Progress in the oceanographic knowledge of Chilean interior waters, from Puerto Montt to Cape Horn.
N. Silva & S. Palma (eds.). 2008
Comité Oceanográfico Nacional - Pontificia Universidad Católica de Valparaíso, Valparaíso, pp. 93-97.
6.2 Primary productivity and phytoplankton size and biomass in the
austral Chilean channels and fjords: spring-summer patterns
Vivian Montecino1 & Gemita Pizarro2
1
Facultad de Ciencias. Universidad de Chile
E-mail: [email protected]
2
Instituto de Fomento Pesquero
E-mail: [email protected]
Phytoplankton occurs in a wide range of sizes
and forms. Smaller organisms (< 5 µm) are more
frequent and abundant in less productive systems,
whereas larger organisms (> 20 µm), or
microphytoplankton, prevail in eutrophic waters,
which are more productive, being rich in
phosphorus and nitrogen. Consequently, the
dynamics of phytoplankton in relation to the local
environment and other organisms are particularly
important when the ecosystem's biological
productivity is estimated. As a component of
biogeochemical processes, primary productivity,
on average 1 g·m–2·d–1, helps explain the function of
phytoplankton in the carbon pump that reduces
atmospheric CO 2.
Primary productivity is studied according to the
timescale on which phytoplankton photosynthetic
processes and growth occur. On a smaller scale,
these experiments are performed in situ or in vitro,
lasting from minutes-hours or hours-days,
depending on the proposed objectives. Larger
scale questions deal with seasonal, intraseasonal,
and interannual variability, both in the water
column (vertical) and horizontally (mesoscale). In
the first case, the uncertainties are physiological,
76°
75°
73°W
74°
47°S
G. de Penas
92
Pacific Ocean
Oceanic primary productivity, generated mainly
by the microscopic autotrophic organisms that
make up the phytoplankton, is an essential
element in marine ecosystems. Primary
productivity is a two-stage process, consisting of
photosynthesis and biosynthesis. Photosynthesis,
or carbon fixation, is driven by the chlorophyll
contained in microalgal chloroplasts (Kirk, 1994).
Chlorophyll-a concentrations (Chl-a) are
universally used as a measure of phytoplankton
biomass. Microalgae form associations that
interact with other microorganisms, constituting a
microbial web that regulates in situ nutrient and
carbon recycling, its transfer to higher trophic
levels, or its sedimentation to deeper waters.
C. Fallos
E. Steffen
91
90
5
12
7
17
E. Mitchel
48°
C. Baker
S. Iceberg
20
C. Messier
A. Inglesa
87
28
C. Ladrillero
S. Eyre
24 27 29
86
77
26
85
C. Picton
E. Falcon
78 31 25
84
32 33
79
C. Trinidad
S. Penguin
81
35
82
36
S. Europa
38 39
73 E. Peel
76
74 E. Calvo
42
71
70
E. Amalia
43
75
C. Concepción
88
49°
50°
51°
44
45
C. Smyth
67
48
50
Str
ait
of
CIMAR 2 Fiordos
Ma
gel
lan
52°
61
53°
Figure 1: Geographic position of the sampling stations used to
determine primary productivity and phytoplankton
biomass in the CIMAR 2 Fiordos cruise.
whereas, in the second case, they are ecological
(Marra, 2002).
The CIMAR 2-4 Fiordos cruises, carried out
from Boca del Guafo to Cape Horn (Fig. 1, 2),
covered the vast geographical area of austral
Chilean channels and fjords, which are
characterized by different water masses (Silva et
al., 1998; Guzmán & Silva, 2002; Valdenegro &
Silva, 2003). Here, phytoplankton biomass,
— 93 —
Montecino, V. & G. Pizarro
P. Dungeness
27
56
54 S
.
til
I nú
B.C. Whiteside
Alm
43ºS
4
Pacific Ocean
ellan
7
54°
a
2 Angostura
6
n
ea
Strait
of Ma
g
25
21
Oc
C.
Deseado
S.
Boca
delGuafo
a
1 Angostura
tic
an
11
20
Atl
53°
ay
Otw
I.hC ilo
é
52°S
6
C.
