1
ICES STATUTORY MEETING 1993
C.M. 1993/L:32 Sess.O
Not to be cited without prior reference to the author.
VARIABILITY OF SURFACE PLANKTONIC COMMUNITY METABOLISM
IN RESPONSE TO COASTAL UPWELLING EVENTS
IN THE RIA DE VlGO (NW SPAIN).
G. Moncoiffe(l), G. Savidge(l), X.A. Alvarez-Salgado(2) and F.G. Figueiras(2) .
•
(1) School of Biology and Biochemistry, Queen's University of Belfast,
Marine Biology Station, Portaferry,
Co. Down BT22 IPF, Northem Ireland.
(2) Instituto de Investigaciones Marinas, CSIC,
Eduardo Cabello 6, 36208 Vigo, Spain.
Abstract
•
Measurements of licrobial photosynthetic and respiration rates based on oxygen light:dark
incubations were carried out twice weekly, frol April to November 1991, at a fixed station in the Ria de
vigo (N.W. Spain). Wind driven upwelling events in the Ria sustained high but very variable chlorophyll
abiomasses (mean: 6.0 ±4.2 range: 0.2-17.5 pg 1-1), gross photosynthetic (GP) rates (Iean: 37.4 ±30.2,
range: 0.9-123.3 pmol 02 1-i d-1), GP:Chl a ratios (Iean: 5.2 ±2.3, ran1e: 0.9-11.6 pg C (pg ChI a)-l h1) and respiration rates (Iean: 12.3 ±9.7, range: 0.6-46.5 pllol 02 1- d- 1) in the surface planktonic
cOIlunity. Chlorophyll increases were associated with both upwelling and relaxation conditions. During
the spring-suuer period dOllinated by regular upwelling and relaxation events, the GP:Chl a ratio
(Productivity Index), showed consistent correlations with the density of the surface layer but was
independent of temperature, nutrient and planktonic dOlinanee. From April to the end of June, upwelling
typically depressed photosynthetie activity while in July-August upwelling was associated with increases
in autotrophie aetivity. Respiration rates showed a lore eOlllplex pattern and varied on a shorter timescale than did chlorophyll a biomass or photosynthetie productivity suggesting a rapid growth or
. physiologieal response of heterotrophie organisms to very transient physieal and biologieal situations.
2
Introduction
Upwelling
ecosystems
are
usually
considered
as
immature
ecosystems with a food web typicallY based on "new production"
of
organic
matter
by
fast
growing
cOlnmunity is then characterized by a
respiration
ratio,
the
new
diatoms.
The
planktonic
high photosynthesis to
production
being
exported
and
remineralized out of the system (Packard 1979) thus generating
a strong spatial heterogeneity. Under an intermittent coastal
upwelling regime such as the one characterizing the Rias of
the
North West coast of
1984),
the occurence of
spain
(Fraga 1981,
Blanton et al.
stratified and unstratified periods
allows the maturation of the planktonic community (autotrophs/
heterotrophs,
prey/
predators,
diatoms/ dinoflagellates)
and
i ts vertical segragation during the periods of stabilization
(Figueiras
& Pazos
1991,
Figueiras
& Rios
1993).
How
the
different components of those complex communities respond to
upwelling and" relaxation is one of
the major objectives cif
upwelling area studies.
•
Since
the" 1950' s,
studied
in
the
phytoplankton
Rias
Baixas,
ecology
especially
has
in
been
regularly
regards
to
the
annual phytoplanktonic succession (e.g. Margalef et al. 1955)
and its relation with the hydrographie regime "(e.g. Figueiras
& Niell 1987). Short-term variability of phytoplankton biomass
and composition on a time scale of less than a week has been
monitored consistently. The present study, based on a twiceweekly sampling frequency is an attempt to outline the major
eonsequenees of strong hydrographie variability ereated by an
intermittent upwelling regime on the planktonic community in
J
3
terms of both autotrophie and heterotrophie aetivity at the
surface.
Materials and methods
From the 15 April to the 11 November 1991,
sampling was
carried out twice a week (typieally between 9.00 and 10.30) at
a fixed station (42°14'1"N,8°46'9"W) in the Ria de Vigo (Fig.
1).
Sampies
were
eollected
with
5
I
PVC
provided with rotating thermometer frames.
