Am j Clin Nutr 1958 Geiger 394 400

7/31/2019 Am j Clin Nutr 1958 Geiger 394 400

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39 4

P rob lem s C onnec ted w ith th e P o ssib le U se

o f P lank ton for H um an N u tr itionEkN EST GE IGER , M .D ., PH .D .*

E VER S IN CE it w as reco gn ized tha t p ro pe rn u tr ition o f th e w o rld p opu latio n rep re -

sen ts a g lob al p rob lem of the h ig hest im por-tan ce , eco nom ists an d nu tr ition ists h av e beenstead ily sea rch ing fo r new sources o f food su p-p ly . B esid es th e te rre str ial so u rces w hkh , ac -co rd in g to som e pred ic tions , m ay no t be ab le tokeep up w ith the g row th of the popu la tion , theo cean h as b een consid e red as the m ost p rom is-ing sou rce of nu trien ts. T oday on ly a sm allfrac tion of the food g row n in th ecean is u ti-liz ed fo r hum an nu tritio n in the fo rm of so n iesu rface f ishes and o ther sea food s. B esidesthe se , how eve r, tw o fu rth er and po b ly m uchrich e r sou rces a re n o t ye t even tap ped . O neo f these is the so -ca lled deepse a an im al w hichliv es in the ba thy pe lag ic zo ne and the o the rfood source is rep resen ted by the driftingm inu te o rgan ism s know n as zo op lank ton .

A ccord ing to som e au th o rs the idea o f u tiliz-in g the pastu re s o f the ocean fo r foo d pro -d uc tion is an anc ien t o ne , and M elv ille qu o tedin M oby D ick , as a pro of, th e fo llow ing passagef rom O bed M acys histo ry o f N an tucke t, I nth e yea r 169 0 som e pe rso ns w ere on a h ill ob -serv in g the w ha les spou ting and sporting w itheach o the r w hen one observed : Th ere -p o in tin g to th e ocean - is a g reen pastu rew here o ur ch ild ren s g randch ild ren w ill g o fo rb read .

S uch pred ictio ns w ere h ow ev er p robab lyn o th in g be tte r than po etic v is ions b ecause th eex istence o f p lank ton w as d iscov e red , acco rd -in g to som e au th o rs , on ly in 1 828 by the B ritish

F rom th e D ep artm en t o f B ioch em is try an d N u t r i -t io n, U ni ve rs it y of South ern C alifo rn ia M edic al sch ool ,L os A nge les , a nd V an Cam p Seafo od Co., T erm ina lI sl an d, C al if or ni a.

* Profe sso r of B io ch em istry an d N utrition , U n ive r-s i t y of Southern C alifo rn ia S c h o o l of M ed icin e.

A rm y Surgeon V aughn T hom as. O ffic ially ,h ow ev er , the g rea t phy sio log ist Joh annesM u ller is c red ited w ith th e firs t de sc rip tion ofp lan k ton ic life in 1847 . H e used a to v ne tfo r the firs t tim e fo r co llec ting p lank ton andreported the am az in g richn es s o f m inu scu lean im als p resen t in th e ocean w a te r a rou ndH elg o land . In 1 872 the fam ous C ha llen ge rexp ed ition supp lied fu rth er im po rtan t da ta tothe m orpho logy and eco lo gy o f p lank to n . T hefirs t o ff icia l s tep tow ard the p rac tica l use o fp lan k ton fo r h um an nu tr itio n seem s to b e therequest o f S ir Joh n G rah am K err in 1941 w henh e ask ed the B ritish P arliam en t to in vestiga tethe ha rvesting an d use o f p lank ton as a po ssib lem ean s o f reliev in g the fo od sho rtage re su ltin gfrom th e G erm an subm arine w arfa re . D uringth e S econd W o rld W ar exp erim en ts w ere a lsoin itia ted and su ppo rted by th e U nited S ta te sG ove rnm en t, investiga ting th e p ossib le u se o fp lan k ton as em ergency foo d fo r su rv iva l on liferaf ts . T he ac tu al in fo rm ation o n c om positio nand nu tr itive va lue o f p lank to n supp lied byth is inv estig a tio n is , h ow eve r, ve ry m eag er .It seem s the re fo re th at no ac tua l da ta bu tw ish fu l th in k ing is re sp onsib le fo r the assum p-tio n , d iscu ssed in m any recen t p ap ers , tha tmarine p lank ton rep resen ts a large sou rce o ffo od and tha t it is on ly a qu estio n of tech -no logy o f ha rv es tin g and o f econ om ics tom ake th is m a te ria l av a ilab le fo r p rac tical

r i734 { 176} In the fo llow ing w e in tend to ana lyze from anu tr ition al v iew po in t th e ava ilab le d ata in the

sc ien tific lite ra tu re . * A v e r y good rev iew of Th e R ole o f A lga e and

Plank ton in M edic ine ha s been recently publishedby M . S chw im m er and D . S chw im nier, G ru ne andS t r a t t o n , I n c . , N e w Y o r k , 1 9 5 5 .


