Daily zooplankton filtration rates off Baja California

Abstract During summer 1986 we generated a 14-day time series (27 June to 10 July) of daily filtration rates at a fixed station off Punta Banda, B.C. Mexico, in the California Current System. Filtration rates were measured for natural zooplankton populations, fed with 14 C-labelled natural phytoplankton populations. Two upwelling events were characterized, at the beginning and at the end of the sampling period. There were mixed responses in the filtration rates: during the first event, zooplankton presented high filtration rates (up to 50 ml copepod −1 day −1 ), while during the last event, minima (5 ml copepod −1 day −1 ) filtration rates were measured. Significant ( P ⩽ 0·05) day to day fluctuations of the zooplankton filtration rates were measured during our study. Due to the great variability of the daily filtration rates, we suggest that to understand fully the coupling between the grazing processes and the environment in upwelling areas, the generation of time and space data series is vital.