-_N_o_4_~-------
___________________________________O_C_E_A_N_O_L_O_G_I_CA
__A_C_T_A_1_9_8_6_-_V_O_L_.9__
Extent, transparency,
and phytoplankton distribution
of the neri tic waters overlying
the Israeli coastal shelf
Chlorophyll a
Transparency
Primary production
Neritic waters
SE Mediterranean
Chlorophylle a
Transparence
Production primaire
Eaux néritiques
Méditerranée SE
T. BERMAN a, Y. AZOV a, A. SCHNELLER a, P. WALLINE a, D. W.
TOWNSEND b
a Israel Oceanographie and Limnological Research, Tel-Shikmona, P.O.B. 8030, Haïfa
31080, Israel.
b Bigelow Laboratory for Ocean Sciences, West Boothbay Harbor, Maine 04575,
USA.
Received 1986, 9, 4, 439-447.
ABSTRACT
Phytoplankton abundance, distribution and activity in the SE Mediterranean near
Israel have been studied on six cruises from July 1981 to June 1984. From spring
through fall a sharply defined surface front of temperature and chlorophyll marked
the transition from a relatively narrow (10-20 km wide) strip of nearshore water to
oceanic waters. This boundary was more diffuse during the winter and early spring.
The neritic region had higher chlorophyll concentrations (euphotic zone averages
ranging from 0.06 to 0.44 mg m- 3 ) than deeper waters (from 0.06 to 0.12 mg m- 3 ).
Highest chlorophyll concentrations were found in late win ter and early spring. Picophytoplankton was generally a major algal biomass component. Frequently 1% or more
of the surface irradiance reached a considerable portion of the shelf sediment. Profiles
at neritic stations often showed increased chlorophyll concentrations near the bottom.
The average values of chlorophyll standing stock and integrated water column primary
productivity were lower in both neritic and pelagie regions than those reported recently
near the Egyptian coast. Nevertheless, no definite gradient of chlorophyll decreasing
South to North along the Israeli coast was observed.
Oceanol. Acta, 1986, 9, 4, 439-447.
RÉSUMÉ
Extension, transparence des eaux et répartition du phytoplancton dans
les eaux néritiques israéliennes
L'abondance, la distribution et l'activité du phytoplancton dans le bassin oriental de
la Méditerranée près d'Israël, ont été étudiées au cours de six campagnes, entre juillet
1981 et juin 1984. Du printemps à l'automne, la surface bien définie d'un front de
température et de chlorophylle marque la transition entre une bande relativement
étroite d'eaux côtières (10 à 20 km de large) et les eaux du large. Cette frontière est
plus diffuse durant l'hiver et au début du printemps. Les concentrations de chlorophylle
sont plus élevées dans la région néritique (0,06 à 0,44 mgfm 3 en moyenne dans la
couche euphotique) que dans les eaux plus profondes (0,06 à 0,012 mg/m 3). ·
Les plus hautes concentrations en chlorophylle ont été trouvées en fin d'hiver et au
début du printemps. Le picophytoplancton a été en général un composant majeur de
la biomasse. Sur une portion considérable du sédiment du plateau continental, l'éclairement atteignait fréquemment ou dépassait 1% de sa valeur en surface. Aux stations
néritiques, les profils de chlorophylle ont souvent montré une augmentation de la
concentration au voisinage du fond.
Les valeurs moyennes de la teneur en chlorophylle et de la productivité primaire
intégrée sur une colonne d'eau sont plus basses dans les régions néritiques et océaniques
que celles relevées récemment près des côtes égyptiennes. Pourtant on n'a pas observé
de gradient de chlorophylle décroissant du Sud au Nord le long de la côte israélienne.
Oceanol. Acta, 1986, 9, 4, 439-447.
0399-1784/86/04 439 09/$ 2.90/@ Gauthier-Villars
439
T. BER MAN et al.
INTRODUCTION
Lebanon (Oren, Komarovsky, 1961; El Din, 1977).
Since the operation of the Aswan Dam in 1965, the
water flow, particulate loading and dissolved nutrient
input of the Nile into the southeastern Mediterranean ·
has greatly diminished. The neritic waters described
here would be the most likely to be affected by these
changes which may have, in turn, imposed altered levels
and patterns of biological productivity in the region.
Our results are compared to recent data for the neritic
zone off the Egyptian coast (Dowidar, 1984) and also
to those from the oligotrophic oceanic waters of the
Levant Basin (Berman et al., 1984).
Since antiquity the coastal waters of the southeastern
Mediterranean have been important fishing grounds,
but there exists relatively little detailed modern
information about these marine ecosystems. In this
paper, we report on recent spatial and temporal patterns of phytoplankton distribution, primary productivity and transparency in the neritic (usually < 100 m
deep) waters off the Israeli coast, roughly overlying the
narrow ( < 15-25 km) continental shelf. Previously, we
have described similar features for the oceanic
(>100 m) waters of this region (Berman et al., 1984a;
b; 1985).