2/7

P r o t e i nFa tAs hCa r b o h y d r a t e

(b y d iffe re nc e)

% o f d r y we i g h t5 2 t o 5 9

4 t o 719 to 3213 t o 1 7

J u l y - Au g u s t , 1958 ] GE IGER 39 5

P lank to n rep resen ts a m ix tu re o f d riftin gm icroscop ic p lan ts an d sm a ll an im a ls w h ich a red isting u ish ed as phytoplankton an d zooplanktonre spec tive ly . Th e m ain im po rtance o f thep hy to p lank to n is tha t theyse rve as good con-v erte rs o f rad ia ting ene rg y to fo od on w h ich theh erb ivorou s zo op lank ton th rives.46 The repre -sen tativ es o f ph y top lan k ton a re u sua lly toosm all (3 to 20 ,nm ) to be harvested and m o st o fthem canno t be sep a ra ted ev en by regu la r cen -trifuges . T hey represen t, in fact, a nu isancein harves ting of zo op lank ton because th ey c logth e h o le s o f th e ne ts .

T he zoop lank to n rep re sen ts a gene ral ca te-go ry o f d rifting inv erteb rate life and no t an yp ar ticu la r sp ecies . T he s ize o f the zoop lank to nva rie s be tw een 0 .5 to 30 mm and th e re la tivep artic ipa tion o f th e d ifferen t com pon en t spec iesshow s cons id e rab le g eo grap h ic an d seasona lvariation s. T hese changes in the spec iescom position o f the p lan k ton w ill have to beconsid e red in eva lua tion of th e av a ilab lequan tita tive d ata w h ich a re based gen era llyon an overa ll ana lysis o fom e p lank to n sam -p les.

C opepod s, crustacean s, liv ing on phy to -p lank to n , p elag ic tun ica te s an d sh rim p-likeeup hasids are th e m o st im portan t food s fo rfish and w ha le s. T he m edu sa and the c teno-phores p resen t in zoo p lan k ton are very vo ra -c ious an im als liv ing o n sm all zoop lank ton .O the rs p re sen t a re syp honophores, sa titta e,fish eggs , and fish la rvae.

Th e dry w eight o f the zo op lank ton va rie sbe tw een 14 , 11 , and 5 pe r cen t acco rd in g to thep relim ina ry trea tm en t su ch as squeezin g , w ash -ing w ith se a or fresh w a ter . T he gene ra l co rn -po sition of zo op lank ton ,#{1 76} based on a m ixedharv es t, is as fo l lows:

Th e pro te in con ten t is ca lcu la ted by m ulti-p ly ing the to ta l n itro gen co n ten t by 6 .25 . W edo no t kn ow , how eve r, how m uch of th is n itro -gen is ac tua lly p re sen t in ava ilab le p ro te in .Th e d a ta o n the am ino ac ids p re sen t in p lan k-

ton pro te in a re qu ite unsa tisfacto ry . M o sto f the essen tia ls seem to be presen t bu t the irre lativ e qu an tities and the ir b io log ic ava il-ab ility have no t been in vestiga ted as y et.#{1 76}

Th e com pos itio n ofat is , accord ing to 5ev-era l au tho rs , ve ry sim ila r to the fat ex trac tedfrom fish .#{176 } I t is cha rac ter ized by lo ng ch ainh ig h ly u nsa tu ra ted fa tty ac ids . It is p rob ab le,the refo re , tha t th e se easily ox id izab le fa ttyac ids affec t th e n u tr itio na l v alu e o f the p lank -to n itse lf .# {17 6} Som e sp ec if ic sterols hav e b eeniso la ted from zoop lan k ton bu t th eir b io log iceffec t h as no t ye t b een inv estig ated .

Th e ino rg an ic com po sition of som e specie sp re sen t in zoop lan k ton is w e ll d iscu ssed inV ino grad ovs m onum en ta l w o rk 48 w hich w asrecen tly pub lished in an E ng lish trans latio n byY a le U niv ersity . (A re la tive ly h ig h m agne -sium , silicon , io d ine , iron , an d arsen ic con ten tis charac ter is tic . P lank ton is re la tive ly low inav ailab le calc ium and su lp hur .) (T ab le I .)

