The nearshore zone during coastal upwelling: Daily variability and coupling between primary and secondary production off central Chile

Prog. Oceanog. Vol. 20, pp. 1~.~0, 1988.

0079-6611/88 $0.00+.50 Copyright © 1988 Pergamon Press plc.

Printed in Great Britain. All rights reserved.

The Nearshore Zone during Coastal Upweiling: Daily Variability and Coupling between Primary and Secondary Production off Central Chile WILLIAMT. PETERSON,*'~ DAGOBERTOF. ARCOS,'* GEORGE B. McMANuS,*** HANS DAM,* DIANEBELLANTONI,*T}~OMASJOHNSON*and PETERTISELIUSt "Marine Sciences Research Center, State University of New York, Stony Brook, NYl1794, U.S.A. **Department of Oceanology, University of Concepcion, Concepcion, Chile "~*Instituteof Ecosystem Studies. Millbrook, NY12545, U.S.A. ~Kristineberg Marine Biological Station, S 45034, Fiskebacksil, Sweden ~Present address: Department of Zoology, University of Cape Town, Rondebosch 7700, South Africa (Submitted A ugust 1986; Revised teyt accepted December 1987)

ABSTRACT

The nearshore region of central Chile is important f o r spawning of sardine (Sardinops sagax ) anchovy (Engraulis ringens

) and jack mackerel

(Trachurus murphyii

) and the importance of

f i s h e r i e s f o r these species has led to an i n t e r e s t in factors c o n t r o l l i n g the area's productivity. We studied daily variations in productivity at a nearshore station (25m depth) off Dichato, Chile (36°30'S) during January 1986 to understand how wind-driven v a r i a b i l i t y

in the hydrography

is translated into pulses of primary and secondary production of the plankton. study period,

we observed three complete cycles of upwelling favourable/unfavourable winds.

Water column d e s t r a t i f i c a t i o n ,

as indicated by the surface-to-bottom gradient of sigma-t,

lagged the wind by about one day. nitrate

During active upwelling, cold water (<11.5°C) of high

and low oxygen concentration

the surface.

During the

(20-25vM and I-2mi

I -I

respectively)

was found near

During subsequent r e l a x a t i o n of upwelling, the water column became s t r a t i f i e d

as temperature, oxygen and chlorophyll increased. The size and taxonomic composition of the phytoplankton varied from one event to the next. Over the course of the study, from 15-100% of the chlorophyll could pass a 20~m mesh screen. Chain-forming diatoms, m i c r o f l a g e l l a t e s , and the autotrophic c i l i a t e Mesodinium rubrum dominated the f i r s t , paruus,

second and t h i r d events, respectively.

Centropages

patagoniensis

brachiatus,

Oithona spp,,

and Calanus chiZensis

In rank order of abundance,Paracalanus

Acartia

tonsa,

dominated the copepod community.

of most species did not c l o s e l y f o l l o w the upwelling cycle. or

other

behavioural

JPO 20:l-A

to

Calanoides

Changes in abundance

Possibly, v e r t i c a l

responses caused zooplankton d i s t r i b u t i o n s

movements of the surface Ekman layer.

Oncaea spp,,

movements

be uncorrelated

with

Fecundity of several of the important copepod species

2

W . T . PETERSONet al.

was measured using the egg ratio and bottle incubation techniques.

Compared to values

reported in the l i t e r a t u r e , egg production was usually suboptimal, despite high nutritional quality of the phytoplankton, as indicated by protein/carbohydrate ratios. Food a v a i l a b i l i t y , due to either small phytoplankton

size or spatial

and temporal uncoupling of phyto- and

zooplankton populations, was probably most important in l i m i t i n g copepod production. Event-scale advection, both zonal and alongshore,

can be important in uncoupling primary

and secondary production and probably determines the degree to which upwelling-generated pulses of phytoplankton production are u t i l i z e d by herbivorous plankton in the nearshore zme.

CONTENTS

I.

2.

3.

INTRODUCTION

3

1.1

Background

3

1.2

Rationale

4

1.3

Working hypothesis

4

1.4

A description of the study site

5

METHODS 2.1

Physical and chemical oceanographic measurements

2.2

Biological oceanographic measurements 2.2.1

Chlorophyll

2.2.2

Protein and carbohydrate analysis

2.2.3

Primary production

2.2.4

Zooplankton abundance

2.2.5

Copepod feeding experiments

2.2.6

Egg production measurements

RESULTS 3.1

I0 Physical and chemical data

I0

3.1.1

Temperature-salinity characteristics

I0

3.1.2

Winds

I0

3.1.3

Upwelling events

II

3.1.4

Vertical temperature gradients

13

3.1.5

Vertical s a l i n i t y gradients

3.1.6 3.1.7

Vertical density gradients

14 14

3.1.8 3.2

Oxygen Nitrate and n i t r i t e

14 14

Biological data

16

3.2.1

Chlorophyll

16

3.2.2

Protein and carbohydrates Phytoplankton growth rates and labelling patterns Distribution and abundance of zooplankton

17 19

3.2.3 3.2.4

22

Nearshore zone coastal upwelling

4.

3

3.2.5

Gut fullness of copepods

25

3.2.6

Copepod fecundity

27

DISCUSSION

30

4.1

Characteristics of the nearshore upwelling system

30

4.2

Comparison of i n d i v i d u a l events

33

4.3

Effects of advection on plankton d i s t r i b u t i o n s

35

5.

CONCLUSIONS

37

6.

ACKNOWLEDGEMENTS

38

7.

REFERENCES

38

1. 1.1

INTRODUCTION

Background

Biological and physical processes associated with coastal

upwelling in Eastern Boundary

Currents received a great deal of attention from oceanographers during the International Decade of Ocean Exploration (IDOE) of the 1970s.

The bulk of the research was carried out

in three regions: Oregon, northwest Africa, and Peru. can be found in RICHARDS (1981).

A review of many of those efforts

Other regions that have been studied include Baja California

(WALSH, KELLY, WHITLEDGE, MACISAAC and HUNTSMAN, 1974), the northern California coast (e.g. HUYER, 1985), Ivory Coast (BINET and SUISSE DE SAINT CLAIRE, 1975), the Benguela Current (ANDREWS, 1974; ANDREWS and HUTCHINGS, 1980; SHANNON, 1985) and the Somali Current (SMITH and CODISPOTI, 1980; SMITH, 1982). During the IDOE years coastal upwelling along the coast of Chile received very l i t t l e attention,

in part because Chile was not a major fishing nation at that time, so that studies

of coastal upwelling processes may not have seemed very urgent. ditions have changed considerably.

Since the late 1970s, con-

As a fishing nation, Chile now ranks f i f t h in the world,

behind Japan, USSR, China, and the USA (THOMPSON, 1983).

Landings of 3.4 million metric

tonnes were recorded in 1981, h a l f of which were the sardine, Sa~dinops sagax. ranked during the l a t e

1960s and e a r l y 1970s, is now sixth-ranked,

Peru, f i r s t -

with landings of 2.8

m i l l i o n metric tonnes in 1981.

Chile's rise in prominence as a fishing nation is apparently due to changes in the distribuPrior to the early 1970s, the anchovy (Engraulis ringens) and sardine (Sa~inops sag~) had a common spawning center off the coast of northern

tion and abundance of clupeid stocks.

Chile, between 18 and 22°S, with limited spawning off Valparaiso (33°S) and Talcahuano (37°S). In 1973, or perhaps a few years earlier,

(G. SHARP, personal communication), the anchovy

populations within the Peru-Humboldt Current collapsed, and sardines became the dominant

4

W . T . PETERSON et al.

clupeid.

The d i s t r i b u t i o n a l

range of the sardine stock expanded and there are now at least

two major spawning centers off

the coast of Chile, one in the north (18 to 22°S) and the

other in the south, in the v i c i n i t y

of Talcahuano (36 to 40°S).

The region off Talcahuano

is also a spawning center f o r the jack mackerel (Trachurus murphyii) and, to a l i m i t e d extent, for

the anchovy.

Because of the economic importance of the f i s h e r i e s f o r

sardine, jack

mackerel, and anchovy, there is considerable value in conducting basic studies of the biological

productivity

and physical oceanography of northern and central

Chilean waters.

One

long-range goal is to gain an understanding of why spawning is r e s t r i c t e d to s p e c i f i c regions of the Chilean coast, in p a r t i c u l a r off Talcahuano. 1.2

Rationale

The focus of our research in January 1986 was on temporal v a r i a b i l i t y logical

p r o d u c t i v i t y at a single f i x e d station

(40km north of Talcahuano). the effects

The project had two objectives.

First,

we set out to study

of d a i l y v a r i a t i o n s in the i n t e n s i t y of the winds on the v e r t i c a l

of a number of physical, chemical, and b i o l o g i c a l biological

in upwelling and bio-

in the nearshore zone near Dichato, Chile

variables,

and on v a r i a t i o n s

distribution in several

rate processes that are coupled both to each other and to physical processes.

Second, we wanted to measure time lags between changes in winds, hydrography and plankton production.

(a)

(b)

The f o l l o w i n g variables were measured d a i l y f o r approximately three weeks:

Time-depth v a r i a t i o n s in: (i)

temperature, s a l i n i t y , density and Secchi depth;

(ii)

oxygen, n i t r a t e , n i t r i t e ,

(iii)

chlorophyll concentration and zooplankton abundance.

and p a r t i c u l a t e protein and carbohydrate;

Temporal v a r i a t i o n s in the f o l l o w i n g rates: (i)

primary production and incorporation of photosynthate into various biochemical pools;

1.3

(ii)

c o p e p o dfeeding rates;

(iii)

secondary production of copepods, using d a i l y egg production as an index.

Working Hypothesis

We chose to study d a i l y v a r i a t i o n s of coastal upwelling zones.

in the above parameters because of the dynamic nature

In many coastal upwelling regions, upwelling-favourable winds

do not blow s t e a d i l y in an equatorward d i r e c t i o n . winds may remain calm, f o r i n t e r v a l s of 2 to 8 days.

Rather, wind d i r e c t i o n may reverse, or These episodic changes in wind speed

and d i r e c t i o n give r i s e to "upwelling events". Episodic events of active upwelling r e s u l t in decreases in the s t a b i l i t y and increases

in n u t r i e n t concentration.

Relaxation of upwelling,

i.e.

of the water column a decreased

rate

of upwelling, leads to s t a b i l i z a t i o n of the water column, a condition believed to be favourable f o r high rates of phytoplankton growth.

Thus, the a l t e r n a t i o n of active and relaxed

Nearshore zone coastal upwelling

upwelling events leads to pulses in primary production.

5

Our central

hypothesis is that

the expected pulses in primary production should in turn lead to pulses in biomass of phytoplankton,

increased feeding

activity

of

copepods,

and to pulses in secondary production

in the form of increased egg production by adult female copepods. One caveat is in order: an important aspect of the alternation of active and relaxed upwelling events is the onshore-offshore

advection of surface waters.

During active upwelling

surface water is carried seaward and is replaced by deep water which moves landward and upward.

During relaxed upwelling, the opposite is true.

I t must be kept in mind that the

processes observed at a fixed station can be affected both by local changes and by changes brought about by zonal and alongshore advection. 1.4

A description of the study site

Our f i x e d station

was located approximately one km northwest of the mouth of Coliumo Bay

in water 25m deep ( F i g . l ) . in t h i s

general region:

shelf to the north. ing center.

Two bathymetric features probably contribute to high p r o d u c t i v i t y a submarine canyon south of Talcahuano, and the r e l a t i v e l y broad

The canyon may serve to focus upwelling, and may therefore be an upwell-

Because of the a n t i c y c l o n i c c i r c u l a t i o n pattern

in t h i s

region,

(R. WILSON,

personal communication) the broad shelf should tend to increase the residence time of shelf waters,

thus favouring retention of plankton w i t h i n t h i s region.

The c i r c u l a t i o n of the region is known in o u t l i n e .

