observations on the fatty constituents of marine … · gives an incomplete account of the relative...

OBSERVATIONS ON THE FATTY CONSTITUENTSOF MARINE PLANKTON

I. BIOLOGY OF THE PLANKTON

BY E. R. GUNTHER.

("Discovery" Investigations, c/o British Museum (Natural History).)

(Received 1st November, 1933.)

(With Three Text-figures.)

I. INTRODUCTION.BRANDT (1898) carried out chemical analyses of plankton collected with a quanti-tative plankton net in Kiel Bay with a view to ascertaining the possible yield ofplant and animal products from a unit volume of sea water. His collections weresmall and investigations of the oils were not attempted. In a series of subsequentpapers he, Apstein, Hensen and others have examined the conditions of organicproduction in the sea, and Johnstonc (1908), quoting estimates by Biebahn andRodewald, has compared the productivity of the sea with agricultural standards.

Since the classioal work of the Kiel planktologists, the chemistry of marineplankton has received comparatively little attention until recently when, as a resultof advances in the knowledge of accessory food factors, biochemists looked toplankton for the origin of vitamin D which was then known to abound in cod-liveroil. These researches were published in a series of historically interesting papersby Hjort (1922), Jameson (1922), Zilva (1922) and others: but when in 1926 theseparate identity of vitamins A and D was accepted, this aspect of the subject wasin need of revision.

The search for vitamin D in dried diatoms obtained from cultures of Nitzschiagrown in the laboratory (Leigh-Clare, 1927) proved unsuccessful; but since theinception of the present work1, Ahmad (1930) has proved that the oil extractedfrom similar cultures of Nitzschia is a good source of vitamin A. In no case priorto 1928 are we aware of vitamins A and D having been found in native plankton,and, since it is the ultimate source of food of most marine animals, plankton mayalso be of importance in a study both of the part played by vitamins in nutritionand of the influence of plankton oils on the fats present in fish, seals, whales andother animals of economic importance.

Little is understood of the r&le of vitamin D in the promotion of calcium andphosphate metabolism in fish; we do not know whether the cartilaginous Elasmo-branchii have the same nutritional requirements as Teleostei, or whether the delicate

1 Drummond (1930).

174 E. R. GUNTHER

and sometimes fibrous nature of the bones in deep-sea fish is attributable to life inthe greater depths of the ocean where they and their food are screened from solarirradiation. Leaving for future investigation the physiological significance of vitaminsin these organisms, there remains the problem of origin of the factors themselves:whether they are absorbed with the food or whether synthesised within the animalby irradiation or other means. Bills (1927) has claimed that there is no increase invitamin activity in the oils extracted from fish that had been subjected to ultra-violet light: and at the same time he notes no diminution of vitamin activity afterthe fish had been kept in the dark for three months. From this he argues againstirradiation. It was therefore deemed advisable, as a first step, to examine the foodeaten by the larvae of most fish and by the adult of so many. A study of littoralplankton from British seas was begun in 1928.

With the progress of the work it became evident that the numerical method ofrepresenting plankton analyses that has been used by the majority of planktologists,gives an incomplete account of the relative importance of the different species.In dealing with the chemical composition of a mixed assembly of organisms orwith its value as a source of food, or with its economic aspects, the relative weightof the various species may be of more significance than their relative strength innumbers, although weight alone, unqualified by chemical analyses, might giveequally misleading results if applied indiscriminately to jelly-fish and other organismsof exceptional composition. A gravimetric method is obviously applicable only togiven organisms of approximately similar constitution, as the more prominentspecies in the present collections are believed to be. The specific gravities of floatingmarine organisms are sufficiently similar to allow of good comparisons of their massby a volumetric method. Tables have been compiled to show the relation betweenthe length and volume of certain selected genera. The application of these data tothe ordinary numerical analyses of the plankton, converts them from figures repre-senting numbers per c.c. of settled plankton into figures representing volumes per c.c.settled plankton. Preliminary results obtained by these methods are advanced in thefollowing sections.

II. COLLECTION AND PRESERVATION.

The phytoplankton and zooplankton were collected respectively in May andJuly, 1928, from the environs of the Isle of Man. It is impossible to separate ona large scale animal plankton from phytoplankton, but fortunately the maximumabundance of the main mass of diatoms occurs in May while the maximum abun-dance of animal life occurs in July, and although the diatom efflorescence in Mayis never without a quota of animal larvae nor the animals in July without a littlephytoplankton, the catches of May and July are sufficiently characteristic to presenta green and a red colour in striking contrast.

The Isle of Man, bathed in oceanic water free of land detritus, is moderatelywell suited as a base for the plankton collector, while the valuable work of thePort Erin Investigations enables prediction with a fair degree of certainty of

Observations on the Fatty Constituents of Marine Plankton 175

the actual week when the phyto- and zooplankton will reach their maximumabundance.

The phytoplankton collected during four days (May 22nd-25th) was taken intwo silk tow-nets of mesh 70 and 150 per linear inch, towed from a 12 ft. fishingboat rigged with mainsail, jib and centreboard. The nets were specially designedto take bulky catches. The net with mesh 70 proved to be the more efficient, sincethe larger mesh allowed better filtration and caught twice the bulk of vegetablematter. Collection was restricted to the plankton at surface depths during daylighthours (11.00-20.30). The weather was usually calm under varying conditions oflight from bright sunlight to overcast. Variable winds never exceeded the force ofa light breeze.

Preservation of the catch was beset by the problem of concentrating settleddiatoms to a reasonably small volume, and the following methods employed toremove surplus water took three or four hours after each day's fishing. The settledplankton was first squeezed lightly through silk of the same mesh as the net andits volume reduced to a third. The volume of the strained plankton was againreduced to a third by filtering on a Buchner funnel. It was found necessary tointerpose two layers of silk netting between the filter paper and the funnel, andeven then filtration was slow and filter papers had constantly to be changed. Twomethods of preservation were employed: to some samples was added an equalvolume of absolute alcohol and to others enough sodium chloride to ensure asaturated solution, e.g. 400 grams NaCl per litre of concentrated diatoms.