TA BLE IT he A verage In org an ic C om po sit ion

Chlor ine% of dry w eight

14 .9Sodium 2 1 . 1P h o s p h o r u s 0 . 7 6Potash 1 .42Ca l c i u m 0 . 9 6Magn e s i um 1.29S u l p h u r 0 . 7 1

T he vitam in - l con ten t w as firs t inv estig a tedby D rumm ond w ho fou nd tha t cod rece ivesits v itam in A th ro ugh seve ra l in te rm ed iar ie ssuch as co pepods, la rva l decap odes, an d m ol-lu sca w h ich a re p re sen t in p lan k ton . The in -v estig atio n of th e actu al v itam in A con ten t o fzoop lan k ton w ith th e g row th te st, w ith thean tim ony tr ich lo r ide test, an d w ith th e ab so rp -tion Spec tru ln gav e, how eve r, nega tive resu lts .It was th e re fo re a ssum ed tha t zoop lank to ncon tain s som e precu rso rs o f v itam in A . R e-cen t inv estig atio ns have show n tha t all p ro -v itam in A ac tiv ity re sides in the n on-caro tin o idfractio n of the p lank to n o il. T h is show s tha tfish use zoop lan k ton p igm en ts o th er than com -m on caro tin o ids fo r th e e lab oratio n o f v itam inA . 7 The questio n a rises n a tu ra lly
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39 6 THE AMERICAN JOURNAL OF CL I NI CAL NUTRI T I ON [V o l. 6 , N o . 4

w hether this material can be used also bymammals for formation of v itam in A .

Th e vi tamin D content o f gav e aw eakly pos itive result w ith the line tes t, butw ith the x-ray ex am ination a negative resultw as obtained. It w as shown that the v itam inD content o f zooplankton w as neg lig ible .Prov itam in D seems to be present in cons ider-able The literature on thenia-cm, 4 vi tamin C,and vi tamin B content is verym eag er. W e did not f ind any data on thevi tamin B,, content. Recent investigationsshow that som e marine bac teria are ex cellentproducers o f v itam in B ,, and there fore w e mayassume that zooplankton may be a good sourceof this fac tor.4

THE NUTRITIVE VALUE OF PLANKTONThe nutritive value o f phytoplankton seems

to be somew hat s im ilar to that o f grass. There-fore , it does not seem to represent a betterpotential source o f pro tein than gras s grow n onpastures . A n additio nal disadvantage is thevery high mineral content o f the diatomes pres-ent in phy toplankton. The preceding mdi-cate s that the available data on the composi-tio n of zooplankton are not suff ic ient to drawany conc lusions as to its nutritio nal value .The inference is usually indirect and is basedon the so -called nutritional py ramid whichshow s that phytoplankton on the base of thispyramid supplies food for zo oplankton, foroy sters, musse ls , and cockle s, and that thisherbivo rous zooplankton represents then thefood for the larg er fishes and for the marinemammals .#{ 176 } Particularly the fac t that somew hale varie tie s that live nearly ex clusive ly onplankton (Krill, euphasia super ba) grow to 60fee t in leng th in tw o y ears led to the conc lusionthat zooplankton must be an exce llent fo od fo rterres trial mammals also . This conc lusion issubject to further inv estigatio n because w edo not know presently (a) the nutritive re-quirem ents o f the w hale ; (b) the particulardigestive facultie s o f this m ammal; (c ) thee ffic iency o f food conv ersion.

W e do know , how ever, that the fo od require -ments o f terrestrial mammals such as , fo r in-stance , that o f horses, o f men, and o f lions arequite different and there fore it do es not seem to

be perm is sible at this tim e to draw far reachingconc lusio ns from the feeding habits o f thewha l e .

B efore the S econd World W ar German sc ien-tists had c laimed that phy toplankton has anutritiv e v alue sim ilar to that o f rye flo ur andthat zooplankton is equiv alent in its nutritivev alue to the best m eat. U nfortunate ly nodata have been published w hich w ould supportthese occasio nal claims . A s a further proo f fo rthe nutritive value of zooplankton, it is usuallymentioned that the Chinese and some Scan-dinav ian nations use zooplankton as a base fora tas ty paste w ith a shrimp-like flav or. Fi-nally , Tho r Heyerdahl, in his repo rt o f theKon-Tiki vo yage , mentioned that zooplanktonconsis ting of copepods , pe lag ic crabs and o thercrustaceans, o f fish eggs and fish larvae w asconsumed by some members o f the crew . N oinfo rmation is g iv en how ev er on how much ofthis m aterial w as consumed and w hat o therfood w as eaten at the same tim e. These re -po rts there fo re show only that zooplankton canbe eaten but do not say anything about itsnutritio nal value o r about its e ffec t on thedigestive organs when consumed chronically inconsiderable quantities .

