PLANKTONBy

Louella E Cable

Marine Biological Laboratory

LIBRARY

OCT 14 1992

V\/oods Hole, Mess. I

UNITED STATES DEPARTMENT OF THE INTERIOR

FISH AND WILDLIFE SERVICE

BUREAU OF COMMERCIAL FISHERIES

Fishery Leaflet 583

UNITED STATES DEPARTMENT OF THE INTERIOR

Stewart L. Udall, Secretary

John A. Carver, Jr., Under Secretary

Stanley A. Cain, Assutant Secretary for Fish and Wildlife and Parks

FISH AND WILDLIFE SERVICE, Clarence F. Paut/.kc, Commissioner

Bureau of Commkrcial Fishiories, Donald L. McKernan, Director

Plankton

By

LOUELLA E CABLE

Marine Biological Laboratory

LIBRARY

OCT 14 1992

Woods Hole, Mass.

Fishery Leaflet 583

Washington, D.C.July 1966

CONTENTS

Page

Introduction 1

Classifications of plankton 1

Distribution 6Reproduction 6Swarms and blooms 6Survival 7Yield 7Uses of plankton 8Manufacture of basic nutrients 8Food for aquatic animals 8Food for man 9Purification of water supplies 10Industrial uses 11Aid to science 12

Luminescence 12Harmful effects of plankton 12References 12

111

Plankton'

By

LOUELLA E CABLE, Fishery Biologist

Bureau of Commercial Fisheries Biological LaboratoryAnn Arbor, Mich.

INTRODUCTION

The word "plankton" was derived from theGreek "planktos," which means "wandering."It is a collective term applied chiefly to all

those small, extremely diverse forms of

plants (phytoplankton, fig. 1) and animals(zooplankton, figs. 2 and 3) that drift aimlesslywith the currents in all natural waters and in

artificial impoundments. Most of the formsswim feebly and are incapable of making longhorizontal journeys except as they are sweptalong by persistent winds and currents. Some,nevertheless, make extended vertical migra-tions in response to stimuli not clearly under-stood. These movennents have been partiallycorrelated with diurnal changes in the inten-sity of light; the salinity, temperature, anddensity of the water at different levels, andcommunity pressures may also be importantfactors. Most planktonic organisms, especiallythe one-celled plants and animals, are ex-trennely snnall and were unknown prior to theinvention of the compound microscope late in

the I 7th century.Although most of the waters of the world

are inhabited principally by plankton, little is

known about these organisms compared with thegreat store of knowledge available on landplants and anin-ials. The plankton and theirenvironment have been difficult to study. Forthe nnost part, knowledge has been gainedindirectly by the use of electronic and otherspecialized instruments that record move-ments of the animals and the depths, tem-peratures, and chemical composition of theaquatic environment, or directly by analysesof samples of water, bottom sediments, andliving organisms brought to the surface andpreserved for later study in laboratories.

Louella E. Cable. Fish. Market News 5(11):6-12.

.Mthough the minute plants (diatoms and blue-green

algae) and very small animals (protozoa, entomostracans,

and larvae of various other forms) make up the great bulk

of the plankton, a few larger forms (Jellyfish and salpae)

that have only weak powers of locomotion are also in-

cluded.

The future holds promise of more intimateobservations of the plankton in their under-water habitats than were possible in the past.Soon the observations will be made fronn ma-neuverable submarines capable of sustainedoperation at great depths and from permanentunderwater research stations. The researchstations are still in the planning stage andmay not become reality for some time, but thedeep-water submarine is already in use forclose scrutiny of the bottom and study ofplankton and other inhabitants in all strata ofthe seas. The Woods Hole OceanographicInstitution has operated the Alvin , one of thefirst of a series of these specialized sub-marine laboratories that are being developed.The Deepster , with an outer hull of fiberglass, and the Alumina ut , with a hull com-posed of a number of thick aluminum ringsbolted and glued together, are joining thedeep-water fleet. Some of these vessels maybe equipped with blue-green lasers for under-water communication and for improvement ofvisibility for television and photography.

CLASSIFICATIONS OF PLANKTON

The major taxonomic units, or primarydivisions, of the plant and animal kingdomsare called phyla. Each phylum is a unit com-posed of organisms sharing one or morefundamental characters that reflect a commondescent. Many levels of this systematic clas-sification of life are represented in the plank-ton, from the simplest one- celled plants(Thallophyta) and animals (Protozoa) to verycomplex little animals such as crustaceansand fish larvae (fig. 4). Certain many-celledanimals are planktonic for a short periodduring early development even though, asadults, they become either sedentary (e.g.,

oysters, clams, and sponges) or free swim-ming (e.g., shrimp and fish). Plankton of lessthan l/600-inch maximum diameter make upthe nannoplankton or microplankton. Formslarge enough to be seen with the naked eye aremacroplankton.

PHYTOPLANKTONALGAE

Diatoms

Peridinium

Chlorella

Ceratium

1

—'i-- \-- S-' ^- v.^

Filamentous Algae Chlamydobotrys

Figure 1.—Some typical forms of phytoplankton (greatly magnified): Peridinum and Ceratium (dinoflagel-

lates), Chlorella (chlorococcales), Chlamydobatrys (volvocales).

INVERTEBRATE ZOOPLANKTON

Euglenomorphq Amoeba

Starfish Larva

Oyster Larva

VERTEBRATE ZOOPLANKTON

\

Sagitta

'. 'y. •' .•••

fi fl

vt:^^;.>..X.J..^£^ALLl:..UCZ;;.^:...t:>-^fir^^

Fish Larva

Figure 2,~Some typical forms of invertebrate and vertebrate zooplankton (greatly magnified).

