THIS PAPER NOT TO BE CITED WlTHOUT PRIOR REFERENCE TO THE AUTHOR
ICES STATUTORY MEETING 1993
ICES CM 1993\ L:62
Session 0
SEASONAL V ARlATION OF THE ZOOPLANKTON BIOMASS OVER THE
PORTUGUESE CONTINENTAL SHELF
M. Emilia CUNHA
Instituto Nacional de Investigac;äo das Pescas, Av.Brasflia, 1400 Lisboa, Portugal
ABSTRACT
•
Seasonal variation of the zooplankton biomass off the Portuguese coast is
analyzed based on data from sampIes collected monthly from October 86 through
January 89 in four transepts over the continental shelf.
The seasonal cycle of zooplankton biomass bas low values during tbe
winter months which increase in early spring and maintain relatively constant till
tbe end of autumn. Tbe maintenance of tbe zooplankton production levels between
spring and autumn is related with tbe enrichment of the euphotic zone with
nutrients and consequent phytoplankton growth as a result of tbe coastal upwelling
caused by persistent northerly winds during this period. This pattern is more
noticeable in the northern region wbere tbe flat and wide sbelf gives origin to
environmental conditions that depend essentially trom the solar radiation, the
deptb of mixing and the northerly wind regime.
INTRODUCTION
Tbe location of Portugal on the northem fringe of the subtropical anticyclone belt and
on the eastem coast of a large ocean determines most of the climatology and oceanography
of its coastal ocean. Tbe seasonal regime of the oceanic semi-permanent high pressure cell
of the AmTes and tbe soutbern migration of tbe subtropical front regulate tbe mean wind
conditions off the Portuguese coast. Winter winds from the southwest, which produce surface
flow from the south and toward the shore alternate with summer winds from the north, which
produce flow from the north and away from shore, generating coastal upwelling.
The enrichment in nutrients of the surface waters caused by upwelling have turned this
area into a productive region. This is attributable to the high rates of supply of dissolved plant
nutrients (primary phosphate and nitrite according to Chelton et al., 1982) to the photic layer
which result in phytoplankton productivity. Since phytoplankton are the food source of
herbivorous zooplankton which are, in turn, the food source for many pelagic fish, there is
correspondingly high productivity at the higher trophic levels as weIl.
Tbis paper describes the seasonal cycle of the zooplankton abuD<lance in relation to
the hydrographic characteristics off the Portuguese coast.
MATERIAL AND METHODS
°w
11
10
9
8
7
42 .---..---..--,....,.---.-----------, 42
Zooplankton biomass were
determined based on sampies collected 0
monthly from October 1986 through
January 1989 with few interruptions.
41
41
Zooplankton was collected along four
GAL
transepts perpendicular to the coast line
F1GUE;lRA DA FOZ
40
40
within a depth range of 20 m to 200 m
(Figure 1). The regions surveyed were
Peniche and Figueira da Foz at the northem
39
39
coast, Sines at southwest and Lagos in the
south. The sampling gear was a 0.6 m
diameter Bongo net with mesh sizes of 505
38
38
and 335 JLm and information of the water
column temperature was obtained with a
bathytermograph.
37
37
During the surveys, zooplankton was
routinely collected by standard oblique net
tows as described by Smith and Richardson
36 '-----'------'-----'-------' 36
(1977) from the surface down to a
11
10
9
8
7
maximum depth 200 m and back to the Figure 1. Loeation of stations and depth
surface and the volume of the water strained eontour of the shelf break (200m).
for each net was determined using
ealibrated flowmeters. Total zooplankton biomass was determined by volume displaeement,
after removal of large (> 1 cm) organisms, and the values for each net were expressed as
ml/l000 m3 •
2
•
•
"
Time series of monthly means of zooplankton biomass were derived for each of the
four areas they represent, hy first lo~ transforming the va)ues from each individual net. Tben
the 10& transformed va)ues were averaged within each area for eaeh ea)eridar month from
1986 to 1989. The numher of net tows per month for each of the four areas is shown in the
Table I. The primary motivation for the lo~ transformation is that, since zooplankton growth
rates are usually an exponential function of population density, log. transformed data are
particularly well suited for visualizing and studying productivity (Le., the ritte of change of
population): linear segments in plots of lo~ transformed time series represent exponential
grO\\th or decay. An additional virtue of the lo~ transformation is that the resulting
zooplaßkton time series are much more nea.rly Normally distributed (Bemal, 1980) which
allows easy determination of the statistical significance of standard error values.