Niskin
bottles
Three depths were
sampled: surface, 1% of light determined by a LICOR underwater
quantum sensor and 40 m (8 m above the bottom). Salinity was
ealeulated
from
the
equation
(6)
of
UNESCO
(1981)
•
from
conductivity measurements with an AUTOSAL 8400A salinometer.
Aliquots for nutrient determination were frozen at -20°C after
sampling
and
analysed
by
Technicon
AAll
systems
following
Hansen and Grasshoff (1983) with some modifieations (AlvarezSalgado et ale 1992, Mourifio & Fraga 1985). Chlorophyll a was
determined after filtration
through Whatman GF/F filters
by
the fluorometrie method (Yentsch & Menzel 1963) using a Turner
Designs 10000R fluorometer. The abundances of bacteria, picoand
nanoflagellates
were
determined
by
epifluorescence
mieroscopy using the DAPI-induced fluorescence method (Porter
&
Feig
1980) •
Photosynthetie
eells
were
identified
by
autofluorescence under blue light exeitation (Davis & sieburth
1982).
For the eommunity oxygen metabolism study,
from
each depth were
pooled
in
three
25 1 of water
darkened
earboys
and
\,
gently shaken
,
,
,
:
before
sUbsampling.
size-fractionation
of
the
•
4
community was performed by gravity filtration through 10 Jjm
mesh. From 15 April to 3 September, prefiltration through 150
Jjm mesh was carried out. After 3 September the sampies were
incubated
without
prefiltration.
Incubations
usually
began
within.2 to 3 h after sampling. Daily net ph6tosynthetic and
respiration
rates
of
the
phytoplankton
community
were
estimated with the oxygen light-dark bottle method (Strickland
&
Parsons
1972).
Triplicated 120 ml
light and dark bottles
were incubated for 24 h in situ.
~
Oxygen
titration
controlled
was
titrator
performed
system
using
by
a
the
SIS
microprocessor
colorimetric
winkler
methode Rates of net photosynthesis (NP), gross photosynthesis
(GP) and respiration (R) are expressed in Jjmol O2 1-1 d-1 •
The
chlorophyll
a
content of
the
sampies
used
for
primary
production experiments was also analysed as described above.
These chlorophyll data were used for the normalization of GP
to ChI a referred to as the Productivity Index (PI) expressed
in
•
Jjg
C
(Jjg
ChI
a)-l
h-1 •
Oxygen
production
values
were
converted to carbon using a PQ of 1.36 (Rios & Fraga 1987) •
Results
During the upwelling season 1991,
regular
intrusions of
Eastern North Atlantic Water (ENAW) in the Ria de Vigo imposed
a
strong
hydrographie
variability
at
the
fixed
station
as
represented .by the temporal evolution of bottom and surface
temperatures
40 m,
(Fig.
2A)
and nitrate+nitrite concentrations at
at the 1% light depth and at the surface
(Fig.
2B).
Maxima in the surfacewards transport of the dense bottom water
5
were refleeted in the surfaee density( values on 22 April,
i
May,
20 May,
6 June,
20 June,
6
4 JUly,l 29 July and 12 August
I
(annotated with arrows on the date axis).
assoeiated with marked deereases
in sea
,
These events were
surfaee temperature
I
during the thermally stratified season! from mfd-April to midI
.
I
Oetober together with strong influxes of nitrate in the bottom
I
.
layer at the fixed station. Nitrate eoneentrations >6 .~M were
regularly measured at the 1% LD (12 ±~ m) with eoneentrations
>2
~M
being observed on five oeeasions
~t
the surfaee.
I
ChI a eoneentrations, gross photosynthesis and respiration
rates
remained
sampling
high
(Table
1)
at
the
surfaee; during the period
I
averaging respeetively 6. 0 ~g ChI a
~
of
1-1
!
(±70%), 37 J,Lmol 02 1-1 d-1 (±81%) and 12.:3 J,Lmol 02 1-1 d- 1 (±79%).
1
The autotrophie eommunity was largely i dominated by organisms
I
>10 ~m which aeeounted for 66% of theibiomass and 77% of the
!
gross photosynthesis while in eontrast 60% of the eommunity
,!
oxygen eonsumption was by organisms <10!J,Lm
(Table 1).
