Concentrations of copepod nauplii associated with the nutrient-rich plume of the Mississippi River

Abstract

During spring and summer, discharge plumes of the Mississippi River were located visually by water color. Temperature, salinity, nutrients, chlorophyll a and copepod nauplii were sampled coincidently in a cross-plume direction. Plume waters contained high concentrations of nitrate, silicate and chlorophyll during both spring and summer. Nitrate was depleted before silicate during summer but not during spring. During spring, concentrations of copepod nauplii (50–100 l −1) were similar to those reported in an earlier wintertime study in this region. Summertime concentrations of nauplii were much higher, sometimes 1000l −1. Nauplii were associated with plume waters. Strong seasonality in zooplankton production is suggested, with greatest production in summer. Consequently, a larger proportion of plume phytoplankton production should sink directly to the bottom during spring and a larger proportion of the summertime production should be consumed in the water column by grazers.