Upwelling indices were obtained and determined based on the mean monthly wind
observed at the meteorological station of Cabo Carvoeiro (39.35°N;9.4 0w) during the years
of 1986 and 1987 and at a point located at 40.5 N; 11.0° W during 1988 and 1989.
0
RESULTS
lWndf and /lydrography
Winds along the Portuguese coast
tAJ"'3/ •• ;.J1OOml
1l0-r----"----------------,
are monsoonal. During winter the winds are
40
most frequently from the southwest
(Novemher-February) whiJe in summer they
are mainly upwelling producing winds
(March-Oetober) from the north <,Vooster er
-20
aI., 1976). Short-term ,,,ind reversals f rom
D caco C,,'v<:e';)
the average, 7 days (Afonso Dias, p.c.),
-40
D Pt 4C5 N, 11: W
produce episodes of downwe~lingduring the
-1l0 """T""T""T.,.,..,--rr"""-'-T"T'"""T"T""'1rT"T"T""T""T"""'''''''''''''''''''TTö......-r'
A 0 D F A J A 0 D F A J A 0 D F A J
upwelling season and upwelling during the
1985
IS87
1968
HlS9
downwelling season. As a result of this Figure 2. Monthly upwellirig indices during
Wind regime, monthly upwelling indices the yea.rs of sampling. (The arrows limit the
obtained from August, 1986 till June, 1989, sampling period)
(Figure 2) show that the indices were
positive, Le. up\\'elling favorable from March till October.
.
Tbe hydrography of the Portuguese coastal ocean is strongly seasonal due, in part, to
the \rarlation of air-sea transfer processes as it may be seem in Figure 3; 4 and 5 that
represents the monthly evoiution of the thermic Structure of the water column along the
sections "off Figueira da Foz, Sines and Lagos during the years of 1987. Tbe evolution of the
thermal structure off Espinho is not shown because it waS similar to the section off Figueira
da Foz. According to those Figures there are a cyc1e of vertical convection in Winter
3
(January, February and March) - horizontal thermic stratification during the months of
Spring, Summer and Autumn off the Portuguese coast. During this period it is possible to
observe in Figure 3 the uplift of the isotherms near the coast indicating coastal upwelling in
16 June, 22 July and 22 September while in August, 15, the isotherms were bent downwards
near the coast indicating downwelling. Although the upwelling index during August were
positive the downwelling must be due to a short-term wind reversal. In the southwest coast
in Sines, the monthly evolution of the thermal structure of the water column (Figure 4)
indicate thermal convection in 17, January and vertical thermal stratification in 16 February
and 19 March. This vertical thermal stratification is the result of the strong influence of the
Subtropical component of the Eastem North Atlantic Central Water (ENACW) that during
winter and early spring approached the southem coast. This component is present off the
Portuguese at temperatures higher than 13 C (Filiza, 1984) and during winter reach the
surface forming a poleward surface current (Frouin et al., 1990; Haynes and Barton, 1990).
From May on, the water column was horizontally stratified being possible to observe that in
23, Julyand 14, November the isotherms indicate upwelling due to northerly winds while in
14 August and 6 September they indicate downwelling. Also in the western part of the south
coast (Lagos section) the vertical thermal stratification shows the strong influence of the
Subtropical component ofthe ENACW (Figure 5), in January, 10, and in March, 20. In this
section upwelling indicating isotherms were found in June, 13 and August, 26. In this part
of the south coast upwelling is only induced by winds from the west and the northwest
(Filiza, 1983).
0
•
Zooplankton seasonal distribution
Table I presents the monthly means of the zooplankton biomass retained by each mesh
size for each transept and total. The number of sampies and standard deviation is also
presented.
Figure 6 represent the monthly evolution off the portuguese coast of the zooplankton
biomass strained by the 335 /Lm and 505 /Lm sieves. According to this Figure the zooplankton
biomass increase in March and maintained high levels till October after which the biomass
decrease. This Figure also shows that the biomass strained by the 335 /Lm sieve was higher
and the levels of production more constant than the retained by the 505 /Lm. This means that
the contribution of the smaller species, that in general are herbivore, for the annual
zooplankton production curve is higher, specially during the spring, summer and autumn
months (April till October).