Prior to the construction of the Aswan High Dam, the
annual Nile flood, with its peak from August through
October, was responsible for the major influx of
nutrients utilized by the primary producers in the
inshore waters of Egypt. The effects of the Nile input
could be detected as far as the coasts of Israel and
STUDY AREA AND METHODS
Our data were collected during six cruises from July
1981 to June 1984 (AID l-AID 6) covering the stations
in Figure 1. Hydrostation coordinates and dates are
given in Table 1, with the neritic locations indicated.
~E
~
~
~
i=====~r=====~====~======~====~======~~~
Figure 1
Map of the southeastern Mediterranean (Levant
Basin) with locations of stations given in Table 1.
0
0
0
Southeastern
Mediterraneen
0
0
0
0
Table 1
3i"N
AID Cruise hydrostation locations and dates.
Coordinates
Coordinates
Station
Date
N
E
Station
Date
N
E
1-2
1-2*
1-3*
1-5
1-7*
1-9
1-10*
2-1
2-2*
2-3
2-4
2-5
2-6
2-7
2-8*
2-9*
24.7.81
25.7.81
27.7.80
28.7.81
29.7.81
30.7.81
31.7.81
10.12.81
11.12.81
11.12.81
12.12.81
12.12.81
13.12.81
13.12.81
14.12.81
14.12.81
32"21.56'
32°20.41'
32°50.57'
32°35.57'
31°42.40'
31°56.38'
32°49.83'
32°50.50'
31°47.00'
31°58.67'
32°25.00'
32°42.00'
33°00.00'
32"48.00'
32°47.00'
32°48.30'
33°28.82'
33°32.59'
34°46.46'
34°31.23'
34°28.32
34°27.42'
34°53.78'
34°50.00'
34°27.00'
33°59.35'
32°17.00'
33°05.00'
32°32.00'
32°39.00'
34°49.00'
34°56.00'
4-1*
4-2
4-3
4-4
4-5*
4-6
4-7*
5-1*
5-2
5-3
5-4*
18.7.82
19.7.82
20.7.82
20.7.82
21.7.82
21.7.82
22.7.82
13.3.83
14.2.83
14.2.83
15.2.83
32°50.00'
32°47.90'
31°48.00'
31 °55.41'
32"25.30'
32°29.70'
32°50.00'
32"49.50'
32°49.50'
32°22.60'
32°26.00'
34°51.80'
33°27.20'
34°31.00'
34°21.15'
34°50.00'
34°39.10'
34°50.00'
34°51.20'
33°43.40'
34°43.40'
34°46.00'
3-1*
3-2
3-3*
3-4
3-5*
3-6
3-7
3-8
9.4.82
9.4.82
10.4.82
10.4.82
11.4.82
11.4.82
12.4.82
12.4.82
32°51.40'
32°58.00'
32°50.50'
32°28.00'
31°47.00'
31°50.70'
32°18.00'
32°32.10'
34°56.00'
34°00.00'
34°53.30'
34°41.00'
34°27.00'
33°54.80'
33°02.00'
33°50.00'
6-7
6-8
6-13*
6-15*
6-16
6-17
6-18*
6-19*
6-20
6-21
6-22
6-25*
11.6.84
11.6.84
12.6.84
13.6.84
13.6.84
13.6.84
14.6.84
14.6.84
14.6.84
14.6.84
14.6.84
14.6.84
32°52.40'
31°51.30'
31°51.30'
32°13.50'
32°17.00'
32°17.00'
32°35.30'
32°34.00'
32°34.80'
32°27.80'
32°51.30'
32°53.50'
33°18.00'
33°52.00'
34°52.00'
34°44.50'
34°36.00'
34°36.00'
34°51.00'
34°49.20'
34°47.90'
34°48.50'
34°50.60'
34°55.00'
• Neritic stations.
440
PHYTOPLANKTON OF ISRAEL! COAST WATERS
,......,---r----,r----.---,33°
At each station in the early morning, sampling depths
were chosen to correspond to approximately 100, 50,
25, 12, 6, 3, 1 and 0.5% of surface irradiation estimated
rapidly, but roughly, by taking the 1% depth as 3 times
the Secchi depth. During the day, more accurate
determinations of photosynthetically active radiation
(P.A.R.) at the surface and in the water column were
also made with a LiCor Quantum meter. Integrated
values for incident daytime P.A.R. were obtained using
LiCor LI-510 Integrator. Water samples from hydrocasts for primary productivity incubations (see below)
were prefiltered through a 130 11m mesh Nitex net to
eliminate larger zooplankton. No significant amounts
of chlorophyll were retained on these nets. For size
distribution studies, samples were subsequently passed
through 20 11m Nitex nets (by gravity) or 3 11m Nuclepore filters ( < 100 mm Hg vacuum). Chlorophyll and
phaeophytin concentrations were determined by fluorometry (Turner Designs 10 Fluorometer, calibrated with
chlorophyll a from Sigma) in discrete samples which
were concentrated by filtering 100 ml through BA83
0.2 11m Schleicher and Schüll membrane filters and theo
extracted into 90% acetone (Holm-Hansen et al., 1965).