Zooplankton was taken in July (i6th-2Oth). Two of the larger 70-mesh netswere towed sometimes by a 26 ft. motor boat, the Redwing, fitted with mainsailand jib, and sometimes by a 12 ft. rowing boat equipped with a lugsail and centre-board. Wind mostly from the west varied in strength and sometimes made thesurface lively. The weather was mostly sunny except on two days when the breezewas at its strongest. As with the phytoplankton, the catches were preserved bothwith salt and with alcohol. Both the pink appearance of the plankton and the micro-scopical analysis showed that diatoms were much in the minority and the freshmaterial was easily strained off from surplus water over silk.

III. BIOLOGICAL ANALYSIS.It is well known (Johnstone, 1924) that even in a very small sea area such as thatin Port Erin Bay there may be differences in the nature and abundance of theplankton at places only a few yards distant from each other or at the same placeafter only a few minutes' interval of time. Catches on a large scale tend to havea variable composition, and unless they are very thoroughly mixed before samplingit is possible that the samples subjected to biological examination may not be trulyrepresentative of the masses of plankton used in oil extraction. Difficulties of anotherkind enter into numerical estimations; plankton catches are frequently measuredvolumetrically in terms of settled organisms, and as Russell (1927) points out,the settled volume occupied by certain species may differ largely from that ofothers, this has been overcome as far as possible by treating separately the plankton

176 E. R. GUNTHER

taken on different days. Errors of a statistical nature are inevitable in an estimatedependent upon random sampling and upon the raising of small counts; we reducedto some extent such errors in estimations of the larger, more important, or rarerspecies by counting larger fractions; and in the identification of closely allied specieswe have frequently used a generic or other categorical heading. Stress is laid on thefact that neither the collections of phytoplankton nor of the zooplankton can claimto be representative of the plankton community as it occurs naturally in the sea,but they represent those species most easily selected by our nets. It is obviousthat the majority of the nannoplankton will at first pass through the meshes, andthat as these are clogged during the course of towing, the filtration coefficient andso the catching power of the nets will vary. These considerations affecting muchless the treatment of plankton collected for quantitative work (the nets being fishedfor relatively short periods), may account for the divergence of these lists fromthe average taken over a number of years and published by Johnstone.

PHYTOPLANKTON.

Collections were made during four days from May 22nd to 25th, and fivesamples each of about 100 c.c. settled diatoms were reserved for biological examina-tion. Two sub-samples of each, (a) and (b), were examined. The first of about 5 c.c.was examined in its entirety for its animal content and after dilution, in a fractionof 1/20 for the larger and rarer species of diatom such as Coscinodiscus andBiddulphia (see Table I, estimations (b)). The smaller and more abundant specieswere also noted but were better estimated from the second sub-sample of about 1 c.c.(Table I, estimations (a)). The latter was made up to a 1 per cent, dilution fromwhich fractions were extracted by the Hensen method. The fraction was then placedon a glass slide ruled in squares and the organisms counted under a microscope.

The results of these analyses, listed in Table I, show that the five samples arematerially similar, consisting principally of the species Chaetoceros densus, Chaetocerosdebile and Lauderia borealis, with lesser numbers of Chaetoceros decipiens andChaetoceros compressus.

The catches of phytoplankton included a quota of animal life which consistedof larval forms and small Copepoda. Their numbers were few, and although theirpresence cannot be ignored they occurred with the diatoms, approximately in theratio of 1:100,000,000. In general appearance the plankton samples were like thickpea soup in which, here and there, the animal organisms could be detected asminute white dots. The comparative bulk of plant and animal matter has notbeen estimated.

ZOOPLANKTON.

Numerical estimation, methods.

Collections were made during five days from July 16th to 20th, and eightsamples of about 100 c.c. of settled plankton were reserved for biological examina-tion. Each sample was examined in the following way: The sample was dilutedwith water, well mixed and shaken up, and enough poured into two 5 c.c. measuring


cylinders to give, in each, a sub-sample of about 5 c.c. settled plankton. Eachsub-sample, (a) and (b), was examined in the usual way by the Hensen methodof counting under a microscope the organisms contained in 1/30 of 5 c.c. Calanusfinmarchicus, which proved itself to be the largest copepod present1, and the mostimportant constituent of the plankton, was analysed in greater detail. Copepodidstages IV to adult were all picked out of one of the 5 c.c. samples of each pair andstages I—III were picked out of 1/20 of the residue. Analysis of the younger stagesof Calanus finmarchicus has importance from two points of view. First, to determinethe percentage of Calanus that is effective towards oil yield, second, because theratio of the different stages in a sample may be of help in distinguishing betweenone type of plankton and another. Data from the less common zooplankton con-stituents were obtained by examining a large sample of 100 c.c. from one of thecatches taken in the middle of the period.

Numerical estimation, results.

The results of these analyses are given as numbers of organisms per 1 c.c. ofsettled plankton in Table II and as percentages of the total numbers present ineach sample in Table III. The analyses of each pair of sub-samples (a) and (b)show a close measure of agreement and therefore each analysis may be taken asan indication of the general characteristics of the sample. The eight samples (ref.Nos. 40-47) are seen to fall more or less naturally into four groups indicatedunder groups I, II, III and IV in Table III. The three samples (40-42) con-stituting group I, collected on July 16th and 17th, are very similar but differfrom the four samples of groups II and III (43-46), collected in the intermediateperiod July 18th and 19th, which also show certain features in common. Theplankton of the last day (sample 47, July 20th) in group IV more nearly resemblesgroup I, but there are differences; for example, in the percentage of oithonids andin the ratio of Calanus finmarchicus stage V to adult. The features of significancein the grouping of these samples have been emphasised by heavy type, and on thisbasis the results of biological analysis have been similarly grouped (pp. 187-190).In Table III the oil yield from each group has also been incorporated together withdetailed analyses of the stages of Calanus finmarchicus. The correlation of oil yieldwith abundance of adult and sub-adult stages of Calanus finmarchicus is the strikingfeature of the table and will be alluded to presently.

