196 Södeiström and Rex: Carbon Uptake: Chlorophylls Ratios in Two Swedish Fjords

Botanica MarinaVol. XVII, p. 196-203, 1974

Carbon Uptake: Chlorophyll a Ratios in Two Swedish Fjords

J. Söderström and Maud Rex

Marine Botanical Institute, Carl Skottsbergs Gata 22, S-41319 Göteborg, Sweden

{Rec. 18. 4. 74)

Measurements of photosynthesis have been made with the in situ 14C method in two fjords in Bohuslän on sevenoccasions during 1973. Rates of carbon uptake have been compared with concentrations of Chlorophyll a and lightintensities. The results suggest that light Inhibition is an unimportant factor in both fjords. Carbon uptake: Chloro-phyll a ratios, äs well äs 1^ values, were lowest in the spring. The highest ratios were found in July when concen-trations of phosphate, nitrate and ammonium were very low. This suggests that differencies in the Chlorophyllefficiency are not dependent on nutrient concentrations in accordance with Steele and Baird (1961) but contraryto Curl and Small (1965).In the middle of May 1973 the phytoplankton in Byfjorden was dominated by Chaetoceros spp., in the end of MayNitzschia actydrophila made more than 70 % of the plankton cell number. Small, unidentified, flagellates dominatedin the beginning of July and Coccolithus huxleyi in the end of July. A species of Thalassiosira dominated when theSeptember measurement was made. The conclusion is that estimation of production from light and Chlorophyll datais not possible without a thorough knowledge of the composition of the phytoplankton populations and theirspecific carbon uptake; Chlorophyll a ratios.

Introduction

Measurements of the primary production with the in situ14C-method have been made in two fjords on the Swe-dish west coast. The two fjords belong to the same areaand are characterized by a stable stratification with asurface layer with about 20%o salinity and a bottomwater with up to 30°/00 salinity. Details of the area,including a map, are given in previous papers (Söder-ström 1971 a and b). Of the two fjords, Byfjorden isheavily polluted by sewage from the town of Uddevalla,Kalvö fjord is cleaner but in comparison with the waterin the outer parts of the archipelago it still must beconsidered äs eutrophicated.For practical reasons we tried a shorter duration of the14C measurements than the usually recommended halfday. Our measurements have been carried out beween10 AM and 2 PM. Our principal aim was to compare thetwo fjords but we also intended to use the results äs amaximum production rate of the day and to calculatethe total daily production from these supposed maximawith the aid of light measurements.The 14C measurements have been made following recom-mendations from the international agency for 14C deter-minations, The agency has also made the countings.Light was measured with a quanta-meter of Jerlov'sconstruction (Jerlov and Nygärd 1969). Chlorophyll wasanalysed according to Strickland and Parsons (1968),Analyses of phosphorous and nitrogen have been madeby Mr. Torgny Johansson at the Institute for analytical

chemistry, University of Göteborg. Phytoplanktonsamples were studied with the Utermöhl method (1958),

The results of seven measurements made during 1973are shown in figure 1. A much higher production inByfjorden is indicated. Two half day measurements in1972 gave the Impression that the difference betweenthe two fjords was smalL A possible explanation is thatnutrients can be exhausted in the 14C bottle during theday and therefore a half day measurement from noon tosunset underestimates the daily production in somecases. On March 29th 1973 the concentration of reactivephosphate (DIP) was 0.6 mgP/m3 at the end of the 14Cmeasurement in Byfjorden, the production at noon atthe same depth was 18 mgC/m3h. According to the con-ventional C : P quotient, 41 : l by weight, this rate ofproduction should use 0.6 mg P in one and a half hourFrom the experiments by McAllister et (1964) itseems that the growth of algae is slowed down whenDIP concentrations are below 0.5—1 mgP/m3. A similarSituation was seen on July 26th when production nearthe surface at noon was 42 mgC/m3h and the DIP con-centration at the end of the measurement was1.4mgP/m3.No correlation between rate of production and nutrientconcentrations could be seen. The winter störe of DIPwas used up already in March, the winter störe of N03

and NH4 in the beginning of June. The highest rate ofproduction was measured in Byfjorden on July 26th, theconcentration of DIP was this day at the surface