At the low pigment concentration levels which were
often encountered ( <0.1 J!g Chi a l- 1 ), the precision
of this technique was about ± 25 %.
Surface chlorophyll was monitored between stations en
route by in vivo fluorescence (Lorenzen, 1966), using a
flow from the ship's intake into the fluorometer. The
in vivo chlorophyll fluorescence signal was calibrated
by measuring pigments in discrete water samples taken
every few hours from the fluorometer outflow and
extracted as above. Surface temperature was simultaneously recorded with a calibrated thermistor probe in
the water flow.
Photosynthetic carbon fixation was determined using a
modified Steeman-Nielsen (1952) technique. We added
14
C-bicarbonate (30-50 !lCi) to 130 ml acid washed
glass botties which were placed in an on-deck simulator
cooled by surface water (temperature ranged from
17.SOC on AID-3 to 28°C on AID-1). Care was taken
to minimize light shock. The light depths were simulated by using severa! layers of netting. This, however,
did not compensate for any changes of light spectral
quality which would have occurred in situ (see below).
After incubations of 4 to 6.5 hours (around local noon),
the contents of the productivity botties were filtered
onto presoaked 0.45 J!ffi BA Schleicher and Schüll filters which were theo rinsed with 10 to 15 ml of filtered
seawater, exposed to HCI fumes, aired and subsequently placed in scintillation fluor (Instagel) for counting
(Berman, 1973). Filters, similarly processed from Lugo!
poisoned subsamples, were used to correct for nonbiologically produced, contaminating contents.
A
D
..
:;~
;.
J!
26.2 - 27.0
.j~lAvlv
/1
:"\ 0 ·
_jLod
...Askelon
~----·-IOOm-'l-tz;~9<;: G~·za
. /f
35°
Figure 2
Surface contours of ch/orophy/1 (J.lg /- 1 ) and temperature ("C). A, B:
AID-3, Apri/!982; C, D: AID-4, July 1982.
water region. In cruises during June, July and December, a sharply defined surface front of chlorophyll and
temperature marked the transition from nearshore to
pelagie waters. This boundary was more diffuse during
the February and April cruises (Fig. 2). These observations correspond with the satellite (Nimbus 7, Coastal
Zone Color Scanner) images from July 1979 and
November 1978 which we have received (Berman et
al., 1984b). There was usually a close correspondence
between the isopleths of surface temperature and surface chlorophyll concentrations. For both parameters,
higher values were associated with the neritic water at
ail seasons. Sorne localized regions of elevated surface
chlorophyll concentration were occasionally noted in
the close vicinity of Ashdod and Haifa ports. However,
the extent of the more productive waters was quite
limited at ali seasons, rarely reaching more than
20-25 km offshore even in late winter-early spring
(Fig. 2).
Optical properties
Secchi dise transparencies in the neritic waters ranged
from 6 to 27 m. The average for ail nearshore stations
was 17.7 (±5.5) rn compared to 37.5 (±6.7) rn for
offshore locations. Similarly, average values for the
diffuse downwelling attenuation coefficient, k, were
0.089 (±0.048) m- 1 and 0.047 (±0.013) m- 1 for neritic and oceanic stations, respectively. This was
RESULTS
Extent of the nearshore water mass
On each cruise we observed a neritic water mass,
roughly overlying the narrow continental shelf, with
higher surface chlorophyll concentr~tions than the deep
441
T. BER MAN et al.
we estimated by extrapolation that the deep chlorophyll
layers (see below) were generally located at 0.5-1.0% of
incident light, similar to observations elsewhere (Cullen,
1982). The depth of 1% 10 (downwelling PAR at surface) varied from about 85 to 130 rn in the pelagie
zone.
Ali light profiles showed higher apparent attenuation
in the uppermost water layers due to rapid selective
loss of the blue and red light (see Jerlov, 1977; Jewson
et al., 1984). Farther down, the linear portion of the
light curve corresponds to the attenuation of a rather
narrow wave band. We did not observe minimum attenuation values between 30 to 10% 10 as noted in oligotrophic waters by Jerlov (1977), but this may be because
our sensor did not go deep enough. There is no doubt,
_however, that the open waters of the eastern Mediterranean belong to Jerlov's type 1 (most transparent) cate·
gory, and even the neritic waters would be rated as
types lB or II (highly transparent).