A coastal surface current known as the

Humboldt Current flows equatorward along the coast of Chile and is part of the large-scale a n t i c y c l o n i c wind-driven system of the southeast Pacific Ocean. The water in is Subantarctic Water,

which off Chile has a s a l i n i t y of <34.

t h i s current

Below t h i s water mass l i e s

the poleward-moving Equatorial Subsurface Water (ESSW). This is the source water f o r coastal upwelling (GUNTHER, 1936), and is called the Peru-Chile Undercurrent, or the Gunther Current. It

is characterised by a r e l a t i v e l y high s a l i n i t y

extremely low oxygen (
>26~M n i t r a t e ,

(>34.4),

low temperature ( < I I . 5 ° C ) ,

with O.2ml I -I commonly occurring).

>I~M n i t r i t e

and

Nutrient concentrations

and >2uM phosphate (AHUMADA, RUDOLF and MARTINEZ,

1983; ARCOS and WILSON, 1984).

2. 2.1

METHODS

Physical and chemical oceanographic measurements

Cruises were made to the study s i t e

(water depth = 25m) from 6 through 31 January 1986,

usually in the morning, every day except Sundays. bottles equipped with reversing thermometers.

Water samples were collected using Nansen

Sampling depths were O, 5, I0,

Water samples were drawn from the Nansen bottles f o r (in

15 and 23m.

l a t e r determination of c o n d u c t i v i t y

the shore laboratory using a Beckman RS 7C Salinometer).

S a l i n i t y and density were

calculated using an HP-85 microcomputer and PRITCHARD's (1980) equations.

Wind data were

6

W . T . PETERSON et al.

0°

40°5

O0°W

5C 8C I000" .,

-37os

74 o

I FIG. I .

Chart showing station location and bathymetry in the v i c i n i t y of our study site (1), approximately Ikm northwest of the mouth of Coliumo Bay.

Nearshore zone coastal upwelling

obtained from the Carriel Sur Airport, Concepcion.

7

The airport is located approximately

3km south of the head of the Bay of Concepcion, and 40km from our study site.

I t is located

near r e l a t i v e l y f l a t terrain where orographic effects on the wind are l i k e l y to be minimal. Samples for oxygen analysis were dispensed from the Nansen bottles through a rubber tube into 300ml BOD bottles, and analyzed following the Winkler procedure. Samples for nutrient analysis were f i l t e r e d through GF/C f i l t e r s ; the f i l t r a t e was returned to the shore laboratory where nitrate and n i t r i t e were analyzed that afternoon,

following standard techniques

(STRICKLAND and PARSONS, 1972). 2.2

Biological Oceanographic Measurements

2.2.1

Chlorophyll.

For chlorophyll analysis, 100ml of water was taken from each Nansen

bottle and f i l t e r e d through a O.Svm pore-size Millipore f i l t e r .

F i l t e r s were immediately

placed individually into 15ml plastic centrifuge tubes and stored on ice in the dark (~I hour).

At the shore laboratory, 90% acetone was added to each tube and the chlorophyll

was allowed to extract overnight in the dark at -20°C.

The next afternoon, fluorescence

was read with the aid of a Turner Model 110 or a Turner Designs fluorometer. 2.2.2

Protein and Carbohydrate analysis.

In

addition

to

the Nansen bottle

sampling,

an integrated sample consisting of equal volumes of water from Im, 3m and 5m, and a sample of water from 15m were collected with a small plastic impeller pump f i t t e d with a Icm diameter plastic hose. hydrate. filters

Duplicate 100ml subsamples were removed for analysis of protein and carbo-

Subsamples for these biochemical analyses were collected on GF/C f i l t e r s .

The

were immediately stored on ice u n t i l the analyses were performed, never more than

f i v e hours after collection.

Protein was determined by the modified Lowry technique (LOWRY,

ROSEBROUGH, FARR and RANDALL, 1951) using a bovine serum albumin standard.

Carbohydrate

was analyzed by the DUBOIS, GILLES, HAMILTON, REBERS and SMITH (1956) phenol-sulphuric acid technique. 2.2.3

Primary production.

Primary productivity measurements using the

14C technique

were made on the phytoplankton collected between 1000h and 1200h using water from the I+3+5m integrated sample and from the 15m sample (grazers were removed prior to all productivity measurements by screening the samples through a 200~m mesh). of these water samples was measured as well.

Chlorophyll concentration

On alternate days productivity of phytoplankton

passing a 20~m mesh was also measured. All incubations were done in 300ml BOD bottles (4~Ci/ bottle).

Samples from 15m were covered with neutral density screens to admit 8% of the

incident solar radiation.

The bottles were then incubated at the shore laboratory, outdoors

in f u l l sunlight, in a running seawater bath for 4 to 5 hours. Incubations were terminated by f i l t e r i n g the entire contents of each bottle through a GF/C filter.

F i l t e r s were placed in s c i n t i l l a t i o n vials and exposed to concentrated HCI overnight

to remove inorganic labelled carbon.

One f i l t e r

from each size fraction and depth was set

aside for extraction into the protein, l i p i d , low molecular weight compounds,and polysacchande

8

W.T. PETERSON et al.

fractions.

Five mls of Ecoscint s c i n t i l l a t i o n

fluid

were added to the remaining f i l t e r s

f o r the determination of t o t a l p r o d u c t i v i t y . Extraction of the biochemical products of photosynthesis followed a modified method of LI, GLOVER, and MORRIS (1980).

Filters

were added to a 2:1

methanol and stored at -20°C f o r at least 24 hours. another GF/C f i l t e r water. for

This mixture was then rinsed through

were placed in 3 ml of hot (90-I00°C) 5% t r i c h l o r o a c e t i c acid (ICA)

This

solution was f i l t e r e d

2 mls of cold (O°C) 5% TCA.

through another GF/C f ~ l t e r

and rinsed with

S c i n t i l l a t i o n f l u i d was added d i r e c t l y to the f i l t e r s .

ml subsample of the f i l t r a t e fluid.

mixture of chloroform and

and washed with Iml chloroform, 2 mls methanol, and 2.7 mls of d i s t i l l e d

The 2 f i l t e r s

30 minutes.

(v:v)

(TCA-soluble f r a c t i o n )

was added to 5 mls

A one

of s c i n t i l l a t i o n

The chloroform f r a c t i o n was separated from the methanol:water f r a c t i o n in a 30 mls

separatory funnel.

One ml subsamples of each were added to 5 mls of s c i n t i l l a t i o n f l u i d .

The chloroform f r a c t i o n

is considered to be the l i p i d s ,

the methanol:water f r a c t i o n to be

the low molecular weight compounds, the hot TCA-soluble f r a c t i o n to be the polysaccharides, and the TCA-insoluble f r a c t i o n by l i q u i d s c i n t i l l a t i o n

(the f i l t e r s )

counting.

to be protein.

R a d i o a c t i v i t y was determined

Quench correction was by the external standards method

except f o r the chloroform f r a c t i o n ,

where an internal standard was used to determine e f f i c -

iency because of high quenching.

Zooplankton abundance.

2.2.4

For zooplankton abundance and species composition, samples

were collected with a O.5m diameter 102vm mesh net hauled v e r t i c a l l y through the 23m water column.

The contents of the cod end were preserved with buffered formalin. In the laboratory

at least two and up to f i v e aliquots were taken with a Iml piston pipette, and various zooplankton taxa were enumerated. other taxa to genus. 2.2.5

The dominant copepods were i d e n t i f i e d to species, and a l l

The number of organisms counted per sample ranged from 350 to 2000.

Copepodfeeding experiments

Estimates of copepod f i l t r a t i o n

were carried out using the gut fluorescence technique.

brachiatus

CaZanus chilensis

and ingestion rates and

Centropages

were chosen f o r study because they were abundant and were large enough to be

handled e a s i l y .

Animals were collected near the surface (O-10m , but usually O-5m) and

at depth (I0-23m, but usually near 15m) with a O.5m diameter, 240vm mesh plankton net. The contents of the cod end were d i l u t e d in buckets containing 101 of surface water.

A subsample

from the bucket was immediately collected on a 500vm Nitex screen, and placed under a dissecting microscope.

Ten to 15 adult females were i n d i v i d u a l l y picked with j e w e l l e r s ' forceps

and placed into p l a s t i c centrifuge tubes to which a few mls of 90% acetone were then added. The tubes were kept on ice in the dark before return to the laboratory f o r analysis. In the laboratory the amounts of chlorophyll and phaeopigments in the guts of the animals were measured using e i t h e r a Turner Model 110 or a Turner Designs fluorometer.

Calculations

followed the procedures described by DAGG and WYMAN (1983) and were corrected f o r the small amount of body tissue fluorescence of the animals (c. chilensis mean = 0.135; c. brachiatus mean = 0.122ng chl. equiv, fem-1).

Nearshore zone coastal upwelling

9

Gut evacuation experiments were conducted at 14°C in a temperature-controlled room.

From

100 to 150 adult females of each species were pipetted into seawater containing a mix of diatoms grown in f / 2 medium (GUILLARD and RYTHER, 1962), allowed to feed f o r I to 2h, and transferred to GF/C-filtered seawater.

The gut contents of the animals were monitored by

p e r i o d i c a l l y removing animals from the f i l t e r e d

seawater and measuring t h e i r fluorescence.

The instantaneous gut evacuation rate was calculated from the slope of the log (gut f ullnes s ) vs time r e l a t i o n . ation rate

Ingestion rates were obtained by m u l t i p l y i n g the instantaneous gut evacu-

by the gut fullness

by d i v i d i n g

(DAGG and WYMAN, 1983).

Clearance rates were calculated

ingestion rates by the mean chlorophyll concentration from each depth layer

(DAGG, 1983). 2.2.6

Egg production

For measurements of copepod fecundity, l i v e copepods

measurements.

were collected during each cruise by setting a O.5m diameter, 240vm mesh plankton net at 5m, or 20m, or both.

The nets were not towed, but were allowed to sample f o r f i v e minutes

while the ship was d r i f t i n g . several

plastic

As soon as the sample was brought aboard, i t

buckets f u l l

were immediately removed.

of

seawater.

Ctenophores

was d i l u t e d into

and other gelatinous zooplankton

Animals were returned to the laboratory within I hour of collection

and held in a 14°C room u n t i l they were sorted f o r the fecundity measurements. At the end of each cruise filled

I

litre

transparent p l a s t i c

bottles

(polymethylpentene)

were

with 6 4 ~ m - f i l t e r e d seawater collected from the depth of the chlorophyll maximum,

usually 5m or 15m. The water was screened to remove copepod eggs that may have been present in the water. parvus

We used a 64~m mesh screen because the smallest eggs (those of

were 75vm in diameter.

Paracalanus

These bottles were used to incubate the copepods f o r the

fecundity measurements. Adult female copepods were sorted into each of four bottles. For Acartiatonsa~nd Paracalanus parvus,

10 females were added to each b o t t l e ; f o r Centropages brachiatus,

and f o r Calanus

and

Calanoides

two or three per b o t t l e .

24h in a walk-in chamber at 14°C on a 14-I0h LD cycle.

f i v e were added;

The females were incubated f o r

To terminate an experiment the con-

tents of each b o t t l e were poured through a 64~m Nitex screen, rinsed with f i l t e r e d seawater into a v i a l ,

and preserved with a few drops of 5% buffered formalin; eggs and females were

enumerated using a dissecting scope. For Calanoides patagoniensis

egg production rates were also estimated by the egg r a t i o tech-

nique, using the data on abundance of eggs and females in the q u a n t i t a t i v e zooplankton net tows, and data on hatching times (of

Calanoides carinatus)

could not be used f o r Calanus chilensis females on other dates were too low. fo r

This method

because abundances of eggs on some dates and/or Calculation of an egg/female r a t i o was not possible

the smaller copepod species because t h e i r

102vm mesh net.

from HIRCHE (1980).

eggs were too small to be retained in the

10

W, T. PETERSON et al.

3.

RESULTS

3.1

Physical and Chemical Data

3.1.1

Temperature-salinity characteristics.

