Marine lipids
nets (80 and 200 µm mesh) for plankton and shrimps. Both surface (one
metre below the surface) and bottom (approximately one metre above
the bottom) waters were collected, every two hours, during 24 hours.
Sampling of 0.1 to 0.4 liter were filtered for lipids (GF/F, pre-ignited
at 450°C, overnight), for chlorophyll a (GF/C filters) and particulate
organic carbon and nitrigen (GF/F filters, pre-ignited at 450°C, overnight). Two incubations were done with shrimps to recover faecal
pellets. For these organisms, contrary to copepods, only stomachs were
subsequently analysed.
Analysis
Salinity and temperarure were determined aboard by means of a probe.
Particulate organic carbon (POC) and particulate organic nitrogen (PON)
were mesured by means of an elementary LECO CHNS 932 analyser.
Chlorophyll a (chla) and pheopigments (pheo) were determined by
absorption spectrophotometry (Lorenzen, 1967). Fatty acids (FAs) and
sterols (STs) were determined following a three steps process (Thoumelin et al., 1997). Total lipids were extracted by means of solvents
following Bligh & Dyer (1959), and after methylation, FAs and STs
were then preseparated by HPI.C and quantified by GC and GC/MS.
Injections were made on a capillary column (30 m long, 0.32 µm internal diameter) with an apolar HP5 phase for STs, and on a capillary column
(30 m long, 0.2 µm internal diameter) with a polar FFAP phase for FAs.
Results
ETM is detected in surface waters by POC maxima at or just before low
tide (fig. 2 A). In bottom waters, maxima are observed before low tide
and also at the beginning of flood. Minima are observed during high tide
slack both in surface and bottom waters. In surface and bottom waters,
maximum concentrations of chlorophyll a (fig. 2 B) are observed around
low ticles while the lowest concentration are noticed around high ticles.
At low tides, maxima of polyunsatured FA proportions are also observed,
both in bottom ancl in surface waters (fig. 2 C and D). Proportions of
branched FAs are relatively constant through the tidal cycles. In bottom
waters, increases in long-chain FAs are noticed during the ebb and flood
resuspensions. Among individual polyunsatured FAs, C20:5 ω3 is
predominant and has maximum proportions at low ticle (fig. 2 E, F).
High proportions of C16:3 ω4 are also noticeable at low tide especially
in surface waters. Maxima are also observed at low tide in bottom
waters for C22:6 ω3 and C18:3 ω3.
The highest and the lowest abundances of copepods were observed respectively around low ticles (about 50 000 to 200 000 ind.m - 3 ) and at
high tides (<10 000 to 80 000 ind.m - 3 ). Fatty acids (FAs) ancl sterols
(STs) compositions of the copepods are reported in tables 1 and 2. High
proportions of C20:5 ω3 and C22:6 ω3 are noticed either at low ancl
at high tides (table 1). The acids C16:2 ω4 and C16:3 ω4 as well as
80
nets (80 and 200 µm mesh) for plankton and shrimps. Both surface (one
metre below the surface) and bottom (approximately one metre above
the bottom) waters were collected, every two hours, during 24 hours.
Sampling of 0.1 to 0.4 liter were filtered for lipids (GF/F, pre-ignited
at 450°C, overnight), for chlorophyll a (GF/C filters) and particulate
organic carbon and nitrigen (GF/F filters, pre-ignited at 450°C, overnight). Two incubations were done with shrimps to recover faecal
pellets. For these organisms, contrary to copepods, only stomachs were
subsequently analysed.
Analysis
Salinity and temperarure were determined aboard by means of a probe.
Particulate organic carbon (POC) and particulate organic nitrogen (PON)
were mesured by means of an elementary LECO CHNS 932 analyser.
Chlorophyll a (chla) and pheopigments (pheo) were determined by
absorption spectrophotometry (Lorenzen, 1967). Fatty acids (FAs) and
sterols (STs) were determined following a three steps process (Thoumelin et al., 1997). Total lipids were extracted by means of solvents
following Bligh & Dyer (1959), and after methylation, FAs and STs
were then preseparated by HPI.C and quantified by GC and GC/MS.
Injections were made on a capillary column (30 m long, 0.32 µm internal diameter) with an apolar HP5 phase for STs, and on a capillary column
(30 m long, 0.2 µm internal diameter) with a polar FFAP phase for FAs.
Results
ETM is detected in surface waters by POC maxima at or just before low
tide (fig. 2 A). In bottom waters, maxima are observed before low tide
and also at the beginning of flood. Minima are observed during high tide
slack both in surface and bottom waters. In surface and bottom waters,
maximum concentrations of chlorophyll a (fig. 2 B) are observed around
low ticles while the lowest concentration are noticed around high ticles.
At low tides, maxima of polyunsatured FA proportions are also observed,
both in bottom ancl in surface waters (fig. 2 C and D). Proportions of
branched FAs are relatively constant through the tidal cycles. In bottom
waters, increases in long-chain FAs are noticed during the ebb and flood
resuspensions. Among individual polyunsatured FAs, C20:5 ω3 is
predominant and has maximum proportions at low ticle (fig. 2 E, F).
High proportions of C16:3 ω4 are also noticeable at low tide especially
in surface waters. Maxima are also observed at low tide in bottom
waters for C22:6 ω3 and C18:3 ω3.
The highest and the lowest abundances of copepods were observed respectively around low ticles (about 50 000 to 200 000 ind.m - 3 ) and at
high tides (<10 000 to 80 000 ind.m - 3 ). Fatty acids (FAs) ancl sterols
(STs) compositions of the copepods are reported in tables 1 and 2. High
proportions of C20:5 ω3 and C22:6 ω3 are noticed either at low ancl
at high tides (table 1). The acids C16:2 ω4 and C16:3 ω4 as well as
80