,
,
ChI a eoneentrations at the surfaeel (Fig. 3A) showed marked
~
seasonal differenees with major inereases associated with the
1
upwelling events of early spring (>15: J,Lg
(~14 ~g 1-1 )
r
1)
and mid-August
while a third bloom in the'autumn, consisting of a
series of short lived peaks >10 ~gl~ decreasing in intensity
towards
the
relaxation
winter,
period
when
was
initiated
stratification
during
was
,the
longest
strongest.
In
,
contrast, in June-July, coneentrations appeared relatively low
with peaks <10 I-'g 1-1 •
The evolution of the productivity index (Fig.
3B)
in the
surface layer did not show such a pronounced seasonal trend as
for ChI a since high values were regularly observed during the
•
6
upwelling season (average of 5.25 ±2.30 J.Lg C (J.Lg ChI a)-l h-1 ).
From
the
15
April
to
6
August,
highly
signifieant
linear
relationships were observed between PI at the surfaee and the
superfieial water density over periods of 3 to 6 weeks (Fig.
4).
As
a
single
(0. 005<p<0. 001)
faetor,
of
density
the variations
variation" explained
of
the produetivity
63%
index
observed from 15 April to 30 May, 93% (p<0.001) from 3 to 27
June and 76%
(0.005<p<0.001)
from 1 July to 6 August.
High
surfaee temperature and inereased water eolumn stratifieation
•
as
estimated
by
diseontinuities
relationships
the
the
in
with
0-40
the
m
density,
parameters
slope
evolving
eorresponded
eharaeterizing
from
-3.44
to
the
(r=0.793,
n=11) in April-May, to -8.70 (r=0.985, n=7) in June and +4.77
(r=O. 871,
over
time,
in July-August.
with
density
estimated
period ,
1.5
sampling
•
n=8)
in
days
the
Contrasts were
greater
signifieanee
2 days
before
before
third
in
the
period.
the
also
between
sampling
PI
in
seeond and the
During
those
apparent
and
the
day
three
the
first
of
the
periods,
although PI was not statistieally eorrelated with ChI a, eaeh
maximum of PI (range: 6.09-9.09 J.Lg C (J.Lg ChI a)-l h-1 ) preeeded
a maximum of biomass in surfaee (range: 4.16-16.71 J.Lg ChI a l-
I). The delay observed between both varied from none (29 July)
to 11 days (2-13 May) but eorresponded typieally to the 3 to 4
days separating eaeh sampling.
The
temporal
evolution
of
marked short-term variabili ty ,
the summer
(Fig.
3e).
the
respiration
rates
showed
espeeially at the begining of
Higher rates were measured during the
thermally stratified period
(mid-April to mid-oetober).
From
mid-May to mid-Ju1y heterotrophie aetivity was depressed when
7
the
maxima
in
during the
two
September,
a
the
upwelling
observed
last upwelling events.
steady
inerease
were
in
it
inereased
From 22 August to 19
signif~eantly
inerease,
surfaee
while
temperature
correlated with
(r=+0.877,
p<0.05)
contrasted with the short-lived peaks observed in. June-July.
However,
physieal
variability
of
the \ water
eolumn
alone
is
insuffieient to explain the strong stiort-term variability of
respiration rates.
Figure 5 illustrates how the strueture of
the
eommunity
heterotrophie
and
its
interactions
with
the
phytoplanktonie eommunity might explain this variability.
In
•
I
the
<10~m
fraetion,
whieh
heterotrophie aetivity,
Figure
5A,
one
group
was
responsible
for
60%
of
two groups of( data were isolated.
(G1)
showed
a
marked
inerease
of
(ChI
a
va lues
>4
~g
1-1
were
observed
In
the
<10~m
respiration rate with chlorophyll eoneentration in the
fraction
the
during
the
marked inerease in surfaee temperature in september) while a
seeond group (G2), eorresponding to the highest rates measured
during the
sampling season
(ineluding most of
the
peaks
of
respiration observed in May-June), was, assoeiated with low ChI
a
eoneentrations
tendeney
larger
to
in
increase
fraetion
the
as
small
the
inereased
fraetion
but
photosynthetie
(Fig.