The t e m p e r a t u r e - s a l i n i t y c h a r a c t e r i s t i c s of

the water at our study s i t e are shown in f i g u r e 2.

S a l i n i t y ranged from 34.005 to 34.651

(median = 34.516), temperature from 11.0 to 15.1°C (median = 11.5°C). data,

equatorial subsurface water (>34.4)

our study.

was present at v i r t u a l l y

Based on the s a l i n i t y all

depths throughout

Fresher water was seen at the sea surface on f i v e dates (15 to 18 January) and

at 5m on 24 January.

16

15

LU

14

°°i" "°J'| Q. ~J 12

II

I 34.0

I 34.1

I 34.2

I 34.3

34.4

34.5

34.6

SALINITY

3.1.2

FIG.2.

Temperature versus s a l i n i t y f o r a l l samples collected during the study. S a l i n i t y >34.4 indicates the presence of equatorial subsurface water.

Winds

Three complete cycles of upwelling favourable/unfavourable winds occurred

during our study period (Fig.3).

At the beginning of the time series on 6 January, the

winds were poleward, favouring a r e l a x a t i o n of upwelling. was i n i t i a t e d by l i g h t and 9 January.

The f i r s t

active upwelling event

southerly winds on 7 January which reached maximum i n t e n s i t y on 8

The second active event began on the evening of 16 January, with strong

winds (approximately 15 to 20 knots) occurring on 18 and 21 January. began with strong winds on 26 and 27 January. January, and 22-23 January, when the winds f i r s t

The t h i r d active event

Two relaxations were i n i t i a t e d ,

on 13-14

shifted to the south, then became calm.

Nearshore zone coastal upwelling

(M :E o

11

0.4

03

bl.l Z >O

0.2

oo o3 w n.-

0.0

F(f)

-0.2

E3 z

i

I 5

I lo

I 15 JANUARY

I 20

l z5

I

86

FIG.3. Wind observations made at Concepcion, Chile during the study period. Bars indicate periods of upwelling-favourable winds. Fog occurred inside Coliumo Bay only during relaxations, on 15 and 25 January. Each upwellingfavourable wind event lasted approximately 7 days (7-13 January; 16-22 January), and each event was interrupted by 3 days of relaxation (14-16 January; 23-25 January). 3.1.3

Upwelling events. The effects of the events on temperature, s a l i n i t y , sigma-t,

and oxygen are illustrated in figure 4 as time-depth plots.

Active upwelling is indicated

by the presence of cool (<12.3°C), high s a l i n i t y water (>34.6) of low oxygen concentration (<2.4mi l - I ) at and near the sea surface.

These conditions were observed from 9 through

14 January, 19 through 23 January, and from 27 January until the end of our time series on 31 January. Periods of relaxed upwelling indicated by warm, fresher water with higher oxygen concentration

(>14.2°C, S <34.317, oxygen >5.2mi l - I ) occurred three times (Table

I). TABLE I :

Physical, chemical and b i o l o g i c a l c h a r a c t e r i s t i c s of surface waters during periods of active and relaxed upwelling at our study s i t e of f Dichato, Chile. Data shown are averages f o r three periods of active upwelling (9-14, 19-23 and 27-31 January) and three periods of r e l a x a t i o n , 6-8, 15-18 and 24-26 January 1986). ACTIVE RELAXED

Temperature Salinity Density Oxygen Nitrite Nitrate Phosphate Chlorophyll

12.3 34.501 26.146 2.4 1.1 20.8 2.8 1.3

14.2 °C 34.317 25.625 sigma;t 5.2 ml 1-~ 0.7 ~g-atom I - I 13.8 ~g-atom I " I 2.0 ~g-atgm I - I 12.2 ~g 1" i

W . T . PEIERSONet al.

12

J A N U A R Y

6

I0 , •

i

I .

I .

o~ .+.#z . .

" I.a...l

,.,o

6 I

.

I

t

' # i

sI

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r /

~7

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',..

m..-:--_'~." •

.

6

i }

.3,4.5 . . . .

!

! !

i

I

I

/

\~/:

'

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I

I

. . . .j//~_,,.~;J

~ , ,

'

31

~ i ,,3.~ .

25 l

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51

" '~J

p ,

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"

6

. . . .

•

I

<~6.oj 0

I

\

"<~i.o

•

.

I

.

25

I

,

"/

I

I

'

l

.

.

,

31

I

I

•

I

I

~o:..~

ml I -j 20

, ,

-

re.--,,.

-

?. •

SALINITY 15

iO '

~

°

??~...

1-

-

.

~':o/•

• ~

0

.-"

25 I

"

•

'

I

OXYGEN 15

5/

rl

i

I

>-.'~.

I0

ok,.

5

i

TEMPERATURE °C 15 20 I I i I , l i l.

, o F /

123

i

~... . ""~~ ,,~\.LsJ~-M~,.o / ~ ; .: .%;__t ~ .1 ;_,.o~1,/.

,o t- . ~

w

20

i

'.- ~. . . ~:. .,~~ ./ / ./ .. \ ~. ..

I0 I I

I

o I-

15

15 I

~ . ' < ~~ P. ~ /A\."---Y/. . /,,%," \

,o

1986

,

.

2O I

I

I

I

•i

'/

{o.0-

31

25 I

I

'

i

il

i i~6~/

•

.~,~, /

io 15

>26.0

>260 •

Z3

.

,

,

.

.

SIGMA -T

FIG.4

Time-depth p l o t s of temperature, s a l i n i t y , d e n s i t y (as s i g m a - t ) and oxygen c o n c e n t r a t i o n during the study. A c t i v e u p w e l l i n g occurred 9-14, 19-23 and 27-31 January, as i n d i c ated by the b l a c k h o r i z o n t a l bars.

Even though the t h r e e periods

of

(seven

active

slightly

days),

each p e r i o d

different

second event f i v e of d i f f e r e n t

of

duration.

upwelling-favourable upwelling

The f i r s t

days, and the t h i r d ,

active

winds were about equal

(as defined upwelling

at l e a s t f i v e

days.

in d u r a t i o n

by the hydrography), event

lasted for

six

was of days,

a

the

Periods of r e l a x a t i o n were also

d u r a t i o n than the three days i n d i c a t e d in the wind data, one l a s t i n g f i v e days

(15-1g January) and the o t h e r only two days (24-25 January).

Nearshore zone coastal upwelling

3.1.4

Vertical

Temperature

Gradients. Vertical

13

temperature gradients

between the

sea

surface and the bottom (Z=23m) were very small during active upwelling, indicating complete mixing.

The minimum gradients were 0.8°C at the end of the f i r s t event (on 13 January),

0.2°C in the middle of the second event (on 21 January), and 0.3°C at the beginning of the third event (on 27 January).

The greatest thermal gradients, indicative of a more stable

water column, were seen during relaxation.

They were 3.6°C on 7 January at the end of the

f i r s t relaxation, 3.0°C on 17 January during the second relaxation, and 2.9°C on 24 January during the third relaxation.

Figure 5 shows that the water column was cooler at a l l sampling depths during active compared to relaxed upwelling conditions.

The differences

in temperature with depth between the

active and relaxed states of upwelling were most pronounced w i t h i n the upper 5m of the water column, but below 5m the "active" and "relaxed" envelopes overlapped.

TEMPERATURE

SIGMA-

°C

II

12

13

14

15

11

•

If

I

I

5

~

25.0

°~°c~/'/'"

.5

54.0 ,o

uJ

.

.... ?'"7 "

0

I 5

F\

i

54.5 . . . . .

.

t!

L \io

0

/

o

: I

I0

-

OQDoO

\ 15 -

25

iT=ooeo

23

FIG.5.

26.0

25.5

I0

Temperature, s a l i n i t y , and sigma-t values from a l l dates plotted against depth to i l l u s t r a t e the differences in hydrographic variables between active and relaxed upwelling (0 = active; Q = relaxed).

T

•

.o

26

oo

o~o

14

W . T . PETERSON et al.

3.1.5

Vertical

salinity gradients, S a l i n i t y

10m and only during r e l a x a t i o n (Fig.5).

gradients

only

occurred

within

the

upper

Pronounced differences in s a l i n i t y at each sampling

depth between days of active and relaxed upwelling were only observed at Om and 5m.

At

and below 10m the water tended to be more saline during active upwelling, but the differences were not s t a t i s t i c a l l y 3.1.6

Vertical

significant.

density gradients. The top-to-bottom density gradient is also a good indica-

tor of changes in the state of upwelling. <4].015 sigma-t u n i t s m- I

On dates of active upwelling a density gradient

was observed (Fig.6).

Changes in the v e r t i c a l

density gradient

were correlated with wind stress (Fig.7), with a lag of one day giving the highest correlation coefficient

(r=O.74,

n=19).

A lag of two days was also s i g n i f i c a n t

(r=0.56,

n=19),

but

the c o r r e l a t i o n c o e f f i c i e n t f o r zero lag (r=0.26) was not s i g n i f i c a n t . The density structure of the water column changed markedly and r a p i d l y between active and relaxed upwelling events (Fig.6).

During periods of r e l a x a t i o n the density of the water

was always less than during active upwelling, but the differences were most pronounced w i t h i n the upper 10m (Fig.5) suggesting that the e n t i r e water column was affected by the upwelling process, and that at least the upper 10m of the water column was exchanged between relaxed and active events.

Oxygen. The concentration of oxygen in the lower half of the water column was

3.1.7

low (<1.0ml I - I ) throughout most of our study (Fig.4),

i n d i c a t i n g that the upwelling source

water, the Gunther Current or the ESSW, was always present at depth. Concentrations decreased to <0.2ml

I -I

at the bottom during each of the three active upwelling events,

indicating

shoreward movement of the ESSW during active upwelling. Oxygen concentrations throughout the water column were on average lower during active upw e l l i n g than during r e l a x a t i o n due to photosynthesis in the upper 5m (discussed l a t e r

in

t h i s paper). 3.1.8

Nitrate and nitrite.

Nitrate

concentrations

increased

during

active

upwelling

(Fig.8, Table I ) .

However, at no time were n i t r a t e concentrations low enough to l i m i t phyto-

plankton growth.

The lowest observed concentration was 4.5~M, at Om on 17 January, during

the second r e l a x a t i o n . Nitrite

concentrations w i t h i n the upper 15m tended to be uniform with depth during active

upwelling and to

increase with depth during r e l a x a t i o n

(Fig.8).

Concentrations in deep

water (15 and 23m) were generally high (1.5 to 2.0pM) during both the f i r s t and the second r e l a x a t i o n , nitrite

concentration

and low (
are c o n t r o l l e d

by local

onshore-offshore advection of surface waters.

other times,

biological

active event

suggesting that changes in

processes rather than by simple

Nearshore zone coastal upwelling

~

15

04 ACTIVE

ACTIVE

~_~.03 ~.02 ~ ,01

I0

2O JANUARY

15

25

30

1986

FIG.6. Variations in the v e r t i c a l density gradient (surface and bottom sigma-t values) versus time at the study s i t e . Active upwelling, as indicated by temperature, s a l i n i t y and oxygen c h a r a c t e r i s t i c s , occurred on dates when the v e r t i c a l density gradient was <0.015 sigma-t u n i t s m-1 corresponding to a wind stress of 0.17 dynes cm-2.

N

b"

0.04

<~ v

Z

0.03

W C~

•

~

Y=

- 0 . 0 # 7 3 X -0.023, r =0.7#

r~

(.9

0.02

>-

I-.(f)

001 o

Z

1,1.1 Q I

FIG.7,

I

I

I

0.4

0.2

WIND

STRESS

I

0

I

I

0.2

(DYNES

I

I

I

0.4

CM - 2 )

Vertical density gradient versus wind stress one day e a r l i e r . The correlation is significant (P<0.001).

I6

W.T. PETERSONet al.

JANUARY I0

1986 20

15

: ,. ,. ,. ,.