In Figure 7 the monthly evolution of the average zooplankton biomass at each transept
is presented. In this Figure is possible to observe that there are similarity between the two
production curves of the northem region, i.e. Espinho and Figueira da Foz. They both
maintained high production levels during the spring, summer and autumn months. In the
sections of Sines and Lagos this pattern is much more irregular with values decreasing
significantly after the spring boom (May/June). The similarity between the annual
4
•
•
•
zooplankton production cycJe off Espinho and Figueira da Foz and their dissimilarity in
relation to Sines and Lagos is more notorious when the monthly cOefficient of variation of
the biomass of each station and transept is compared (Figure 8). In this Figure it is observed
that the coefficientS of variation of the biomass in the Espinho and Figueira da Foz transepts
were very similar among them arid that they present the same variation aiong the year while
they are very different from the transepts off Siries and Lagos.
The similarity among the production curves in the riorthem cirea reveal a homogeneity
in the production system of this area which 100 that a unique production curve would be
determiried
for this region. Sines and Lagos transepts presented values of .zooplankton
.
biomass that were not only very different among them but also the evolution of their
coefficient of variation along the year \vere very different. However these differences were
not significant due to the small number of sampIes. Therefore an unique production curve was
found for the southem area. FigiIre 9 resumed these informations. Although the prOduction
levels of the two regions were simitar their annual productiori cyc1es scemed to be different.
According 10 this Figure arid after ielatively low production levels in Januafy and February
the northern region presented production values that increased till June followed by a small
decrease in July. After this month the production levels are mainuiined more or less constant
decreasing again in November and December. In the southem region this pattern was more
variable although it is possible to observe significant increases in the productiori cycJe during
spring (March/April), summer (July/August) and autumn (October). In Figure 10, which
represent the coefficients of variation of the biomass retained by the 335 /Lm and 505 /Lm
sieves in the two regions by inonth, supports the idea that the production cyc1es in the
northem and southem n~gioris were different. The monthly coefficient of variation are very
similar in the northem region during the spring, summer and autumn while in the southern
region its variation is higher along the same period.
DISCUSSION AND CONCLUSIONS
The zooplankton production cyc1e off.the Portuguese coast is characterized by the
maintenance of relatively high production levels during spring, summer and autumn ~onths
only diminishing in the winter months. The maintenance of the production levels during
summer and beginning of autumn seems to result from the eririchment of the euphotic zone
with nutrients which in temperate waters is the limiting factor for phYtoplankton growth
(Chetton et al., 1986). In the PoriUgtiese coast, where runoff is of very little importance
during summer and autumn, the flcit responsible for the enrichment of the euphotic zone muSt
be coastal upwelling. In fact, during the sampling period the wind stress favored the existerice
of coasul upwelling during March-April to October-November.
Although the general pattern in the portuguese coast is the mentioned above, this is
not true when we consider more restricted regions. Tbe differences between the production
5
•
curves in the northem and southem regions are in accordance with the areas referred by Fiuza
(1983) as having different upwelling patterns. According to this author the region north of
Nazare canyon, and where the Espinho and Figueira da Foz transepts were located, is an
hydrographie homogeneous area and the upwelling pattern is bidimensional as a result of the
wider and flat shelf. Tbe homogeneity in the hydrographie regime is reflected in the
zooplanl..'ton production cyc1e where high prOduction levels are maintained during the months
of northerly winds as a result of corresponding high primary production levels. In this region,
where the enrichment of the euphotic zone in nutrients is more or less constant and the
amount of sunlight is high a11 around the year, the depth of mixing must be the most
important factor to limit the phytoplankton gro\\1h as can observcd by the drop in the
production levels in winter when the water column was not stratified.
Tbe differences, although not significantly different, between the production cycJes
and the coefficients of variation for the Sines and Lagos transepts seemed also to reflect the
two kinds ofupwelling patterns referred by Fiuza (1983) for this two regions. However, the
sma11 number of sampIes and the great variability in biomass in these two regions do not
permit to concJude about the differences in the zooplankton productiori cyc1es in these two
areas.