Other interesting correlations between groups I and IV on the one hand andII and III on the other are the association of naupliar larvae with adult Calanusand also the respective ratios of 40:60 and 60:40 of Calanus finmarchicus, stages Vto adult. This and other evidence points to the conclusion that we are dealing withtwo independent plankton communities, and the probability seems to be that theywere from different water masses. It is convenient to note here that the samples ofgroup I included much mucilage which may be correlated with the presence of thediatom Rhizosolenia in rather larger quantities than in the other samples. Thisseems to afford an explanation of the larger volume of settled plankton for the

1 With the exception of Anomalocera pattersoni.

Tab

le I

. Preliminary

anal

ysis

of j

ive

sam

ples

of

phyt

opla

nkto

n.

I Abundance o

f ro

oplm

kxo

n

o o

r8

0.

013

0.03

0.003

I I

For

each

um

ple

th

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sulh

of

two

ati

mn

tiom

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) Pnd

(b

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iven

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abu

nd

ance

of

ench

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nu

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cen

tage

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the

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ber

of

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nis

ms

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he

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ple

. - - - -

- . -- h

te

...

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aa

. v. 28

23.

v. 28

23.

v. 28

14. v

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s. v

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30

33

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(b)

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m AB

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i 8 z E. R. GUNTHER

samples of this group, and in consequence of the numerical poverty in the totalnumber of organisms per unit volume. The mucilage may have entangled theCeratium and Radiolaria and prevented their passage through the net, whichwould account for the high percentage in group I. Groups I and IV, however, havea further similarity in the higher percentage of Acartia and of Calanus finmarchicus,stages III and IV. The material collected on July 19th, amounting to 3300 c.c, wasincluded in group III for oil extraction, but analysis of the plankton suggests thatit is intermediate in composition between groups I and IV on the one hand andgroups II and III on the other.

The analyses in Tables II and III are essentially little more than a generalisedstatement of the abundance of the more easily recognised species, and those suchas Acartia may even be underestimated, some having been included under'' Copepodaalia."

Table IV. Analysis of plankton organisms in sample No. 43, 18. vii. 28.The genera and specie* are arranged in natural groups listed in order of abundance.

Genera and species

CopepodaCalanus finmarchicusParacalanus parvuiOithonidsAcartia clauxiTemora longtcornisPuudocalamit elongatusI si as clavipexCentropages hamatusCalanus sp. juv.Centropages typxeusParaponttlla brevicormsHarp act icoideaArwmalocera pattrrsont

Naupln

Tunicata: Oikopleura dioicaPeridinialefl: Ceratium triposChaetognathaCladocera

Evadne nordtnanniPotion xnUrmtdiut

DecapodaCancer pagurut zoeaeEbalia sp.Upogebia sp.Urachyuran larvaCnHumassa sp.

Noe. perIOO C.C.

settledplankton

37.00032,00030,00029,00015,0006,5002,6002,6002,400

320280803 0

24,000

8,500

3.900

2,200

1,2002 0

2 7 040302 0

2 0

Genera and specie*

Decapoda (cont.)Hippoiyte variansPandalus sp.Portunus megalopaGaiathea ip.Eupagurus tp.Pinnotheres sp.Porcellana sp.

EuphausiaceaNyctiphanes calyptoptsN. cyrtopiaN. fur aha

Moll us caGastropoda post-larvaI^amell 1 branch post-larva

Echinodermata: Ophiuroid post-larvaPolvchaeta

Tomopteris sp.Folycnaeta post-larvaeSpionidn 11 J

r>ylliaAmphipoda: micromscusPisces: larvaeOva

Medusae: Aequorea albidaCtenophora

Total organisms

Nos. perIOO C.C.

settledplankton

2 0

2 0

821

i

r

I O O

8021

So

2 0

2 O

5

52 0

2 0

2 O

3

1

108,461

NOTE. The list is compiled from an examination of four different sized fractions. The largest and rareat animals werenoted from the whole loo c.c, the others respecti\ely from 20. 5 and } c.c. The large number of about 1085 organismsper c.c. Bhows that this sub-sample was more closely packed than other sub-samples of the same plankton analysed inTable II.

The fauna has been treated in greater detail in Table IV, which gives a list ofthe organisms noted in ioo c.c. of a sample (ref. No. 43) taken in the middle of theperiod.


Volumetric estimation: methods.

The sorting out from every sample of enough animals for experimental deter-mination of their volumes by direct displacement, would have involved unduelabour, and we have resorted to an indirect method. The method requires a know-ledge of the numerical estimation of the different species in each sample, a knowledgeof their length, and a graph to show the relation between the length and volumeof the various genera. The lengths of the respective species are easily measuredby means of a micrometer eyepiece; and hence by means of the appropriate curveit is possible by interpolation to read off their volume and so to convert the nu-merical estimate into a volumetric estimate.

Table V. Displacement measurements of Chaetognatha of different lengths.

Nos.examined

462

54

918

649

56

1 421

2

418

3711

3388

1 0 32 7

79

Mean lengthmm.

5755755'554-25348-884645-24 2 542-338-838-663735-333'528-527-124-422-7218-817-517-11 4 3

8-8

DisplacementNos. per c.c.