,

,

,

,,,

I

31

25 I

I

I

1

I

I

I

i

I

0 5

Z

I0 15

~

"

:

"

2~

CHLOROPHYLL I0

6 E

i

0

i

t

I

~g I "~

15 I

I

P

'

20 '

'

I

J

31

25 I ,,,I

I

'

I

o

•

.

5 -r I0 I15 o.. LU a 2:5

;.¢. •

25

•

.

NITRATE I0 I

6

'

I

°I / 5

J 0.5

I0

I

I

1.0

/

I

.

.

IJM

15 I

25

/ .... 20 1

,

,

I

25 I

I

i

i

31 t

"°

L .~

I.O i.o

15 1.5

¢'./~

.

23

NITRITE

FIG.8.

NM

Chlorophyll a, n i t r a t e and n i t r i t e concentrations contoured versus depth-and time f o r the study period• Black h o r i zontal bars indicate periods of active upwelling.

3•2

Biological Data

3•2.1

Chlorophyll.

Four "blooms" were seen during the study period (Fig.8),

r e l a t i o n to the state of the upwelling was not always clearcut. time

series,

during

the f i r s t

relaxation,

we observed a sub-surface chlorophyll maximum

that persisted through the e a r l y stages of the f i r s t did decrease near the end of the l a t t e r transported offshore,

active event. Chlorophyll concentrations

(as one would expect i f

away from our s t a t i o n ) .

January, one day p r i o r to r e l a x a t i o n .

but t h e i r

At the beginning of the

the surface layers were

A bloom began in the upwelled water on 14

During the second r e l a x a t i o n (15-18 January) a bloom

developed which reached a peak of 30ug chl I -I at the sea surface on 17 January.

Chlorophyll

Nearshore zone coastal upwelling

17

concentrations dropped suddenly with the onset of the second active upwelling event, suggesting seaward displacement of the upper 10m of the water column. started,

chlorophyll

concentrations

increased b r i e f l y ,

As the t h i r d r e l a x a t i o n

then declined at the onset of the

t h i r d active event. During the t h i r d period of active upwelling (27-31 January), a subsurface chlorophyll maximum was again observed. The size and taxonomic composition of the phytoplankton were h i g h l y variable. forming diatoms were retained January,

Large chain-

in our 102um mesh zooplankton nets only from 9 through 14

and 29-31 January during the f i r s t

and t h i r d

active upwelling events.

This is

reflected in the chlorophyll s i z e - f r a c t i o n data: on 11-14 January only 15-40% of the chlorophyll passed through a 20um mesh, and on 29 and 31 January only 15% did, whereas on nearly all

other dates between 70 and 100% of a l l

We also observed that Phaeooystis 31 January.

chlorophyll passed the 20um screen (Fig.9).

was conspicuous in samples taken on 11-14, 23-24 and 29-

The bloom represented by the chlorophyll peak on 23-25 January also contained

large numbers of the photosynthetic c i l i a t e

Mesodinium rubrum

(also known as Myrioneota

rubrum) which caused the water to appear red in some places.

100

J

8O E 60

0

V

40 20

5

, 10

I 15

I 20.

I 25

, 30

January FIG.9. 3.2.2

Percentage of t o t a l chlorophyll in c e l l s capable of passing a 20~m mesh screen. Black bars indicate active upwelling.

Protein and Carboyhydrate The concentration of p a r t i c u l a t e protein and carbohydrate

w i t h i n the upper 5m of the water column was highest during r e l a x a t i o n of upwelling (averages of 850 and 570~g I - I respectively) compared to means of 480 and 320~g 1-1 during the active upwelling events

(Table 2).

Figure 10 shows that p a r t i c u l a t e

protein

concentrations

in

the surface water tracked the peaks of phytoplankton biomass closely, but that carbohydrate bore l i t t l e (Table

2)

apparent r e l a t i o n to phytoplankton biomass. showed s i g n i f i c a n t

relationships

However, l i n e a r regression analysis

between p a r t i c u l a t e

protein

and c h l o r o p h y l l ,

and p a r t i c u l a t e carbohydrate and chlorophyll both f o r the upper 5m and f o r 15m. For p a r t i c u -I late protein the y - i n t e r c e p t was very high, 450~g 1 , which probably indicates a large heterotrophic biomass, including copepod n a u p l i i , protozoa and bacteria, as well as d e t r i t u s . The y - i n t e r c e p t s f o r the carbohydrate regressions were 300 and 140ug I - I f o r the upper 5m and 15m, respectively.

These values again suggest that non-phytoplankton p a r t i c u l a t e matter

comprised a substantial proportion of the t o t a l . JPO

20:I-B

18

W . T . PETERSON et al.

TABLE 2:

Upper. Linear regressions of the relationships between particulate protein (PRO) and carbohydrate (CARBO) versus chlorophyll. Lower, Average concentration of particulate matter ur-d-u-rTng active upwelling and relaxation loQ ~ upwelling. All concentrations have units of ~g - . The 15 January data were excluded from the 15m linear regressions, and an anomalously high P/C ratio of 6.8 on 23 January was excluded from the 5m P/C ratio. 15m s t r a t u m

Upper 5m of water column PRO

=

(R 2 = 0 . 7 9 ,

CARBO =

PRO

432.2 + 2 6 . 1 C H L - A ,

(R 2 = 0 . 5 9 ,

(R 2 = 0 . 5 0 ,

n = 15)

CARBO =

307.1 + 15.2 CHL-A n = 15)

458.0 + 90.0 CHL-A

139.4 + 77.8 CHL-A (R 2 : 0 . 6 4 ,

PROTEIN CARBOHYDRATE P/C R a t i o

n : 14)

15m s t r a t u m

Upper 5m of water column ACTIVE

n = 14)

RELAXED

ACTIVE

RELAXED

848

623

590

323

565

314

233

1.57

1.77

2.47

2.76

476

Nearshore

>, tt-,

2

o

I,.::L

-

i,j

zone coastal upwelling

19

15

2520. 15 10 5

10 5

1.2-

~e)

1.0.~

0,8-

-.-i

P 0..

0.6-

--4

0.4-

E

0.2

-t I I

i

f

I

,

I

10

15

20

25

" "~

1.2t c)

"~ ¢..,

0.8--

2

0 .a

I

,

I

i

10

15

20

I

1.0-

0.60.4-

(")

¢:m

E

0.2-

25

January

FIG. IO. Concentrations of chlorophyll, protein, and carbohydrate in surface (pooled 1,3 and 5m samples; a,b & c) and deep (15m; d,e & f) particulate material. Black bars indicate active upwelling. The r a t i o protein:carbohydrate (P/C) is a good i n d i c a t o r of the physiological state of phytoplankton

(BARLOW, 1982a).

P/C should be low f o r

phytoplankton growing under conditions

of high l i g h t and high n u t r i e n t concentrations and high under conditions of low l i g h t - h i g h nutrients.

This expectation was met during the present study: the r a t i o was lowest during

active upwelling f o r p a r t i c u l a t e matter from the upper 5m (average P/C=I.57)

and highest

during relaxed upwelling at the 15m sampling depth (average P/C=2.53). 3.2.3

Phytoplankton growth rates and ~abelling patterns.

Changes in primary productivity

and chlorophyll concentration at the surface (1,3,5m integrated) tracked each other closely (Fig. 11).

The lowest p r o d u c t i v i t i e s and chlorophyll

concentrations occurred during active

upwelling and the highest occurred during the early part of the r e l a x a t i o n episodes. The c o r r e l a t i o n between chlorophyll and primary production was highly s i g n i f i c a n t :

20

W . T . PETERSON et al.

T

50-

A

20

r-

15

::k

10

25-

5 I

,

I

I

surface

30-

D 15

_../

2

20-

Ideep

10

t-

O.

10

5

o .C:

I

I

10

FIG.11

15

20

25

1'0

January

I 15

, 20

l 25

Primary p r o d u c t i v i t y and chlorophyll concentrations in surface (pooled I, 3 and 5m samples; a & b) and deep (15m; c & d) water. Open c i r c l e s represent <20~m f r a c t i o n s ; f i l l e d c i r c l e s are t o t a l s . Black bars indicate active upwelling.

PRODUCTIVITY = 2.81 CHL - 0.045 (r = .93, <200~n f r a c t i o n , 17 January excluded from regression). The highest p r o d u c t i v i t y within the upper 5m of the water column (57mg C m-3 h- l ) on 15 January during the second r e l a x a t i o n . 16-18 January. After

occurred

This peak was followed by high production on

The peak in biomass (33~g chl 1- I )

occurred two days l a t e r , on 17 January.

a period of lower production and biomass during the second active upwelling event,

a second peak occurred on 24 January, when both carbon f i x a t i o n and the concentration of chlorophyll reached maxima. ivity

For surface samples during r e l a x a t i o n chlorophyll and product-

in the <20um s i z e - f r a c t i o n were very close to the values in the <200um size f r a c t i o n ,

i n d i c a t i n g that most of the phytoplankton was in the <20um f r a c t i o n . was on 24 January when a large Mesodinium rubrum

The only exception

bloom caused most of the production to

be in the 20-200 m size f r a c t i o n . Daily v a r i a t i o n s

in

the

assimilation number (carbon f i x a t i o n per unit

not c l o s e l y related to the state of upwelling.

chlorophyll)

were

In both the <200um and <20um size f r a c t ions

N e a r s h o r e zone coastal upwelling

21

the highest a s s i m i l a t i o n numbers were found on 13, 20, 23 and 27 January, a l l dates of a c t i v e upwelling

(Fig.12).

and r e l a x a t i o n .

Low a s s i m i l a t i o n

numbers were observed during both a c t i v e upwelling

A s s i m i l a t i o n numbers did not increase during r e l a x a t i o n because c h l o r o p h y l l

concentrations

and carbon f i x a t i o n

rates

increased simultaneously.

Assimilation

numbers

were only high when c h l o r o p h y l l concentrations were low.

a) 6 ¸

6-

4

4-

I

I

2-

2 ~

t0

I

(J O~

E

. . . .

I

. . . .

I

. . . .

0

....

< 20pm

b)

o~

I

d)

< 20pm

8

E 6

4

20

I ....

10

I ....

15

'

I'

I

'

i

o

,

I ....

I . . . . . . . .

10

25

20

15

i ....

20

25

Jonuory FIG.12

Carbon f i x a t i o n (Fig.ll),

A s s i m i l a t i o n numbers (photosynthesis per u n i t c h l o r o p h y l l a) f o r surface (pooled 1,3 also 5m samples; a&b) and deep T15m; c&d) water. A & c are t o t a l s ; b & d are <20~m f r a c tions. Bars i n d i c a t e a c t i v e upwelling.

rates and c h l o r o p h y l l concentrations were lower at 15m than at the surface

except on 10 and 11 January,

when c h l o r o p h y l l

The highest c h l o r o p h y l l concentration (18.3ug chl (23.2mg C m-3hr - I ) sustained f o r

occurred on 15 January.

1- I )

concentration

c e n t r a t i o n of c h l o r o p h y l l .

There was a second,

rates on 24 January, but only a s l i g h t

Values f o r

the

rate

These high production and biomass values were

only one day, u n l i k e the case at the surface.

peak in the 15m carbon f i x a t i o n

at 15m was higher.

and the highest carbon f i x a t i o n

<20~m f r a c t i o n

smaller

increase in the con-

were s i m i l a r

to

those f o r

the

<2OO~m f r a c t i o n except on 15 January, when they were considerably lower. Assimilation

numbers in the

<200~m samples from 15m (Fig.12)

increased from a low of 0.2

on 11 January to more than 5.5 on 25, 27, and 29 January, in a manner unrelated to the s t a t e of upwelling.

The a s s i m i l a t i o n numbers of the <20~m size f r a c t i o n

than those of the <200~m f r a c t i o n ,

e s p e c i a l l y on 13, 15 and 20 January.

were g e n e r a l l y higher

22

W. T, PETERSONet al.

Data on incorporation of carbon into proteins,

lipids,

low molecular weight compounds, and

polysaccharides in the surface waters are summarized in Table 3. differences in l a b e l l i n g patterns between upwelling events.