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Södcrström and Rex: Carbon Uptake: Chlorophyll a Ratlos in Two Swedish Fjords 197

1.4 mgP/m3, no nitrate could be detected and there wasonly 6 mgN/m3 äs ammonium. This suggests that theproduction is kept in balance with the nutrient supplyfrom terrestrial sources and from regeneration also inthis eutrophicated water.The primary production in a polluted fjord like Byfjor-den depends on supply of nutrients from sewage andthrough eddy diffusion from the nutrient rieh bottomwater äs well äs on nutrient regeneration, light condi-tions and the size and composition of the phy toplanktonStanding stock. The Standing stock in its turn is a func-tion of production, sinking rates and grazing. In Byfjor-den the average daily supply of phosphorous fromsewage is about 8 mgP/m2 and together with the phos-phorous transported from the bottom water it representsabout half the daily requirements. Furthermore, theproduction is restricted (because of a very low trans-parency) to the upper half of the mixed layer above thehalocline. The degree of mixing inside the surface layeris therefore also of importance. Very little of all this canbe supposed to be the same inside the I4C bottle. In thesummer when the production is in balance with thecontinuous supply of nutrients one must suspect aconsiderable difference between the production in aclosed and in an open volume of water. Half day 14Cmeasurements would in that case badly represent thereal conditions.One way to overcome this difficulty could be to makeseveral short time measurements during the day, How-ever, in many cases this will for practical reasons bedifficult to accomplish and the question arises if it ispossible to make one short time measurement at noonand calculate the daily production with the aid of lightmeasurements. We do not know if the balance betweenthe primary producers and the nutrient supply goes sofar that a real nutrient shortage never arises during theafternoon but it seems probable. With this obstacleeventually removed we have to consider the possibilityof light Inhibition of the photosynthesis near the surfaceon sunny days.

Light Inhibition

A comparison between light intensities and the oxygenSaturation in coastal water in Bohuslän (lat. N 58° 20')shows such a close relation between periods with strongsunlight and periods with high oxygen Saturation in thesurface layer that a light Inhibition does not seem veryprobable in these waters (Söderström 1971 b, fig. land 4).Ryther (1956) found in experiments carried out at New-port, Rhode Island (lat. N 40° 30'), a strong light Inhibi-tion of the photosynthesis at füll sunlight. Bis diagramof daily relative photosynthesis suggests that sunny andcloudy days differ little in production per surface unitsince the losses during cloudy days in deeper layers arecompensated by less light Inhibition at the surface. Thiseffect has, for tropical waters, also been discussed by

