3
Primary production, phytoplankton and light in
Straumsbukta near Tromsø
JAHN THRONDSEN & BERIT RIDDERVOLD HEIMDAL
Throndsen, J. & Heimdal, B. R. 1976. Primary production, phytoplankton and
light in Straumshukta near Tromsø. Astarte 9, 51—60.
The investigation includes measurements of primary production in situ, light
extinction at 450 nm, 522 nm, 583 nm and 653 nm, and phytoplankton composition
at one station in Straumsbukta (60°33.5’N, 18°37’E) at four different seasons.
Primary production varied with a factor of 1013 from winter to summer, and
production in summer was at noon 60 times that of midnight. Size fractions passing
a 5 ~tm nylon net contributed with 6 0/~ (summer) 73 °/o (winter) of the production
in surface water samples. Nanoplankton flagellates, Phaeocystis pouchetii,
Chaetoceros debilis and Coccolithus (E7niliania) huxleyi were the main phyto
plankton species in December, April, July and September, respectively.
—
J.
Throndsen, Department of Marine Biology and Limnology, Sect. Marine Botany,
University of Oslo, Blindern, Oslo 3, Norway
B. R. Heimdal, Institute of Biology and Geology, University of Tromsø, N—9001
Tromsø, Norway. Present adclress: Biological Station Es~,egrend, N—5065 Blomsterdalen, Norway
1terature regarding primary production and
light on the coast of Norway is very scarce,
especially for the northern part. For the
phytoplankton, considerably more informa
tion is available (for references, see e.g.
Heimdal 1974, Schei 1974).
The present investigation was planned to
give an irnpression of the conditions for
primary production in the Tromsø area in
the four seasons. The localitv is well north
of the Arctic Circle and hence is subject to
distinctive seasonal changes in light condi
tions, a major factor for phytoplankton devel
opment at high latitudes. In Tromsø there
was midnight sun from 18 May to 25 July
in 1974 and the dark season lasted from late
November to the middie of January.
The Tromsø area is relatively open and
the sea can often be too rough for primary
production work to be carried out from the
27 feet research vessel available for the in
vestigation, except in some sheltered places.
The position of the station in Straums
bukta, southwest of Tromsø (Fig. 1), used
for the measurements, sampling and incuba
tions in situ, was 69°33.S’N, 18°37’E. The
outer part of Straumsbukta is relatively ciose
to Rystraumen and the eastern part of
Straumsfj orden. The hydrography of the
area is characterized by strong tidal currents,
the current velocity of Rystraurnen probably
reaching 4.6 m/sec (McClimans
1974).
Thus the stratification of the water masses is
negligible even in summer; salinity, tempera
ture and oxygen content are relatively uni
form
throughout
the
water
column
(McClimans 1974).
The dates for the field work had to be
fixed weIl in advance so weather conditions
could not be chosen. Even so the weather
experienced during the investigations seemed
to be fairly representative for the different
seasons that year (R. Mook, pers. comm.).
Light conditions varied considerably with
the time of the year, mostly due to the high
latitude, irradiance being (R. Mook, pers.
comm.):
‘0’ ly/24 hours in the period 4—6 December
1973
52
Jahn Throndsen & Berit Ricidervold Heimdal
~8°E
Fig. 1. Map of the area including the sampling
and incubation station in Straurnsbukta. Inserted
map of Norway shows the location of the detail
map.
290 ly/24 hours in the period 17—19 April
1974
380 ly/24 hours in the period 3—5 July 1974
95 ly!24 hours in the period 24—26 Septem
ber 1974.
Measurements from 2 ancl 4 December 1975
(B. Schei, pers. comm.) showed that the
irradiance at this time of the year varied
between 0.64 and 0.1 ly/24 hours.
MATERIAL AND METHODS
Q ualitative light measurernents were made
by means of a four sensor time integrating
light meter designed by Professor Per Halldal (Department of Botany, University of
Oslo) and kindly put at our disposal by him.
The instrument gives quantum relative
irradiance values for wave-length bands with
peak transmission at 450 nm, 522 nm, 583
nm, and 653 nm.
Quantitative light measurements were
obtained in July and September with a LI185 (Lambda Instruments Comporation)
quantum meter fitted with a LI-COR LI-
192S underwater sensor as well as LI-COR
LI-190S sensor for deck measurements. The
instrument gives total number of quanta
received in the spectral range 400—700 nm.