5B).
showed
aetivity
Correlation
a
elear
in
the
between
,
epifluoreseenee
counts
and
respiration
rates
(Table
2)
;
indieated
that
small
heterotrophie 'flagellates
(pieo-
and
nanoflagellates)were assoeiated with the respiration data of
the .first group while bacteria gave the major contributionto
,
the variation of the respiration rates measured in the second
group.
•
-
-----------
8
Diseussion
The
study
earried
in
out
the
Ria
de
Vigo
during
the
upwelling season 1991 showed that the intermittent intrusions
of deep oeeanie water in the Ria oeeured with an approximate
frequeney
of
autotrophie
2
weeks
biomass
and
and
allowed
deve~opment
the
produetion
and
high
of
high
heterotrophie
aetivity as weIl as strong interaetions within the planktonie
eommunity.
The
events
response
of
the
planktonie
eommunity
appears very eomplex and the
response based on data from a
to
upwelling
interpretation of
sirigle
fixed
station
this
is not
neeessarily easy.
The three signifieant and eontrasting relationships found
between the produetivity index of the surfaee eommunity and
the surfaee density within the three eonseeutive periods 15
April-3D May, 3 June-27 June and 1 July to 6 August underline
two eurrently observed aspects of phytoplankton response to
upwelling:
the lag-time following upwelling stress
(MacIsaac
et ale 1985, Wilkerson & Dugdale 1987, Dortch & Poste1 1989,
•
Duarte 1990) and the control of phytoplanktonic production by
physical proeesses
(Huntsman
&
Barber 1977,
Small
&
Menzies
1981). Since those relationships were apparently independent
of temperature, phytoplanktonie succession and nutrient influx
with
the
deep
suggested
that
overall
by
the
water
(Moncoiffe
phytoplanktonic
physical
et
al.,
in
productivity
variability
of
during
the
period
upwelling and relaxation events.
was
the
associated with the succession of upwe11ing,
stratification
prep.),
it
is
controlled
surface
layer
relaxation and
dominated
by
regular
9
I
In the Ria de Vigo, because of the scarcity of freshwater
I
input, surface densi ty depends mainly lI on the strength of the
I
upwelling and the rate at which therm~l stratification is reI
established. The strength of the upwelling will determine the
I
stress applied to the system while thelverticai stability will
.
I
condition the degree of maturity of the ecosystem in terms of
,I
the nitrogen source supporting phytoplankton growth,
I
relationships
and
light
adaptation.
I
tIn
conditions
trophic
of
weak
I
stratification
(April-May)
high phytoplankton biomasses were
I
rapidly
reached
following
the
maximum
of
density
at
the
surface while nitrate concentrations fell to values <1 pM in
I
the photic
layer suggesting a
rapid :growth response of the
i
phytoplankton.
However,
the productivity index varied little
I
and its slight decrease following the maximum of density could
I
non~ftrncEronal-chl
-----Eüther -be - due- to - higher--cohcentration 70f
a
or to photoinhibition known to occur when a water sampIe taken
from
a
mixed
water
& Barber
(Huntsman
thermocline
was
column
is
I
exposed
Harris
1977,
established
(June,
to
1980).
!
July,
high
Once
irradiances
the
August),
seasonal
upwelling
occurences had major consequences on the productivity index of
the phytoplanktonic community resulting either in low values
,
in June (61 and 89% lower than underlstratified conditions),
or in high va lues
in July-August decreasing by
85
and 81%
relationships
between
J
!
under
relaxation
conditions.
Negative
!
phytoplanktonic
community
and
interpreted with reference te
stability
the
have
usually
lew average
been
light regime
experienced by the microalgae during! strong mixing and
increase
as
the
water
column
stabilizes
as
a
i ts
progressive
l
i
adaptation to high surface irradiances
(Malone et al.
1983,
•
10
Demers & Legendre 1982). In an upwelling area,
be
related to the
upwelled cells
population
time-lag riecessary
(Wilkerson
(Duarte
for adaptation of the
Dugdale 1987)
&
1990)
to
it could also
near
or phytoplanktonic
surface
conditions.
A
positive relationship or the absence of lag would correspond
to
either
a
irradiances
preconditioning
of
(MacIsaac et ale
the
1985)
upwelled
or to a
cells
to
high
fertilization of
nutrient-limited surface population (Dortch & Postel 1989).
The
~
respiration
rates
measured
(mean
and
range)
were
highest than the values for surface coastal waters reviewed by
williams
(1984).