The only approach to evaluate the nutritivevalue of zo oplankton experimentally has beenattempted by Clarke and B ishop. Theseautho rs inv es tigated the g row th and surv iv alof w eanling rats fo r a period o f 1 3 days and ofadult rats fo r a period o f 22 day s. The plank-ton used w as obtained from the V iney ardSound and w as frozen at 1 8#{ 176 } after reachingthe laboratory . It w as squeezed w ith moderatepressure to remov e ex cess sea w ater and con-tamed about 14 per cent o f dry material. Thedie t m ix tures w ere prepared on the basis o f thedry w e ight. A s contro l feed Purina-Grow enaw as used. Rats fed on plankton only lostw eight rapidly and died w ithin 4 to 1 9 days,but surv iv ed about 30 per cent lo nger thancontro ls on to tal starvation. Rats fed on adie t composed o f tw o-thirds meal and one-thirdplankton and tw o-thirds plankton and one-third meal failed to g row as fast as rats on afull die t. The autho rs do no t present de taileddata on food consumption but state only thatthe rats ate only about tw o-thirds o f the ration
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July-A ugust, 19 58] GEIGER 39 7

offered when it contained plankton. They ,therefore , arrive at the conc lusio n that therats derived some nourishm ent from planktonbut w ere able to assim ilate only a small frac-tion o f it. They observed also that the stom-ach of the animals contained undig estedmaterial and that fecal material w as congestedin the cecum and in the hind inte stine .They investigated also the e ffect o f planktonconsumption in man. A bout these expen-ments they write as fo llow s:, N o to xic ef fec ts dev eloped after eating 100-2 00

grams (w e t w eight) of the material during the course ofa day . The maximum quantity eaten by any o e ofthe subjects at one tim e w as 100 grams . Larg eramounts w ere de finite ly unacceptable and distasteful.It is probable that psycholog ical fac tors ente red intothe matter of the palatableness and dige stibili ty of theplankton in the laborato ry and at sea. S uch facto rsare no t easy to ev aluate . It w as certainly true that aquantity of o ,,lv 30-40 grams o f plankton gav e the im -pre ssio n of re,naining undig ested in the stomach forsev eral hours after eating .

Clarke and B ishop perfo rm ed these experi-ments w ith particular observation o f life raftconditions and came to the fo llow ing conc lu-sions:

Plankton w ith the observed chem ical conipo sitionw as calculated to have an approximate max imum en-ergy content of 4 cal./g . dry w eight. The 2400 cc. o fplankton w hich could theo retical ly be obtained from alife raft in 24 hours w ould thus prov ide78 8 calories, i f itcould all be as si,nilated, or about / o f a mans averaged ai ly re qu ire me nts .

A critical rev iew of Clarke and B ishops re -sults show s that the ir m ethods w ere not up tothe present s tandards by w hich nutritionalexperiments should be des igned. S om e of theobjectio ns are that the rats consumed muchsmaller quantitie s from the die t containingplankton than from the contro l die t. Further-iore, w e see that due to the high w ater content(S per cent) o f the experim ental die t, too larg equantitie s have been offered. The high w atercontent o f the die t may lead to an abnormaldilution o f the digestive juice s. The high saltcontent o f the die t m ay hav e influenced theutilization. Furthermore , large quantitie s o fundig ested material w ere s tagnating in the in-te stinal trac t. This may hav e influenced notonly the utilization o f the die t itse lf but alsothe ilnportant nutritio nal func tion of the in-

te stinal flo ra. It is quite amazing that Clarkeand B ishops experiments w ere w ide ly publi-cized w ithout po inting out the w eak po ints inthe ir experim ental approach. It is surpris ingalso that no other fundamental inv es tigationson the nutritive v alue of zooplankton hav e beenpublished. In our opinion, the experim ents o fClarke and B ishop do no t supply enough Ina-terial to draw any conclusion as to the foodvalue of zo oplankton.