For both instruments measurements were
carried out with the underwater sensors
suspended frorn a boom at a distance of about
3 metres from the side of the vessel.
Primary production measurements were
based on the C~-method (Steernann Nielsen
1952) with in situ incubation of samples in
125 ml botties suspended in perspex cylinders
at different depths. Additional incubations
were made in the laboratory at sea tempera
ture, but under standardized light conditions
(fluorescent tubes, type cool white). Size
fractionations of incubated samples were
made with 5, 20, and 45 ~m mesh nylon
(Nytal, Swiss) just prior to membrane
filtering.
The filters with radioactive algae were
dried and later counted in a Philips PW
4510/Ol liquid scintillation counter after
dissolution in Unisolve I (Koch Light LTD)
scintillation fluid.
~ CO~ of seawater was determined by
measuring the change in pH due to the addi
tion of 25 ml 0.01 N HC1 to 100 ml water
(Strickland & Parsons 1968).
Serial dilution cultures were made by
inoculation of seawater samples into modified
Erd-Schreiber medium (Throndsen 1969) in
short test tubes which immediately were
sealed with Parafilm, brought to Oslo in
insulated containers and cultured at approxi
mate sea temperatures (5C, 3—4C, 7—8C and
8—lOC in winter, spring, summer and autumn,
respectively).
Water samples preserved with neutralized
(with hexamethylenetetramine) formaldehyde
(0.4°/o) were analyzed by the inverted
rnicroscope method after sedimentation of
exact volumes (Utermöhl 1931, 1958). Net
hauls were collected in order to obtain gene
ral information on the larger phytoplankton
species.
All water samples were collected with
a non-toxic, plastic-covered water sampler.
RESULTS
Light measurements
The quality of the submarine light changed
in accordance with the season. The light in
Primary production, plzytoplankton and light
Guanta /crn2
/7
/7/
/7
The
janta
nm,
were
nsors
~bout
sec
iol7
~ULY~
53
1016
503
* 023
were
elsen
es in
iders
tions
)era
tions
Size
were
Lylon
~rane
were
24 SEPT
17 APRIL
~
24
32
3.4 JULV 1974
-~ti
V4L.
,a
11.15
•/.
,~
~
Fig. 2. Attenuation of four different light qualities
with depth at four seasons.
14.25
Fig. 3. Distribution of light in the 400—700 nm
band with depth at different times of the day at
station Straumsbukta 3—4 July 1974.
Pw
after
~TD)
by
.ddi
iater
by
ified
)) in
were
) in
.oxi
and
imn,
ized
iyde
rted
i of
Net
ene
kton
with
)ler.
winter was characterized by the absence of
direct sunlight and showed a dominance of
blue and green light; yellow (583 nm) and
red (653 nm) constituted only about 50 o/~ of
the green (522 nm) when measured as quanta.
When the sun was present in spring, summer,
and autumn, the corresponding values were
90 0/~ and 70—80 0/0 for yellow and red light,
respectively.
The attenuation of different wave lengths
varied considerably with colour in accordance
with the seasonal change in water quality
(Fig. 2): Red light (653 nm) showed the
smallest variation in extinction and the i 0/~
light depth for this light quality was approxi
mately 12 metres in winter and 10.5 metres
in summer and autumn, with a lower value
of 9.5 metres in spring. For blue (450 nm) and
green (522 nrn) there was a marked increase
in attenuation from December to September,
the i O/~ level of surface light rising frorn
Table 1. Trarnsniusion nf light in the spectrul regiorn 400—700 nu
an percent of surface value
depth, ni
Date
iged
t in
0
1
2
4
8
4 July
100
25 Sept.
100
71
55
33
16
64
47
27
3
16
24
32
40
5.4
2,5
1.2
-
4
1.4
0.6
0.3
40 m to 17.5 in and frorn 53 m to 30 in, re
spectively. Yellow (583 nm) followed the same
pattern from December to April, but changed
only littie to July and slightly more to Sep
tember.
The amounts of light received at the sea
surface varied greatly during the years as
shown by the data for energy measurements
cited on p. 52. In December, for which month
no energy measurements are available, the
irradiance at noon was probably about 10’~
quanta/cm2. sec (estimate based on surface
measurements with the four sensor light meter
and quantum rneasurements from summer and
autumn) or approximately 0.5—0.1 ~/o of that
in summer, As the spectral composition of
light is different in the dark and the sunny
season, the quanturn estimate (for winter)
inay be slightly too high, and an estimate of
energy irradiance was avoided for thc same
reason.
