detrital POC utilisation, (see Newell et al., 1985, 1986). Elsewhere, we have found that in
the unproductive Antarctic system encountered in May 1984, bacteria also utilised
detrital POC as a carbon source (Painting et al., 1985).
In conclusion , calculations of carbon flux through the bacterioplankton depend greatly
upon accurate estimates of bacterial production and net growth yield. While the 3 HThymidine incorporation method of Fuhrman and Azam ( 1980 and 1982) for measuring
bacterial production is convenient to use, our evidence suggests that their conservative
calculation of bacterial production agrees with the predator-free incubation method and
would seem the more realistic (but see also Lucas, 1986). On this basis, it appears that
carbon flow through heterotrophic bacteria can readily be accounted for by PDOC
utilisation in the euphotic zone during a spring bloom and detrital POC utilisation in the
euphotic or aphotic zones when phytoplankton blooms senesce, decay and sink through
the water column.
AKNOWI.EDGEMENTS
We would like to thank Mr 1. Humphries for counting the bacterial samples. We are also grateful to Professors
R.C.Newell, J.G.Field and F.Robb for their helpful and critical appraisal of the manuscript. We would like to
acknowledge receipt of SANCOR funding in support of this work.
AZAM F., FENCHEL T., FIELD J.G., GRAY J.S., MEYER-REIL L.A. & THINGST AD F. 1983. The ecological role of
water- column microbes in the sea. Mar. Ecol. Prog. Ser.10 : 257-263.
BAUERFEIND S., 1985. Degradation of phytoplankton detritus by bacteria : estimation of bacterial consumption
and respiration in an oxygen chamber. Mar. Ecol. Prog. Ser.2I : 27-36.
BROWN P.C., 1984. Primary production at two contrasting nearshore sites in the Southern Benguela upwelling
region, 1977-1979. S.Afr. J. Mar. Sci.2 : 205-216.
COLE J.J., LIKENS G.E. & STRAYER D.L., 1982. Photosynthetically produced dissolved organic carbon : an
important carbon source for planktonic bacteria. Limnol. Oceanogr. 27 : 1080-1090.
FALLON R.D., NEWELL S.Y. and HOPKINSON C.S., 1983. Bacterial production in marine sediments : will
cell-specific measures agree with whole system metabolism ? Mar. Ecol. Prog. Ser.I I : 119-127.
FUHRMAN J.A. and AZAM F., 1980. Bacterioplankton secondary production estimates for coastal waters of
British Columbia, Antarctica and California. Appl. environ. Microbiol.39 : 1085-1095.
FUHRMAN J.A. and AZAM F., 1982. Thymidine incorporation as a measure of heterotrophic bacterioplankton
production in marine surface waters : evaluation and field results. Mar. Biol.66 : 109-120.
FUHRMAN J.A. and MCMANUS G.B., 1984. Do bacteria sized marine eukaryotes consume significant bacterial
production ? Science 224 : 1257-1260.
HAGSTROM A., LARSSON U., HORSTEDT P. and NORMAK S., 1979. Frequency of dividing cells, a new approach
to the determination of bacterial growth rates in aquatic environments. Appl. environ. Microbiol. 37 : 805-812.
HOBBIE J.E., DALEY R.T. and JASPERS., 1977. Use of Nuclepore filters for counting bacteria by fluorescence
microscopy. Appl. Environ. Microbiol. 33: 1255-1228.
JOINT I.R. and MORRIS R.J., 1982. The role of bacteria in the turnover of organic matter in the sea. Oceanogr.
mar. Biol. A. Rev.20 : 65-118.
JOINT I.R. and POMROY A.J., 1982. Aspects of microbial heterotrophic production in a highly turbid estuary. J.
Exp. Mar. Biol. Ecol. 58 : 33-46.
JOIRISC, BILLEN G., LANCELOT C., DARO M.H., MOMMAERTS J.P., BERTELS A., BOSSICARTM., Nus J. and
HECQ J.H., 1982. A budget of carbon cycling in the Belgian coastal zone : relative roles of zooplankton,
bacterioplankton and benthos in the utilisation of primary production. Neth. J. Sea. Res. 16 : 260-275.
