Variations in planktonic bacterial biomass and production and phytoplankton blooms off A Coruña (NW Spain)

Abstract

Bacterial abundance, biomass and heterotrophic activity, along with hydrographic and phytoplankton variables, were measured from February 1998 to September 1999 at two coastal stations off A Coruña (Galicia, NW Spain). Bacterial abundance varied from 0.1 to 1.8 x 106 cells ml^-1 and water-column integrated bacterial production ranged from 34 to 1132 mg C m^-2 d^-1. Two annual maxima of bacterial abundance and production were observed, in spring and summer, although relatively high abundance values remained until autumn. In autumn and winter production values were low with the exception of the results obtained in November 1998, when the highest values of bacterial production of the whole study were observed at both stations. Bacterial biomass constituted a significant, but low, fraction of particulate organic carbon (4-21 %) and was always lower than phytoplankton biomass (up to 40% of phytoplankton carbon). Also, bacterial production was generally < 30% of primary production, but in some situations (as in early spring or in autumn) bacterial production exceeded primary production, suggesting a delayed response of bacterial activity after a phytoplankton bloom.