There were no consistent

Over a l l

samples, protein

in-

corporation varied between 15 and 50% of the incorporated labelled carbon, the l i p i d and low molecular weight compounds (LMWC) ranged between 25 and 65%, and the polysaccharide f r a c t i o n accounted f o r 12 to 58% of the t o t a l

production.

During the second bloom (14-18 January)

most of the carbon in both size f r a c t i o n s was incorporated into the l i p i d incorporation ranging from 67% on 15 January to 41% on 17 January.

and LMWC pools,

During the t h i r d bloom

(24-25 January) the largest share (45%) of the label in the<2OOpm size f r a c t i o n was detected in the polysaccharide f r a c t i o n ,

but in the <20vm size f r a c t i o n more label was detected in

the l i p i d and LMWC f r a c t i o n s (42%). TABLE 3: P a r t i t i o n i n g of photosynthetic 14C incorporation into d i f f e r e n t biochemical f r a c t i o n s ; Mean ± S.E.(n). U = active upwelling; R = relaxed upwelling; LMWC = low molecular weight compounds. Surface sample consisted of water pooled from c o l l e c t i o n s at I, 3 and 5m depths. Values are percent of the t o t a l incorporation. Protein SURFACE <200vm (I+3+5m) <201am DEEP (15m)

Polysaccharides

Lipids + LMWC

U R U R

37.9 36.3 31.7 29.8

-+ 2.9 ± 7.9 +- 2.2 ± 7.4

(7) (5) (7) (3)

25.8 30.8 24.4 22.0

± 5.6 ± 7.3 ± 2.2 -+ 6.2

(7) (5) (7) (3)

36.3 32.9 43.9 48.2

± 6.4 ±q2.0 ± 3.5 ± 7.0

(7) (5) (7) (3)

<2001am U R <201am U R

39.4 28.4 36.7 35.5

-+ 3.2 ± 6.5 ± 4.1 +- 4.3

(7) (4) (7) (3)

25.1 28.4 23.5 20.1

+ ± ± ±

(7) (4) (7) (3)

35.5 43.2 39.9 44.4

± ± ± ±

(7) (4) (7) (3)

2.7 4.6 3.8 1.8

4.0 6.5 4.0 3.5

There was no apparent pattern to the p a r t i t i o n i n g of photosynthate into the d i f f e r e n t biochemical pools in the 15m samples e i t h e r .

Approximately 30% of the carbon went into each

of the measured pools in each size f r a c t i o n . 3.2.4

Distribution and abundance of zooplankton.

The dominant copepod species (in rank

order of abundance) were Paraoalanus parvus,

Centropages brachiatus, Oithona spp., Aoartia

tonsa, Oncaea spp. Calanoides patagoniensis,

and Calanus chilensis (Table 4). Other copepods

that were encountered included

Rhincalanus nasutus(5 of 20 samples), Calanus tenuicorniss.l.

(5/20), Calocalanus pavo (~201, a Microcalanus species (13/20), Drepanopus forcipatus (I0/20)~ Heterostylites spp. (3/20), and in one sample each~ Scolecithricel~a, Heterorhabdus, Pleuromamma, Aetideus

and a Corycaeus species.

Figure 13 shows that there were large f l u c t u a t i o n s in the abundances of the dominant species. Changes in abundance of upwelling, with

A c a r t i a tonsa

were closely related to changes in the state of the

low abundances being observed during active upwelling and high abundances

during periods of r e l a x a t i o n .

The same pattern was seen f o r two other species

patagoniensis and Paraoalanus parvus)

(Calanoides

during two upwellin9 events. For the other four dominant

species, there were no consistent r e l a t i o n s h i p s between upwelling and abundances.

This was

Nearshore zone coastal upwelling

23

,ooof 5

0

.,ooll

0

~

6,000

C ENTROPAG E S

4,000 2,0

L

"?'E

_

'

.....

2,000

1,0OO

4,000 2 ,ooo

10

15

20

25

30

January FIG.13 Changes in abundance versus time for the dominant species of copepods. Black bars indicate active upwelling.

24

W.T. PETERSONet al.

TABLE 4.

Average abundance of the seven dominant copepod species which occurred at our study s i t e during January 1986.

Copepod Species

Average Abundance Nos m-3

12,009

Paracalanus parvus Centropages brachiatus

2,130

Oithona spp

1,589

Acartia tonsa

1,332

Onoaea spp

869

Ca~anoides patagoniensis

594

Calanus chilensis

288

Taxa

Calanoid copepods

Active Upwelling

Relaxed Upwelling

Nos m-3

Nos m-3

10,661

24,983

912

1,703

Cyclopoid copepods

t e s t e d by c o r r e l a t i n g day to day changes in water column s t a b i l i t y (Y),

using data shown in f i g u r e

patagoniensisand

(i.e.

6 and f i g u r e

13.

Abundance of

Paracalanus parvuswas s i g n i f i c a n t l y

with the v e r t i c a l Y = I03,358X Y : 31,915X

density gradient).

r : 0.51,

n = 19,

for

of Paracalanus

Acartia tonsa

Paracalanus parvus

abundance with s t a b i l i t y

January data were excluded from the c a l c u l a t i o n ,

were:

Calanoides patagoniensis

Y = 489,054X + 2,233, r : 0.48, n = 19, f o r The c o r r e l a t i o n

Acartia tonsa, CaZanoides

c o r r e l a t e d with water column s t a b i l i t y

Equations and c o r r e l a t i o n c o e f f i c i e n t s

- 535, r = 0.80, n = 19 f o r + 0.4,

(X) with copepod abundance

was g r e a t l y

improved when the 11

yielding:

Y = 607,612X + 1,750, r = 0.76, n = 18. C o r r e l a t i o n s f o r the o t h e r f o u r species were not s i g n i f i c a n t .

The r e s u l t s of these analyses

suggest the hypothesis t h a t A. tonsa, C. p a t a g o n i e n s i s and P. parvus~re probably most abundant within

the surface Ekman l a y e r

(i.e.

w i t h i n the upper 10m of the water column) and t h a t ob-

served l o c a l changes in abundance were due p r i m a r i l y to zonal advection. Oxygen c o n c e n t r a t i o n u p w e l l i n g zones.

is

also known t o a f f e c t

the d i s t r i b u t i o n

and abundance of copepods in

JUDKINS (1980) and BOYD, SMITH and COWLES (1980) have shown t h a t o f f Peru

Calanus chilensis and Centropages brachiatus

are f a r more abundant in water of >O.5ml I - I

Nearshore zone coastal upwelling

oxygen concentration.

25

At our study s i t e , although the upper 5m of the water column was well-

oxygenated, the lower layers had oxygen concentrations that were usually
during active upwelling (Fig.4).

I - I , with

Therefore, we sought possible

c o r r e l a t i o n s between oxygen concentration and copepod abundances.

The abundances of six

of the seven dominant species were p o s i t i v e l y correlated with the concentration of oxygen in the lower layers of the water column (average of the 15m and 23m values). and t h e i r c o r r e l a t i o n c o e f f i c i e n t s were: Calanoides p a t a g o n i e n s i s , r = 0.77,

Centropages braohiatus, r = 0.64,

r = 0.57, and Oithona, cantly to

r : 0.53.

Paraca~anus parvus

r

r = 0.87, =

The species A c a r t i a tonsa

0.62, Calanus chilensis,

The Calanus c h i l e n s i s c o r r e l a t i o n was improved

signifi-

r= 0.81 when the 21 January data were excluded. Onoaea was uncorrelated with oxygen

(r = 0.01).

We conclude that even though onshore-offshore Ekman transport explains the v a r i -

ations in abundance of some of the copepods, the fact that oxygen was correlated with most species suggests that the behaviour of i n d i v i d u a l s may be an important factor as well. Animals may be moving v e r t i c a l l y upward and away from low-oxygen water (cf JUDKINS, 1980), a process which contributes to v a r i a b i l i t y in abundance in a manner somewhat independent of zonal advect ion . 3.2.5

Gut fullness of copepods. Gut fullness

chilensis

and

Centropages brachiatus.

and feeding rates were studied in CaZonus

Changesin the gut fullness of i n d i v i d u a l s of

both species collected from the upper 10m of the water column appeared uncorrelated with changes in chlorophyll

concentrations (Fig.14).

For example,

two pronounced chlorophyll

peaks occurred during the study period, on 17 and 24 January, but peaks in copepod gut fullness occurred only p r i o r to 14 January, when "net" diatoms were present at our study s i t e during the f i r s t

active upwelling event (10-14 January).

f u l l n e s s of Calanus ohilensis samples of

In the deeper water (I0-23m), the gut

did f o l l o w changes in chlorophyll concentrations.

Too few

were obtained to y i e l d any r e l a t i o n s h i p between gut fullness and

Centropages

chlorophyll concentration. The gut f u l l n e s s of Centropages braahiatus varied between 0.14 and 14.2ng chl equiv.female-I in the upper 10m and between 0.48 and 4.65ng chl equiv, female- I gut f u l l n e s s of Calanus chilensis

in the I0-23m layer.

varied between 0.3 and 9.5 ng chl. equiv, female- l

The in

the upper 10m and 0.21 and 8.86ng chl. equiv, female-I in the 10-23m layer. As Table 5 shows, statistically

s i g n i f i c a n t r e l a t i o n s h i p s between gut fullness and chlorophyll concentrations

were apparent only f o r

Calanus o h i l e n s i s

in the deeper waters.

Gut evacuation was rapid in both species; ehilensis

and 0.037 min -I f o r C. braohiatus

respectively. > 0.05).

WYMAN, 1983),

equivalent to gut passage times of 28 and 27 min

Analysis of covariance (ANCOVA) of the gut evacuation rates indicated that

there was no s t a t i s t i c a l l y p

the gut evacuation rates were 0.035 min -I f o r C.

detectable difference between the two species (F = 0.03; 1,12 df;

Copepod gut evacuation rates are p o s i t i v e l y related to temperature (DAGG and and since in s i t u

temperatures were usually below our 14°C laboratory incu-

bation temperature, our rates should be considered maximum values f o r the study period.

26

W . T . PETERSON et al.

150~E

100100 °

o'~

E 50-

50-

10-

10-

Calanui chllensl$

-/k

0

5-

i

t

(.~ ¢m r" 10U) Ul (1) r-

15-

Centropmges brachlatus

10-

5-

(3

5-

I

10

15

i

20

25

10

J

,

15

20

i

25

January

FIG.14.

Variations in copepod gut fullness (ng chlorophyll a equivalents per adult female) with time for animals ~ollected in the upper 10m ( l e f t hand panels) and below 10m ( r i g h t hand panels), compared to chlorophyll concentrations integrated from I-I0m (upper l e f t panel) and I0-23m (upper r i g h t panel). Means and ranges are shown where duplicate samples were taken ( f i l l e d circles; ranges sometimes smaller than symbols). Black bars indicate active upwelling.

Nearshore zone coastal upwelling

TABLE 5:

27

UPPER: Regressions of copepod gut fullness on in situ chlorophyll concentrations. LOWER: Mean ingestion rates and clearance rates, calculated from gut evacuation rates and chlorophyll concentration.