Table 2
Ratio of upwelling to downwelling irradiance, R, at neritic and oceanic
stations.
Neritic
Station 4-3
Depth
0
5
10
15
20
25
30
Pelagie
Station 6-7
Depth
0
5
10
15
20
25
30
38
40
50
60
70
R
0.019
0.031
0.048
0.058
0.069
0.064
0,070
Station 4-5
R
0.024
0.039
0.046
0.045
0.071
0.046
0.045
0.045
0.048
0.039
0.038
0.042
Station 4-4
Depth
0
10
15
20
25
30
R
0.018
0.029
0.042
0.050
0.059
0.067
0.087
Depth
0
R
0.018
5
5
10
15
20
25
30
38
40
50
60
70
0.034
0.052
0.042
0.042
0.039
0.036
0.034
apparently due not only to higher ambient concentrations of chlorophyll in the neritic waters but also resulted from increased attenuation and scattering from
other suspensoids. Whereas for the deep stations, the
ratio of upwelling to downwelling irradiance was fairly
constant, for the nearshore water this parameter
increased steadily with depth (Tab. 2), indicating a corresponding increase of light scattering (Hutchinson,
1957; Morel, 1982).
Sorne profiles of downwelling attenuation of photosynthetically available radiation, PAR, as measured with a
eosine collector quantum meter, are shawn in Figure 3.
Even in the more turbid nearshore waters, at least
1-5% of the incident light frequently penetrated down
to the bottom of the shelf, and measurements of average and daily total incident PAR (Tab. 3) indicate
that relatively large absolute amounts of light energy
may reach a considerable area of the coastal shelf
sediment surface throughout the year.
Since the cable of our light meter was too short to
enable us to measure full profiles at oceanic stations,
Chlorophyll
Chlorophyll levels were highest from mid-winter to
early spring. During the summer and autumn, in the
nearshore waters, chlorophyll concentrations (mg rn- 3 )
were generally 3-8 fold those in the upper levels of
the oceanic region; in winter the difference was less
Table 3
Average and total dai/y incident photosynthetical/y avai/able radiation (PAR)
measured during cruises AID 1-6.
Cruise
Date
1-1Ein
Sunlight m- 2 s- 1
AID-1
AID-2
AID-3
AID-4
AID-5
AID-6
July 1981
Dec. 1981
Apr. 1982
July 1982
Feb. 1983
June 1984
12.5
8.5
11
12.5
10
12.5
Ein
1400
639
1100
1254
700
1275
m-2 d-1
{g C m- 2 d- 1}*
63.00
19.56
43.96
58.69
25.20
54.68
348
108
243
324
139
305
• Theoretical equivalent amount of photosynthetic carbon fixation (lOO%
efficiency). Approximate calculation based on conversions:
52,000 cal. Ein. vis- 1 9.33 cal.mg.C- 1
0
x
20
2-6
40
x
x
x
x
1-9
x
x
4-2
60
.: 80 x
::t:
~ 0
w
..
0
20
...
40
Figure 3
Diffuse downwelling attenuation of photosynthetical/y
available radiation (P.A.R.) for some oceanic (upper panel)
and neritic stations (lower panel).
...
•
...
... ...
•
1-7
•
•
4-5
• 2-2
6
[
1
r.
10
1
10
1
442
100%
10
100%
PHYTOPLANKTON OF ISRAELI COAST WATERS
Table 4
Chlorophyll concentrations averaged for neritic and oceanic stations on AID cruises and percentage of chlorophyll associated with picophytoplankton
( <3 J.lm).
Neritic ( < 100 m)
Pelagie(> 100 m)
#of
stns.
Chlorophyll*
mgm- 2
Av. Chi**
mgm- 3
Av.Chlt
(37%1)
mgm- 3
5
4
3
3
4
2
6
5
9.7
5.4 (73)tt
8.0 (61)
3.9 (70)
8.2 (72)
4.9 (65)
0.17
0.11
0.25
0.11
0.12
0.16
0.17
0.10
0.26
0.07
0.11
0.15
Cru ise
1
2
3
4
Cru ise
1
2
3
4
3
6
5
2
2
7
5
6
mg rn
Av. Chi**
mgm- 3
Av.Chlt
(37%1)
mgm- 3
8.7
13.9 (81)
12.9 (71)
7.2 (70)
14.7 (72)
10.8 (80)
0.07
0.11
0.09
0.06
0.12
0.08
0.03
0.07
0.04
0.03
0.12
0.03
Chlor~~hyll*
#of
stns.
• Integrated down to 0.05% Io orto the bottom when 1>0.05% Io at the sea floor.