4 0

2 92-2

3-63'33-26 9

3-o3 34-0

5-95 0

1 1 7

8-96-7

30-82 5 749-478-0

94'31955172-0270-0

1580-0

To construct these curves, it was necessary in the first place to measure thevolumes of animals of widely different length which had been sorted out into lengthgroups. For the larger organisms like Chaetognatha and the larger calanoids a dis-placement method was used: and Table V shows the relation between the meanlength of each group and the numbers of Chaetognatha per c.c. For the smallerorganisms such as nauplii, oithonids and young calanoids, a packing method wasadopted. The organisms of a like length to be measured, are laid out on a glassslide ruled in millimetre squares, and the individual organisms are so packed togetherthat, one animal deep, they cover as near as possible a square measuring alongone side 1, 2, 3 or 4 mm., etc., according to convenience and the length of theanimal. Assuming that the shape of the animal is fusiform, the number of organisms

JEB-Xlii 13

184 E. R. GUNTHER

that would occupy a cube built up on a square is calculated by multiplying thenumber of packed animals by the number lying side by side along one side ofthe square.

From theoretical considerations a graph of the reciprocal of the length plottedagainst the cube root of the numbers of organisms per c.c, should give a straightline provided that there is no change in the shape of the animal with growth norwith increasing experimental error (Fisher, 1933). Fig. 1 shows such a curve fromthe figures obtained from estimates of Chaetognatha. To a lesser degree the samerelation is illustrated by displacement measurements of the larger calanoids(Table VI and Fig. 2, curve (ii)). The packing method gives rather greater values

o-i 11—

0-10

0O9

0-08

0-07

Co

I O05a

'§ (MM5

0-03

0-02

0-011 1 i 1 s (> 7 a 9 10 11 12

Cube root of numbers of Chaetognatha per c.c.

Fig. 1. (See Table V.)

for the volume of each animal because of the spaces which are included betweenthe animals, and this divergence from the true volume probably increases as thesize of the animal diminishes. The volumes of calanoids, oithonids and naupliiobtained by this method are listed in Table VI, and the calanoids when plotted(Fig. 2, curve (i)) lie on a curved path. The nature of this curve is due partly tothe packing method of measurement, partly to the different shapes of the youngerindividuals and especially of the nauplii which are on the whole more globular inshape than adult Copepoda. The more attenuated slender shaped oithonids lieoutside the curve altogether. The volume of the large diatom Coscinodiscus hasbeen obtained by calculation on the assumption that it occupies a cubic volume of0-0068 c.mm. which is probably a very liberal estimate. In view of the preliminary


Table VI. Volumetric measurements of Copepoda, NauplU and Coscinodiscus.

Genusexamined

CoscinodiscusNaupliiOithona

Calanus juv.

C. acutus

Meanlengthmm.

0-190-420-7560-870 7 1

0-671 241 6 52-O

2-192-6452-0853-5254'4

Estimated numbers per c.c.

Bycalculation

278,000—

———

—————————

Packingmethod

"5,5OO157,50072,00066,00050,0009,37°6,4003,5°°2,34O1,260

9944 0 02 7 0

Displace-ment

————————

500019231667667444

Weight gm.control

measure-ment

_—————

—0-0330-05350-2960-1385

Nos.examined

—————

—1751 2 55 0 01 0 0

O-75 333

5-Or

-Curve (ii)• - Oithonid• = Coicinodiscus

12 16 20 24 28 32 36 40 44 48Cube root of numbers of organisms per c.c.

Fig. 2. (See Table VI.)

nature of this inquiry it was decided that the amount by which the packing methodoverstates the volume might not be enough to matter and the curve (i) in Fig. 2was adopted for interpolation not only of Calanus but for other genera of Copepodaalso. The results obtained by this curve will therefore overstate the volume of thesmaller and slenderer Copepoda.

13-2

186 E. R. GUNTHER

Volumetric estimation: results.

Volumes of each of the species listed in Table II have been deduced by oneor other of the methods just described and are tabulated as numbers per c.c. inTable VII. The mean length of each species is calculated from the frequenciesgiven as an appendix in Table XIII. One mean only is calculated for a specieswhose length frequencies lie within a small range, i.e. not exceeding 0-6 mm. Butfor those species whose length frequencies extend over a wider range than o-6 mm.,and especially if they lie on a multimodal curve, two or more means are calculated.The volumes found for each of these means are then adjusted according to theproportion of organisms furnishing the lesser or the greater mean, and a compoundfigure for the volume of the species results.

Table VII. Specific volumes of the organisms listed in Table II.

Nos.examined

649423 132 %49 | 6 8 %37262427

2 1

19 1 2 5 %58 ( 7 5 %20 I 20 "178 ( 8 o %78

196 I74 " o

69 \ 26 " 0

1 10-4 ",

2537

5111

1\

\1i1

)D )

Species

Calanui finmarchicus

NaupliiAcartia clausi

Temora longicornitM

OithunnCopepoda alia

,,AppendiculariaChaetognathaEvadne nordmatmiPodon intermcdiusRadiolariaCeratium

•s?VV

IVIIIII

I

Mean lengthmm.

33 - i2-832 4 82-1I-65

1-250 9 4

O-5850-871 2 309051-60 9

o-88i - 3 92 2

2

8-5o-88

—O'lo - i

Nos. per c.c.

830658

1,1251,8163.2437,078

14,88024,90070,96033,08015,26030,380

7,76330,950*32,76811,2402,863

166,3752,1973<4°°3.4OO

1,000,0001,000,000

• Estimated on the basis of the calanoid curve, Fig. 2.