Steemann Nielsen (1958). Steemann Nielsen also des-cribed an experiment showing light Inhibition in tropicalwater (ibid. fig. 2).In a study of short-term variations of phy toplanktonChlorophyll by Yentsch and Ryther (1957) light Inhibi-tion appears äs the result of a decrease in the Chlorophylla content. However, Steemann Nielsen and J^rgensen(1962) states that light Inhibition is not coupled with adestruction of Chlorophyll and the daily variations inChlorophyll concentrations are instead explained bythem äs the result of grazing. Light Inhibition is there-fore best expressed in terms of photosynthesis: Chloro-phyll ratios.A difference between light adapted and dark adaptedalgae has been demonstrated by Steemann Nielsen(1961). Light Inhibition was in this case only foundwhen dark adapted algae were exposed to supraoptima]light intensities.McAilister et al. (1964) äs well äs Jitts et al. (1964)failed to find a decrease in photosynthesis at light inten-sities corresponding to sunlight at the surface duringsummer days. McAilister suggested that absence of uhra-violet light in their experiments could explain that lightInhibition failed to come off.Steemann Nielsen (1964) studied the effects of uhra-violet light on photosynthesis in marine plankton algaeat Friday Harbour (lat. 48° 30'). He found that surfaceplankton is protected against negative effects from theultraviolet light by a 3 mm thick glass cover. Darkadapted algae were found to be more sensitive. Stee-mann Nielsen concluded that füll sunlight without theultraviolet pari had only a slight influence on the rate ofphotosynthesis in surface plankton.Steemann Nielsen and Tai Soo Park (1964) found that aperiod of three days was needed before algae were darkadapted at a light intensity equaJ to 5% of the surfaceIllumination. Due to strong vertical mixing the planktonalgae off Friday Harbour were neither typically darkadapted nor typically light adapted. According to Stee-mann Nielsen and Hansen (1959) vertical mixing and thedepth of the homogenous surface layer are of importancefor the light adaption of surface algae. Surface algae inthe strongly stratified Swedish coastal water shouldtherefore be expected to be light adapted. However, onrainy summerdays the light at the surface may be onlyabout-1/5 of the light on sunny days (fig. 2). It ispossible that on the first one or two sunny days follow-ing a period of rainy and dark days the surface algaereact äs dark adapted and a light Inhibition appears inthe hours around noon. Even then the important factorshould be the ultraviolet light. According to Jerlov(1968) the transmittance of ultraviolet light in sea waterfluctuates much. In tropical parts of the oceans thetransmittance may be 50 to 80% per m while in coastalareas the maxima values does not exceed 10%.The measurements we have made during 1973 give someexamples when the carbon uptake: Chlorophyll a ratio

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198 SÖderström and Rex: Carbon Uptake: Chlorophyll a Ratio» in Two Swedish Fjords

29.3. 73B K

10 20 10mqC/m 3 h

10 m depth

\\10

B25.4.73

K10v

10B30

29.5.73

50K

1016.5.73

B20 30

K

3. 7.73

10 30 50K

10 30B

26. 7. 73

50K

10

/

10B

24. 9.73

30K

10

Fig. 1. Carbon uptake at noon äs a function of depth. Based on 14C measurements between 10 AM and 2 PM. B = Byfjorden,K = Kalvö fjord.

was higher at a depth of l or 2.5 m than at the surface(fig. 3). On July 3rd there was light enough to makelight Inhibition probable. However, in Kalvö fjord,though the highe st ratio was found at a depth of 2.5 m,the lowest was at l m and not at the surface (the surfacevalue for Byfjorden this day has been questioned becauseit is too high to be credible, we strongly suspect someaccident with this sample). A marked decrease at thesurface was found in both fjords on July 26th. This waspartly a very dark day, for some short periods the sur-face light was nearly silboptimal, but there was alsoperiods before and at noon (flg. 2) with füll sunlight andlight Inhibition is not improbable. On the other hand

May 29th was extremely sunny but in spite of this thehighest ratios were found at the surface.The conclusion is that light Inhibition might be an im-portant factor in the open sea, especially in tropicaloceans, while the decreased carbon uptake: chlorphyll aratio near the surface sometimes observed also in tem-perate coastal water probably should have another or atleast an additional explanation.Low total production near the surface can in some casesbe explained äs due to low concentrations of Chlorophyll,for instance caused by uneven distribution of the plank-ton in Langmuir convection cells (Smayda 1970). Sincespecies of plankton algae differ in their sinking rates

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Söderström and Rex: Üwediih Fjords 199

29,3,73

09

. . 25.4.73

500

6 0916.5,73

' 06 09

29.5.73

1000-tOKQ/cm2 s

500

09

3.7. 73

06 09' ·

12_L 15 18

25.7. 73

1000

500

24.3.73

06 S 09

10 50 10

500·

103*101'

dateJJSecchi depth 1

Fig. 2. Light at the surfaqe on the seven occassions of 14C measmements. Cloudy periods May 16th and July 3rd drawn formalJy. Noattempt has been made to correct for inaccuracy eaused by the use of a cosinus collector. Bottom right: Examples of the penetrationof light in the two fjords.

