Size distribution of algal pigments and phytoplankton assemblages in a coastal--estuarine environment: contribution of small eukaryotic algae

Abstract

Direct observations as well as nutrient enrichment experiments have revealed the existence of a close relationship between the chlorophyll a (Chl a) content of water and the organization of the phytoplankton assemblages by size classes. Thus, picophytoplankton and small nanoplankton make up a great proportion of the assemblages in the more oligotrophic areas, whereas most of the autotrophic biomass and production lies generally in the large nanoplankton and microplankton in nutrient-replete waters The availability of nutrients in coastal areas is generally higher than in offshore waters. However, after the spring phytoplankton bloom, coastal waters experience a depletion of nutrients, which precludes the growth of the larger cells, which are known to be less efficient in taking up nutrients at low concentrations than pico-and nanophytoplankton. Consequently, coastal waters may exhibit during part of the year characteristics that are similar to those of marine oligotrophic systems, with dominance of pico-and nanophytoplankton cells These organisms are strongly controlled by grazing