For the conversion of numbers to volume the numbers of organisms per c.c.may be regarded as a factor to be applied to the numerical estimations that havealready been made. These numerical estimations (Tables II and III) showed thatthe plankton samples fall naturally into four groups and it will be preferable totreat them as groups instead of separate estimations. A mean estimation repre-senting the numbers of each of the species present in i c.c. of settled plankton iscomputed for each group and is given in Table VIII A. Dividing by the appro-priate volume factors in Table VII, the numbers in Table VIII A are converted tothe volumes of each species. These are expressed in c.mm. in Table VIII B. InTables IX A and B the same data are reduced to percentages of the total present


Table VIII.

A. Mean number of animals per cc . settled plankton in groups I-IV.

Group No.

Reference No. of planktonincluded in each group

Calanus firtmarchicut o"V

Copepodid VIVIII

III

NaupliiAcartia clausiTemora longicormtOithonaCopepoda aliaAppendiculariaChaetognathaEvadne nordmarmiPodon intermediusRadiolariaCeratium

Total

I

4 0 , 4 1 . 42

0-2662-5334-0

2-53348334-733

14-6661 0 2

16681

148

31968

894

17H5

IIOI

II

43

12-4

7756-811-41 2 634-257-6

2341 2 91 3 2186

333571560

924

1387

III

44. 45. 46

4 1 0

463433-o810-71

6 8 238-2528-20

207-218

1741864 3 i

4924

72

21 1

1279

IV

47

i-o

n o9 67-2

4*488

i77228

234528

79545

30

36

33

2101

NOTE. The means in groups I, II and IV are computed from the estimations given in TablesII and I I I . The means given under group III are compound figures and are constituted as follows:57'7 % represents the meaned estimation of samples 44 and 45 (the volume of settled plankton ofthese samples is 4500 c c . ) ; 4 2 3 % represents the meaned estimations of sample 46 (the volumeof settled plankton of this sample is 3300 c c ) .

B. The mean volume expressed as c.mm. per c c . settled plankton in each group I- IV.

Group No. ...

Calanus finmarcfricus cJ

Copepodid VIVIII

III

NaupliiAcartia clausiTemora longicornisOithonaCopepoda aliaAppendiculariaChaetognathaEvadne nordmanmPodon intermediusRadiolariaCeratium

Total

I

0 3 23-8526480 7 80-6830-3180-590-1449 4 48-9084785

14-840-4083-542 6 51-1760-017

O-I45

55242

II

I4-451 1 7

37-43-521-782-323183'37-3I7

11-4566

I5-52O-3436-841-760

0-0090-024

231-337

III

4-947O-521-84

3'30-9652-571-132-921-041

19-176

20-230-295

10-92-06

o-59O-OO2

o-on

168-464

IV

1-205

16-76-432-2180-6210-588O-32I2-5

12-9225-6517-136-890-27

i-370

0-8840-0060-033

125-706J

i88 E. R. GUNTHER

Table IX.

A. Mean number of animals per c.c. expressed as a percentage of total numberof organisms present in each group.

Group No.

Calanus finmarclacus $'+

Copepodid VIVIIIIII

NaupliiAcartia clausiTemora longicornisOithonaCopepoda aliaAppendiculariaChaetognathaEvadne nordmanniPodon intermediusRadiolariaCeratium

I

0-020-230-360-230-440-431-329-28

15-27-36

I3-48295-69o-730-830 3 61'54

1 3 2

II

I - I 2

5-554 1O-820-912-464/16

16-99'39-53

13-41244 - n1-080-4300-65i-73

III

0-323-622 5 90-84O'S33-002-2O

16-20I-4I

I3'6oi4'S733'7°3-84i-880'540-150-15o-86

IV

0 0 50-520-460'34O-2I0-380-38

H210-8511-1425-0137-8

2-140-1400-140-291-57

B. Volumes are expressed as percentage of total volume in each group.

Group No.

Calanus finmarchicus

Copepodid

NaupliiAcartia clausiTemora lotigiconrisOithonaCopepoda aliaAppendiculariaChaetognathaEvadne nordmanniPodon intermediusRadiolariaCeratium

1 VIVIII

III

I

0-587-04-81 4 11-240-581-070 2 6

17-11 6 1

8-652 6 9

0 7 46't4-82 0 50-030-25

II

6-255 0 616-17

1-52O 7 7o-951-021 433 1 64 9 52-66-730-152 0 60-7600-004O O I

III

2 9 342-012-97

1 96o-571-530 6 71-740 6 2

11-393-56

I2-OO0-176 4 81-240-35o-ooi0-006

IV

0 9 61 3 35-n1 7 60 4 90-470-251 9 9

1 0 32O-213-62 9 4

0-21I 09O0 7OOO5O-O2

in each group. The data are illustrated by a series of histograms in Fig. 3, and itis at once apparent that the volumetric method conveys a materially different ideaof the plankton than is to be gained from a review of numbers alone.

Calanus finmarchicus is invariably represented as of greater importance volu-metrically than numerically, while the small organisms such as nauplii and Ceratiumshow the reverse. Again it is seen that Copepoda alia which are always morenumerous than Calanus finmarchicus, are in only two groups (I and IV) of largervolume. The total yield of oil from each group has also been added and shows a

190 E. R. GUNTHER

The total volume of Calanus finmarchicus that has been extracted is calculatedfrom the foregoing data by multiplying together the estimated volume of Calanusin 1 c.c. settled plankton, and the numbers of c.c. settled plankton extracted. Thevolume of Calanus extracted and the total oil yield from each group is shown inTable X and shows fair correlation. No such correlation exists between any of theother species, which have therefore been omitted from this table. Nor do theirseveral volumes considered collectively under the heading "Animalia alia" showany particular correlation. On the other hand in groups I and IV, which have theleast percentage of Calanus, the oil yield is, in proportion, slightly higher; thissuggests that some of the oil has been contributed by other species. Such contri-bution is probably small in consideration of the absence of any correlation betweenthe oil yield and either the total volume of animals extracted, or of the animals,less Calanus., extracted. Owing to the very rough manner in which the volume ofsettled plankton was measured and for reasons outlined at the beginning of thissection, the data here summarised do not allow of too precise interpretation, andthe relations between the oil yield and the various organisms in the plankton shouldbe regarded as an approximation.

