Seasonal variations in the production and consumption of amino acids by coastal microplankton

A seasonal study on coastal microplankton was conducted in surface waters near Boothbay Harbor, Maine. Phytoplankton biomass, particulate production and extracellular organic release were examined in conjunction with microheterotrophic biomass and the uptake and respiration of amino acids. In situ dissolved free amino acid (DFAA) concentrations were also determined. Several phytoplankton blooms occurred throughout the year, in mid-summer, late autumn and in mid-winter. Heterotrophic activity and biomass paralleled phytoplankton extracellular release more closely than either phytoplankton particulate production or biomass. DFAA concentrations were not wholly dependent on extracellular release. Heterotrophic uptake did not appear to be dependent on DFAA concentrations but rather on rates of production of DOC by phytoplankton.