Organisms
<10
Jjm
(mainly small
flagellates
and bacteria), by accounting for 60% of the oxygen respired by
the whole microplankton fraction and representing on average
44%
(±66)
of the gross photosynthetic production against 20%
(±18) for the organisms >10 Jjm, appear as a major component of
the biological transfer of organic matter in the surface layer
______ during __the _upwelling__ season.
weak
dependence
of
the
_More_surpr.ising_is_the_~ela_ti~ely
respiration
evolution _of the surface layer,
rate
on
the
_
physical
especially during the summer
time, -since previous seasonal studies of small flagellates and
bacteria activity have revealed a strong temperature influence
(Marrase
et
ale
1992,
Velimirov
& Walenta-simon
1992).
the -respiration
rates
this . fraction
remained
- - - ----Although
- ...,-- - -....- - --- --- in
---. ----_
-----.._ - -<10
- --_.._ - - Jjmol O2 r 1 d-1 when the temperature fell below lSoC, the lack
-_._~-*
'-~-
of correlation at higher temperature was probably related to
the
partitioning
fractions.
of
the
heterotrophie
community
into
two
In the first fraction respiration rates increased
with chlorophyll
significantly
concentration in
correlated
with
<10
the
/-&m
fraction· and were
small
flagellates
'11
population.
increased
the
In
with
the
respiration
fraction,
second
photosynthetic
activity
,
in
the
rates
>10
fJm
fraction and was more closely relatEid to variations of the
bacterial
biomass.
short-term
without
respiration
however
variability
explaining
observed
totally
in
the
June-July,
,
those correlations suggest the rapid establishment of complex
relationships
community
between
(through
components
different
the
remineralization
and
grazing
of
activity
the
in
the small fraction) following upwelling events. The dependence
of bacterial production on photosyntl1etic production through
the
release
of
extracellular
organic
,
compounds
(EOC)
by
I
photosynthetically active cells
R"~
_
••
_.~_
__
is weIl
.~
_
_
, •..••
established.
_ _ ._~_.-
In the
-~__________________
,.
-
_
present instance where the bacterial population was separated
from
the
main
source
of
EOC
(organisms
>10
by
prefiltration, the correlation observed between respiration in
the small fraction and photosynthetic activity of the larger
organisms would require an accumulation of EOC in the surface
layer.
Such an accumulation does not: seem to be of general
occurence - (Riemann
observed
in
Furthermore ,
the
&
Sondergaard 1984)
Peruvian
bacteria
although it has been
upwelling ,system
I
assimilation rates
(SelIner
depend
the quality of the dissolved organic matter (SeIl
1981).
strongly on
&
Overbeck
1992).
,
In conclusion, the Ria de Vigo appears as a very productive
production. The diversity of the trophic relationships in the
microplanktonic community observed at the surface is likely to
be reflected by a similar diversity of· larger predators giving
rise
to
the
high
productivity
of
the
Galician
Rias.
The
-.
l2
importanee
thermal
of
upwelling
strength
stratifieation
produetivity. is
likely
in
to
have,
relative .to
regulating
together
the
seasonal
phytoplankton
with
upwelling
frequeney, a major influenee on the interannual yariability of
exploitable resourees.
Aeknowledgements
The authors would like to thank the staff of the Marine
Biology station in Portaferry and of the Instituto de
Investigacions Marifias in Vigo for their help during the
project. special thanks go to Ricardo Casal for his assistance
during the work at sea and to Ana Mosquera for the
epifluorescenee counts. G.M. is also grateful to the IIM for
providing aeeomodation and seientifie faeili ties during the
seven months study in the Ria. This work was supported by CEC
MAST Contract Ng
0017 on the Control of Phytoplankton
Dominanee.
Referenees
Alvarez':':Salgädo,
X.A",-· Perez,
F.F. ,-FräCjä-,-- -F:----(1992J-.------·---Determination of nutrient salts by automatie methods both
in seawater and braekish water. Mar. ehern. 39: 311-319.
Blanton, J. 0., Atkinson, L. P., Fernandez de Castillero, F.,
Lavin-Montero, A. (1984). Coastal upwelling off the Rias
Bajas, Galieia, Northwest spain, I: Hydrographie studies.
