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 Coruna (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.
Highlights
Planktonic bacteria are one of the main components of aquatic ecosystems, often constituting a significant fraction of total biomass and participating to a great extent in the flux of energy and elements like carbon
Given the relatively large variances observed for each station, we applied the respective mean carbon content of bacteria from stations 2 or 4 in all subsequent computations of biomass or production
Large additions of leucine are used to avoid the utilisation of unlabeled leucine and for repressing de novo synthesis of intracellular leucine (Kirchman, 1993)
Summary
Planktonic bacteria are one of the main components of aquatic ecosystems, often constituting a significant fraction of total biomass and participating to a great extent in the flux of energy and elements like carbon. The main sources of dissolved organic carbon for bacteria are the phytoplankton exudation and the release of dissolved substrates as a result of sloppy feeding of zooplankton (Azam et al, 1983; Furhman, 1992). It has been observed that the bacterial production is correlated with phytoplankton biomass and production (Cole et al, 1988; White et al, 1991). The availability of extra food sources often results in complex seasonal variation of coastal bacterioplankton, and some studies report the lack of covariation between bacteria and phytoplankton (Hoch and Kirchman, 1993). Other authors have found time-lags in the response of bacterioplankton to phytoplankton blooms (Ducklow, 1993; Li et al, 1993)
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