Table X. Synopsis of data on oil yield and organisms extracted,

Group No

Oil yield, c.c.Calanus finmarchicw. Volume extracted, c.c.Animalia alia. Volume extracted, c.c.

I

16-553" 3567

II

26-8493°489

III

51715822494

IV

93356

195

It has been shown that mixed with the phytoplankton is a quota of animalorganisms, and the question arises whether the yield of oil from those samples hasnot been given by the animals and rendered green by chlorophyll dissolved fromthe plant cells by the light petroleum used in the process of extraction. The datacollected above is insufficient to form a conclusion.

IV. DISCUSSION.

An attempt is being made in the present paper to translate by means of suitablemeasurements, the figures representing the numbers of a species present in a givenquantity of plankton into figures representing the volume occupied by that species,believing that it may be possible, by this method, to convey a more precise ideaof the relative importance of each species.

It is shown that in plankton giving a high oil yield, the copepod Calanusfinmarchicus takes a more prominent position than any other species; and that inplankton poor in oil, this organism is present in very small quantity: otherCopepoda, though as numerous, are of smaller volume and consequently contributeless to the oil yield. Fig. 3 shows that some organisms, like Ceratium and naupliarlarvae numerically abundant, occupy negligible volume as compared to lessnumerous though larger organisms. The volume measurements are only tentative,


but it would seem that the fatty constituents from zooplankton that are noted inParts II and III, are derived mainly from Calanus finmarchicus.

The volumetric method, if it had been used, might have shown more clearly therelation between species in the plankton and the results of its chemical analysesobtained by previous investigators. Thus a plankton sample classed by Brandt (1898)as Peridinian contained 4,000,000 diatoms, 50,000,000 Peridinians and 89,000 Cope-poda. If, as might reasonably be expected, each of these Copepoda were a thousandtimes the bulk of one Peridinian, the bulk of the Copepoda would exceed thatof the Peridinians and the origin of the oil from this sample would be in doubt.

Again, the important results obtained by Wimpenny (1929) promise to indicatea new and significant orientation of planktology. The fat content of plankton iscompared with the distribution of herring catches off the east coast and showscertain correlations. But we should first demand a correlation between the distri-bution of herring and of such plankton organisms as constitute its food. We are toldthat the herring, before they spawn, feed upon the copepods of the plankton. Wehave not been able to find a correlation between the fat yield of the sample and thepercentage of Copepoda in it from the numerical estimations given. It is of coursepossible that the fat yield which is expressed as the weight of ether-soluble matterper 1000 organisms, fails to give a true indication of the condition of the plankton,since the size of the organisms is not taken into account. The part played byCalanus finmarchicus, for example, would be clearer if it were stated whether thenumbers in the tables represent young, adult, or sub-adult stages.

Schuette (1918) and Belloc (1930), in their investigations of the chemical com-position of plankton, did not include numerical estimations of the various species.This difficulty does not, of course, arise in work with monotypic plankton (a) byKlem (1932) who collected Meganyctiphanes norvegica from the stomach of a Seiwhale, (b) by Ahmad (1930) and others who have grown cultures of Nitzschia in thelaboratory, and (c) by Becking (1927) who, with collaborators, obtained collectionsof the diatom Aulacodiscus kittoni, in almost pure culture during an efflorescenceoff the Californian coast.

If the application of a volumetric method were extended, more accurate factorsindicating the numbers of an organism per c.c. could probably be obtained. Noattempt has been made in the present paper to measure the volumes of the separatephytoplankton species; the total oil yield amounting to 12 c.c. was obtained mainlyfrom Lauderia borealis (13-36 per cent.) and from several species of Chaetoceros(59-85 per cent.). Included among the phytoplankton, however, was a distinctquota of animal organisms, and although they were outnumbered by plant cellsto the extent of 1125,000,000-622,000,000, yet the possibility of their contributingto the oil yield should not be overlooked. These oil samples were charged withvitamin A (or its precursor) and other chlorophyll pigments in a quantity whichcannot have been supplied by the animal organisms, but the origin of the fats isless easily decided; it appears from microscopic examination that, as in immaturefish (Bruce, 1924), the younger stages of plankton organisms contain comparativelylittle oil in contrast to the adult stages, and it seems likely that the oil from the

192 E. R. GUNTHER

May plankton samples represents diatom oil. This view is strengthened by thechemical constants which distinguish this oil from those of purely animal origin.

The oil content of the phytoplankton (approx. 6-89 per cent, dry weight) isintermediate between the values obtained by Brandt, Becking and Schuette, whoreport respectively that they found a percentage of 2<2i-4-24, 9-7, and g-SS-io^oSof the dry weight. Mann (1916) states that oil in diatoms rarely falls below 5 percent, and that he has "samples of diatom material in which a careful measurementof the contained oil shows a proportion of 50 per cent." The measurements orthe precautions taken are not given. We suggest that the oil content may vary withthe species and fluctuate during the life history.

The oil content of the zooplankton collected from the Isle of Man varies be-tween 15-05 per cent, and 19-3 per cent., a higher figure than the majority ofdeterminations summarised below in tabular form1.

Table XI.