•• Average value for the layer to the depth of integration.
t Average chlorophyll concentration in the surface layer down to 37% 1•.
In parentheses, percentage of chlorophyll associated with picoplankton ( < 3 J!ID).
Chl·l- 1
pg
02
10
10
10
25
25
There was no consistent indication of gradient in
pigment concentrations from south to north (Fig. 7) ..
Thus, although the chlorophyll biomass decreased in
nearshore profiles from opposite Ashkelon to opposite
the Oceanographie Institute just south of Haifa in July
01
5-4
FEB.
25
3-1
APR.
50
·c
17 lB
21
pg
23 25 'C
E
Chl·l- 1
OJ
16 17
:r
oc
/
//
1-
a.
LIJ
0
r
6-8
1
~
30
50
1
1
/
JUL.
œc.
1
1
t
1
1
1
l1
21
1
1
1
23 25 27 "C
1
•1
1
100
1
.
1
1
1
20 21
OCT_
1
1
1
1
1
60
DC-B
1
4-2
2-1
,
50
'JY,../'
/
JUNE
1
1
1
1
1
40
0
6-17•
1
20
1
1
,,/,)(
1
1
1
1
10
f1
/
(
02
0
0
oz
0.2
1
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oc
J
E I!SO
16
18 2022 Z4"C
82022Z426'C
151719
21
2325'C
I
l-
a..
w
01
02
0
i
t
Figure 4
Depth profiles of chlorophyll (Jlg /- 1) and temperature ("C) at neritic
stations off the Israeli coast in different seasons. Chlorophyll (o----o),
temperature (x---x), bottom indicated by stippling.
1
1
1
1
1
't
1
1
pronounced (Tab. 4, Fig. 4 and 5). However, during
the latter season sorne of our hydrostations, although
at depths > 200 rn, may not have been sufficiently
distant from the Israeli coast to have been in true
"oceanic" Levant Basin· water. As noted above, in
winter there appears to be westward spreading of the
more productive neritic water. In the nearshore region,
greater fluctuations of total standing stocks and chlorophyll concentrations were observed than in deeper
waters (Tab. 4, Fig. 4 and 5).
Many neritic profiles showed a marked increase of
· chlorophyll concentration near the sediment surface
(Fig. 4, 6 and 7). Generally, concentrations of chlorophyll decreased gradually with increasing distance
from the shore (Fig. 6), with a sharp drop and an
obvious change of water color at the surface fronts.
3-B
APR.
5·3
1
FEB.
1
1
1
1
1
t
!1
1
1
1
1
1
~1
1
t
J
1
1
1
'
i
zef~
16
1
t
~
1
8 "C
15
17
19"C
Figure 5
Depth profiles of chlorophyll (J.lg l- 1) and temperature ("C) at oceanic
eastern Mediterranean stations in different seasons (locations as
marked, e.g. 4-2=AID-4, station 2, etc. DC-B was taken during a
day cruise in October .1981 at 32°51.74'N, 34°44.51'E). Chlorophyll
(o----o), temperature (x---x). A pump profile of chlorophyll
determined by in vivo fluorescence was made at AID 6-8, and samples
from·discrete depths were calibrated by filtration and extraction into
acetone (o).
443
1
T. BER MAN et al.
l'g
Chl·l- 1
(from 75 to 125 rn) were observed on all croises with
the exception of February 1983.
Despite the higher chlorophyll concentrations (mg Chi
· rn- 3 ) usually observed at nearshore stations, the much . ·
greater depths of the offshore photic zones and the
presence of the deep chlorophyll maxima account for
the generally higher areal standing stocks (mg Chi rn- 2 )
found at the latter (see Tab. 4). In the oceanic profiles,
a considerable proportion ( 40-60 %) of the total standing stock of chlorophyll was contributed by the deep
'chlorophylllayers.
We have previously presented data from AID croises 1
through 4 (Berman et al., 1984 a; b) showing that the
majority of the chlorophyll biomass in both oceanic
and neritic waters consisted of pico- (or ultra-) phytoplankton, in our case operationally defined as organisms passing through 3 JliD Nuclepore filters. This
predominance of picophytoplankton was also observed
during A ID croises 5 and 6. From the data given in
Table 4, it appears that in summer months there was
a tendency for higher proportions of picophytoplankton to occur in the oceanic than in the neritic water
but not at other times. We did not observe any clear
trend towards increased proportions of picoplankton
with depth (Berman et al., 1984a) as had been found
elsewhere (Li et al., 1983).
O.----..--'T---""ili-
10
20
30
18 20 22 24 26 "C
E
40
50
18
:I:
20 22 24 "C
l-
a..