Light quantum rneasurements for the 400—
700 nm band were carried out in summer and
autumn. In summer, five series of quantum
measureinents were made at 8 depths during
a 24-hour period 3—4 July; the results of four
of these are shown in Fig. 3, together with
a surface value from midnight. The latter,
obtained at 0005 hrs. (solar time) was about
0.7 o/~ of the highest surface irradiance
54
Jahn Throndsen & Berit Riddervold Heimdal
r~~g Cfo~
recorded during the same 24-hour period.
The midnight irradiance at the surface was
also roughly comparable to the 4 metres
value at 0200, 8 rn at 2130, 21 m at 1115 and
29 m at 1425 hrs. It has to be remembered,
however, that the spectral composition of light
varied with depth as well as with the time
of the measurernent.
The penetration of light in the 400—700 nrn
band to different depths can be read from
the transmission values in Table I. In accor
dance with the data for blue (450 nm), green
(522 nm), and yellow (583 nm) light, therc
was an increase in attenuation from summer
to autumn.
ho~r
10
4
II!
16
24
32
10
4
8
1~
IV
24
32
60
Primary prodztction
.~
In winter the light conditions even in the
surface water were very poor and the primary
production was nearly negligible. An incuba
tion in situ over 23.5 hours (4—5 December
1973) showed a photosynthetic carbon uptake
of 1.5 X 10_lo mg C (or an average of
6.2 >< 10~2 mg C/hour). This is in good
agreernent with the fact that the estirnated
irradiance at sea surface (see above) was
approximately 0.5—0.1°/o of that recorded in
summer (3—4 July 1974). The winter condi
tions may therefore be ciose to the light
compensation point for photosynthesis e.g. of
shade plankton (Steemann Nielsen & Hansen
1959).
The laboratory incubations improved the
carbon uptake (Table II), 0.04 rng C/hour
was found at light saturation, which here was
probably lower than 4 )< 1015 quanta/cm2 .sec.
200
50
40
30
~‘
/~
/
20
0
0~
1200
1800
2400
0600
1200
HOURS
Fig. 5. Prirnary production and light at station
Straumsbukta 3—4 July 1974. Upper five curves
show carhon uptalce ciuring clifferent periods of
the day: I — 12.25—16.25, II — 16.25—22.25, III —
22.25—02.25, IV — 02.25—08.25, V — 08.25—12.25.
Lower curve shows irradiance during the periods
of production measurements (I—V).
Table II. Photosynthetic carbon
uptake in sea water samples fran
four different depths (three in
winter) incubat~. for f~ur hours
at 4-5 x 1015 quanta/cm
sec.
8
rng C/m3
hour
Season
Om
4m
16m
32m
Winter 0.04
0.04
0.04
Spring 2.5
3.1
2.7
3.3
32
Surrnner 9.7
10.0
9.0
5.2
Fig. 4. Primary production at station Straums
bukta in spring (17—18 April), summer (3—4 July)
and autumn (25—26 September) at different depths.
Autunin 7.0
5.6
3.0
1.1
—
Prirnary
Table III. PhotoSynthCtiC carbon uptake at different levels during
4—hourS incubatiOns in the middie of the day, average values for
each peribo, n.g C/m3hour
~th inn
2m
.3
.2
.1
48
16
~32
1.8
1.9
2.0
2.8
2.3
1.4
0,4
0.37
3 July
(1225-1625)
13.6
11.7
11.6
13.5
9.9
2.9
0.9
0.2
7.7
8.0
7.0
6.1
4.4
1.4
0.4
0.05
3.1
3.6
3.4
3.4
1.5
0.4
0,09
0.03
25 Sept.
(1005-1405)
rbon
fran
in
Durs
~c.
2
18 April
(0945-1345)
4 July
(0825—1225)
tation
~urves
ds of
III —
12.2i~.
2riods
~
-
The values were nearly the same for 0 m,
4 m, and 16 m, indicating a uniform phyto
plankton distribution in accordance with the
unstable hydrographical conditions at the
locality.
