools to determine diversity in this group. Our objective was to determine the cephalopod species composition in three areas of MPO, based on the presence of their planktonic PL. Analyzed zooplankton samples were collected by means of oblique Bongo and Meter net (505µm) tows during 15 oceanographic cruises. Five cruises were made in front of the west coast of Baja California Peninsula (WCBCP, 1997-1999), eight in the Gulf of California (GOLCA, 2004-2007), and two in the Gulf of Tehuantepec (TEHUA, 2007-2008). We recorded a total of 50 taxa at the species level included in 14 families. The most important in WCBCP were Ommastrephidae (73.8%), Onychoteuthidae (8.8%), and Cranchiidae (7.5%); in GOLCA the families Ommastrephidae (44.8%), Pyroteuthidae (32.3%), and Argonautidae (12.3%), while in TEHUA the Enoploteuthidae (39.1%), Ommastrephidae (30.4%), and Cranchiidae (15.8%) were the most important. Ecological indexes (based in total abundance of species in all areas) indicated higher paralarvae abundance in GOLCA with richness S=44, followed by WCBCP (S=36), and TEHUA (S=16). WCBCP had the highest diversity (H´=3.17) and evenness (J´=0.61). In GOLCA dominance (D=0.30) was determined by three taxa, in comparison with TEHUA (D=0.18) where six taxa dominated. PL of tropical-subtropical affinity were the most abundant, temperate ones were scarce, and only one cosmopolitan species was recorded in the three areas. The ENSO 1997-2001 influenced the important presence and abundance of tropical species in WCBCP region; for GOLCA, inter-annual seasonality determined the presence of the temperate component only during winter, while in TEHUA sampling limitations did not allow us further explanations. The sistematic list of cephalopod PL from the MPO is presented.

Palabras clave: biodiversity; Paralarvae; mexican Pacific Ocean

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