,
,
ACKNOWLEDGMENTS
Tbis work was supported in part by Junta Nacional de Investiga<;äo Cientffica e
Teenol6gica (Proj. n° 87344/Mar). I am grateful to C.M. Afonso Dias by the <lata on the
upwelling indiees as weB as to my coBeagues who participated in the collection and
processing of the sampIes.
•
BIBLIOGRAPHY
Bemal, P.A., 1980. !Arge scale biological events in the Califomia Current: The low
jrequency response oj the epipelagic ecosystem. Ph.D. dissertation, Scripps Institution of
Oceariography, Univ. of Calif., San Diego, 184 pp.
Chelton, D.B., Bemal, P.A., McGowan, J.A., 1982. Large-scale interannual physical and
biological interaction in the California Curient. J. Mar. Res., 40, 1095-1125.
Cushing, D.H., 1971. Upwelling and the production of fish. Adv. Mar. Biol., 9, 255-334.
Cushing, D.H., 1978. The upper trophie levels in upwelling areas. In Upwelling Ecosystems,
B.Boje e M.Tomczak (cd.), Springer, Berlin, 303 pp.
Fiuza, A.F.G., 1983. Upwelling patterns off Portugal. p. 85-98. in Coastal Upwelling. fts
sediment record, Part A:, E.Suess e J. Tbiede (cd.), Plenum Press, 604 pp.
Fiuza, A.F.G., 1984. Hidrologia e dinamica das dguas costeiras de Ponugal. Ph.D. thesis,
6
Departamento de Ffsica, Universidade de Lisboa, 294 pp.
Fiuza, A.F.G., Macedo M.E., Guerreiro M.R., 1982. Climatological space and time
variation of the Portuguese coastal upwelling. Oceanologica Acta, 5, 31-40.
Frouin, R., Fiuza, A.F.G., Ambar, 1., Boyd, T.J., 1990. Observations of a poleward
surface current offthe coast of Portugal and Spain during winter. J. Geophys. Res., 95, 679691.
Haynes, R., Barton, E.D., 1990. A poleward flow along the Atlantic coast of the Iberian
peninsula. J. Geophys. Res., 95, 11.425-11.441.
Smith P., Richardson S.L., 1977. Standard techniques for pelagic fish eggs and larva
surveys. FAO Fish. Tech. Pap., 175, 1-100.
Wooster W.S., Bakun A., McLain D.L., 1976. Tbe seasonal upwelling cycle along the
eastem boundary ofthe North Atlantic. J. Mar. Res., 34,131-141.
•
•
7
3
Table 1- Monthly means of the zoplankton biomass (Log., [(ml/lOOOm )+ 1]) and respective
number of sampIes and standard deviations.
Fm
JAN
HAR
APR
MAY
JOH
AUG
JUL
SIlP
OCT
JIOV
Dlle
Sl.v.: 505 ,..
Il.plnbo
M• •n
11
STD
4.0
17
0.5
2.8
6
1.0
Flqualra da Fo.
4.2 4.5
Maan
4.6
12
0.8
4.0
12
1.5
4.6
6
0.5
4.3
6
0.3
4.5
11
0.6
4.7
12
0.7
--
4.6
9
0.6
4.4
14
1.2
4.3
12
0.5
11
STD
18
0.6
7
1.0
4.6
13
0.8
4.6
14
0.8
4.3
7
1.4
4.9
7
0.5
4.2
14
1.0
4.7
7
0.7
4.5
7
0.5
4.4
13
0.4
4.2
21
1.0
4.4
14
0.7
Slna.
Maan
4.2
•
0.3
3.1
3
0.2
4.7
6
0.3
4.0
3
0.3
3.2
3
0.7
3.9
6
0.5
5.2
6
1.0
4.5
6
0.4
4.3
3
0.4
4.7
3
0.4
4.5
5
0.5
4.5
6
0.7
3.5
8
0.7
2.5
4
1.2
5.0
8
1.1
5.2
•
0.7
5.1
4
0.3
4.2
4
0.5
5.0
8
0 ••
5.5
7
0.3
4.3
2
0.0
5.2
4
0.7
3.8
12
1.1
4.0
8
0.5
4.0
51
0.6
3.4
20
1.3
4.7
39
0.8
4.5
37
1.2
4.4
20
1.1
4.3
23
0.6
4.6
39
0.9
4.9
32
0.7
4.4
12
0.5
4.6
29
0.6
4·.2
52
1.1
4.3
40
0.6
---
5.2
9
0.4
5.0
14
1.0
4.6
12
0.7
11
8TD
Lag08
Maan
11
8TD
To~a1
Mean
11
8TD
Slava: 335 ,..