55°
32
urn
34 35
ckb
o
C
C.
o
r
e
llen
Ba
C.
51
37
nta
z
go
40
41 C. Beagle
42
I. Navarino
47
B. Nassau
56°
44
I. W
olla Cape Horn
ston
7
Laguna
San Rafael
26
27
CIMAR 3 Fiordos (Phase 2)
74°
72°
66°W 75º
68°
74°
45º
46º
28
Golfo Elefantes
CIMAR 4 Fiordos
70°
44º
Canal Jacaf
10
Canal Puyuguapi
12A
Isla Meninea
12
13
17A
16
14 15
21Fiordo Aysén
1718 19
21A
34 22
33
23
31 Estero Quitralco
32
24 30
29
25
Estero Cupquelán
48
Pacific Ocean
Canal Moraleda
8
9
ira
rd
wa
Fro
5
73º
47º
72°W
Figure 2: Geographic position of sampling stations to determine primary productivity and phytoplankton biomass in the CIMAR 3
(Phase 2) and 4 Fiordos (Phase 1 and 2) cruises.
expressed as Chl-a, was measured along with
species diversity (estimated through the ShannonWeaver index, H') and the variety of sizes found in
the surface samples taken from the euphotic or
well-lit zone. Carbon fixation was also estimated by
using an incubator with an artificial light source,
according to the methodology described by Pizarro
et al. (2000).
In the study area, the fractioning of the total
biomass showed that phytoplanktonic organisms
larger than 20 µm (microphytoplankton) were
recurrent on meso and macro scales. Moreover,
species richness was 17-27 for the maximum H'
diversity values and 5-10 for the minimum H'
values. The surface abundances and most
recurring (> 45 %) microphytoplankton species in
the three studied zones were Skeletonema
costatum (67 %) in October 1998 and Guinardia
delicatula (65 %) in February 1999 between Boca
del Guafo and Laguna San Rafael (northern zone);
Thalassiosira minuscula (91 %) in August 1995
and Chaetoceros cinctus (36 %) in October 1996
from Golfo de Penas to Strait of Magellan (central
zone); and Chaetoceros sp. (56 %) in October
1998 from Strait of Magellan to Cape Horn
(southern zone).
The most frequent distribution pattern showed
that the numerically predominant species were the
same in only a few places, whereas the rarest
species were found at nearly all the sites. A similar
situation was observed in terms of biomass, with a
heterogeneous distribution of satellite chlorophyll
(Chl-sat) and high concentrations (> 10 mg Chla·m-3) at specific sites (Fig. 3). The vertical
distribution of phytoplankton biomass showed a
significant relationship between Chl-a at the
surface (0-5 m) and at 10 m depth (Fig. 4). Sites
with differences of one order of magnitude
between these two depths were relatively rare.
Most phytoplankton concentrations greater than 1
mg·m-3 were made up by the fraction exceeding 20
µm (Fig. 5). When considering the average vertical
Chl-a profiles in the three zones, the northern zone
clearly had higher and deeper concentrations (> 2
mg·m–3; > 20 m), whereas the largest abundances
were found to 10 m depth in the central zone; the
southern zone presented a more uniform depth
distribution (≤1 mg·m–3) (Fig. 6). Comparatively,
heterogeneity in the values at 20 m depth was
large, and the variability was not lower at the
vertical peaks, which is consistent with the
classical patterns determined for estuaries.
According to these patterns, the euphotic zone
— 94 —
Primary productivity and phytoplankton size and biomass in the austral Chilean channels and fjords: spring-summer patterns
Northern, Central and Southern Zones
(August 1995 - October 1998)
–3
Chlorophyll-a 10 m (mg·m )
100
10
1
0
0
1
10
100
–3
Surface Chlorophyll-a (mg·m )
Figure 4: Comparison of the chlorophyll-a values at the surface
and at 10 m depth for each oceanographic station.
Most of the results fit a homogeneous vertical
distribution of the values.
a
reached an average of 20 ± 8 m depth, considering
all the measurements carried out in the fjords,
channels, and oceanic areas.