Rapp. P.-v. Reun. Cons. int. Explor. Mer 183: 79-90.
Davis, P.G., Sieburth, S.Me.N. (1982). Differentiation of the
photosynthetie and heterotrophie populations in marine
waters by epifluoreseenee mieroscopy. Ann. Inst. Oeeanogr.
Paris, 58(5): 249-259.
Demers, S., Legendre, L. (1982). Water eolumn stability and
photosynthetie eapaeity of estuarine phytoplankton: long
-term relationships. Mar. Eeol. Progr. Sero 7: 337-340.
Dorteh, Q., Postel,. J.R. (1989). Bioehemieal indieators of N
assimilation by phytoplankton during upwelling off the
Washington eoast. Limnol. Oeeanogr. 34(4): 758-773.
Duarte, C.M. (1990). Time lags in algal growth: generality,
eauses and eonsequenees. J. Planke Res. 12(4): 873-883.
Figueiras,
F.G.,
Niell,
F.X.
(1987b).
Composiei6n
deI
fitoplaneton de la Ria de Pontevedra (N.O. de Espafia). Inv.
Pesq. 51(3): 371-409.
Figueiras, F.G., Pazos, Y. (1991). Mieroplankton assemblages
in three Rias Baixas (Vigo, Arosa and Muros, spain) with
13
subsurface chlorophyll maximum: Itheir relationships to
hydrography. Mar. Ecol. Progr. Sero 76: 219-233.
Figueiras, F.G., Rios, A.F. (1993). Phytoplankton succession,
red tides and the hydrographie regime in the Rias Bajas of
Galieia. In: Smayda, T.J., Shimizu, Y.
(eds.) Toxie
Phytoplankton
Blooms
in
the
Sea,
Elsevier
Seienee
Publishers B.V., p~ 239-244.
I
Fraga, F. (1981). Upwelling off the Galieian eoast, Northwest
spain. In: Riehards, F.A. (ed.) Coastal upw~lling, Ameriean
Geophysieal Union, p. 176-182.
I
Hansen,
H. P. ,
Grasshof ,
K.
(1983) •
Automated
eherilieal
analysis. In: Grasshof, K, Ehrhardt, M., Kremling, K.
(eds. ), Methods of seawater analysis, Verlag Chemie, p.
347-379 ~
i
Harris, G.P~ (1980) •. The measurement of photosynthesis in
natural populations of phytoplankton. In: Morris,I. (ed~),
Studies in Eeology, Vol. 7: The physiologieal eeology of
phytoplankton, Blaekwell Seientifie publieations, Oxford
London, p. 129-187.
Huntsman, S.A., Barber, R.T. (1977).! primary production off
northwest Africa: the relationship to wind and mitrient
conditions. Deep-sea Res. 24: 25-33.
MacIsaac, J.J., Dugdale, R.C., Barber, R.T., Blasco, D.,
Packard. T.T.
(1985). Primary production cycle in an
upwelling center. Deep-Sea Res. 32: 503-529.
Malone, T.C., Falkowski, P.G., Hopkins, T.S., Rowe, G.T. ,
Whiteledge, T.E. (1983). Mesoscale response of diatom
populations to a wind event in. the plume of the Hudson
River. Deep-Sea Res. 30(2A): 149-170.
.
Margalef, R., Dur~n, M.,Saiz, F. (1955). EI fitoplanetonde
la Ria de Vigo de enero 1953 a marzo 1954. Inv. Pesq. 2:
85-129.
I
Marrase, C., Lim, E.L., Caron, D.C. (1992). Seasonal and daily
changes in bacterivory in a coastal plankton community •
Mar. Ecol. Prog. Sero 82: 281-289.!
.'
...
Mourifio, C., Fraga, F. (1985). Determinaci6n de nitratos en
agua de mare Investigaci6n Pesq. 49: 81-96.
Packard, T.T. (1979). Respiration and respiratory electron
transport . activity in plankton fram -- the Northwest Africanupwelling area. J. Mar. Res. 37(4): 711-742.
Porter, K~G., Feig, Y.S.
(1980) ~ :The use of'- -DAPI for
identifying and counting aquatic microflore.
Limnol.
Oceanogr. 25 (5): 930-948.
