bohydrate content of sediments, while their contribution to the S-BPC varied seasonally.
Sedimentary carbohydrate concentrations
ranged between 0.8 mg g-l (station B. January)
and 70.5 mg g-l (station B, April). Soluble carbohydrates accounted on annual average for
8.3% (range 0.3-26.7%) of the total carbohydrate
pool. Protein concentrations ranged between 2.2
mg g-l (station B. January) and 12.1 mg g-l (station D, August). Lipid concentrations ranged
between 0.3 mg g-l (station A, March) and 4.5 mg
g-l (station C, June). The biopolymeric fraction
of sedimentary organic carbon (S-BPC) varied
seasonally. Carbohydrates were the dominant
class among labile organic compounds (annual
average, 51.2%), followed by proteins (39.0%)
and lipids (9.8%). The carbohydrate contribution to the sedimentary BPC was higher in stations 3 and 4 (52.5% and 59.6%, respectively),
whereas proteins increased their relative importance (36.9% and 31.1 %) with respect to stations
A and B (44.9% and 43.1%. respectively). On
annual basis, lipid contribution to sedimentary
BPC ranged between 8.4% (station 1) and 10.7%
(station C).
Discussion
Origin and Biochemical Composition
of Suspended and Sediment Organic Matter
Little difference in phytoplankton biomass (in
terms of chlorophyll-a concentrations) was
found when compared to the results of other studies previously carried out in the same area
(Magazzu 1982; Giani et al. 1995) or in the adjacent open sea (Carrada et al. 1996). The study
area can be defined oligotrophic. as P-Chl-a concentrations had an annual average of <1.0 Jlg 1-1.
However, photosynthetic rates have been reported to be quite high (2 mg C m- 3 h- 1 ), with high
specific phytoplankton growth rates (Jl = 0.93 ±
0.55; Magazzu 1982). These results may indicate
the presence of rapid nutrient recycling and are
supported by the high biomass values and activity of heterotrophic bacterial assemblages
found by Genovese (1969). Throughout the study
period, P-Chl-a concentrations were consistently
dominant (on average, 75% of CPE) with respect
to phaeopigments. indicating the presence of
photosynthetically active phytoplankton.
Nevertheless, phytoplankton biomass accounted
Pelagic-benthic Coupling in a Semi-enclosed Marine System
441
on average for a very low fraction of the total
suspended matter pool (annual average approximately 0.1%). Assuming an average P-Chl-a carbon content of 54 ~g C Jlg-l (Nival et al. 1972),
with respect to total particulate organic carbon,
chloroplastic pigments accounted for an annual
average of approximately 13%. Thus, we may
assume that most of the suspended organic matter in the study site (annual average approximately 87%) was of detrital (non-living) and/or
heterotrophic origin. Particulate proteins were
the dominant biochemical compound, accounting for approximately 66% of the biopolymeric
fraction of particulate organic matter, followed
by lipids (23.0%) and carbohydrates (11.0%).
Dominance of particulate proteins over carbohydrates is generally characteristic of highly productive areas. Indeed, proteins have been reported to dominate in coastal lagoons (Pusceddu et
a1. 1996), estuarine lagoons (Navarro et al. 1993;
Sorokin et al.. 1996) and mariculture impacted
areas (Mazzola et al. 2000). Particulate protein
concentrations in the study area were higher
than those encountered in open sea waters, comparable to those encountered in an estuarine
lagoon in southern Chile (Navarro et al .• 1993)
but about two-fold lower than those found in a
true Mediterranean lagoon (Pusceddu et al.
1996). Since chlorophyll-a represented a very
limited fraction of the particulate organic matter
throughout the year, we might expect most of the
particulate protein not to be associated with
phytoplankton. POC:PON ratio values were relatively low in the whole basin. ranging from 4.9 to
10.9 (annual average, 6.9), In contrast, as the
POC:PON ratio for phytoplankton is reported to
range from approximately 6 (e.g. green algae) to
approximately 11 (e.g. Peridineans) (Valiela
1984), we could expect a large fraction of POC to
be accounted by phytoplankton. However, as
discussed above, phytoplankton biomass (in
terms of chlorophyll-a) accounted for only 13%
of the POC. Thus, other ON sources have to be
present. To this regard a possible explanation
could be found in the large biomass of bacterioplankton reported for the study area (Genovese
1969) that might provide freshly generated nitrogen, as the POC:PON ratio for bacteria ranges
from 3.5 to 5.0 (Lee and Fuhrman 1987).
However, only data on bacterial abundance and
biomass will clarify and confirm our contention.
