Temporal variability of zooplankton biomass (ATP content and dry weight) in the St. Lawrence Estuary: Advective phenomena during neap tide

In order to assess the temporal variability of living zooplankton in a tidal estuary, the ATP content and dry weight of mixed zooplankton populations (mainly copepods) were measured during a period of 175 h at an anchor station in the Upper St. Lawrence Estuary. Vertical tows were made every 30 min. Hourly vertical profiles of the current speed and direction, temperature and salinity were also obtained during the experiment. A strong tidal influence was found in all series. Maxima and minima of the ATP content (living biomass) and the dry weight (total biomass) were correlated with low and high water slacks. The serial autocorrelation and cross-correlation showed, in both series a 12 to 13-h cycle, and the ATP:dry weight ratio showed a significant 24-h cycle. The cross-correlation with the Kendall τ was used to detect the relationship between biological components and physical indices (stratification and Ri). It is suggested that the proportion of living zooplankton biomass in the Upper St. Lawrence Estuary is most likely the result of a combination of diurnal migration and longitudinal advection.