E.plnbO
M"an
11
8TD
4.2
17
0.6
3.2
6
1.2
Flqu"lra da Fo.
4.9
4.3
Mean
11
8TD
Slna.
4.9
12
0.9
5.0
6
0.5
5.3
6
0.6
4.9
6
0.8
5.0 5.0
11 12
0.4 0.7
1.
0.9
7
1.0
4.8
11
0.8
5.2
12
0.5
5.2
7
0.4
5.5
7
0.5
5.0
14
0.5
5.1
7
0.8
5.1
7
0.6
5.0
13
0.6
4.7
21
0.8
4.6
14
0.7
4.6
8TD
0.3
•
3.8
3
0.2
5.1
6
0.2
4.8
3
0.2
4.1
3
0.6
5.0
6
0.4
5.5
6
0.8
4.9
6
0.3
5.0
3
0.8
5.0
3
0.1
5.1
5
0.6
4.4
6
0.7
Lago.
Mean
4.1
•
0.5
3.6
4
1.1
5.4
8
0.7
5.3
7
0.7
5.7
4
0.4
5.5
4
0 ••
5.5
0.7
5.7
7
0.7
5.2
2
0.2
5.9
4
0.8
4.3
12
1.2
4.2
8
0.8
4.3
51
0.7
4.0
20
1.2
5.0
37
0.8
5.0
29
1.1
5.2
20
0.7
5.2
23
0.7
5.2
39
0.6
5.1
32
0.7
5.1
12
0.6
5.2
29
0.6
4.7
52
1.0
4.5
40
0.7
M"an
11
11
STD
To~a1
Maan
11
8TD
8
•
Distance offshore (km)
65
51
36
20
28
Distance offshore (km)
12
.t···· ... ~..
"
.
: -:. .... : 13.0
"
:
"\
'j
50
~':
65
4
150
C
50
\.~
...
da Foz
'\
p ••••••
..c
"<li ISO
Temperature (OC)
..
14/15 Feb. 1987
250 L-L
250
---J
Distance offshore (km)
65
36
51
28
20
Distance offshore (km)
12
65
4
50
,.
~
~ ~~
_140
Figueira da Foz
c
Figueira da Foz
27/28 Apr. 1987
250 ' - ' - - - - - - - - - - - - - - - - - - - '
51
36
28
Distance offshore (km)
20
12
65
4
51
36
28
20
12
".
c..
<li
Temperature (OC)
c
/
250
- 1 4 . 0 ~14.0·
da Foz
150
Temperature (OC)
22 Jul. 1987
15 Jun. 19B7
/
250
L-L
---J
Dislance offsbore (km)
Distance offshore (km)
65
50
l
51
36
28
20
12
4
65
.~~
150
28
20
12
4
da Foz
.c:
.....
~ 150
Temperature (OC)
L.L~
36
l
Temperature (OC)
c
22 Sep. 1987
15 Aug. 1987
250
51
50
Figueira da Foz
..c
~
3~:_~~~~~:~~{(~:??~~4~-1l··~
50
'/
<li
.
.c:
150
4
Temperature (Oe)
..c
c
12
22 Mar. 1987
50
c..
20
Temperature (OC)
'.
65
•
28
·0
ISO
Distance offshore (km)
<li
36
'~"""'~'40
"
250
c..
51
±~~-~~~;:~}~~~~j.~
l~.~\
50
l
:tj,
Temperature (OC)
_........ "
C
4
<>
da Foz
.
16 Jan. 1987
c"
12
l
..c
.....c"-
20
{:
. ,'
..,;
'-0_-
.§.
<li
28
36
0
~
c..
51
~
--.J
250
L-L
---J
Figure 3. Monthly evolution of the thermic structure of the water column along the section
off Figueira da Foz. (Continue in next page)
Dislance offshore (km)
65
51
36
28
20
Dislance offshore ! km)
12
4
65
51
36
28
2~
12
4
o r---------,--o-~.:-~-.:_.."..__-,
...:.:.'.