The in situ incubations in spring and
auturnn gave carbon uptakes of the same
order of size (Fig. 4), but their depth distribu
tion patterns were characteristically different.
The curve for 17 April shows a slight inhibi
tion effect at the surface and a compensation
point probably welI below 32 metres. This is
what can be expected from the relatively
high solar radiation received in the area at
this time of the year (290 ly/24 hours, R.
Mook, pers. comrn.), and the high water
transparence indicateci by the light measure
rnents (1°/o depth of green light, 522 nm at
40 m).
The depth distribution of the carbon uptake
on 24 September did not indicate an inhibition
at the surface and the compensation depth
was prohably at 17—18 metres. At this time
the insolation was 95 ly/2’l hours only (R.
Mook, pers. comrn.) and the attenuation of
light in the sea had increased (1°/o depth of
green light, 522 nm at 30 rn).
The 4 hours incubation made on 24 Septem
ber in the period 1200—1600 hours with an
initial light intensity of 15.4 X 10~ quanta/
cm2 scc (probably declining during the incu
bation) did not show any inhibition at the
surface either. Another 4 hours incubation
from 1005 hours the next day (25 September)
showed, however, inhibition of photosynthesis
in the 0 m bottle. In this period the initial
irradiance at surface was 43.4 X 10’~ quanta/
crn~ sec, probably increasing till noon and
then declining.
In July there is a situation of continuous
production,
55
production in the surface layer, and the total
carbon uptake per 24 hours was found to be
221 mg C/m3 (from two 12 hours incubations).
The compensation depth for photosynthesis
was probably ciose to the surface at midnight,
and deeper than 35 metres at midday. Alto
gether this results in a production curve (for
24 hours) with a very rapid decline in carbon
uptake values frorn the surface to deeper
layers (Fig. 4, 3—4 July).
A series of five short term in situ incuba
tions carried out during the same 24 hour
period (3—4 July, see above), showed the
change in primary production with time of
the day and depth (Fig. 5). The curves apply
only to the 24 hour period in question (3—4
July 1974) as the light conditions are influ
enced by variable cloudiness which modified
the natural change in irradiance due to
change in solar elevation. The depression of
the insolation is particularly pronounced in
the last 4 hour incubation period (0825—1225
hour, 4 July) (Fig. 5). The production would
probably have been significantly higher if the
sky bad been clear.
A comparison of short term (4 hours)
rnidday incubations frorn the four seasons
gives an indication of the variation in natural
production capacity (here meaning the
highest observed production rates under natu
Table IV.
Primary pr~uction of
surface water ~lankton pass ing
nylon nets of different mes~ size
at different seasons (for d~tes
see text), carbon uptake of each
fraction as percent of total Le.
with no net
mesh size
Season
5pm
20~rn
45pm
no
net
Winter
73
85
100
100
Spring
28
43
100
Surrrner
6
7
II
100
Auturnn
53
65
79
100
.
.
/,hytoplankton and light
56
Jahn Throndsen & Berit Riddervold Heimdal
fabie V.
i’iuxinuin recorded ccli numbers for the3iuost abundant
groups and specius at station Straunisbukta,
JO
Teble V cont.
celis/1
liantoni el le squamata
Speci ca
Desember
April
Jaly
.0(sp)
Meringosplnaera mcdi terranen
Micrononas pusilla
0.2
-
0.0
-
0.5
1.0
0.5
4100.0
1300.0
490.0
8.5
1.5
5.0
Anthosphaera robusta
1.0
Calycamonus cf. gracilis
0.5
0.5
1.0
4.5
ilinuscula bipes
-
1,0
-
6.0
10.0
14.5
limnoniga marine
-
4.0
0.1
01
1.1
1.5
llannmchioris cf. elongutus
7.0
—
-
6.7
28.5
2.0
ilitzscinia ectydrophila
0.2
2.3
Carteria sp
Chaetoceros affinis
C. conipressus
-
0.S(sp)
September
—
-
31.0
C. curvisetus
-
0.1
0. i
6.4
N. “grunowii”
C. debilis
-
35.0
785.0
0.5
9. seriata
..
1.4
-
C. furceiiatus
-
67.0
Ochronmnas mininla
-
-
2.0
C.
—
—
5.1
27.0
1.2
Pheeocystis pouchetii
-
C. septentrionalis
-
2.0
15.0
—
PonLmsphaera pietschmannii
-
-
6.5
laciniosus
C. similis
—
2.5
C. socialis
-
73.0
C. subsecundun
-
3.8
3.4
C. cf. tortissinius
Chaetocerms Sp.
