— 93 —

6.2 Primary productivity and phytoplankton size and biomass in the austral Chilean channels and fjords: spring-summer patterns

1 2Vivian Montecino & Gemita Pizarro1Facultad de Ciencias. Universidad de Chile E-mail: vivianmontecino@uchile.cl2Instituto de Fomento Pesquero E-mail: gpizarro@ifop.cl

Progress in the oceanographic knowledge of Chilean interior waters, from Puerto Montt to Cape Horn.N. Silva & S. Palma (eds.). 2008Comité Oceanográfico Nacional - Pontificia Universidad Católica de Valparaíso, Valparaíso, pp. 93-97.

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.

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,

–2 –1on average 1 g·m ·d , 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,

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,

74°76° 73°W75°

52°

51°

50°

48°

49°

47°S

53°

91

G. de Penas

C. Messier

S. Eyre

E. Falcon

S. Penguin

S. EuropaE. Peel

C. Smyth

C. Concepción

C. Ladrillero

Strai of Mgellan

ta

C. Baker

E. Steffen

E. Mitchel

S. Iceberg

A. Inglesa

C. Picton

C. Trinidad

E. Amalia

C. Fallos

CIMAR 2 Fiordos

Oea

nP

acifi

c c

E. Calvo

92

17

7590

8586

8788

81

84

82

77

7879

12

44

43

42

4548

50

61

67

74

73

70

75

71

2927

28

26

25

24

20

393836

35

32 3331

76

Figure 1: Geographic position of the sampling stations used to determine primary productivity and phytoplankton biomass in the CIMAR 2 Fiordos cruise.

— 94 —

Montecino, V. & G. Pizarro

expressed as Chl-a, was measured along with species diversity (estimated through the Shannon-Weaver 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 Chl-

-3a·m ) 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

-3mg·m 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

–3mg·m ; > 20 m), whereas the largest abundances were found to 10 m depth in the central zone; the southern zone presented a more uniform depth

–3distribution (≤1 mg·m ) (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

66°W68°70°72°74°

52°S

53°

56°

55°

54°

c

Atlanti Ocean

oI. W

llastonCape Horn

CIMAR 3 Fiordos (Phase 2)

Pacific Ocean

Cck urn

. Cob

twS. O

ay

mS. Al irantaz og

1 Angosturaa

2 Angosturaa

C. Beagle

C.Deseado

I v. Na arino

rao

el

Stit

f Mag

l an

B. nútilI

C.a lenero

Bl

owar

C. Frd

P. Dungeness

C. Whiteside

B. Nassau

11

44

42

4140

47

48

20

21

25

7

6

56

54

51

27

3234 35

37

75º 74° 73º47º

46º

45º

44º

43ºS

72°W

Fiordo Aysén

Estero Cupquelán

Estero Quitralco

Canal Puyuguapi

Canal Jacaf

Golfo Elefantes

I.hilo

Cé

BocadelGuafo

Canal Moraleda

Isla Meninea

CIMAR 4 Fiordos

5

27

21191722

14

4

10

9

87

1312

3418

1615

24

23

3032

21A

17A

26

2529

28

3133

6

12A

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.

Pac

ific

Oce

an

LagunaSan Rafael

Surface –3

Chlorophyll-a (mg·m )

Primary productivity and phytoplankton size and biomass in the austral Chilean channels and fjords: spring-summer patterns

— 95 —

reached an average of 20 ± 8 m depth, considering all the measurements carried out in the fjords, channels, and oceanic areas.

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

–2 –1northern zone, < 1 g·m ·d 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).

a

Csat: Chlorophyll images SeaWiFs (±DS)

0

5

10

15

43 44 45 46 47

10-mar-99

09-jan-99

23-jan-99

24-jan-99

Lat S

Cm

·m)

(g

tsa

-3

b

0

1

10

100

0 1 10 100

–3

hl

roh

ll-

1 m

(mg

·C

op

ya

0

m)

Northern, Central and Southern Zones(August 1995 - October 1998)

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).

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.

