For the transformation of biovolume into bacterial biomass (Simon &
Azam, 1989; Norland, 1993).
• Primary production was estimated by in situ diumal
14 C incorporation
(Steemann-Nielsen, 1952). Incubations at different depths were carried out
in polycarbonate bottles attached to a drifting system in the upper
euphotic layer.
• Bacterioplankton heterotrophic production: incorporation of
3 Hthymidine (Fuhrman & Azam, 1980; Moriarty, 1990) was performed by
means of short incubations at in situ temperatures. Exoproteolytic activity
(Chrôst et ai, 1989; Hoppe, 1993) of planktonic and macroagrregate bacteria was estimated at in situ temperatures, using a non-fluorescent substrate analogous of proteins (I eu-MCA).
• The fate of phytoplankton was estimated by measuring both mesozooplankton (gut contents, Bautista & Harris, 1992) and mictozooplankton
(I andry & Hasset, 1982, dilution method) grazing processes.
• Bacterial loss due to bacterivory was determined by incubations into
dialysis systems with and without microzooplankters (Wright & Coffin,
1984; Herndl et al., 1993).
• Particulate organic carbctn (POC) stocks and fluxes were determined on
filtered material (suspended matter and aggregates) using a Carlo Erba
1500 CHN analvser.
Results and discussion
Three situations were defined in a theoretical chronological order by
considering both their hydrological and microplanktonic characteristics
(fig. 3), during a regular survey conducted in the area from 1992 to
1995 (Artigas, 1998). The phvtoplankton community was dominated by
< 20 pm cells in early and mid-spring periods, whereas in late spring periods, the accumulation of > 20 gm cells below the pycnocline (at the
bottom of the euphotic zone) was responsible for the change of the integrated size distribution (fig. 4).
Nano and picoautotrophic cells accounted for 54 to 98.5% of the integrated primary 7 production in spring (fig. 4; Herbland ef ai, 1998), and
bacterial heterotrophic production (131ÎP) represented from 10 to 33% of
the primary production (tab. 1; Artigas etai, 2000). Therefore, using a mean
efïïciency’ rate of 0.3 (Yan Wambeke, 1992), we could estimate that a mean
of 33 to 110% of primary production was channelled to the heterotrophic
bacterioplankton, suggvsting the utilization of allochtonous organic matter
for sustaining microbial growth.
129
Azam, 1989; Norland, 1993).
• Primary production was estimated by in situ diumal
14 C incorporation
(Steemann-Nielsen, 1952). Incubations at different depths were carried out
in polycarbonate bottles attached to a drifting system in the upper
euphotic layer.
• Bacterioplankton heterotrophic production: incorporation of
3 Hthymidine (Fuhrman & Azam, 1980; Moriarty, 1990) was performed by
means of short incubations at in situ temperatures. Exoproteolytic activity
(Chrôst et ai, 1989; Hoppe, 1993) of planktonic and macroagrregate bacteria was estimated at in situ temperatures, using a non-fluorescent substrate analogous of proteins (I eu-MCA).
• The fate of phytoplankton was estimated by measuring both mesozooplankton (gut contents, Bautista & Harris, 1992) and mictozooplankton
(I andry & Hasset, 1982, dilution method) grazing processes.
• Bacterial loss due to bacterivory was determined by incubations into
dialysis systems with and without microzooplankters (Wright & Coffin,
1984; Herndl et al., 1993).
• Particulate organic carbctn (POC) stocks and fluxes were determined on
filtered material (suspended matter and aggregates) using a Carlo Erba
1500 CHN analvser.
Results and discussion
Three situations were defined in a theoretical chronological order by
considering both their hydrological and microplanktonic characteristics
(fig. 3), during a regular survey conducted in the area from 1992 to
1995 (Artigas, 1998). The phvtoplankton community was dominated by
< 20 pm cells in early and mid-spring periods, whereas in late spring periods, the accumulation of > 20 gm cells below the pycnocline (at the
bottom of the euphotic zone) was responsible for the change of the integrated size distribution (fig. 4).
Nano and picoautotrophic cells accounted for 54 to 98.5% of the integrated primary 7 production in spring (fig. 4; Herbland ef ai, 1998), and
bacterial heterotrophic production (131ÎP) represented from 10 to 33% of
the primary production (tab. 1; Artigas etai, 2000). Therefore, using a mean
efïïciency’ rate of 0.3 (Yan Wambeke, 1992), we could estimate that a mean
of 33 to 110% of primary production was channelled to the heterotrophic
bacterioplankton, suggvsting the utilization of allochtonous organic matter
for sustaining microbial growth.
129