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200 Södcrström and Rex: Carbon Uptake: ChlorophylU Ratios in Two Swedish Fjords

(Eppley et al 1967) we must also expect that the com-position of the plankton populations varies with depth.A possible example of this can be seen in table 1. Com-pare 0 m and l m, Kalvö fjord. Different carbon uptake:Chlorophyll ratios in the light saturated layer may thenbe caused by different efficiency of Chlorophyll accord-ing to which plankton species is carrier of the Chloro-phyll·

BYFJQROENK A L t f O FJORD

A Ü Ü

25.4.73

iÜO 6UO 9001—

3. 7. 73

60Ü BOO

24.3.73

200

Fig. 3. Carbon uptake: Chlorophyll a ratios äs functions of light.

Fluctuations in the maximum carbon uptake:Chlorophyll a ratio

The carbon uptake: Chlorophyll a ratio was sometimeslower in Kalvö fjord, the least eutrophicated of the twofjords, sometimes in Byfjorden. The ränge of the maximawas from l to 10 with a seasonal Variation which seemsindependent of nutrient concentrations. About the sameratios have been reported by Steemann Nielsen and Han-sen (1959). Their lowest values were obtained from darkadapted arctic plankton, low values were also characte-ristic of temperate winter plankton- The highest valueswere connected with temperate summer plankton andwith tropical plankton. This suggests a relationship withlight adaption and temperature but the explanationcould also be different photosynthetic efficiency in thesuccessive plankton populations. The seven occasionswhen we made our measurements were characterized byquite different plankton populations. In spring diatomsdominated (fig. 5). Small unidentified flagellates weremost numerous on July 3rd and Coccolithtts hüxleyi onJuly 26th. A species of Thalassiosira dominated whenthe September measurements were made.

Steele and Baird (1961) found a seasonal Variation in themonthiy average ratios. The maximum at Fladen (NorthSea) appeared in June and July but at Aberdeen Bay inAugust and September. The maximum at Fladenoccurred when phosphate and nitrate were more or lessdepleted. Neither light adaption nor nutrient limitationseems therefore sufficient äs explanation s of the differ-ent ratios.

Studying primary production west of Newport, Qregon,Curl and Small (1965) observed high assimilation:Chlorophyll ratios in connection with recently upwelledwater and suggested that ratios below 3 should indicatenutrient depletion and ratios above 5 nutrient rieh water.

Thomas (1970) found only slightly lower ratios in nitro-gen poor tropical water than in nitrogen rieh water,

Lorenzen (1963) studied diurnal variations in photo-synthetic activity of natural phytoplankton populations

-lQmgC/mgCh/3 h

Fig. 4, A comparison bctween maximumcarbon uptake; Chlorophyll a ratios found inthe two fjords and ratios predicted accor-ding to the equation proposed by Williamsand Murdoch: log(mgC/mgChl.ö h) = 0.138+ 0.0353 X temp. °C. B = Byfjorden,K = KalvÖ fjord, black = predicted values.

29.3, 24,9.

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Söderström and Rex: Carbon Uptake: Chlorophyll a Ratios in Two Swedish Fjords 201

[ Skeletonema costatum

| Chaeiocero$ spp single cetls

[Chaetoceros socialis

[Chaetoceros borest 13

[ Chaeroceros decipiens

| Chaetoceros danicus

| Chsetoceros constnctus

| Leptocylindrus danicus

| Nitzschia actydroph/fa

| Apedinella spmifera 100%

Fig. 5. Percentage of the total cellnumber for the ten dominatingspecies at the depth of 2.5 m in Byfjorden during spring 1973.

in a small estuary near New York. The daüy ränge waslow in the winter and high in the summer. The fluctua-tions were found to depend on both changes in theamount of Chlorophyll and in the assimilation: Chloro-phyll ratio.A relation between assimilation: Chlorophyll ratios andwater temperature was found by Williams and Murdoch(1966). Their ratios from Beaufort Channel, North Caro-lina, ranged from 1.9 to 19.8 and could be predictedfrom the temperature. The equation they used for thisprediction does not function too badly in our researcharea (fig. 4) though on July 26th the ratios differedmuch in the two fjords with the same temperature. Thissuggests that it is not the temperature in itself but aplankton succession, partly controlled by temperature,that determines the assimilation: Chlorophyll ratio.