—
23.5
24.5
Chrysochromuiina spp.
Coccolithus huxieyi
Cryptomones acuta
Dicrateriu inornata
0.2
-
-
-
-
9.0
0.8
Pseudopedineila sp.
—
5.0
-
—
10.5
Pyramimonas grmssii
-
-
5.0
14.0
7.5
Pyramimonas spp.
-
7.0
34,0
3.3
8.0
Prorocentruni balticuni
-
0.5
1.0
2.0
14.0
8.5
0.8
—
0.5
0.5
276.0
Smienicola setigera
1.5
-
-
-
0.2
4.0
7.0
Stichococcus baciliaris
6.0
-
-
-
5.0
0.8
Totranelmis Sp.
4.0
-
-
2.0
1.0
2.0
Thalassimnema nitzschimides
—
23.5
5.0
-
—
0.1
9.0
-
0.1
5.5
0.1
Eugl enaceae
-
0.5
0.1
1.9
1.0
0.5
3.0
13.5
—
2.5
1.5
3.0
5.0
2.0
Hennseimis brunnescens
6. virescens
2.0
-
0.2
-
-
—
1.7
Heteromastix pyriforniis
Leptocyl indrus danicus
L. rnininius
Leucocryptos marine
Katodiniuni rotundutuni
8.0
P. cf. tricosteta
-
soselmis obconica
-
-
Pseudopedinella pyriformis
-
Heisiselmis spp.
-
0.2
Dinobryon petiolatuni
Gyrodiniuni grenlandicum
0.1
2.0(sp)
4.0
Dinobryon SP.
Gymnodiniaceae
640.0
—
0.5
1.5
C. pseudobaltica
CryptcmonaS spp.
6.0
27.0
7.0
2.0
13.0
2.6
37.0
0.2
—
-
1.0
1.5
4.0
-
2.0
-
4.0
0.1
0.7
30.5
2.0
-
3.4
2.7
0.2
T. nordenskioeldii
-
29.7
2.4
T. pmlychorda
-
2.2
0.3
0.5
3.0
2.0
—
—
—
-
Unidentified
Chmanoflagei lete
Coccmi ithophoridu
-
3.5
Fl egel i uten
2.5
53.5
79.0
52.0
Monad s
7.5
150.0
202.0
227.0
=
nusidentif Led srxy’inienu of ±e sanno gonus
1.6
ral conditions). As the values from December
are practically zero, only carbon uptake
values for April, July, and September (1974)
are shown in Table III. In April and Septem
ber, the incubation period lasted from about
two hours before noon to two hours after.
The amount of photosynthesis was slightly
higher in the 0—1 m layer in September than
in April and the production at 32 m in April
was comparable to that of 16 m in September.
Together this indicates a larger amount of
phytoplankton to be present in the auturnn
samples.
In July the best 4 hour incubation series
started about noon, and no series was incu
-i
0.1
Thaiassimsira gravida
sp)
1.6
—
Skmletonenia costatuni
bated at a time directly coinparable to that
of April and September. It seems unlikely,
though, that this would have changed the
fact that the summer values are 4—6 times
higher than those of September and April. The
high daily production in July is a combined
effect of high natural production capacity
and continuous production in the surface
layer, the compensation depth not reaching
the surface even at midnight.
Laboratory incubations at about the sea
temperature at sampling and a light intensity
4—5 >< 10’~ quanta/crn2 sec (Table II), may
indicate the production capacity at light sat
uration for December, April and September.
For July, however, light saturation probably
occurs at somewhat higher light intensities,
and the values for summer in Table II are
therefore assumed to be suboptirnal. Com
parison with the in situ incubation values in
Table III seems to confirm this. The labora
Primary /,roduction, ~bhytoplankton and liglzt
Taisie VI.
Tablo VI
PhytoflagellatoS r€cordba by the serial dilution culture
57
000t.
methDd, t4PN as celis/mi
~,
SpecieS
Om
4m
Dicrateria inornata
0.6
5
-
—
—
0. 2
0.2
-
-
~ IsochrySiS galbana
~ Mantoniella squamata
~ MicraaDnas pusilla
.5
~ Psebaopbainella pyrif.