50
50
]
]
..c:
~
c
100
..c:
~
150
c
~~,;
0
;/?14
200
250 LL
.-I
Figueira da Foz
150
250 LL-
3 !\ov. 1987
-.J
Figure 3. Monthly evolution of the thermic structure of the water column along the section
off Figueira da Foz. (Continuation of the preceding page)
•
•
D;slenee ol:shore (km)
20
12
llislence o:!'sho!"f' (km)
4
20
.'
50
12
!
100
!
125
•
Q
.'
.
:'
~~
./
:!!'
/
Sim's
.. !J
temperalure ("C)
l?~
~
;/
15 Feb, 1967
20:>
200
225
225
250
250
275'----L...------_--.J
275'----'-----------'
275 ' - - - ' - - - - - - - - - - '
Distance of!shore (km)
20
12
Dislanee on.hore (km)
4
20
12
....'
50
,
75
100
!
.::.
~ 150
:5
Q
Q
~
175
23 Jul 1987
Sines
12 Jun, 1967
200
250
250
275'---L-----------'
275 ' - - - - ' - - - - - - - - - -
Dlslenee offshore (km)
08 Mey 198
7
II
II
!
!
275'----'----------I
Dlslene. offshore (km)
4
20
25
I
temperalure f~C)
("C)
225
12
I 5.0
150
225
20
F
125
1?5
200
"
..... \~~
100
125
.
4
25
25
!
4
,/
..
.
•/
("C)
175
•
)
125
Sines
12
.!
J,s
:S
c. 15:>
20
. \j
'0
100
DisLant'e or:share (km)
4
.. _-
~--_._-_._~
12
Distenee offshore (km)
20
4
12
4
25
50
75
100
!.::.
g.
.
~.-----_
'.
100
!m
125
150
Q
175
100
!
125
:5
c.
150
~
Sines
Q
("C)
200
175
200
Sines
Sines
("C)
06 Sep, 1987
19 Oet. 1957
225
225
250
250
250
215'---J-----------'
275 ' - - - ' - - - - - - - - - '
275'---'----------'
Figure 4. Monthly evolution of the thermic structure of the water column along the sectiml
off Sines. (Continue in next page)
Distence o::shore (km)
20
12
4
100
!.,
i
125
150
Cl
I?~
200
Sines
rerr:peralure rC)
15 Nov. 1987
22~
2M
275'----'-----------'
Figure 4. Monthly evolution of the thermic structure of the water column along the seetion
off Sines. (Continuation of the preceding page)
•
tislenc~ or~shore
28
20
(kr.::l.)
12
tlsb.nce
28
50
!
"'e-
.0
(km)
Dlsh.nC't' or~si1ore (km)
20
12
4
••. o ~
.~
25
o~!ahoN'
o ~-_2~8'----2'::,;...--;:12'--.;.___,_-
I
25
)
50~
}150
50
75
75
'5
100
.00
.00
.25
]: .25
!
125
:5
150
g.
Lagas
Q
16
200
JOb.
oe
ISO
Lages
'.5
Temperature ("C)
Q
Temperature ("C)
175
1961
]- 150
20 W.r. 1981
225
250
250
275l------l'--
-'
Dish.Dce onshore (km)
20
28
275'-_ _'--
---l
DistaDce ollshore (km)
12
Dlstance of1shore (km)
2820124
25
--'
28
20
12
25
50
I
:5
t
75
75
.00
100
I
.25
:5
l~O
Q"
Lages
Q
~
{·C}
.75
125
15C
175
08 lIoy 1961
200
250
20
12
28
25
·&3f.·k~2H:gy&o.
50
.~
•
25
·3:<"~5.:1·-=:?·:~
:.---'
•
.:
/'/
..~.''''.:.".Q
·'.::0/...····
/ :' .;
150
200
23 J\Il. :967
//
I/
20
Distance
12
·lb~
~'
....
Temp~t::e
1
("C)
26 Au;:. 1961
(km)
.
:r
~~~~o
1
. ·.·~.·i~~~;~::~:~ . ;'.0
.•..•......~
25,
:./
'-,~~
......-...
.~ ••_.,}
19 5
..
.."'.~
_;.
