In order to understand the processes that determine changes in zooplankton abundance and composition in the CARIACO (Carbon Retention in a Colored Ocean) Time Series Station, zooplankton biomass, composition and density were studied aboard the O/V Hermano Ginés from November 2002 to January 2003. Salinity, temperature and dissolved oxygen were measured in situ. Zooplankton samples were collected by vertical tows using a Bongo net (mesh size 333 and 555 mm) at a speed of 2 knots at the intervals 0-30, 30-70, and 70-100 m. Chlorophyll (chl a), zooplankton biomass (dry mass) and density were estimated. The maximum values of biomass (0.039 mg m-3 dry mass) and zooplankton density (582 ind. m-3) for the three strata were measured during the upwelling period. On the other hand, the lower values for these variables (0.030 mL m-3, 0.007 mg m-3 and 7 ind. m-3, respectively) were recorded in May 2003. In general, the greatest values were detected within the 30 to 70 m range. Even though, the variability of the different strata was similar. The zooplankton community was dominated by copepods, cladocerans and appendicularians. The results showed a great temporal variability en zooplankton biomass and composition in spite of the fact that the station is located in a tropical area due to the effect of seasonal coastal upwelling.