Resumen del producto

This study represents the first attempt to understand the vertical distribution pattern of the epipelagic copepods in the Gulf of California. This area is probably one of the most studied regions in Mexico due to its high productivity, high biodiversity, and economical relevance. Zooplankton studies, however, have been focused mostly on copepod distribution and abundance obtained mainly from oblique Bongo net collections. Vertical zooplankton samples were collected using horizontal opening and closing nets at five depth strata (0, 25, 50, 75 and 100 m) during January and July 2007 in the central Gulf of California. Vertical distribution of environmental conditions during winter, showed a well mixed water column (average 90 m depth), and an oxygen minimum layer depth (<1.5mgO2 L-1) at 120 m. Whereas during summer we observed a relatively shallow thermocline (20 – 50 m), and the low oxygen minimum layer depth (90 m) extended further north than during winter. These shifts in the thermohaline vertical structure and hypoxic conditions determined a strong change in the copepod community. During winter, Pleuromamma gracilis, Calanus pacificus, Rhincalanus nasutus and Scolecithrix danae accounted for the highest copepod abundance (weighted mean depth) and distributed in the first 50 m depth independently of the day / night collection time. This suggests non - migratory vertical behaviour, closely associated with the maximum chlorophyll - a depth (50 m). In contrast, the chlorophyll maximum occurred near the surface in summer, the weighted mean depth indicated higher density copepod populations located below the thermocline, and the copepod community was composed mainly of small tropical species like Centropages furcatus, Clausocalanus furcatus and Canthocalanus pauper. Our results suggest that the water mass circulation prevailing during each season of the year in the central gulf is the main driving force that structures the copepod vertical distribution relating most copepod species with the thermo - haline vertical structure of the water column and less with the availability of food, in terms of chlorophyll - a concentration.

Palabras clave: vertical distribution; Specialist; copepods

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