':
Riemann, B., Sondergaard, M. (1984). Baeterial growth in
relation
to
phytoplankton
primary
production
and
extracellular release of organic carbon. In: Hobbie, J.E.,
Williams, P.J.leB. (eds.), Heterotrophie activity in the
sea, Plenum Press, New York, p. 233-248.
Rios, A.F., Fraga, F. (1987). Composici6n quimica elemental
deI plancton marino. Inv. Pesq. 51(4): 619-632 •. ' .
SeIl, A.F~, Overbeck, J.
(1992). 'Exudates: phytoplankton
-bacterioplankton interactions in !Plußsee. J. Plank. Res.
14(9): 1199-1215.
j
Sellner, K.G. (1981). Primary productivity and the flux of
dissolved organic matter in several marine environments.
Mar. Biol. 65: 101-112.
I
.
Small, L.F.,
Menzies, D.W.
(1981).
Patterns of primary
produetivity and biomass in a eoastal upwelling region.
Deep-Sea Res. 28(A): 123-149.
strickland, J.D.H., Parsons, T.R. (1972). A praetieal handbook
of seawater analysis, 2nd edn. Bull. Fish. Res. Bd. Can.
167: 1-310.
UNESCO
(1981).
Tenth
report
of
the
joint
panel
on
oeeanographie tables and standards. Teeh. Pap. mar. sei.
(UNESCO) 36: 25pp.
Velimirov, B., Walenta-Simon, M. (1992). Seas'onal ehanges in
speeifie growth rates,
produetion and biomass of a
baeterial
eommunity
in
the
water
eolumn
above
a
Mediterranean seagrass system. Mar. Eeol. Prog. Ser. 80:
237-248.
Wilkerson, F.P., Dugdale, R.C.
(1987). The use of large
shipboard barrels and drifters to study the effeets of
eoastal upwelling on phytoplankton dynamies.
Limnol.
Oeeanog. 32(2): 368-382.
Williams,
P.J.leB.
(1984). A review of measurements of
respiration rates of marine plankton populations. In:
Hobbie, J.E., Williams, P.J.leB. (eds.), Heterotrophie
aetivity in the sea, Plenum Press, New York, p. 357-389.
Yentseh,
C.S.,
Menzel,
D.W.
(1963).
A method for the
determination of phytoplankton chlorophyll and phaeophytin
by fluoreseenee. Deep-Sea Res. 10: 221-231.
15
Table 1. Means, coefficient of variation (C. v. ), range and
numbers of observations (n) at the surfaee of chlorophyll a
(ChI a, fJg 1-1), gross photosl,nthesis (GP, fJrnol 02 1-1 d-I) and
respiration (R, fJrnol 02 r 1 d-) for the whole sampIe (TOT) and
for >10 fJrn fraetion as proportion of total.
TOT
rnean
C.V.
range
n
>10 J.lm
ChI a
GP
R
6.0
70
0.2-17.5
61
37.5
81
0.9-123.3
49
12.3
79
0.6-46.5
49
(66 ±20)% (77 ±27)% (40 ±28)%
Table 2. Correlation coeffieients reeorded for the two groups
of surfaee data G1 (n=27) and G2 (n=11) between respiration
rates in <10 fJrn fraction (R <10 fJrn) and epifluorescenee counts
of
baeteria,
autotrophie
(A)
and
heterotrophie
(H)
pieoflagellates and nanoflagellates (bald type: p<0.05).
R <10 fJrn
H. nanoflagellates
H. picoflagellates
A. nanof1age11ates
A. pieoflagellates
Baeteria
G1
G2
+0.634
+0.663
+0.427
+0.210
+0.224
-0.065
+0.045
+0.127
+0.318
+0.577
16
Figure Legends
Figure 1. The Rias Baixas on the North-West coast of Spain arid
the Ria de Vigo with the position of the fixed station.
Figure 2. Temporal evolution of: A) temperature at 40 m (thin
line) and surface (bold line); B) nitrate + nitrite at 40 m
(thin
line),
1%
light depth
(crosses)
and surface
(bold
line). Arrows on the date axis denote the maxima of density
observed at the surface.
Figure 3. Temporal evolution at the surface of: A) chlorophyll
a,
B)
productivity index and C)
respiration rate,
in the
whole sampIe.
Figure
4.
Surface
community
productivity
index
(PI)
versus
surface density during the following periods of the survey:
A) 15 April-30 May, B) 3 June-27 June, C) 1 JUly-6 August.