E C O N O M IC PR O B L EM SA not neg lig ible problem seems to be the

economics o f zo oplankton co llec tio n. B e fo rethis questio n and the technical approach ofharv es ting can be serious ly considered, thefo llow ing matters w ill have to be c larif ied:firs t, w hether zooplankton can be used directlyfor human nutritio n or indirec tly by feeding itto poultry and to other liv es tock. In thisconnec tion w e w ill hav e to consider that pres-ently large quantities o f low -priced pro teinsupplem ents w ith high bio log ic v alue are avail-able such as fish m eal, m eat scrap, o r bloodmeal . We also hav e to realize that the chemi-cal industry recently made some essentialv itam ins and amino acids available at pricesw hich are generally much low er than the co stof production from natural material.

A further problem is one of lo cating w hichare the best harv es ting grounds and the bestseasons to co llect zooplankton.6 424 The var-iability o f plankton is such that it w ould beexceeding ly diff icult to predic t w hat type andw hat amount w ould be encountered in anyg iven situation, at least until that area hasbeen s tudied fo r a long time .9 It w as foundby several authors that the distribution o f zoo -plankton 44 is patchy , that there are abruptchanges in composition as w ell as in amounts,that there is avertical diurnal variation so thatsome spec ie s c limb several hundred fee t in theevening tow ard the surface o f the ocean. B e -sides this , there is the recently disco vered sea-so nal vertical va riation in plankton distributio n.A lso recently described as an impo rtant sourceof zooplankton is the scattering layer2 whichex ists be tw een 900 and 2 ,700 ft and ap-proaches the surface betw een sunset andsunrise and which consis ts mainly o f smallrus-
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39 8 THE AMERICAN JOU RN AL OF CLIN ICAL NU TRITION [Vol .6 , No .4

taceans. We have to realize furthermore thatthe gro vth of zo oplankton depends on theavailable The phy to -plankto&6 needs sunshine and minerals fo rits deve lopm ent and if the m inerals are ex -hausted, or if the w ater is not plow ed, i.e., ifthe m inerals are no t replaced from the deeperlayers , the phytoplankton die s.213 9 This m ix -ing w ith deeper w ater or w ith river w ater oc -curs at the shallow coas ts o f W es t A frica andthe w estern South American coast.3 5 Inv esti-gations in the N orth A tlantic sho v a mainfib v ering in spring and w aning of the popula-tion in summer and a second crop in autumnor w inter. N o t w e ll explained, how ever, isthe abno rmally high density in the high lati-tudes near the Poles .

The questio n as to the feasibility o f co llec t-ing plankton has been discussed by sc ientistsand lay authors and w e hav e to realize thatbo th usually go overboard in the ir predic -tio ns.* S ome autho rs, for instance, c laimthat the sea y ie lds from one to three tons o f o r-g anic material per acre per year. This meansabout as much as one acre o f fo rest. B ecausethe ocean represents about 7 0 per cent o f theearths surface the se a produces about tw ice asmuch as the land.4 Other autho rs , how ever,do not agree w ith these calculations , and N ie l-son assumes that plants in the ocean fix 12million tons o f carbon yearly compared w iththe 19 Inillion tons fixed by land plants .947Most o f these es timates inc lude phy to and zoo-plankton. The ac tual y ie ld on zooplanktonw as experimentally de term ined by B ig elowand Sears4 who found in the upper w ater layersduring maximal production 0 .5 to 0 .8 m l zoo -plankton per m3 of w ater. Clarke and Bum -pus found in the shallow s tratum 0.3 to 1 .0 m i.8Heyerdahl obtained during one day 2 .5 to 5 kgof zooplankton. Hardy# { 176 } predic ts that w ithsuitably constructed nets tw o men could co l-lec t daily 588 lb of plankton on the coasts o fS co tland enough to feed 357 people . W ethink how ever, that it should be added: pro -

* I t wa s sug ges ted rec ently , in an artic le based onsheer speculatio n, that traw hing of kril l in the Antarc tica r e a , ma y b e more profitable than w haling and mayhelp to so lve the w orlds food prote in shortage . (W . E.Pequegnat: Scient. Amer . 1 9 8 : 8 4 , 1958 .)

v ided that people w ould eat, digest, and utilizethe zooplankton. A further complicationseems to be that zo oplankton cannot be har-vested w ithout admixture o f some phyto -plankton.The co llec tion o f phytoplankton alw ay s rep-resents a hazard because there are differenthighly tox ic representatives kno vn, fo r in-stance Gonyaulax catenel l a in the Californiaw aters and Gymnodium dinoflag galate s w hichproduce extens ive fish mortality . W e hav eto as sume that there are many other tox icplankton forms liv ing in different g eo graphiclocations w hich may lead to po isoning of f ish o rw hich turn o therw ise edible fish and seafoodinto a highly tox ic oo# { 17 6} A nother dang er inconsumption of plankton may be the sw allow -ing of sting ing fo rm s as for instance the con-sumption o f Portuguese Man-O-W ar may haveserio us consequences .