‘0 Tetraseimis sp
‘.0(sp)
0.2
4
-
-
-
-
4
chrysochranuiina spp.
Ceccolithus huxleyi
cryptasnoas acuta
0.2
-
-
-
24
6
8
13
0.2
—
-
-
~ Katcriini’.Sfl rotur~atoS
~ MicrononaS p.~si11a
‘~‘
PhaecoystiS puuchetii
“
Pse~xiOpbainella Sp.
PyraminonaS spp.
.0
5
0.2
32m
cryptaecnaS Spp.
~ Heciseimis Spp.
.0
16m
—
2
140
130
80
5
50
50
—
-
5
—
2
0.2
2
7
2
-
cryptctzonas acuta
—
2
4
—
crypbarcnas psmxlobaltica
—
—
—
5
Q~yptaecnas spp.
i
0.5
—
—
Omsiseimis brunneScenS
4
5
—
—
.0
.0
.2
Hcmiselmis virescens
—
2
-
0. 5
~ Heterasastis pyriformis
-
-
4
7
—
—
—
2
0. 8
—
—
MicrcmanaS pusilla
OchrassnaS minOma
4
—
500
2
Pyramiannas grossii
—
—
5
0. 2
34
5
—
—
‘~
Isoseimis obaonica
~‘
Mantoniella squamata
n
Pyramiecnas spp.
1300
—
—
cont.
0
hat
~ly,
the
nes
~he
ied
ity
~tce
ing
sea
ity
iay
ater.
)ly
es,
~re
in
4
-
0.0
0.2
—
0.5
-
-
2
Matreptiella Sp.
—
—
0.2
—
Hasiseimis brunnesccns
—
2
—
-
Hmaiseimi.s spp.
7
i
22
27
1.4
13
0
2
4
0.4
-
0.2
~ Mantoniella squamata
6
0.2
-
-
.~
MicraecnaS pusitla
340
490
240
240
~
Nephroselmis gilva
Ochraecnas spp.
0.2
-
-
-
—
—
0.2
2
—
-
9
-
7
0.4
-
—
--
—
0.8
Pyramimanas grossii
5
,0
7
—
Pontosphaera pietschm.
330
tory incubations from December, April, and
July showed a relatively uniform carbon
uptake from the surface down to 16 m,
whereas in September some reduction with
depth could be traced.
In all four seasons one series of incubations
were size-fractionated through nylon filters
before the algae were collected on membrane
filters for counting of radioactivity. In De
cember this was done on laboratory incubated
0 in sample only; in April, July and Septem
ber 4 hours in situ incubations from several
depths were used. The data for the surface
samples (which did not deviate much from
the deeper ones) are expressed in relative
units in Table IV. In December (1973) the
photosynthetic potential appeared to be main
ly connected to celis passing the 5~.tm mesh
filter. Further, it seems as if all phytoplankton
(which showed photosynthetic response upon
illumination) present belonged to the nano
8
2
~ Psmmiopm0inella cf. tricosta
.0
.8
2
4
Cryptasonas spp.
8~
.3
—
2
cryptaecnas pse~oba1tica
Heterasastix pyriformis
-
3
Cryptaecnas acuta
~ Katmibaimn rotumiatan
4100
—
17
14
Pyraminmnas spp.
—
3.3
2
—
Tetraseimis Sp.
—
2
—
—
plankton, i.e. 1000/0 passed the 45 ttm filter.
In April the netplankton fraction constituted
more than half of the photosynthesis, and in
July this fraction was nearly 90°/o, the smallest fraction now being responsible for 60/0 of
the surface water primary production. A
relative increase in the nanoplankton produc
tion towards winter was indicated by the
high values of the 5, 20 and 45 ~m fractions
in September.
Phyto1blankton occurrence
A large number of phytoplankton species
was recorded in preserved samples, and anal
ysis of serial dilution cultures added some
more fragile species (Tables V & VI).
The December plankton (4 and 6 Dec.
1973) appeared to be dominated by small
flagellates and coccoids, many of them prob
ably heterotrophic species. Among the photo
synthetic ones Dicrateria inornata, Micro
monas ~busilla,
Coccolithus (Emiliania)
huxleyi, Sphaerocalyptra ~bapillifera, Syra
cos~bhaera cf. nodosa and some unidentified
green algae seemed to be most important. This
agrees well with the apparent importance of
ultraplankton species in potential primary
production (cf. 5 ~im fraction in Table IV).