SPECIES

REGRESSION EQUATION

r

R2

F

C. chilensis

Y = 2.92 + 0.230X

0.08

0.64

O. 08 NS

Y = 1.19 + 0.536X

0.57

32.50

9.77 **

Y = 3.55 - 0.28X

-0.25

6.25

I . 35 NS

Y = 1.780 - O.08X

-0.18

3.24

O. 39 NS

(O-10m, n = 14) C. ehilensis

(I0-23m, n = 22) C. brachiatus

(O-lOm, n = 21 C. brachiatus

(I0-23m, n : 13)

r: correlation coefficient; * * : p <0.01; F: F s t a t i s t i c

R2: coefficient of determination (%)

Ingestion Rate (ng chl. equiv, fem-I hr - I )

SPECIES

O-10m

I0-23m

C. chilensis

7.0

6.3

C. brachiatus

5.9

3.4

Clearance Rate (ml fem-1 hr " I ) O-10m

I0-23m

C. chilensis

4.9

2.9

C. brachiatus

4.3

2.4

Ingestion

and clearance r a t e s

concentration) dent of

( c a l c u l a t e d from gut f u l l n e s s ,

gut clearance and c h l o r o p h y l l

were h i g h l y v a r i a b l e and, except f o r Calanus o h i l e n s i s

chlorophyll

concentration.

ohilensis and Centropages brachiatus

Table 5 shows t h a t

from 15m, were indepen-

the average clearance r a t e s f o r c.

were about equal, 110mi female-ld -I when feeding within

the upper 10m of the water column and about 60ml female-ld -I when feeding within the lower 13m (assuming no diel periodicity). 3.2.6

Copepod Fecundity.

Figure

15

shows that

fluctuations

in the rates of egg production of three of the species studied (Acartia tonsa, Ca~us ohi~nsis and Calano~des patagoniensis) were correlated with chlorophyll concentration.

Egg production

was high during relaxed upwelling when phytoplankton was abundant and low during active upwelling when phytoplankton was greatly reduced. duction occurred during phytoplankton blooms; for

For A. tonsa

and C. chiZensis high egg pro-

C.patagoniensis

the i n i t i a l burst in egg

production in mid-January lagged the bloom by 2-3 days but the second burst in egg production observed in late January coincided with the phytoplankton bloom.

28

W . T . PETERSON et al.

3O A c a r t l a tonsa

R

59.2

2O 10-

7 chllensls

0

"0 i

20-

E 10(/J

60

Calanoldes patagoniensls

40

20

3O t_.,

CHLOROPHYLL

20

~L 10

I

10

I

25

20

15

30

January FIG. 15.

Temporal v a r i a t i o n s

of c h l o r o p h y l l

w i t h i n the upper 5m

of the water column, and egg production by Aoartia tonsa, Calanus chi~ensis and Ca~anoides patagoniensis. Fecundity data f o r Calanoides are from the egg r a t i o method ( s o l i d l i n e ) and from 24h i n c u b a t i o n s (open c i r c l e s ) . Data f o r A c a r t i a and Calanus are from 24h i n c u b a t i o n s . Black bars i n d i c a t e a c t i v e u p w e l l i n g .

Egg production and c h l o r o p h y l l were l i n e a r l y (Fig.16).

Correlations

p a t a g o n i e n s i s were not

r e l a t e d f o r A c a r t i a tonsa and Calanus c h i ~ e n s i s

of egg p r o d u c t i o n with c h l o r o p h y l l significant

because of

the

time

lag

concentration for

Calanoides

between the mid-January bloom

and egg p r o d u c t i o n discussed above. Egg p r o d u c t i o n by a d u l t female aentropages b r a c h i a t u s was c o r r e l a t e d with c h l o r o p h y l l c o n c e n t r a t i o n but only at the P = 0.08 l e v e l : EGGS = 1.21 CHL + 8.08; r = 0.44; n = 20 Egg p r o d u c t i o n by a d u l t female Calanus c h i l e n s i s w a s h i g h l y c o r r e l a t e d with gut f u l l n e s s : EGGS = 1.9 GUT FULLNESS - 0.18; r = 0.69, n = 14 o m i t t i n g 24 January data but the same c o r r e l a t i o n f o r Centropages

was not s i g n i f i c a n t .

Nearshore zone coastal upwelling

30- A

29

B o

"0

o

70J -~ O

z~

E

r:0.63, I

10

n:19

I

r=0.69,

I

210

~0

I

5

ChLorophyLL (/~g L-~)

10

Gut fuLLness (ng femaLe-~)

o / 1

D

°

.o

o

/

1o-

/

o

~-

o

o o

o

n--14

I

~o n o

Acartla r:0.56,

~'o

I tO-/oI

lonsa n:20

2%

~

40

ChLorophyLL (#g L-i)

Clntroplgll o

o

~'o

r:0.45,

2'o

brlchlltul n:20

~'o

'

ChlorophyLL (/~g L-I)

FIG. 16 Scatter diagrams of egg production versus chlorophyll (upper 5m of the water column) for Calanus chilensis (a), Acartia tonsa (C), and Centropages braohiatus (d), and egg production versus gut fullness for C.ohilensis. (b). Filled circles in (b) were not included in the regression analysis. Regression equations are: (a) EGGS = 0.57 CHL + 3.65 (b) EGGS = 1.8 GUT - 0.20 (c) EGGS = 0.81 CHL + 4.72 (d) EGGS = 1.21 CHL + 8.08.

Paracalanus parvus

produced eggs only during the f i r s t

last day. Calanoides patagoniensis

few days of our study, and on the

only produced more than 5 eggs d"I in the incubations

on three dates (6, 24 and 31 January, when 25, 12 and 18 eggs were produced each day). both of these copepods there may have been uncontrolled containment artifacts cussion).

For

( s e e Dis-

30

W . T . PETERSON et al.

4.

DISCUSSION

Characteristics of the Nearshore Upwelling System

4.1

On a d a i l y time scale the hydrography of the nearshore waters o f f central Chile showed a high degree of v a r i a b i l i t y . episodic.

It

was clear that the coastal

upwelling was wind driven and

The winds observed in January 1986 were r e l a t i v e l y gentle, with wind stress seldom

exceeding 0.4 dynes cm-2,

s i m i l a r to Peru at 16°S (BRINK, JONES, VAN LEER, MOOERS, STUART,

STEVENSON, DUGDALE and HEBURN, 1981).

The hydrographic f i e l d responded to changes in wind

d i r e c t i o n with a lag of one day. This is expected from Ekman theory: the response time should be near the i n e r t i a l period, which f o r the l a t i t u d e of Dichato (37°S) is 20 hours. -I Chlorophyll concentrations observed o f f Dichato ranged from I to 30~g 1 , s i m i l a r to values commonly observed o f f

Oregon (SMALL and MENZIES, 1981; HOLBROOK and HALPERN, 1974), Peru

(MAClSAAC, DUGDALE, BARBER, BLASCO and PACKARD, 1985), and the southern Benguela (BROWN and HENRY, 1985) but higher than the 2 to 10 ~g I -I reported f o r Baja C a l i f o r n i a by WALSH, KELLEY, WHITLEDGE, MACISAAC and HUNTSMAN (1974). and ranged from 18 to 57 mg C m-3 h"I f o r Oregon and Peru. chl-lh -I

Primary p r o d u c t i v i t y was highest during r e l a x a t i o n (mean = 40mg C m-3h- I )

s i m i l a r to values reported

Assimilation numbers in our study ranged between 0.5 and 7.9 mg C mg

with a mean of 3.5 during active upwelling and 2.8 during r e l a x a t i o n .

These are

low compared to other areas, such as Peru (during 1977) and NW Africa, f o r which ranges of 4 to 7, and 3 to 7 mg C mg c h l - l h - I PACKARD (1985)

were reported by MAClSAAC, DUGDALE, BARBER, BLASCO and

and HUNTSMAN and BARBER (1977)

respectively,

but about the same as

those

reported for Baja C a l i f o r n i a (mean of 1.9 from WALSH, KELLEY, WHITLEDGE, MACISAAC and HUNTSMAN, 1974), Oregon (I to 5 by SMALL and MENZIES, 1981) and Peru during 1976 (range of I to 3 mg C mg c h l - l h -I by HUNTSMAN, BRINK, BARBER and BLASCO, 1981). The concentrations of p a r t i c u l a t e protein for

at our station were higher than values reported

the Peruvian upwelling system (GARFIELD, PACKARD and CODISPOTTI, 1979).

May 1977 a mean of 334 ~g I "I

Off Peru in

(range 28-1157) was found in the surface layers compared to

an average of 500 and 800pg I - I during active upwelling and r e l a x a t i o n r e s p e c t i v e l y at our study s i t e .

Linear regression of protein

slope of 64 which compares f a i r l y

(Y) on chlorophyll

(X) in t h e i r data produced a

well with our data (slope = 26.1 for samples from the upper

5m of the water column and slope = 90 f o r samples from 15m). The concentration of p a r t i c u l a t e carbohydrate at our station

was about twice as high as reported for the northwest A f r i c a

upwelling system by HITCHCOCK (1977). phyll from

was 33 o f f Northwest A f r i c a ,

The slope of the regression of carbohydrate on chlorointermediate between our observed slopes of 15 (samples

the upper 5m) and 78 (samples from 15m).

The p a r t i t i o n i n g

of f i x e d carbon into d i f f e r e n t

to determine the effects BARLOW (1982b)

biochemical end products was investigated

of the upwelling cycle on the physiology of the phytoplankton.

described carbon assimilation patterns

Benguela Current,

reporting

in upwelled water in the

that polysaccharide and protein

southern

synthesis were highest during

periods of active phytoplankton growth, and that most of the protein synthesis occurred at

Nearshore zone coastal upwelling

night.

31

At the peak of a bloom he found that the 14C assimilation rates were lower and that

a higher percentage of the label was found in the l i p i d f r a c t i o n . the same pattern during the spring bloom in Narragansett Bay.

HITCHCOCK (1978) observed

We also saw t h i s pattern in

that there was a decrease in polysaccharide incorporation in the upper 5m and a concomitant increase in l i p i d bloom occurred.

incorporation during 10 to 16 January when the "net plankton"

(= diatom)

No other patterns were observed, possibly because the second and t h i r d up-

welling events were too b r i e f

and too strong to allow any long-term physiological changes

in the phytoplankton to occur.

An a l t e r n a t i v e explanation is that Phaeooystis

and other

nanoplankton which prevailed during the second and t h i r d relaxations had a d i f f e r e n t physiological response than the large diatoms which were present during the f i r s t

relaxation.

The copepod fauna encountered at our study s i t e was t y p i c a l of the open coast (as indicated by the dominance of Paraoalanus parvus),

rather than of coastal embayments, which are domin-

ated by A o a r t i a tonsa and Drepanopus f o r o i p a t u s

(ARCOS, 1975).

Most of the dominant copepod

species found o f f Dichato were the same as those reported f o r the Peruvian upwelling system by SMITH, BRINK, SANTANDER, COWLES and HUYER (1981) GEYNRIKH [=HEINRICH] (1973).

JUDKINS (1980), MIKHEYEV (1977)

and

The only differences between our observations and those at

16°S o f f Peru were that we did not catch any Eucalanus inermis, and Calanoides patagoniensis, common at our s t a t i o n , has not been reported f o r Peruvian waters. The abundances of copepods at our study s i t e were as high as, or higher than those at other eastern P a c i f i c coastal upwelling regions.

The range in abundance of a l l copepods combined

(1,000 to 46,400m-3) was s i m i l a r to that observed by PETERSON and MILLER (1975) during the June-September upwelling season at t h e i r nearshore station (water depth = 20m) o f f the Oregon coast (1,023 to 51,400m-3).

This comparison was possible because the mesh of the plankton

net used in the Oregon study was nearly i d e n t i c a l to that used o f f Chile (116um mesh versus 102 ~m).

Overall mean abundances were 16,354m-3 o f f Dichato compared to 16,344m-3, 16,196m"3

and 5,082m-3 o f f Oregon during the 1969, 1970 and 1971 upwelling seasons.

Abundances o f f

Peru during March-April 1976 (SMITH, BRINK, SANTANDER, COWLES and HUYER, 1981) were considerably lower, t o t a l l i n g no more than 50,O00m-2 over a 50m water column, equivalent to 1,000m-3. The nets used in t h e i r study were 300~m mesh which may p a r t l y explain the difference.

SMITH,

BOYD and LANE (1981) reported abundances of "small calanoids" ranging from 1,000 to 10,O00m-3 in November 1977 using 158~m mesh nets.

