Relationship between biomass and enzymatic activity of a bloom-forming dinoflagellate (Dinophyceae) in southern Chile (41 S): a field approach

In a coastal area of southern Chile (41° S), the major ammonium assimilating enzyme glutamine synthetase (GS) was detected in a green dinoflagellate bloom during April 2003. High chlorophyll a concentrations (1000 μg L−1) attributable to Gymnodinium cf. chlorophorum in surface waters were associated with high and very low nitrate reductase activities. Coincident with the bloom, dissolved inorganic nitrogen concentrations were near the detection limit (NO3− + NH4+ <0.5 μM). Since GS correlates with the use of ammonium as an external nitrogen source, we suggest that GS activity seems to be a good indicator of ammonium utilization in a period dominated by a single dinoflagellate species.