In April a wide variety of diatom species
were present: Chaetoceros debilis, G. furcel
latus, G. socialis, Skeletonerna costatum and
Thalassiosira nordenskioeldii being parti-
58
Jahn Throndsen
Berit Riddervold Heimdal
&-
Table VII. Summary mf observation data fram four seasons at sta
tinn Straumsbukta
Insolation
ly/24 8
December
April
July
September
0
290
380
95
x
Surface irradiance
(day)
400-lOOnni, quanta/cm2. sec
(night)
6-.8.4x1&6
5.5x1013
4,301016
0
450nni
.07—10
.16
.19-28
.24
Extinction
522nm
.07
.11
.14-17
.16
coefficiemt
583nn1
.09
.14
653nv
.37
.44
.34-49
.38
604
2300
380
.15
.16
Primary prod.
mg C/m2
24 h
l.5xl0~0
Primary prad.
0.045
13.5
7.0
nlax. og C/m~~ h
(lab)
(in situ)
(in situ)
(lab)
53
40
35
30
Depth of euphotic
zone: 1% of 522 nm
Dominant algal
specios
0Data fram 8.
Flagellates
4.8
Phaencystis
psschntii
Chaetoceros Cnccolithss
debilis
huxleyi
1nok, University of Tromsø, pers, conso.
cularly prominent. Resting spores of C. Jur—
cellatus and G. socialis were numerous, mdi
cating that these species had passed their
maxima. The most important component at
this time, however, appeared to be Phaeocystis
/,ouchetii with concentrations up to 640,000
cells/l. Most of the Cliaetoceros species (15
in al]), partly also Skeletonerna costatum,
77zalassiosira nordenskioeldi and Phae3cystis
/ouchetii, were probably kept back by the
45 tm filter (Table IV). Among the smaller
phytoplankton species, Ivlicromonas /mszlla
and some Gry ptomonas species seemed to
dominate. (Phaeocystis rnay contribute to all
fractions as the colonies may break up.)
The 4 July samples showed a considerable
increase in the number of diatorn celis, espe
cially for Chaetoceros debilis (maximurn re
corded 785,000 cells/1), which, together with
Chaetoceros compressus, G. laciniosus, C sep—
tent rionalis, Leptocylindrus 7niflimus, i”!ilz—
sc/iia actydrophila and Thalassionema nitz—
schioides seemed to constitute the main part
of the phytoplankton community at that time.
Chaetoceros debilis and probably most of the
other species will be kept back by a 45
nylon filter, hence the main photosynthetic
activity can be expected in the netpiankton,
as shown in Table IV. The ultraplankton
which at this time contributed about 6°/o of
,
the surface water primary production ap
peared to consist mainly of Pyranziinonas
spp., Hemiselmis brunnescens, and Micro—
monas /.nisilla. Celis and thekae of Dinobryon
petiolatum probably also passed through the
5 ~trn filter.
In September the diatoms, though still rich
in number of species (38), showed decreased
cell concentrations. Maximum concentrations
of Chaetoceros cf. tortissionus, the most abun—
dant diatorn species were 10,500 cell/1 (0 m,
24 Sept. 1974). Increased numbers were found
for naked dinoflagellates, especially Gyro
dinium grenlandicum, which, together with
a variety of ultra- and nanoplankton species
contributed to the relatively high production
in the 5 ~m fraction (Table IV) at this time.
The most important species, however, was
probably Coccolit hus (Emiliania) huxleyi,
which was recorded in concentrations up to
276,000 cells/l.
In all cases a large number of unidentified
celis were recorded in the preserved samples.
These may or may not be primary producers,
of which some were revealed in the serial
dilution cultures. Many of them were prob
ably colourless flagellates and amoebas.
DISCUSSION
The hydrographical conditions of the soLinds
and fjords in the Tromsø area are affected
by tidal water movements. In Straumsbukta,
which is situated close to the strong tidal
current Rystraurnen, a clear stabilization of
the water masses was not evident at any of
the sampling dates. McClimans (1974) found
only small vertical gradients in density and
oxygen content during a one year survey at
a station in Straumsbukta. In May, June,
and July (1972) the water was even super
saturated with oxygen down to 100 metres
(deepest sample). This also
s reflected
by the phytoplankton distribution which was
fair[y even except perhaps for a few species
in the September samples. The production
capacity
of
lahoratory-incubated water
samples likewise showed small variations
with sampling depth, except for 32 metres in
July. A continuous decrease with depth,
however, was clear in the September series
(Table II).