(0),
(-1.5)
and
(-2)
denote
respectively
the
values
measured on the day of sampling and the values derived by
interpolation 1.5 or 2 days prior to sampling.
Figure
4t
5.
A)
Respiration
<10
J,tm
(J,tmol
O2
1-1
d-1 )
versus
chlorophyll a <10 J.tm (J.tg 1-1). Open circles denote the data
used in Figure SB and referred to as "G2" in the text. B)
Respiration <10 J.tm versus productivity index >10 J.tm (J,tg C
(J.tg Chl a)~ h~) relationship in G2.
Figure
1
'\
.•.... - ...
..
,
",
R1A de
~,
0,
,...,.:::::> ~ ~ '
Q:
o "
Q.. "
"
SPAIN.
...
' , ..
e• •
_ _ ...
...' ...
-
.
,--.'
Nitrate + Nitrite (IImol'-')
0
15-Apr
22-Apr
29-Apr
06-May
13-May
20-May
27-May
03-Jun
10-Jun
17-Jun
24-Jun
01-Jul
~
IV
".
N
0
Ci>
<J)
... ...
".
<J)
Ci>
t~
~~
...
0
...
IV
Temperature ( Cl
...
".
...
Cl
...
'"
IV
0
IV
IV
~
t/
"
08-Jul
15-Jul
"'Tl
<C.
C
..,
22-Jul
29-Jul
05-Aug
CD
12-Aug
I\)
19-Aug
26-Aug
02-Sep
09-Sep
16-Sep
23-Sep
30-Sep
07-0ct
14-0ct
21-0ct
28-0ct
04-Nov
11-Nov
--t::----...
-~+
~'
"'+
t
......t
i
'~
G
Respiration (~mol 02
o
~
0
~
N
.....,
(",)
0
~
0
r' cl')
L)
U1
Produclivily Index (~g C (~g Chl)-' h-')
~
A
U1
0
U1
0
o
15-Apr
I
'"
I
06-May
13-May
20-May
~
,/
03-Jun
10-Jun
24-Jun
...._.w.__···
22-Jul
12-Aug i-~
19-Aug
26-Aug
02-Sep
09-Sep
I
I-~
o
U1
(~g
1-')
N
U1
o
-.....
(J
"=~'
~
~"
...
·'....."0
n""---
I
11
(0'
e
CD
w
11-·.-11
IJ
(J --
_
~
~
30-Sep
~
07-0ct
14-0ct
28-0ct
04-Nov
11-Nov
/~=:=~:::=~ [§J
./
er"
~
U1
~~=O
16-Sep
23-Sep
21-0ct
'"
~
~
.........
p
29-Jul-r~
05-Aug -
g
'"
~
:3=
15-Jul
I
o
~
17-Jun
08-Jul
I
OJ
...
o
~
27-May
01-Jul
<»
r=
22-Apr
29-Apr
....
Chlorophyll a
@]
[8
~
•
-
Figure 4
B) 3 June-27 June
A) 15 April-30 May
::,8
I
.r::.
~7
C1l
:cu
6
Cl
• •
••
2::5
U
~4
'-'
e
C'~_~.-
"'
• •
•
••
..
0: 3
26.0
26.5
Density (-2)
27.0
8
7
6
5
a. 4
3
2
1
0
25.0
•
C) 1 July-6 August
.. '-'- t, ~'-
••
••
•
•
25.5
26.0
Density (-1.5)
26.5
8
7
6
5
0: 4
3
2
1
0
24.5
~----.~~.-
••
•._-• ••
-.,~--
25.5
....... ,.
__.._--
26.5
Density (0)
-.
._"-~<"--
"'-_ .. - ....
_.~
.-
Figure 5
40
::::l..
8
ev 30
o
35
.§
°
20
"§
'Ci 10
30
E
Q)
0:::
o
0
v
.~ 20
•
o
o
15
10
0 0
•
Cec.
••
5
'e
•
0
0
2
•
4
6
Chlorophyll a <10
8
~m
2
0
4
6
8
Productivity Index >1 0
•
°
•
••
° •
Q)
0:::
0
co
0°0 °
ocP 0
l/l
....~ 25
ca...
'g.
B
E 40
10
~m
10