JUDKINS (1980), using nets of 100~m mesh, found

approximately 5,000m"3 each of Paracalanus parvus, Oithona

and Centropages brachiatus,

and approximately 80m-3 of Calanus c h i l e n s i s in A p r i l 1977. Our measurements of gut f u l l n e s s of Calanus chilensis and Centropages brachiatus were s i m i l a r to those reported by BOYD, SMITH and COWLES (1980) f o r Calanus ohilensis, Centropages brachiatus

and Eucalanus inermis

from the Peruvian upwelling system.

stomach f u l l n e s s f o r bothC, o h i l e n s i s (from 0 to 8 ng animal - I ) As with our study, contents and of

The range in values of

from Chile and Peru was i d e n t i c a l

with most values w i t h i n the range of about I to 3 ng animal - I

BOYD, SMITH and COWLES (1980)

in situ

the regression

and C. b r a e h i a t u s

found a l i n e a r r e l a t i o n s h i p between gut

chlorophyll concentration only f o r

C. o h i l e n s i s

of gut contents (Y) on chlorophyll concentration

although the slopes (X) were considerably

32

Nearshore zone coastal upwelling

different:

0.54 (Chile)

versus 1.32 (Peru).

and chlorophyll f o r C e n t r o p a g e s b r a c h i a t u s t h i s copepod is omnivorous.

The lack of c o r r e l a t i o n between gut f u l l n e s s led BOYD, SMITH and COWLES (1980) to suggest that

Based on our gut contents data and the fecundity data discussed

below, we would agree. Egg production rates for Calanus chilensis, Centropages brachiatus, Calanoides patagoniensis were f a i r l y

well

correlated

with

Acartia

chlorophyll

highest rates during blooms associated with r e l a x a t i o n of upwelling. from b r i e f periods of high fecundity,

seen on 24 January during the Mesodiniu~n on 6,

bloom.

The highest rates f o r Calanus

January during the Mesodinium

rates of 46 and 50

bloom.

and on 24

Maximum egg production rates f o r these four species

closely related forms the maximum observed rates

100 eggs d -I f o r Centropages typicus Acartia

were about

14, 15 and 24 January, each during periods of r e l a x a t i o n when

were observed on 20 January, two days f o l l o w i n g the second r e l a x a t i o n ,

are not known but f o r

dates.

(95 eggs female-ld - I ) andAcartia (60 d - I ) were

chlorophyll values were r e l a t i v e l y high; for Calanoides patagoniensis eggs d -I

with

For a l l species, apart

egg production was f o o d - l i m i t e d on nearly a l l

Highest egg production rates byCentropages 20 eggs female-ld - I ,

and

tonsa

concentration,

are approximately

(DAGG, 1978), 40-65 eggs d- I f o r estuarine forms of

t o n s a (DURBIN, DURBIN, SMAYDA and VERITY, 1983; SULLIVAN and RITACCO, 1985;

and PETERSON, 1986; BELLANTONI and PETERSON, 1987), 19-24 eggs female-ld - I f o r

BECKMAN Calanus

marshallae (PETERSON, 1980), and 70 eggs d-I f o r Ca~anoides carinatus (80RCHERS and HUTCHINGS

1986). Food q u a l i t y can also a f f e c t fecundity.

However, the protein and carbohydrate data indicate

that food q u a l i t y was uniformly high throughout the study period.

The r a t i o of protein to

carbohydrate in the p a r t i c u l a t e organic matter was always >1.0 i n d i c a t i n g that the phytoplankton was " p h y s i o l o g i c a l l y young" ( f o l l o w i n g SAKSHAUG and MYKLESTAD, 1973); i . e . d i v i d i n g in the presence of an adequate supply of n u t r i e n t s . tioning

Our measurements of the p a r t i -

of carbon into d i f f e r e n t biochemical end products provide additional evidence that

the phytoplankton was not n u t r i e n t - l i m i t e d protein,

rapidly

l i p i d s and carbohydrates.

since carbon was p a r t i t i o n e d

about equally into

Cells stressed by n u t r i e n t depletion tend to synthesise

a greater percentage of storage products such as l i p i d s and polysaccharides rather than protein (see MORRIS, 1981). Fecundity of food.

Centropages brachiatus

may also have been l i m i t e d by a shortage of metazoan

To test t h i s hypothesis, one experiment was conducted (on 31 January) in which small

calanoids were added to some of the experimental containers at a concentration of 80 1- I . Egg production in these bottles

was compared to egg production in a standard incubation.

Egg production with added copepods as food was 40.4 eggs female-ld - I compared to 1.9 on phytoplankton alone, suggesting that carnivory was important f o r c. b r a o h i a t u s . Egg production of Acartia tonsa was probably l i m i t e d by temperature rather than food.

AMBLER

(1985) found maximum rates of egg production of an estuarine v a r i e t y of t h i s species to be 20 eggs d "I at 15°C, compared to 40 and 60 eggs d- I at 19° and 24°C respectively.

W. T. PEI'ERSON et al.

Paraca~anus parvus

For B. parvus,

and Calanoides patagoniensis

33

seldom produced eggs during the incubations.

we hypothesize that adult females of this species have some special diet ar y

requirement not met in our experiments; large numbers of eggs ( >20 eggs female-ld - I )

were

produced only on 6-9 January and 31 January, days when the water used f o r the incubations was collected in a bucket at the sea surface rather than by pump from the depth of the chlorophyll

maximum.

We speculate that perhaps there is some neustonic food resource whichPora-

calanus requires f o r egg production, or that t h e i r preferred foods were damaged by our pump. We have no explanation f o r the f a i l u r e of C. patagoniensis

to produce eggs during the incub-

ations. Since animals were not kept separate from t h e i r eggs during the incubations, i t that some egg cannibalism took place.

is possible

To minimize this problem, the number of females added

to each b o t t l e was kept s u f f i c i e n t l y small so that no more than 20% of the container volume would be swept clear during the 24 hour incubation. We assumed that we could discount cannibalism as a problem f o r Calanus chilensis, Calanoides patagoniensis

and Paracalanus parvus

because these species are generally believed to be herbivorous. Centropages

and Acartia

are omnivorous and are capable of eating t h e i r own eggs (DAGG, 1977), but empty egg membranes ( i n d i c a t i v e of egg cannibalism according to DAGG, 1977) were seldom observed suggesting that cannibalism was not a problem. 4.2

Comparison of Individual Upwelling events

The primary objective of our study was to determine the effects of d a i l y v a r i a t i o n s in the i n t e n s i t y of the winds on hydrography and plankton dynamics at a single f i x e d station in the nearshore zone.

The time-series approach was taken so that we could observe several

consecutive upwelling events and how they affected the production and abundance of planktonic organisms, and to determine the appropriate time scales of v a r i a b i l i t y f o r hydrography and plankton. We had the good fortune to sample three complete cycles of active upwelling and r e l a x a t i o n during the 25 day study period. density,

oxygen and n i t r a t e )

Only a l i m i t e d number of variables (temperature, s a l i n i t y ,

responded to v a r i a t i o n s in wind stress

in a predictable way:

cold, n u t r i e n t - r i c h water of low oxygen content was always found at the surface during active upwelling,

and warm oxygen-replenished water lower in nutrients was at the surface during

relaxation. Apart from these general observations, each event had unique c h a r a c t e r i s t i c s . data indicate that the f i r s t ical

active event was a r e l a t i v e l y weak one.

temperature gradient was as much as 0.8°C.

The physical

The top-to-bottom v er t -

Mixing during the second and t h i r d events

seems to have been much stronger, reducing v e r t i c a l temperature gradients to 0.2°C and 0.3°C, respectively.

The winds were stronger during the second and t h i r d events, with a d a i l y mean

stress of 0.21 and 0.25 dynes cm-2 respectively, compared to 0.16 dynes cm-2 f o r the f i r s t event. first

The top-to-bottom density gradients averaged 0.0144 sigma-t units m- I

during the

active event, but were 35-50% lower during the second and t h i r d active events (0.0093

and 0.0072 sigma-t units m-I r e s p e c t i v e l y ) . JPO 20:I-C

34

W . T . PETEe, SON et al.

The chemical c h a r a c t e r i s t i c s

of each upwelling event cycle also varied.

For example, deep

water oxygen concentrations did not increase and decrease in concert with changes in the state of the upwelling.

Concentrations were higher during the f i r s t

January) than during the second h a l f (Fig.5). in that n i t r i t e first

The n i t r i t e

h a l f of the study (7-18

data also showed a s i m i l a r pattern

concentrations in the deep water (15m and greater) were highest during the

h a l f of the time series and lowest during the second h a l f .

The b i o l o g i c a l

data also indicate that each upwelling event was unique.

data conform to the idea that the f i r s t tively

weak one: chlorophyll

phase of the f i r s t

The phytoplankton

active upwelling event (9-14 January) was a r e l a -

concentrations did not drop dramatically during the spin-up

active event.

The second and t h i r d active upwelling events were consider-

ably stronger in that they produced the expected r e s u l t of transporting the c h l o r o p h y l l - r i c h surface layer some distance away from our study s i t e and replacing i t with cold, n u t r i e n t r i c h , c h l o r o p h y l l - f r e e deep water. Each i n t e r v a l of relaxed upwelling was unique as well.

The r e l a x a t i o n observed at the s t a r t

of the time series was characterised by a sub-surface maximum (at 15m) of "net" diatoms; the second r e l a x a t i o n

(15-18 January) by a near-surface maximum (15-30 g chl I -I ) of small

c e l l s and the colonial Phaeoeystis red t i d e of

and the t h i r d r e l a x a t i o n (24-26 January) by a massive

Mesodinium rubrum,

The size composition of the phytoplankton w i t h i n the upper 5m of the water column responded somewhat predictably:

large c e l l s (>20vm) dominated during the f i r s t

and t h i r d active upwell-

ing events and small c e l l s (<20pm) during each of the periods of r e l a x a t i o n . ted;

This was expec-

large c e l l s should dominate when a water column is well mixed and small, motile c e l l s

when i t

is s t r a t i f i e d

(e.g. HOLLIGAN and HARBOUR, 1977).

However, large c e l l s did not domin-

ate during the second active event, the strongest event. non-motile c e l l s

was l i g h t - l i m i t e d

Possibly, the growth of the large

during the second event due to a greater water column

mixing rate and a population of large c e l l s may have been prevented from developing. Egg production seemed to be event-specific as well.

During the f i r s t

week of the time series

a sub-surface chlorophyll maximum was present between 10 and 15m, composed of large diatoms, presumably an ideal food resource f o r herbivorous copepods. were low during t h i s period.

One explanation for t h i s

was embedded in water of low oxygen (<0.5 ml I - I ;

However, rates of egg production

is that the high chlorophyll patch

compare Figs. 4 and 8),

phytoplankton was unavailable to the copepods because the l a t t e r

so perhaps the

were avoiding low oxygen

water. The second phytoplankton bloom (15-18 January during the second r e l a x a t i o n ) should have led to maximum egg production rates because chlorophyll concentrations were in excess of 10~g I - I , high enough to produce saturated feeding and egg production rates. low and egg production rates were moderate. too small to be e f f i c i e n t l y f r a c t i o n during t h i s bloom.

grazed.

Yet, gut f u l l n e s s was

One explanation is that the phytoplankton was

V i r t u a l l y a l l of the chlorophyll was in the <20pm size

Nearshore zone coastal upwelling

During the t h i r d

35

r e l a x a t i o n , the bloom was characterised by "red water".

Egg production

rates f o r a l l copepods were the highest observed f o r the e n t i r e time series, suggesting that some organism associated with the "red water", perhaps M e s o d i n i w n rubru~n,

was a prime food

resource. Based on a l l

of the above observations we conclude that even though the food q u a l i t y (based

on protein and carbohydrate data) was high on a l l on most dates.

dates, egg production was f o o d - l i m i t e d

Even on days when chlorophyll concentrations were very high (7-11,

15-18

and 24 January) egg production rates were less than maximal, possibly because of low oxygen water, because phytoplankton c e l l s were too small to be ingested e f f i c i e n t l y or because the phytoplankton species composition was unsuitable in some unknown way.