Primary production, phytoplankton and light
I,
cl
h
s
tI
$
0
0
0
$
.1
f
f
-1
EI
t
s
EI
5
5
I
r
s
I
5
The light measurements revealed a very
deep euphotic Iayer, in accordance with the
fact that at no time the phytoplankton con
centration exceeded a few million cells per
litre. There was a general increase in extinc
tion of all four wave lengths measured, from
December to September, but only in summer
did the extinction coefficient for 522 nm
exceed that of 583 nm (Table VII). Lorenzen
(1972) points out that the extinction of light
in waters with euphotic zones of 30—40
metres is only partially caused by phyto
plankton.
Displacement of the in situ incubation botties
by the stress of the tidal current was a prob
lem for shorter periods, occurring twice in
the 24 hour cycle. It was very difficult to
estimate the influence of the dispiacement
on the results, but the errors are probably
fairly small. (With a wire angle of 450
the calculated production per square metre
may be about 25°/o too high.) In summer the
production estimate would have been reduced
by about 4°/o when •four hours of strong
current are assumed.
The production (per unit surface area)
measured in winter was extremely small
(Table VII), only 10’~ of that in summer,
or 10-12 of the spring and autumn values.
The light in winter, though low in intensity,
was sufficient for some photosynthesis to be
carried out in the surface water. This is prob
ably the key to survival for many species
which need a minimum of light (see e.g.
Hellebust & Terborgh 1967, Umebayashi
1972). The circulation of the water masses
will bring species suspended throughout the
water column to the surface for some period.
Actively swimming species like Micromonas
/iusilla and Dicrateria inornata are probably
unable to override the water movements at
this time and were consequently found at all
depths sampled.
In summer (3—4 July) the production mea
sured in a four hours period around midnight
was approximately 2.7 rng C/m2 hour and at
noon about 60 times higher (168 mg C/m2
hour). This means a continuous photosynthesis
for the species at the surface, whereas those
at 8 to about 40 metres will be above the
compensation depth (for photosynthesis) for
part of the day only.
In spring and summer the highest carbon
uptake rates (Table VII) were found in the
59
in situ incubations, whereas in winter and
autumn the laboratory incubations gave the
best results. This indicates both that light
saturated photosynthesis was not achieved at
the laboratory light level (4—5 >< i0’~ quanta/
cm2 sec) for spring and summer populations,
and that it was not achieved in the sea in
winter and autumn. (Increased light inten
sity did not improve the laboratory incuba
tions in winter and autumn any further.) This
seems quite reasonable for the winter situa
tion with very low natural light intensity,
but is surprising for the autumn samples
which in situ got more than sufficient light
in the sea down to 4—8 metres. The reason
may be that the populations sampled for the
two series (in situ and laboratory) were too
different for comparison.
Regarding the size fractionation of incu
bated samples it is important to remember
that the mesh size does not necessarily cor
respond to maximum cell size let through,
since larger cells may squeeze through
(McCarthy et al. 1974) and small ceils with
long firm protrusions may be caught readily.
The value of the information gained is thus
dependent on an analysis of the phytoplank
ton community.
In summer, when only I l°/o of the carbon
uptake was due to species passing the 45 ~tm
net, the main producer appeared to be
Chaetoceros debilis, the cells of which are
only 9—20 ~ but with long setae. Species
with palmelloid colonies such as Phaeocystis
pouchetii, which dominated the phytoplankton
in April, represent another fractionation
problem, as the colonies may partly break up
during filtration and hence be present in all
size groups. The main species in the autumn
samples, however, represent no problem as
all celis probably pass through even the 5 ~im
net. In Narragansett Bay, USA, Durbin et
al. (1975) found that the nanoplankton pro
ductivity was relatively most important in
the low production period which occurred in
summer there.
The general composition of the phyto
plankton in Straumsbukta was characterized
by a large number of Chaetoceros species in
addition to other diatom species at all seasons,
except in winter when the phytoplankton was
generally poor. In winter, nanoplankton
flagellates and coccoids were predominant.
rfhe material is too scarce for a study of the