Recently Dunstan (1973) has compared photosynthesis:light intensity relations in phylogenetically differentplankton algae. Under the same culturing conditions IKvalues (Talling 1957) varied little, showing that adaptionto the used light was well established, while a consider-able Variation in the maxima values of the photosynthe-sis: Chlorophylls ratio could be demonstrated.

The conclusion is that the carbon uptake: Chlorophyll #ratio in marine plankton algae is subject to variationswhich have some relations to conditions in the environ-ment but are not directly caused by these conditions.

The contradictory results of Steele and Baird äs com-pared with Curl and Small can be brought together withthe findings of Williams and Murdoch and those ofDunstan if we assume specific ratios characteristic forthe different plankton populations following each otherduring a production period or met with in waters withdifferent nutrient concentrations. If that is the case thedifferent ratios in Byfjorden and Kalvö fjord on July26th (fig. 3) - difficult to understand if only the tem-porary environmental conditions are considered -should reflect some difference in the composition of theplankton populations in the two fjords.

Composition of the phytoplankton on July 26th and itsrelation to carbon uptake: Chlorophyll ratios

The phytoplankton present in Byfjorden and Kalvö fjordon July 26th could be divided into three groups:

A/ Diatoms with Leptocylindrus danicus, Cerataulinabergonü and Rhizosolenia fragilissima äs dominants.Cerataulina was absent in Kalvö fjord.B/ Dinoflagellates, in both fjords strongly dominated byProrocentrum micans.C( A group of small algae. 70 to 80% of the ceJls in thisgroup were Coccolithus huxleyi,In numbers group C dominated in both fjords but sinceProrocentrum has a volume about 200—500 times biggerthan Coccolithus group B represented more of the bio-mass than group C in Byfjorden. There was little ofgroup B in Kalvö fjord and this was the main quaJitydifference between the population in this fjord and thatin Byfjorden.The groups had a relatively constant composition in thedifferent samples. It is therefore possible to assume thata certain amount of Chlorophyll a per cell characterizeseach group and does not change from sample to sample.Since the total amount of Chlorophyll is known for eachsample the following equation can be used.Aj X a + BJ X b + Cj X c = Chl. a / literi = l, 2, 3, etc.Capital letters are the number of cells per liter of thethree groups in sample nr l, 2, 3, etc., small letters theamount of Chlorophyll a per cell characteristic for eachof the three groups. The equation can be solved by theuse of data from three samples. Since the assumptionthat a, b, c are constant from sample to sample is onlyapproximately correct, it is not possible to find a solu-tion that suites all samples. Of possible Solutionsa = 27 · 10'9, b = 45 · 10'9 and c = 0.2 · 10'9 mgChl. a/cell is correct for the samples from 0 m in Byfjorden andfrom 0 and l m in Kalvö fjord. The differences betweenthe measured concentrations and those obtained byusing these values in the other samples from July 26thare shown in table 1.In table l is also shown the percentage of Chlorophyllbelonging to each of the three groups if the above valuesfor Chlorophyll per cell are correct. Group B is now

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202 Söderström and Rex: Carbon Uptake: Chlorophyll a Ratlos in Two Swedish Fjords

Tab. 1. Data from July 26th 1973.

Numbersof cells X 103/literA = DiatomsB = DinoflagellatesC = Coccolithus huxleyi +

small flagellates

c'So^X

CG

UN

O

:O•j|

*

Depth

O mI m2.5 m5 m10m

O mI m2.5 m5 m10m

Total

41914115402645021371

33982936309028402389

A

734251

10124

124430

99

B

101111702934

678

106

C

40173962390543721313

33802885305228212374

mg Chl. a/m3 % of total Chl. a(based o n calcu-lated values)