100
]125
"'
of~s~ore
o rl_ _~28'-_--=,20;_-.....;;12'--..;...._-
100
]
125
oe
150
Lagos
"5
Temperature ("Cl
200
225
i
lSl)
Lage.
175
Temper.ta..... ("C)
Q
22 Oct. 1987
24 }öov. 1981
225
250
275l---_L-
---l
:..---- /600
'/"/;'
175
1967
Dis\..ance orrshore (km)
•
! ..:/.:.!a.ll..~~'f..\>·~.Q.
}"'
JUD.
2SC
28
125
13
2'5 ' -_ _'--
---l
Dimnce o!!!ho:"e (km)
]
Lage.
Tf'r.'lpE'rat'.J..-e (Oe)
225
275l----l-----
100
Lage.
Terr.perllture (eC)
200
225
•
Te"'perature ("Cl
17S
225
275l----L.------
•
Lage5
Q
16 Feb. 1967
200
225
'"c
25r
250
---l
275l----L - - - -
250
_
275l--_---l.
-'
Figure 5 Monthly evolution of the thennic structure of the water column along the section
off Lagos.
•
6 ,....A;.__
w.:..r_a_~ge-=--=b...:...:io~m...:...:a.:..:.s.:..s-.:.U...:...:n-.:.[.:.:..(m:......:.I __
/1:...:.0__
0...:...0...:...m...::.3.:.....)+--=1]:.:....1_ _---,
5
4
3-+----,---,---,--,----,--,----,--,----,--,----,,---r---I
J
FMAMJ
JASOND
Months
Figure 6. Monthly evolution of the rnean zooplankton
biomass offthe Portuguese coast. (Verticallines: standard
error; continuous line: strained by 335 /lrn; dashed line:
strained by 505 /lrn)
7 ~ bIomaaa
l'" (mV1OOOm3)+1D
8
IS
--..1-"'""14
"
S
2
ESPINHO
1
FIGUEIRA DA FOZ
0+.-...-...-...................--.-.....--.--.--.---.---.--1
J F M A M J JA' 0 N D
M<lnthe
J F M A M J JAS 0 N D
Montha
•
I
SINES
O+-..,..-..,..-...-~.....-..,....._r__r_.....,.......,.._.,...-....-l
J F M A M J JA' 0 N D
MonthI
LAGOS
O+.-..,..--.--~.....-..,.....-r-_r__r_.....,.......,.._.,...-....-l
J F M A M J JA' 0 N D
MonthI
Figure 7. Monthy evolution of the mean zooplankton biomass off the four studied
sections. (Verticallines: standard error; continuous line: strained by 505 pm; dashed
line: strained by 335 /lm)
~
~
Coarrlo!ant cf wr1$tion
Coemdent 01 wrlat10ll
-+- blllMo
-+-
180'
....-'--
-....
~nllo
- lll_
PlQveIl'Q
-g..
.-0- - 81_
F'lgueIre
1&0'5
lOOS
1000.
&Q44
sn
,
lJ.--e__ Qo...G
,.
,. ..,
,
(b)
..
"
""
Figure 8. Monthly evolution of the coefficient of variation of the mean of the non-log.
0'1
N
•
0
"
K
D
l
.. A .., l
l
0
H
D
zooplankton biomass along the sampled sections. «a) - strained by 335 ILm; (b) strained by 505) .
•
G'
• 1e
4
8
•
35
4
I
8
335
2
..
,..,,...,,,
..
um
505 um
,.IO"D
2
"
.. ..,,...,
MonthI
..
",.IO"D
Uontht
Figure 9. Monthly evolution of the mean zooplankton biomass in the northern region
(continuous Hne) and in the southern region (dashed Hne). (Vertical lines: standard
error)
•
~
~ Coomdent d
eo.mCSlUlt ot ~
-G- HorlbWn coaIl
.... Soulber. coaIl
1&0'5
1sos
l~
100s
&Oft
sos
1'a11atSou
(b)
(a)
K
J
,
.. A .. J
J
A I
0
H D
010
J
,
.. A .. J
J
A
I
0
H D
Figure 10. Monthly evolution of the coefficient of variation of the mean of the nonlog. 'zooplankton biomass off the northern and southern coasts. «a) - strained by 335
ILm; (b) .- strained by 505 ILm)