OJ
02
02
OJ
o~-T----",!1"---
IO
)
/
25
/
/
/
/
/
/
/
/
'
6-21
75
18 20 22 24 "C
Figure 6
Profiles of chlorophyll (J!g r 1) and .temperature
. ("C) in a transect from close inshore (AID 6-18)
to past the shelf break (AID 6-21). Chlorophyll
(o----o), temperature (x---x), bottom indicated by stippling.
01
10
0.2
0.1
10
20
.
20
4-3
30
30
26
2
JULY
1
27
•
28 "C
24
E
:r
f-
~g Chi 1-1
OJ
a..
zs •c
25
LU
0
10
10
I
25
Figure 7
.....
Profiles of chlorophyll ()!g 1- 1 ) and temperature
("C) at southern and northern neritic stations in
summer (AID-4) and winter (AID-2). Chlorophyll
(o----o), temperature (x---x). Insert I shows
concentrations of surface chlorophyll (J!g r 1 )
monitored during AID-6 by in vivo fluorescence
. as ihe Rf V Shikmona moved along the coast from
Ashdod to Zichron (20 km South of Haïfa).
l
:2~ 1
50
2-2
20
21
1
2~
DECEMBER
i
..."'
TEL AVIV
20
s
21 "C
~
N
N
ASHDOD
1982 (stations 4-3, 4-5 and 4-7; Fig. 7), this pattern was
not observed in December 1982 (stations 2-2 and 2-8;
Fig. 7) or in July 1984 (AID-6).
The amounts of oceanic chlorophyll, integrated where
possible down to about 0.5% 10 , only fluctuated about
two-fold for all our observations (Fig. 5, Tab. 4).
Highest levels of standing stock (mg Chi rn- 2 ) were
observed during the winter months, from about October to April.
Occasional continuous profiles made by pumping and
monitoring in vivo chlorophyll fluorescence (Berman,
1972) showed that the discrete samples accurately
reflected the general shape of the profiles (e.g. Fig. 5,
stations 6-8 and 6-17). Deep maxima of chlorophyll
I
•c
10
ZD
3.0
Primary productivity
Generally, .but not always, the photosynthetic rates in
thè neritic zone were 3 to 5 times higher than those in
the upper layers of the offshore waters, but assimilation
numbers were similar for both regions (Tab. 5, Fig. 8).
Maxima of photosynthesis were usually observed
between 10-30 m. The much greater depth of the
euphotic zone offshore caused the integrated values of
photosynthetic carbon fixation to be similar in both
water masses. As would be expected from the size
distribution of the chlorophyll, the picophytoplankton
was responsible for the majority of the primary production in both neritic and oceanic regions.
444
!
PHYTOPLANKTON OF ISRAEL! COAST WATERS
Table 5
Photosynthetic carbon fixation, assimilation numbers and percentage activity associated with picoplankton ( < 3 ll1'l) for neritic and oceanic stations
in the eastern Mediterranean.
Pelagie
Neritic
AN
AN
Stn
(rn)
(mg C mg
P.
(mg C m- 2 h- 1) ChJ-1 h-1)
1-7
20
4.95
Depth
2-2
2-8
3-3
3-5
4-3
4-5
5-4
65
75
25
45
30
25
60
Range
x
Depth
%
pico
1.3
3.59
5.01
2.27
3.73
5.11
5.36
5.92
1.3
0.9
0.5
1.73
2.1
3.1
1.0
2.27-5.92
4.49 ( ± 1.19)
0.5-3.1
1.49 (±0.82)
26
82
73
92
70
68
P.
m- 2
%
(mg C mg
h- 1) Chl- 1 h- 1)
Stn
(rn)
(mg C
1-1
1-5
1-9
2-4
2-6
3-7
100
100
100
100
100
100
1.62
2.10
3.83
2.87
3.31
9.79
1.6
1.2
1.4
0.5
1.1
5.4
98*
88*
60
61
88
4-2
100
5.31
5.3
76
5-2
90
7.39
1.8
1.62-7.39
4.53 ( ± 2.82)
0.5-5.4
2.29 ( ± 1.93)
pico
• Organisms < 20 J.lffi.
Our values for primary production in the neritic region
may be underestimated. For example, we have no
information concerning photosynthetic rates of benthic
algae, but because of potentially high nutrient levels
and favorable light conditions at much of the sediment
surface in shallow waters (Tab. 3, Fig. 3), such organisms may be responsible for considerable photosynthetic carbon fixation. Another cause for underestimation
could be our inability to determine accurately the photosynthetically derived, dissolved organic carbon
released by algae which, under conditions of high irradiance and low nu trient levels, could amount to 50%
or more of the carbon fixed (Berman, Holm-Hansen,
1974; Larsson, Hagstrom, 1979; Jensen, 1984). For the
oceanic area, our measurement techniques may also
have given low values for the photosynthetic activity
of phytoplankton in the deep chlorophyll layers,
because the incubations were conducted without any
spectral compensation for light spectral quality (Glover
et al., 1984).