o

17.36.76.6—0.5

1.32.11.31.42.2

'S

7.3 .6.95.34.92.4

1.32.11.81.31.0

A

2716265527

25'57451924

B

6272592764

2015203527

C

11u151811

5227344347

DIP

mg P/m3

1.4—1.9—

3.3

1.0-

0.7—1.6

N03 + NH4 N/P

mg N/m3

6—7—9

4—7—48

4.3—

3.7—2.7

4.0—10.0—

30.0

shown äs the dominant in Byfjorden whüe A and C sharethe dominance in Kalvö fjord, Since the maximumcarbon uptake: Chlorophylls ratio was 10.1 in Byfjor-den and 4. l in Kalvö fjord this suggests that Chlorophyllbelonging to group B (Dinoflagellates) has a higherefficiency than Chlorophyll belonging to the other twogroups. In spring diatoms dominated (flg. 5), the carbonuptake: Chlorophyll a ratio at iight Saturation was thenfrom l -3. If we assume from this a ratio of 2 for theChlorophyll in groups A and C, which in Byfjordenrepresented 28% of the Chlorophyll at the depth werethe maximum ratio was measured, group B must begiven a ratio just above 13 to make the measured ratioof 10 possible. In Kalvö fjord the maximum ratio wasfound at 2,5 m depth and here the calculated distribu-tion of Chlorophyll was 20% in group B and 80% in theother two groups (tab. 1), If we use the same ratios,2 and 13, in this case the ratio for the whole populationin Kalvö fjord will be 4.2, which should be comparedwith the result from the measurements: 4.1.This looks fine but can äs well be a mere coincidence.We have only measured the growth factors Iight, phos-phorous and nitrogen, Something must have caused thepoor development of Prorocentrum micans in Kalvöfjord and this unknown factor could also have loweredthe carbon uptake: Chlorophyll a ratio for all species inthe Kalvö fjord population, It must also be pointed outthat Dunstan (1973) found a higher ratio for Coccoli-thits huxleyi and Thalassiosira pseudonana than forProrocentrum micans. However, it seems evident thatthe ratios to a great extent depend on the compo-sition of the plankton populations. Many problems con-cerning marine primary production would probably seemless obscure if the chemical and physiological researchwork to a higher degree was combined with systematicand sociological analyses of the plankton populations.A mere counting of the cells in the water, for instance,äs it is often done, with an electronic counter is clearlyinsufficient. On May 29th 1973 three million cells at the

surface in Byfjorden contained about the same amountof Chlorophyll äs fifteen million cells at a depth of onemeter. The only explanation is that the species thatdominated innumbtt$,Nttzschiaacfydrophila, waspracticaliy without Chlorophyll. Altogether relationsbetween the composition of phytoplankton populationsand the metabolic rates of sea water ought to be subjectof intensive studies. 7>2 situ studies should be reconvmended since abnormal behaviour in culture must besuspected.There is an increasing demand for quantified studies ofmarine food webs, These studies must be based on moredetailed knowledge of the primary production than weusually have today. 14C measurements are technicallycertainly the best method but the number of measure-ments that can be made is restricted. The 14C methodought to be combined with a method that allows rnoreor less continuous measurements and a close network ofmeasuring points. A method for estimation of the pro-duction from Chlorophyll and Iight data, involving amean assimilation: Chlorophyll ratio of 3.7, was pro-posed by Ryther and Yentsch (1957). Light measure-ments can be put on a recorder and in situ methods forChlorophyll determinations are being developed. Moreknowledge of carbon uptake: Chlorophyll ratios indifferent phytoplankton populations can perhaps makefast and easy measurements of the primary productiona reality.

Acknowledgement

This investigation has been made äs a part of the "Byfjor-den Survey" with financial aid from the National Swe-dish Environment Protection Board, For assistance inthe field work thanks are due to Mr. T. Johansson,Mr. B. Rex and Mrs. K. Söderström. Prof. David Dyrssen,the Institute for analytical chemistry, and Prof. ToreLevring, the Marine botanical Institute, University ofGöteborg, have given us laboratory space and resources.

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Soderström and Rex: Carbon Uptake: Chlorophyll a Ratlos in Two Swedish Fjords 203

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Botanica Marina / VoL XVII / 1974 / Fase. 4 16A*Brought to you by | University of Virginia

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