maintained in a light/dark regime at 12°C and simulating an upwelling event. This
allowed us to improve our understanding of small scale temporal processes wich occur
during and after upwelling.
Measurements of phytoplankton production and biomass
Primary production was measured according to the 14 C-uptake method of Strickland and
Parsons (1972). The details are given by Brown (1984). Chlorophyll a, as an index of
biomass, was measured spectrophotometrically following the procedure of the SCOR/ UNESCO Working Group 17 (1966) as described by Brown (1984).
CHN analysis
Water samples filtered onto Whatman GF/ F filters were analysed for particulate carbon
and nitrogen with a Hereaus (CHN Rapid) Analyser using cyclohexanone (20.14 % N ;
51.79 % C) as a standard.
Bacteria! biomass and production
Bacterial numbers and biomass were estimated from the acridine orange direct counting
(AODC) fluorescence microscopy method of Hobbie et al., (1977) and S.E.M. estimates
of biovolume and biomass as described by Tinley et al., (1981). For estimates of bacterial
production, the 3 H-Thymidine incorporation method of Fuhrman and Azam (1980,
1982) was followed and compared with direct estimates of bacterial growth in small
volume (125 ml) predator-free (3µm filtered) incubations in the dark. Details of this
method are given by Meyer-Reil (1977) and Linley et al., (1983). Although Fuhrman and
McManus (1984) noted that a number of small and apparently bactivorous microflagellates were evident in the <0.6µm fraction, SEM studies of samples from our mesocosm
showed no evidence of bacterial predators in the <3µm fraction. We therefore regard this
fraction to be essentially predator-free or subject to only insignificant predation pressure
on bacterial growth.
Bacterial activity
Bacterial activity was estimated as a function of percentage plateability and the number of
colony forming units for samples taken from a 60 L. mesocosm.
RESULTS AND DISCUSSION
Bacterial biomass, activity and production
- Biomass
Profiles for bacterial biomass recorded for three days of the cruise are given in Figure
I .A maximum bacterial biomass (80 m.g.C.m
3 ) was associated with maxima for chlorophyll a concentration and total particulate carbon concentration present in the euphotic
zone on 17.03.83. As the chlorophyll «concentration and POCconcentration declined in
subsequent profiles (19th and 20th March), so too did bacterial biomass. Indeed, irrespective of chlorophyll a concentration, bacterial biomass was found to closely follow
(Fig. 1) and correlate with total particulate carbon (POC) in the water column; Y =
1.96 + 0.060 X, r = 0.77 and n = 85 where Y = bacterial biomass (mg.C.m -3 ) and X =
POC (mg.C.nf 3 ). Bacterial biomass did not have a simple correlation with chlorophyll a
concentration which is to be expected since the latter was not well correlated with total
POC. The presence of detrital POC may therefore sustain bacterial biomass and production in the absence of living phytoplankton. Bacterial biomass was similarly correlated
with detrital POC during the SIBEX I cruise to Antarctica in May 1984, (Painting et al,
1985).
377
allowed us to improve our understanding of small scale temporal processes wich occur
during and after upwelling.
Measurements of phytoplankton production and biomass
Primary production was measured according to the 14 C-uptake method of Strickland and
Parsons (1972). The details are given by Brown (1984). Chlorophyll a, as an index of
biomass, was measured spectrophotometrically following the procedure of the SCOR/ UNESCO Working Group 17 (1966) as described by Brown (1984).
CHN analysis
Water samples filtered onto Whatman GF/ F filters were analysed for particulate carbon
and nitrogen with a Hereaus (CHN Rapid) Analyser using cyclohexanone (20.14 % N ;
51.79 % C) as a standard.
Bacteria! biomass and production
Bacterial numbers and biomass were estimated from the acridine orange direct counting
(AODC) fluorescence microscopy method of Hobbie et al., (1977) and S.E.M. estimates
of biovolume and biomass as described by Tinley et al., (1981). For estimates of bacterial
production, the 3 H-Thymidine incorporation method of Fuhrman and Azam (1980,
1982) was followed and compared with direct estimates of bacterial growth in small
volume (125 ml) predator-free (3µm filtered) incubations in the dark. Details of this
method are given by Meyer-Reil (1977) and Linley et al., (1983). Although Fuhrman and
McManus (1984) noted that a number of small and apparently bactivorous microflagellates were evident in the <0.6µm fraction, SEM studies of samples from our mesocosm
showed no evidence of bacterial predators in the <3µm fraction. We therefore regard this
fraction to be essentially predator-free or subject to only insignificant predation pressure
on bacterial growth.
Bacterial activity
Bacterial activity was estimated as a function of percentage plateability and the number of
colony forming units for samples taken from a 60 L. mesocosm.
RESULTS AND DISCUSSION
Bacterial biomass, activity and production
- Biomass
Profiles for bacterial biomass recorded for three days of the cruise are given in Figure
I .A maximum bacterial biomass (80 m.g.C.m
3 ) was associated with maxima for chlorophyll a concentration and total particulate carbon concentration present in the euphotic
zone on 17.03.83. As the chlorophyll «concentration and POCconcentration declined in
subsequent profiles (19th and 20th March), so too did bacterial biomass. Indeed, irrespective of chlorophyll a concentration, bacterial biomass was found to closely follow
(Fig. 1) and correlate with total particulate carbon (POC) in the water column; Y =
1.96 + 0.060 X, r = 0.77 and n = 85 where Y = bacterial biomass (mg.C.m -3 ) and X =
POC (mg.C.nf 3 ). Bacterial biomass did not have a simple correlation with chlorophyll a
concentration which is to be expected since the latter was not well correlated with total
POC. The presence of detrital POC may therefore sustain bacterial biomass and production in the absence of living phytoplankton. Bacterial biomass was similarly correlated
with detrital POC during the SIBEX I cruise to Antarctica in May 1984, (Painting et al,
1985).
377