Although our data are inadequate to draw conclusions
concerning seasonal fluctuations in primary productivity, the highest integrated values for photosynthetic
activity were observed in February 1983 and in April
1982. These data are compatible with our chlorophyll
observations and are in agreement with the conclusions
of Oren (1970) and Azov (1986) that the most favorable
conditions for algal production in this region occur
during the late winter and early spring.
concentrations is more widely extended westwards
during the stormy season of water winter-early spring.
Also at this time, when seasonal irradiance is low
but turbulence is maximum, the highest phytoplankton
concentrations were observed for both neritic and deep
water regions. During most of the year, the offshore
waters had much lower chlorophyll concentrations in
the upper photic zone and greater light penetration
than nearshore regions. Neritic waters generally had
higher surface temperatures than the offshore waters;
thus if there was any cross-shelf upwelling, it did not
appear to reach the surface.
The apparent levels of areal primary productivity were
extremely low, perhaps no more than about 10-20 g C
0
1
\
25
\
'a
1
1
1
50
5C
{
1
1
5-2
75
2-6
DEC.
1
1
FEB.
f
1
1
1
1
1
1
1
00~
100
E
:r
2AN
2 AN
2AN
2AN
•
1<l.
"'
2
0
DISCUSSION
006
.
0.1 0.2
25
5-4
FEB.
The data presented here on the neritic waters off the
Israeli coast complement previous information on the
oceanic waters of this region (Berman et al., 1984a; b).
From late spring to earl y winter, the neritic and oceanic
zones are separated by a clearly defined surface front
of temperature and chlorophyll roughly corresponding
to the shelf-break region.-This boundary becomes more
diffuse, and the neritic water with higher chlorophyll
50
Figure 8
Profiles of primary productivity (mg C m- 3 h- 1) and assimilation
numbers, AN (mg C mg Chl- 1 h- 1 ), for sorne oceanic and neritic
eastern Mediterranean stations. Primary productivity (o----o), assimilation number (x---x), bottom indicated by stippling for neritic
stations.
445
T. BER MAN et al.
m- 2 y- 1• By a rough estimate, the areal efficiency of
PAR utilization in photosynthesis would be only about
0.01% (Tab. 3), which seems suspiciously low (Odum,
1971; Dubinsky, Berman, 1976). As noted above, possibly our results are seriously underestimated because of
various methodological problems. There has been much
recent criticism of 14C techniques for primary productivity measurements (e.g. Gieskes et al., 1979; Eppley,
1980; Smith, 1982; but see also Platt et al., 1984), and
we emphasize that our results should be regarded with
caution. It is noteworthy that Oren (1970) reported
higher photosynthetic rates in 1962-67 for a nearshore
(75 m) station (ranging from 33.2 to 205 mg C m- 2
d - 1 in May and February, respectively), but we have
no way of critically comparing our data sets.
Despite the apparent low levels of primary productivity,
recent measurements of the growth rates of clupeiform
fish larvae (Walline, in prep.) indicate that food items
for these organisms in the coastal waters may be fairly
abondant. Also, despite the low apparent levels of
primary productivity and chlorophyll standing stocks,
active coastal fisheries have existed since historie times.
Future studies of the food webs in these waters will ·
have to determine the true levels of productivity of the
major components of both neritic and pelagie ecosystems.
The impact of the Nile River on the biological productivity of the coastal waters of Egypt and Israel was
undoubtedly drastically changed with the construction
of the Aswan High Dam. Prior to 1965, the Nile
discharged approximately 43.6 x 109 m 3 of nu trient and
silt-laden water annually, with the major flood occurring during August through October (Sharaf El Din,
1977). In the first period after the dam went into
operation (1965-79), as the newly formed Lake Nasser
was filling, the discharge volume dropped to a minimum (4.4 x 109 m 3 per annum), and a severe decline
in Egyptian and Israeli coastal fisheries took place.
Subsequently to 1979, there bas been an increase in the
amount of Nile discharge to 10 x 109 m 3 and sorne
recovery of the fisheries. However, the major inflow of
the Nile waters is no longer concentrated in the autumn
months, and of course the sediment load is also much
diminished in comparison to pre-Aswan times (Dowidar, 1984).
As a result of the former nutrient inflow pattern, phytoplankton (or at !east the net-phytoplankton species
which were then sampled) were observed to have a
major biomass peak from August to October and a
smaller peak from January to March (Dowidar, 1984).