Csat: Chlorophyll images SeaWiFs (±DS)
15
09-jan-99
-3
Csat (mg·m )
23-jan-99
24-jan-99
10
10-mar-99
5
b
0
43
44
45
46
47
Lat S
Figure 3: a) Distribution of surface chlorophyll concentrations
between Puerto Montt and the Península Taitao
according to the SeaWiFs satellite image of 24 March
1999 (Laboratorio de Modelación Ecológica,
Universidad de Chile); b) Surface chlorophyll values
between 43º and 46º S extracted from four SeaWiFs
satellite images taken between January and March
1999).
By graphing the average primary productivity
values for each cruise and the values obtained at
each one of the studied stations, spatial variability
was observed to be high in the three geographic
zones: average values were around 3 in the
northern zone, < 1 g·m–2·d–1 in the central zone (Fig.
7), and more heterogeneous in the southern zone.
The physical factors that control estuarine systems
(Garret & Marra, 2002) are responsible for this
variability and are consistent with the primary
productivity results obtained in the three analyzed
areas. Thus, vertical distribution patterns of
phytoplanktonic biomass can be attributed to local
differences in the intensity of the mixing and
stratification processes and, therefore, to the
photo-acclimatization processes of the autotrophic
organisms. Similarities among the three zones
indicate that the Chl-a abundance is determined by
the size structure of the phytoplanktonic organisms
(Montecino, 2001).
— 95 —
Montecino, V. & G. Pizarro
100
Chl-a fraction >20 m (mg·m )
y = 0,8962 x -0,8538
R2 = 0,9407
Total Chlorophyll (mg·m–3)
1:1
-3
0
1
2
3
4
6
5
7
0
10
Depth (m)
10
1
20
30
40
CIMAR 2 Fiordos, Central Zone 95-96
50
0
0
1
10
CIMAR 3 Fiordos, Southern Zone 98
CIMAR 4 Fiordos, Northern Zone 98-99
60
100
–3
Non fractionated Chl-a (mg·m )
Northern Zone 98
12000
Figure 6: Comparison of vertical profiles of average total
chlorophyll for the northern (1998-1999), central
(1995-1996), and southern (1998) zones.
Northern Zone 99
Central Zone 96
Southern Zone 98
–2
–1
Daily primary production (mg·m ·d )
Figure 5: Relationship between total biomass (unfractionated
chlorophyll-a) and chlorophyll-a estimated for the
largest size fraction (> 20 µm) at the stations analyzed
in the channel and fjord region.
10000
8000
6000
4000
2000
Aver. Northern Zone 98
Aver. Northern Zone 99
Aver. Central Zone 96
54
37
21
7
50
35
26
24
20
17
16
11Y
10
7
27
17
0
11
Station
Number
Aver. Southern Zone 98
Figure 7: Daily primary productivity measured in vitro by the 14C method at different stations and on different cruises from north to
south. Non-shaded bars indicate the average value of primary productivity (mg·m–2·d–1) estimated for each cruise.
— 96 —
Primary productivity and phytoplankton size and biomass in the austral Chilean channels and fjords: spring-summer patterns
Primary productivity and Chl-a abundance
patterns are also congruent with studies on the
quantity of organic matter in sediments and the
effect of glaciers in the zone (Silva et al., 1998).
These glaciers release inorganic matter known as
glacial silt that, in some sectors, “dilutes” the
organic content of the sediments and attenuates
primary productivity due to decreased light
penetration.
However, photosynthetic pigments absorb
light, also causing an endogenous light-limitation
(Pizarro et al., 2005). This light limitation, together
with the scarcity of other resources such as
dissolved nutrients, tends to favor smaller-sized
phytoplankton fractions as the predominant
component in the total biomass. The patterns
described are a tool for quantifying the variability of
these ecosystems on meso and macro scales.
References
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physical processes (turbulence, advection and airsea interaction) on oceanic primary production. In: A.
Robinson, J. Mc Carthy & B. Rotschild (eds.). The
Sea, 12: 19-49.
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