382
the unproductive Antarctic system encountered in May 1984, bacteria also utilised
detrital POC as a carbon source (Painting et al., 1985).
In conclusion , calculations of carbon flux through the bacterioplankton depend greatly
upon accurate estimates of bacterial production and net growth yield. While the 3 HThymidine incorporation method of Fuhrman and Azam ( 1980 and 1982) for measuring
bacterial production is convenient to use, our evidence suggests that their conservative
calculation of bacterial production agrees with the predator-free incubation method and
would seem the more realistic (but see also Lucas, 1986). On this basis, it appears that
carbon flow through heterotrophic bacteria can readily be accounted for by PDOC
utilisation in the euphotic zone during a spring bloom and detrital POC utilisation in the
euphotic or aphotic zones when phytoplankton blooms senesce, decay and sink through
the water column.
AKNOWI.EDGEMENTS
We would like to thank Mr 1. Humphries for counting the bacterial samples. We are also grateful to Professors
R.C.Newell, J.G.Field and F.Robb for their helpful and critical appraisal of the manuscript. We would like to
acknowledge receipt of SANCOR funding in support of this work.
AZAM F., FENCHEL T., FIELD J.G., GRAY J.S., MEYER-REIL L.A. & THINGST AD F. 1983. The ecological role of
water- column microbes in the sea. Mar. Ecol. Prog. Ser.10 : 257-263.
BAUERFEIND S., 1985. Degradation of phytoplankton detritus by bacteria : estimation of bacterial consumption
and respiration in an oxygen chamber. Mar. Ecol. Prog. Ser.2I : 27-36.
BROWN P.C., 1984. Primary production at two contrasting nearshore sites in the Southern Benguela upwelling
region, 1977-1979. S.Afr. J. Mar. Sci.2 : 205-216.
COLE J.J., LIKENS G.E. & STRAYER D.L., 1982. Photosynthetically produced dissolved organic carbon : an
important carbon source for planktonic bacteria. Limnol. Oceanogr. 27 : 1080-1090.
FALLON R.D., NEWELL S.Y. and HOPKINSON C.S., 1983. Bacterial production in marine sediments : will
cell-specific measures agree with whole system metabolism ? Mar. Ecol. Prog. Ser.I I : 119-127.
FUHRMAN J.A. and AZAM F., 1980. Bacterioplankton secondary production estimates for coastal waters of
British Columbia, Antarctica and California. Appl. environ. Microbiol.39 : 1085-1095.
FUHRMAN J.A. and AZAM F., 1982. Thymidine incorporation as a measure of heterotrophic bacterioplankton
production in marine surface waters : evaluation and field results. Mar. Biol.66 : 109-120.
FUHRMAN J.A. and MCMANUS G.B., 1984. Do bacteria sized marine eukaryotes consume significant bacterial
production ? Science 224 : 1257-1260.
HAGSTROM A., LARSSON U., HORSTEDT P. and NORMAK S., 1979. Frequency of dividing cells, a new approach
to the determination of bacterial growth rates in aquatic environments. Appl. environ. Microbiol. 37 : 805-812.
HOBBIE J.E., DALEY R.T. and JASPERS., 1977. Use of Nuclepore filters for counting bacteria by fluorescence
microscopy. Appl. Environ. Microbiol. 33: 1255-1228.
JOINT I.R. and MORRIS R.J., 1982. The role of bacteria in the turnover of organic matter in the sea. Oceanogr.
mar. Biol. A. Rev.20 : 65-118.
JOINT I.R. and POMROY A.J., 1982. Aspects of microbial heterotrophic production in a highly turbid estuary. J.
Exp. Mar. Biol. Ecol. 58 : 33-46.
JOIRISC, BILLEN G., LANCELOT C., DARO M.H., MOMMAERTS J.P., BERTELS A., BOSSICARTM., Nus J. and
HECQ J.H., 1982. A budget of carbon cycling in the Belgian coastal zone : relative roles of zooplankton,
bacterioplankton and benthos in the utilisation of primary production. Neth. J. Sea. Res. 16 : 260-275.
382