Investigator

Brandt* (1897)

Schuette (1918)

Wimpennyf (1929)

Klem (1932)

Nature of plankton

Mainly Ceratium and other Peridiniae

Copepoda, fresh waterCopepoda, mixed, marineMixed, fresh water (Daphma, Diaptomus, Cyclops)

Mainly Daphnia pulexMarine animal plankton (species not given)

Copepoda, Calanoidea

Meganyctiphanes norvegica

Oil yield% of dryweight

1-772'203-214-716-017-4°8-oi

I3-4721-25

3-5719268

T*lrot8-7St

2-5-4-iJ

• Analyses of other samples of mixed plankton have been omitted from the table.f These results were obtained by extracting the plankton in a Soxhlet apparatus; other results

obtained by shaking the wet macerated plankton with ether cannot be considered comparable andhave been omitted.

X These percentages represent wet weight.

The wet weight percentage of oils from Copepoda and Meganyctiphanes, ifcalculated properly from the data given by Klem (1932, p. 7), show an enormousdiscrepancy which is hard to reconcile with the other findings.

1 I am indebted to Mr M. H. Hey for the following chemical analyses of settled plankton. 5 c.c.each of samples Nos. 36 (phytoplankton). 42 and 45 (zooplankton) gave dry weights of 27-3 mg.,391 mg., and 154-4 mg- The phytoplankton contained 33 per cent, silicate, whereas the two zoo-plankton samples contained -7 per cent, and -45 per cent., figures that are in agreement with the bio-logical analyses in Tables I and II. The dry weight figures suggest No. 45 has four times the animalmatter as compared to No. 42, and this also accords with biological observation. Oil content whenbased on these figures works out at 689 per cent, dry weight of phytoplankton and 1505 per cent,and 19-3 per cent, of zooplankton. Thus the oil yields of these two zooplankton samples are in theratio 1 : 1 -28, whereas the oil yields per volume of total animal extracted as given in Table X, ofgroups I and III, are in the ratio 1 : 1-59. The agreement is close. Determinations of calcium inthese three samples gave 4-6 per cent., 13 per cent, and -12 per cent. CaO of the dry weight.


As regards the chemical nature of both phyto- and zooplankton the quantityof oil extracted was unfortunately too small for an analysis of the fatty acids bythe method of fractionating the methyl esters, and we have no data to comparewith the very excellent results presented by Guha, Hilditch and Lovern (1930) onthe composition of mixed fatty acids present in the glycerides of fish liver andother marine oils. Determination of the constants of plankton oils showed thatthey were generally similar to fish oils of the type characteristic of Clupeoids andGadid liver oils. Of special interest in the plankton oils is the presence of a high pro-portion of polyethylenic acids of the Cg,, and Cj, series and the presence of a hydro-carbon, probably squalene. We may then look to plankton as a possible origin of thefatty compounds in such widely different oils as those of fish like Centrophorus andScymnorhinus with a high percentage of squalene or Raia where the highly unsaturatedacids predominate. It would appear probable that these highly unsaturated acidscontained in the fat of marine birds are also traceable ultimately to plankton.

Methanolysis of 123 gm. of the oil of the planktonic organism Meganyctiphanesby Klem (1932) was found to yield esters with constants suggestive of the presenceof myristic, palmitic, hexadecenic and oleic acids. Higher unsaturated acids werealso indicated by a yield of 10 per cent, of octobromide. These are among thecommonest of the fatty acids found among marine oils, and without further quanti-tative data we are unable to ascribe them to any one class of marine oils or todetermine the extent to which the oils of Meganyctiphanes and of calanoid Copepodaresemble one another. The iodine values of Meganyctiphanes oil is 167-5; °f threeoil samples of calanoid Copepoda, 157*9, I57'5 anc^ 158*1 (Klem, 1932); theconsistency of these determinations is remarkable in view of the fact that theplankton samples from which the oils were extracted were collected on the datesMay 1929, June 1929 and June 1930. The iodine values of our own calanoid oilswere as low as 125-128. It might be appropriate here to mention that a qualitativetest to find squalene in the unsaponifiable fraction of the calanoid oil examined byKlem, gave a negative result.

Table XII.

Type of oil

Aulacodiscus (Becking)Phytoplankton (Collin)Daphma (Schuette)Zooplankton, fresh (Schuette)

Calanus (Klem)>»

Meganyctiphanes (Klem)fZooplankton (Collin)

Iodinevalue

138-144172-8887-58

IO2-8157-9157-5158-11675125-128

Saponifi-cation No.

86-7*184-5208-562486

—1 3 4107-11 3 2

119-129

% non-saponifi-

able

65-7*1 7 9—————

2 5

23'3-32'4

Iodinevalue of

non-sapo-nifiablefraction

7 0—————

95—

56-70

Sp. gr.

———————

0-9108——

• Semi-solid oils remaining after decolorigation of extract and separation of unknown sulphurcompound.

t 123 gm. of oil yielded 40 gm. of methyl ester.

194 E. R. GUNTHER

The principal constants of plankton oils from these and other sources are setforth in Table XII.

The ether extracts from fresh-water Crustacea, and especially from Daphnia,have been described as having the odours of fish oil (Schuette, 1918). Determina-tion of the usual constants showed a great range in the iodine values from 87-58to 172-88. On exposure to air crystals of glycerides were deposited.

Very few data are available on the composition of phytoplankton oils.The quantity and physical nature of the ether extracts of Fragillaria, Microcystis

and of the blue-green algae Aphanizomenon and Anabaena from Lake Mendota,did not permit of the determination of the usual constants (Schuette, 1918).1-82 gm. of the oil of Aulacodtscus kittoni was found to contain an unknown sulphurcompound whose properties are given and which represents 11-3 per cent, of thechlorophyll-free extract. The remaining semi-solid oils had a saponification valueof 86-7 and non-saponifiable matter amounting to 65-7 per cent. The authorsconclude: "I t is quite apparent that the acids of the diatom oil are a mixtureof the higher, wax-like fatty acids and lower unsaturated fatty acids" (Becking,1927). Our own results (Collin, 1934) would therefore appear to stand alone.