An alternate explana-

t i o n , discussed b r i e f l y below, is that the copepods do not reside in the surface Ekman layer on a 24 hour basis, and thus are not t i g h t l y coupled to changes in the concentration of t h e i r food resource.

They simply may not be able to adjust on a d a i l y basis to the high frequency

changes in t h e i r food occurring above them in the water column. 4.3

Effects of Advection on Plankton Distributions

Variations in phytoplankton biomass observed at our study s i t e were probably controlled by a combination of onshore-offshore advection, in s i t u

growth and grazing.

The r e l a t i v e con-

t r i b u t i o n of each of these three variables was estimated in the f o l l o w i n g manner: f o r each date, the expected phytoplankton biomass was calculated from the product of d a i l y primary production and observed biomass (converting chlorophyll to carbon assuming a carbon:chlorophyll r a t i o of 40). data (in Fig.]O)

Daily (24h) primary production was calculated by m u l t i p l y i n g the hourly

by 10 hours; this value was added to the biomass observed on that day to

get biomass expected on the next day.

Considering the imprecise nature of these calculations

we w i l l be conservative and only attach significance to very large differences (~90%) between observed and expected biomass. Expected and observed phytoplankton biomass are compared in f i g u r e 17. Observed phytoplankton biomass was f a r greater than expected on only two dates, 15 and 24 January. to expected r a t i o s were 2.5 and 7.9 respectively.

These were the f i r s t

The observed

dates of each of

the two periods of r e l a x a t i o n , suggesting that blooms observed during r e l a x a t i o n are initiated from an offshore seed stock advected into the nearshore zone.

Observed biomass was f a r less

than expected on two dates, 18 and 25 January (observed:expected biomass r a t i o s of 0.14 and 0.05, r e s p e c t i v e l y ) . in Fig.3),

These were both dates of spin-up of active upwelling (see wind data

suggesting that the dramatic declines in biomass observed at the beginning of

active upwelling events were indeed due to offshore advection of the surface layers. For most other dates, observed and expected phytoplankton biomass r a t i o s were nearly in balance, with most r a t i o s between 0.5 and 2.0.

Values within the range of 0.5 to 1.0 r e a l i s t i c -

a l l y span the amount of grazing which could take place in one day (0 to 50% of the standing crop per day),

but also, values between 0.5 and 2.0 span the range that one might expect

from patchiness alone.

Thus, on the f i r s t

day of an active upwelling event, and on the f i r s t

36

W.T.

PET[RSON et al.

1500-

i,

!

,

il

IE

•

~.,

!

i

!i

,/,i i

E tO

"

I

i

looo-

i

i_ 0

i i i

tO

!i

',

ii i,i i

i

i

'/i

t-

i

r"

n

,

5

i

1

10

15

20

i

I

I

25

30

January FIG.17.

Measured v a r i a t i o n s in phytoplankton biomass ( s o l i d l i n e ) compared to expected values (dashed l i n e ) based on l i n e a r e x tr a p o l a ti o n of each day's biomass and prod u c t i v i t y to the next day. Black bars indicate active upwelling.

day of r e l a x a t i o n , changes in phytoplankton biomass in the nearshore zone seem to be cont r o l l e d by advection; but on most other dates v a r i a t i o n s could be a t t r i b u t e d to i n s i t u g r o w t h , grazing or patchiness. Variations in the abundance of most copepod species did not f o l l o w any of the upwelling event cycles in a predictable way. one might expect t h e i r

I f the copepods resided wholly within the surface Ekman layer,

abundance to decrease during active upwelling and increase during

r e l a x a t i o n as a r e s u l t of onshore-offshore advection. ation,

suggesting that

it

Only A o a r t i a tonsa met this expect-

alone is r e s t r i c t e d to the upper Ekman layer.

Fluctuations in

the abundance of a l l other species were independent of the state of the upwelling, suggesting that the copepods move f r e e l y throughout the water column and that each species is controlled by variables other than zonal movements of the upper Ekman layer.

Fluctuations in copepod

abundances were w e l l - c o r r e l a t e d with oxygen concentration within the lower 10m of the water column at our study s i t e

suggesting the p o s s i b i l i t y of an active behavioural i n t e r a c t i o n

whereby copepods avoid water of very low oxygen concentration (
Since the

Ncarshore zone coastal upwelling

37

presence of low oxygen water was independent of the state of upwelling,

the question of

whether or not the f l u c t u a t i o n s in copepod abundance are patchy, because of either advection or t h e i r

active avoidance of oxygen-deficient water cannot be resolved without a detailed

study of the v e r t i c a l and HUYER (1981)

it

d i s t r i b u t i o n of each species.

From SMITH, BRINK, SANTANDER, COWLES

is clear that onshore-offshore advection alone can explain remarkably

well changes in abundance of some of the copepod species which reside within the surface Ekman layer.

From JUDKINS (1980) i t

is also clear that the oxygen minimum layer does deter-

mine the lower l i m i t of the v e r t i c a l d i s t r i b u t i o n of most copepod species in the upwelling zone o f f

Peru and Chile.

When physical processes

in the nearshore zone bring the oxygen

minimum layer very close to the sea surface (within

15m), nearly adjacent to the surface

Ekman layer, copepods which would o r d i n a r i l y prefer a depth range intermediate between the upper Ekman layer and the lower oxygen-depleted layer may have to modify t h e i r behaviour. It

should not be surprising,

then, that observed f l u c t u a t i o n s in copepod abundance in the

shallow nearshore zone cannot be explained by advection alone.

5.

CONCLUSIONS

We observed three complete cycles of upwelling during our 25 day study. salinity,

density,

Only temperature,

oxygen and n i t r a t e responded to wind v a r i a t i o n s in a predictable way.

Most of the b i o l o g i c a l data did not show a consistent response to the wind. upwelling event cycle seemed to produce a d i f f e r e n t b i o l o g i c a l response. in p a r t i c u l a r , there was l i t t l e

In f ac t , each

For the copepods,

evidence f o r any t i g h t coupling between feeding, egg produc-

tion rates, and phytoplankton biomass. The main problem in i n t e r p r e t i n g b i o l o g i c a l observations in the nearshore zone is that this region is dominated by event-scale advection.

W i t h the advent of active upwelling, f r e s h l y

upwelled water occupied much of the water column at our station, some of the copepods were transported some distance offshore.

and the phytoplankton and

As active upwelling proceeded,

alongshore transport j u s t offshore of our s i t e probably brought a somewhat d i f f e r e n t assembinto the area.

With the next

r e l a x a t i o n , this

lage of plankton, with perhaps a d i f f e r e n t previous history,

assemblage would be the one to "seed" our nearshore s i t e .

B e c a u s eof

vertical

shear, d i f f e r e n t

current

assemblages of phytoplankton and copepods (which occupy

the Ekman layer and deeper layers, respectively) can be brought together in the nearshore zone during r e l a x a t i o n . degree.

This would "uncouple" the copepods from the phytoplankton to some

Thus, primary and secondary production may be uncoupled by the upwelling cycle in

the nearshore zone, and more closely coupled in offshore regions where complete replacement of the water column with newly-upwelled water does not occur. The design of our study was advantageous from several perspectives. three complete upwelling cycles in a r e l a t i v e l y short time.

We were able to document

Also, d a i l y sampling over the

course of the month allowed us to study the upwelling cycle at several important scales, from the period of events themselves (8-12d) down to the generation time of phytoplankton (I-2d ) .

We chose to p a r t i t i o n our resources in such a way that high temporal resolution

38

W . T . PETERSON et al.

was achieved.

To some degree, t h i s was done at the expense of spatial

resolution.

importance of advection in determining hydrographic and b i o l o g i c a l v a r i a b i l i t y

The

in the near-

shore zone leads us to suggest that in future nearshore studies, d a i l y measurements be placed in a broader spatial

context.

In p a r t i c u l a r ,

comparison should be made of the degree of

coupling between phytoplankton and zooplankton production in the nearshore zone with that in regions some distance offshore, where advection is less important.

6.

ACKNOWLEDGEMENTS

This study was supported by the US-Latin American Program of the National Science Foundation, Division of I n t e r n a t i o n a l programs (NSF Grant # INT-8415581) and by Universidad de Concepcion Grant #20.37.09.

We are p a r t i c u l a r l y grateful to the crew of the R/V Lund and to the f o l l o w -

ing i n d i v i d u a l s for t h e i r cooperation during the cruises and in the laboratory: Edgardo Munoz, Ramon Monardes, Marco Salamanca, Erik Montes, Sergio Nunez, Nestor Navarro, Leonardo Castro, Aquiles Sepulveda, Andres Caamano, Gonzalo V i l l o u t a

and Alex Daroch.

We are grateful

to

three anonymous reviewers f o r t h e i r comments and suggestions.

7.

REFERENCES

AHUMADA, R., A. RUDOLF and V. MARTINEZ (1983) C i r c u l a t i o n and f e r t i l i t y of the waters of Concepcion Bay. Estuarine Coastal and Shelf Science 16, 95-105. AMBLER, J.W. (1985) Seasonal factors a f f e c t i n g egg production and v i a b i l i t y of eggs of Acartia tonsa Dana from East Lagoon, Galveston, T e x a s . Estuarine Coastal and Shelf Science, 20, 743-760. ANDREWS, W.R.H. (1974) Selected aspects of upwelling research in the southern Benguela Current. Tethys 6, 327-340. ANDREWS, W.R.H, and L. HUTCHINGS (1980) Upwelling in the southern Benguela Current. Progress in Oceanography, 9, 1-81. ARCOS, D.F. (1975) Copepodos calanoideos de la Bahia de Concepcion, Chile. Conocimiento Sistematico y Variacion estacional. Gayana, 32, 1-31. ARCOS, D.F. and R.E. WILSON (1984) Upwelling and the d i s t r i b u t i o n of chlor phyll a within the Bay of Concepcion, Chile. Estuarine Coastal and Shelf Science, 18, 25-~5. BARLOW, R.G. (1982a) Phytoplankton ecology in the southern Benguela Current. I. Biochemical composition. Journal o f Experimental Marine Biology and Ecology, 63, 209-227. BARLOW, R.G. (1982b) Phytoplankton ecology in the southern Benguela Current. I I I . Dynamics of a bloom. Journal of Experimental Marine Biology and Ecology, 63, 239-248. BECKMAN, B.R. and W.T. PETERSON (1986) Egg Production by Acartia tonsa in Long Island Sound. Journal of Plankton Research, 8, 917-925. BELLANTONI, D.C. and W.T. PETERSON (1987) Temporal v a r i a b i l i t y in egg production rates of Acartia tonsa Dana in Long Island Sound. Journal of Experimental Marine Biology and Ecology,

107, 199-208,

BINET, D. and E. SUISSE DE SAINTE CLAIRE (1975) Contribution a l'~tude du Copepods planctonique Calanoides carinatus: r ~ p a r t i t i o n et cycle biologique au large de la COte d ' I v o i r e . Cahiers ORSTOM set Ooeanographique, 13, 15-30. BORCHERS, P. and L. HUTCHINGS (1986) Starvation tolerance, development time and egg production of Calanoides carinatus in the Southern Benguela Current. Journal of Plankton Research B, 855-874. BOYD, C.M., S.L. SMITH and T.J. COWLES (1980) Grazing patterns of copepods in the upwelling system o f f Peru. Limnolog W and Oceanography, 25, 583-596. BRINK, K.H., B.H. JONES, J.C. VAN LEER, C.N.K. MOOERS, D.W. STUART, M.R. STEVENSON, R.C. DUGDALE and G.W. HEBURN (1981) Physical and b i o l o g i c a l structure and v a r i a b i l i t y in an upwelling centre o f f Peru near 15°S during March 1977. In: Coastal Upwelling F.A. RICHARDS, e d i t o r , American Geophysical Union, 473-495.

Nearshore zone coastal upwelling

39

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