W e w a n t t o em p h a s ize t h a t in st e a d o f h a r -vesting zooplankton it w ould be more realisticand more econom ical for the time be ing to in-crease the catch of herring -v arie tie s , o f man-haden and trashfish. This could be doneeas ily prov ided the human demands for thisnutritious fo od w ere augmented. In manycountries w here the animal pro te in is not av ail-able in suffic ient quantitie s , the most urg entp r ob lem seem s tobe the preserv ation o f thefishcatch in palatable form ready for transpor-tation from the fishing areas to the interior.4

The reluctance to accept f ishflour as fo od in-gredient fo r human consumption, as observedrecently in many underpriv ileged countries ,in my opinion, raise s a serious doubt as towh e t h e r dried zooplankton w ill ever be ac -ceptable as prote in supplement fo r human nu-trition.

It seem s that first the problems connec tedw ith the nutritive value of plankton and thefeasibility o f feeding it to men and animals mustb e so lved , a n d th en th e d iffe r en t h a r v es t in gterrito rie s w ill hav e to be investigated for pos -sible contam ination o f the crop w ith to x ic ma-terial. This latter problem seems of m inor im-portance , how ever, because o f the g eo graphicand seasonal lim itation of tox ic forms.

A further problem in plankton co llec tion isthe deve lopment o f e ff ic ient harvesting and
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dry ing equipment.4 Recently exce llent rotaryfilters and driers have been deve loped for otherpurposes and it seem s that such equipmentcould be w ell adapted for plankton harvesting .The final step in connectio n w ith our problemseems to be the evaluation of the economics ofplankton co llec tion in do llars and cents. Ourpresent abundance of food resources seems tobe responsible for the fact that this questio nhas never been actually investig ated. U ntilnow there has no t been an urgent necess ity toso lv e o r even seriously study these problems,but w e quote in this connec tion the fo llow ingstatements made by Lucas : I n the presenceof certain alternatives there may no t be theincentiv e to attempt to so lve the technicalproblem s w hich m ight easily -and pro fitably -be so lv ed if these alternativ es w ere no longer.The result m ight be a much cheaper source offood, in far greater quantity , than tho se w hoseabundance orig inally discouraged the urge totap a new source .SUGGESTIONS FOR FURTHER NUTRITIONAL RESEARCH

B efore any economic or technical problemsconnected w ith the utilization of plankton areserious ly cons idered, the question should f irs tbe investigated w hether plankton can be usedas such or as a supplementary food for humanfeeding or fo r lives tock nutrition. In order toc larify these po ints the amino ac id compositionand the digestibility o f plankton prote in w illhave to be investig ated.

A nimal experim ents may g ive information onthe bio lo g ic value of this prote in and on itseffic iency as a supplementary food. The pos-sible presence of unidentified g row th facto rsmay be studied and also the questio n w hetherthe pro v itam ins present in plankton w hich canbe utilized by f ish have the same nutritionalimportance in mammals and birds . It w illalso be nece ssary to study how the excess o fminerals and particularly o f some cations suchas magnesium can be e lim inated.

The nutritive v alue of crops harv ested atdifferent localitie s should be compared.

Finally , as a crucial experiment, planktonshould be fed toma n under w e ll contro lledconditions, contro lling the utilization of plank-ton prote in by nitro gen balance experim ents.

These inv es tigations may be time consumingand expensive but they w ould y ie ld some basicansw ers to our problem . A s such, they w ouldrepresent a great serv ice not only to the sc ienceo f nutrition but also to humanity because theymay answ er the questio n o f w hether there is ashort cut po ssible in the nutritional pyram id,i.e ., w hether plankton can be utilized directlyfo r feeding of man and terrestrial animals.There is a possibility that the utilization o fplankton fo r such purposes ma y not be feasibleand that w e w ill have to re ly in the future alsoon intermediary fo od conv erters in the fo rm off ish and other conventio nal seafoods w hich con-vert the nutrients present in plankton to aform w hich is acceptable to and can be utiliz edby man and terrestrial animals .

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Am j Clin Nutr 1958 Geiger 394 400