This effect was discernible as far as the northern coast
of Israel and Lebanon (Oren, Komarovsky, 1961) but
has apparently not occurred since the High Dam came
into operation (Schneller et al., 1984; Azov, 1986). In
the absence of information· on chlorophyll concentration or on the abondance of pico- and nanophytoplankton in the years preceding the construction
of the Aswan Dam, we cannot determine if there have
been changes in the amounts of the smaller phytoplanktonic forms relative to the net algae. We have found
no data which might indicate how far the nutrient input
from the former Nile flood extended into the pelagie
areas of the Levant Basin, if at ali. Ali pre-Aswan data
along the lsraeli coast were taken from shallow water
stations, with the exception of those from the 1965
Pillsbury cruise (Kimor, Wood, 1975) which are mainly
descriptive and not quantitative. Therefore, no definitive analysis of the long-term effects of the operation
of the Aswan High Dam on the biological productivity
of the neritic and oceanic waters near the Israeli coast
is possible at present.
A recent paper by Dowidar (1984) provides much
information concerning the present patterns of phytoplankton and chlorophyll distribution in the waters
overlying the Egyptian shelf, and these data can be
usefully compared to ours (Tab. 6). A salient feature
is that in the region along the Israeli coast, chlorophyll
concentrations and total areal standing crops, even for
the more productive neritic region, are much lower
than those reported for the shelf waters of Egypt.
Although we suspect that sorne of the chlorophyll
values given for the Egyptian oceanic waters must be
greatly overestimated (judging by the relatively deep
1 % penetrating light levels of 80-120 rn which are
reported), undoubtedly the amounts of phytoplankton
standing crop in Egyptian waters are greater than those
prevailing off the lsraeli coast. Likewise, our estimated
rates of photosynthetic carbon fixation for Israeli neritic waters are 3-5 fold lower than those reported by
Dowidar (1984). However, the highest water transparencies and minimum chlorophyll concentrations
observed in the deepest Egyptian stations correspond
weil with our oceanic data.
Table 6
Range of average chlorophyll concentrations 1 and primary productivities2 in the S.E. Mediterranean, close to the Egyptian (Dowidar, 1984)
and Israeli coasts.
Egyptian Region 3
Israeli Region
Nearshore Oceanic
Nearshore Oceanic
(<100m) (>100m)
(<100m) (>100m)
Chlorophyll (mg.m 3) 0.13-1.87 0.09-0.79
Primary productivity
(mg C m- 2 d- 1)
40-488
33-207
0.06-0.44 0.06-0.12
19-89
15-71
1
Average concentrations for euphotic zone.
These figures must be taken as very rough estimates only (see text).
A further uncertain factor is the conversion of hourly to dai! y carbon
fixation rates.
3 Egyptian data are based on seasonal averages, Israeli data are
taken from ali stations.
2
As yet, we have only a few analyses of the ambient
macro-nutrient concentrations. Schneller et al. ( 1984)
and Azov (1986) observed considerable short-term fluctuations of total phytoplankton biomass population
composition and size distribution in the lsraeli neritic
zone. We have also noted patchiness of surface chlorophyll concentrations in this region (Fig. 7), but have
no good evidence for a concentration gradient of chlorophyll decreasing northwards along the Israeli coast,
as might be expected if there is a nutrient input from
the Egyptian shelf region carried by the circumMediterranean geostrophic current. Azov (1986) sug-
446
~
1
PHYTOPLANKTON OF ISRAEL! COAST WATERS
neritic waters of Israel and Egypt. In addition, elucidation of the nutrient regime upon which the exceedingly
low standing stocks of phytoplankton in the main pelagie region of the Levant Basin subsist could be an
important contribution to understanding the ecosystems of oligotrophic oceans.
gested that the occasional blooms of net-phytoplankton
may be related to elevated levels of orthophosphate,
and sorne nutrient addition experiments (not reported
here) have indicated that both phosphorus and nitrogen
may be limiting algal growth at different times. Possibly, the nutrient inputs responsible for the observed,
localized phytoplankton outgrowth are not delivered
by the dominant northeasterly coastal currents from
the Egyptian shelf area but derive from other sources
such as sediment resuspension, cross-frontal mixing or
upwelling, terrestrial runoff or riverine discharge.
The extent to which such processes, in addition to
lateral advection of nutrients and organisms from the
relatively rich Egyptian shelf, contribute to the present
levels of biological productivity in the nearshore waters
of Israel still require clarification. This will be a necessary background for any rational strategies of fisheries
management or marine resource development for the
Acknowledgements
We thank the captain, A. Tsur, and crew of the R/V
Shikmona 1 and II for cheerful and dedicated assistance
throughout this program. This research was supported
by a grant from the US Agency for International Development and is a contribution from the Israel Oceanographie and ·Limnological Research and the Bigelow
Laboratory for Ocean Sciences (No. 85012).
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447