As regards the non-saponifiable fraction of our zooplankton oil, besides a hydro-carbon suggestive of squalene we have found cholesterol, cetyl alcohol, eicosylalcohol and possibly batyl alcohol. A Qo alcohol such as eicosyl alcohol noted inthe head oils of the Sperm whale constitutes, as far as we are aware, the onlyprevious record of its occurrence in marine oils. That traces of ergosterol werepresent in addition to cholesterol may be inferred from the slight antirachiticactivity shown by these oils. This accords with the results of Belloc, Fabre andSimonnet, who extracted detectable quantities of ergosterol from Porcellana larvae,calanoids and Cydippe. These authors also extracted, among other sterols, ergo-sterol from plankton consisting exclusively of Cydippe, Beroe and AcephalineScyphomedusae.

It is now well established that phytoplankton can be a source of the carotinoidprecursor of vitamin A (Ahmad, 1930) and that zooplankton may be a source ofvitamin D (Belloc, 1930); our own work confirms this but assigns a lower order ofvitamin activity to both phyto- and zooplankton. That variation in the amount ofvitamin D occurs in zooplankton has been shown by Belloc. The sterols extractedfrom spring plankton were inactive, while those from summer plankton wereactive; a fact correlated by Russell with the depth of the plankton and the conse-quent amount of illumination (? irradiation) at those seasons. The precautions wetook to prevent oxidation of vitamins through overheating or access to air whileextracting the specimens collected from the Isle of Man should have been sufficient togive a reliable indication of vitamin content; on the other hand the plankton sampleswere stored for several months before extraction and may have undergone somedeterioration. Our own results gave negative values for vitamin A in zooplankton butthe absence of vitamin D or its precursor in phytoplankton we do not regard as settled.

The low order of vitamins consistently found in plankton compared with therich sources of A in the liver oil of cod, halibut and whale has considerable interest.


MacPherson (1933) finds that the intensity of the blue colour developed by cod-liver oil with antimony trichloride increases steadily with the age of the fish andbears no direct relation to its size. He notes too that the red and yellow colourof the oil increases with age. The increasingly rich stores of vitamin A and ofpigments in the older codfish and the rich stores in the halibut and certain otherfish and in the rorqual point to a retentive capacity of the liver for these substanceswhich has not yet been accounted for. MacPherson states that the vitamin Acontent of the cod's food is low, and we know that the quantity in zooplankton iseither low or zero. It is worth considering whether the vitamin A present in theseliver oils is not derived from phytoplanktonic organisms ingested with othernutriment. Opportunities for ingesting diatoms would be smaller among predatoryforms and greater among phytoplankton feeders like the herring, the basking sharkand the whale.

SUMMARY.

1. Collections of phyto- and zooplankton made off the Isle of Man wereexamined for vitamin content, and for chemical and biological characteristics.

2. The important species entering into the composition of the plankton arenoted, and a new method of estimating plankton catches is described. Figureswhich represent the numbers of a species present in a given quantity of planktonare translated into figures representing the volume occupied by that species. Com-parisons are drawn between the numerical and volumetric estimations of the variouszooplankton species.

3. The phytoplankton catches taken in May showed a fairly uniform com-position throughout the collecting period, species of the genera Chaetoceros andLauderia forming more than 90 per cent, of the material. The zooplankton takenin July consisted mainly of Copepoda. The catches were of two types: those havinga higher percentage of Acartia, Calanus copepodid stages IV and III, and thePeridinian Ceratium; and those containing less of these but rich in the adult andother stages of Calanus finmarchicus.

4. By the use of curves correlating length and volume, measurements of im-portant species are translated into factors representing numbers per c.c.; appli-cation of these factors converts the numerical estimation of a species into anestimation in terms of volume. The numerical and volumetric estimations of variousspecies in four separate groups of plankton are compared and the yield of oil fromeach group is also recorded. The volumetric method conveys a significantly differentpicture of the plankton than is to be gained from the numerical method alone.Calanus finmarchicus is shown to constitute a relatively larger part of the planktonthan other more numerous but smaller species and likewise its adult or sub-adultstages than its earliest copepodid stages. The correspondence of a good oil yieldwith those groups having a high Calanus content is held to be suggestive of apossible correlation between the two.

5. Chemical and biochemical analyses of planktonic organisms by other in-vestigators are reviewed and their results compared with those obtained during

196 E. R. GUNTHER

the present work. The role of plankton organisms in the nutrition of various otherorganisms is discussed.

The thanks of the author are due to the many individuals who have helped inthis investigation. At Port Erin, Miss Catherine Herdman very kindly placed heryacht Redtuing at his disposal for the purpose of towing plankton nets. To SirF. G. Hopkins and to the staff (especially to Dr and Mrs Needham) at the SirWilliam Dunn Institute of Biochemistry, he is indebted for the facilities grantedfor the work of extraction of the plankton; a monetary grant was made from theThruston Fund by Gonville and Caius College. To Mr Robin Hill, to Dr F. H.Carr and to the author's wife, Dr Mavis Gunther, who have been in close touchwith all stages of the work, the writer desires to record his special gratitude.

APPENDIX.

0-5o-60-7o-809

-o•1•2

•6

1-92-02-12-2232-42-52-6

2-930

333-43 57-6

Table XIII . Copepoda length frequencies. The measurements are fromtip of rostrum to tip of caudal furea.

.3

S

216454391712142411332oooI

1

2.afc8

16241710

1

30IS7

§

24

11

1961

1

42028196

41720147

•i

43

111516

51052

1̂

ftis

13

107

ISI

§3!

I!0

41066

i

IS72

I:

<3

41110

2

3

514

2


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observations on the fatty constituents of marine … · gives an incomplete account of the relative...

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