Northern Zone 98 Northern Zone 99 Central Zone 96 Southern Zone 98

— 96 —

Montecino, V. & G. Pizarro

0

10

20

30

40

50

60

0 1 2 3 4 5 6 7

–3Total Chlorophyll (mg·m )

De

pth

(m

)

CIMAR 3 Fiordos, Southern Zone 98

CIMAR 4 Fiordos, Northern Zone 98-99

CIMAR 2 Fiordos, Central Zone 95-96

y = 0,8962 x -0,8538

R2 = 0,9407

0

1

10

100

0 1 10 100

–3Non fractionated Chl-a (mg·m )

ha

rati

0C

l-f

co

n>

2m

m·m

)(

g-3

1:1

0

2000

4000

6000

8000

10000

12000

11 17 7

2

7 01

11Y 6

1 17 0

2 24

26

35

50 7 21

37

54Station

Number

–2

–1

ail

r

r

rd

ut

n (

··d

Dy

pim

ay

po

cio

mg

m)

Aver. Southern Zone 98Aver. Central Zone 96Aver. Northern Zone 98 Aver. Northern Zone 99

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.

Figure 6: Comparison of vertical profiles of average total chlorophyll for the northern (1998-1999), central (1995-1996), and southern (1998) zones.

Figure 7: Daily primary productivity measured in vitro by the 14 method at different stations and on different cruises from north to C–2 –1south. Non-shaded bars indicate the average value of primary productivity (mg·m ·d ) estimated for each cruise.

Primary productivity and phytoplankton size and biomass in the austral Chilean channels and fjords: spring-summer patterns

— 97 —

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

Garrett, A. & J. Marra. 2002. Effects of upper ocean physical processes (turbulence, advection and air-sea interaction) on oceanic primary production. In: A. Robinson, J. Mc Carthy & B. Rotschild (eds.). The Sea, 12: 19-49.

Guzmán, D. & N. Silva. 2002. Caracterización física y química y masas de agua en los canales australes de Chile entre boca del Guafo y golfo Elefantes (Crucero CIMAR 4 Fiordos). Cienc. Tecnol. Mar, 25(2): 45-76.

Kirk, J. T. O. 1994. Light and photosynthesis in aquatic ecosystems. Cambridge University Press, London, 509 pp.

Marra, J. 2002. Approaches to the measurements of plankton production. In: P. J. le B. Williams, D. N. Thomas & C. S. Reynolds (eds.). Phytoplankton productivity: carbon assimilation in marine and

freshwater ecosystems. Blackwell Science, New York, pp. 78-108.

Montecino, V. 2001. Alometría y biodiversidad en fitoplancton en relación con la productividad primaria en ecosistemas pelágicos. In: K. Alveal & T. Antezana (eds. ) . Sustentab i l idad de la biodiversidad, un problema actual, bases científico-técnicas, teorizaciones y proyecciones. Universidad de Concepción, Concepción, pp. 199-215.

Pizarro, G., J. L. Iriarte, V. Montecino, J. L. Blanco & L. Guzmán. 2000. Distribución de la biomasa fitoplanctónica y productividad primaria máxima de fiordos y canales australes (47°-50° S) en octubre 1996. Cienc. Tecnol. Mar, 23: 25-48.

Pizarro, G., V. Montecino, L. Guzmán, V. Muñoz, V. Chacón, H. Pacheco, M. Frangópulos, L. Retamal & C. Alarcón 2005. Patrones locales recurrentes del fitoplancton en fiordos y canales australes (46º-56º S) en primavera y verano. Cienc. Tecnol. Mar, 28(2): 63-83.

Silva, N., J. Maturana, J. Sepúlveda & R. Ahumada. 1998. Materia orgánica, C y N, su distribución y estequiometría, en sedimentos superficiales de la región norte de los fiordos y canales australes de Chile (Crucero CIMAR-Fiordo 1). Cienc. Tecnol. Mar, 21: 49-74.

Valdenegro, A. & N. Silva. 2003. Caracterización física y química de la zona de canales y fiordos australes de Chile entre el Estrecho de Magallanes y Cabo de Hornos (CIMAR 3 Fiordos). Cienc. Tecnol. Mar, 26(2): 19-60.