Sediment chlorophyll-a and CPE concentrations in the sediments of the study area, when
Sedimentary carbohydrate concentrations
ranged between 0.8 mg g-l (station B. January)
and 70.5 mg g-l (station B, April). Soluble carbohydrates accounted on annual average for
8.3% (range 0.3-26.7%) of the total carbohydrate
pool. Protein concentrations ranged between 2.2
mg g-l (station B. January) and 12.1 mg g-l (station D, August). Lipid concentrations ranged
between 0.3 mg g-l (station A, March) and 4.5 mg
g-l (station C, June). The biopolymeric fraction
of sedimentary organic carbon (S-BPC) varied
seasonally. Carbohydrates were the dominant
class among labile organic compounds (annual
average, 51.2%), followed by proteins (39.0%)
and lipids (9.8%). The carbohydrate contribution to the sedimentary BPC was higher in stations 3 and 4 (52.5% and 59.6%, respectively),
whereas proteins increased their relative importance (36.9% and 31.1 %) with respect to stations
A and B (44.9% and 43.1%. respectively). On
annual basis, lipid contribution to sedimentary
BPC ranged between 8.4% (station 1) and 10.7%
(station C).
Discussion
Origin and Biochemical Composition
of Suspended and Sediment Organic Matter
Little difference in phytoplankton biomass (in
terms of chlorophyll-a concentrations) was
found when compared to the results of other studies previously carried out in the same area
(Magazzu 1982; Giani et al. 1995) or in the adjacent open sea (Carrada et al. 1996). The study
area can be defined oligotrophic. as P-Chl-a concentrations had an annual average of <1.0 Jlg 1-1.
However, photosynthetic rates have been reported to be quite high (2 mg C m- 3 h- 1 ), with high
specific phytoplankton growth rates (Jl = 0.93 ±
0.55; Magazzu 1982). These results may indicate
the presence of rapid nutrient recycling and are
supported by the high biomass values and activity of heterotrophic bacterial assemblages
found by Genovese (1969). Throughout the study
period, P-Chl-a concentrations were consistently
dominant (on average, 75% of CPE) with respect
to phaeopigments. indicating the presence of
photosynthetically active phytoplankton.
Nevertheless, phytoplankton biomass accounted
Pelagic-benthic Coupling in a Semi-enclosed Marine System
441
on average for a very low fraction of the total
suspended matter pool (annual average approximately 0.1%). Assuming an average P-Chl-a carbon content of 54 ~g C Jlg-l (Nival et al. 1972),
with respect to total particulate organic carbon,
chloroplastic pigments accounted for an annual
average of approximately 13%. Thus, we may
assume that most of the suspended organic matter in the study site (annual average approximately 87%) was of detrital (non-living) and/or
heterotrophic origin. Particulate proteins were
the dominant biochemical compound, accounting for approximately 66% of the biopolymeric
fraction of particulate organic matter, followed
by lipids (23.0%) and carbohydrates (11.0%).
Dominance of particulate proteins over carbohydrates is generally characteristic of highly productive areas. Indeed, proteins have been reported to dominate in coastal lagoons (Pusceddu et
a1. 1996), estuarine lagoons (Navarro et al. 1993;
Sorokin et al.. 1996) and mariculture impacted
areas (Mazzola et al. 2000). Particulate protein
concentrations in the study area were higher
than those encountered in open sea waters, comparable to those encountered in an estuarine
lagoon in southern Chile (Navarro et al .• 1993)
but about two-fold lower than those found in a
true Mediterranean lagoon (Pusceddu et al.
1996). Since chlorophyll-a represented a very
limited fraction of the particulate organic matter
throughout the year, we might expect most of the
particulate protein not to be associated with
phytoplankton. POC:PON ratio values were relatively low in the whole basin. ranging from 4.9 to
10.9 (annual average, 6.9), In contrast, as the
POC:PON ratio for phytoplankton is reported to
range from approximately 6 (e.g. green algae) to
approximately 11 (e.g. Peridineans) (Valiela
1984), we could expect a large fraction of POC to
be accounted by phytoplankton. However, as
discussed above, phytoplankton biomass (in
terms of chlorophyll-a) accounted for only 13%
of the POC. Thus, other ON sources have to be
present. To this regard a possible explanation
could be found in the large biomass of bacterioplankton reported for the study area (Genovese
1969) that might provide freshly generated nitrogen, as the POC:PON ratio for bacteria ranges
from 3.5 to 5.0 (Lee and Fuhrman 1987).
However, only data on bacterial abundance and
biomass will clarify and confirm our contention.
Sediment chlorophyll-a and CPE concentrations in the sediments of the study area, when