ZOOPLANKTONCRUSTACEA

Young of shrimp

Figure 3.~Invertebrate zooplankton (greatly magnified).

PHYUW Kxmaples PHYLUM Examples

ARTHROPODA <Class -Crustacea

Order-CladoceraSub-class-Ostracoda

-CopepodaOrde r-Amphl poda

-DecopodaShrimps

(Early stages)LobstersCrabs

Order-MysidaceaGenus-Mysls

Order-EuphauslaceaGenus-Kuphausla

ASCHELMINTHESRotifers

CHAKTOGNATHAGenus-Sagltta

ANNELIDASegmented worms

COELENTERATAJellyfish

(Early stages)

PORIFERA

PROTOZOA

Sponges(Early stages)

Class-MastogophoraGcnera-Woctiluca

-Euglena- Euglenamorpha

Order-Dlnof lagellatuGenera-Peri dinium

-Ceratium-Gonyaulax

Class-Sarcodl na

Genus

-

AmoebaOrder-Foramini fera

Genus-Globigcrina

CHORDATAClass - Pisces

Pish(Eggs and larvae)

ECHINODBRMATA

MOLLUSCA

(Early stages)

Starfish(Larvae)

OystersSnailsClansSquids

Completedigestive tract

-^ CTENOPHORAComb Jelly

(Early stages)

Digestive sacand nerves

tMany-celledorganisms

THALLOPHYTASubdivision-AlgaeClass-Chlorophyceae

Filamentous algaeDiatomsOther forms

Gene ra-ChlorellaChlamydobotrys

Class-DinophyceaeSubclass-Dinoflagellatae

Genera-Peri dinium-Ceratium-Gonyaulax

Subdi vi si on-FungiClans -Schizomycetes

Genus -Bacte ri a

Single cell

Figure 4.—A geneological tree showing the probable relationship of some of the more important phyla inthe plant and animal kingdoms that are represented in the plankton at some stage in their lives.

Marine plankton also naay be classified in

general ternns as oceanic and neritic (coast-bound). Oceanic plankton contains forms thatnormally inhabit areas of the open sea, suchas certain species of copepods, diatoms, andperidinians that thrive best in intercontinentalareas (arctic, tennperate, and tropical seaforms differ from each other). Neritic planktonis made up of forms that remain connparativelyclose inshore and may include: (1) the pelagiclarvae of the bottom dwellers such as oystersand starfish; (2) pelagic eggs and larvae offish; and (3) organisms held inshore by spe-cific requirements for food, temperature,water chemistry, and possibly other environ-mental demands related to land masses. Thedistinction between oceanic and neritic plank-ton becomes difficult when members of eithertype are transported by wind or water cur-rents from their usual habitat into that of theother.

DISTRroUTION

The distribution of planktonic organisms is

almost universal in aquatic environments. Theyare in the oceans, rivers, lakes, and ponds theworld over. Some cosmopolitan forms of plank-ton are found at all latitudes, while otherforms have disconnected distributions andoccur in scattered discrete areas where con-ditions favor their existence. No climate is

too warnn or too cold to support plankton of

one type or another. The greatest concentra-tions of phytoplankters occur in the upperlayers of water down to the limit of effectivepenetration by light (100 to 130 feet). Maxi-mum density of zooplankters also occurs in

the surface strata where the herbivorousspecies feed on the phytoplankton. Some forms,prinnarily zooplankton, inhabit the bottom zonesof lakes and streanns, and also the profounddepths of the oceans.

REPRODUCTION

Reproduction of planktonic forms, as ofland creatures, provides for the nnultiplica-tion of individuals to ensure preservation ofspecies. The various groups in the planktonreproduce in different ways. The resultingdiversity of methods to accomplish this verynecessary biological function nnakes it pos-sible to trace nature's gradual developmentof the reproductive process from asexual(without sex) to sexual. The nnost primitivemethod is simple asexual division, in whichthe protoplasm of one-celled plants and ani-mals divides into two equal parts to form twonew individuals. In slightly more advancedorganisms an intermediate stage of sexualbehavior is found. Individuals that are alike insize and structure reproduce only after they

fuse and exchange naicronuclear nnaterials. In

general, morphologically connplex forms havemore highly developed sexual organs andbehavior. Rarely, individual animals of all

species may have both male and female organs(hermaphroditism), and at least one group of

common animals, the oysters, may changesex from time to time.

SWARMS AND BLX)OMS

Especially dense concentrations of a singlespecies of zooplankton or phytoplankton arepopulation explosions known as swarms, andflowers or blooms. They occur seasonally orat irregular intervals when environmentalconditions are exceptionally favorable for thegrowth and reproduction of a particular spe-cies. Swarming or flowering comnnunitiesoccur most often when the water is enrichedby runoff from agricultural land, by upwellingfrom the bottom, by overturn of a body of

water due to wind and thermal changes, or bythe addition of small quantities of organicwastes from urban communities.A bloom in the Vermillion River, S.Dak.,

lasted 2 or 3 days after the spring runoff in1923. It formed a thick red scum from bank to

bank for many miles along the river's course.Under the microscope, the scum was seen to

be made up of Euglena, a single- celled or-ganism. Some authorities believe Euglena is

a plant because it contains chloroplasts (greenbodies containing chlorophyll); others believeit is an animal because its body structure andhabits of life are more similar to those ofanimals than to those of plants.

The bloon-iing or swarming of Euglena wasnot an annual occurrence, and large crowdsgathered to view this unusual phenomenon.Most of these people had lived near the rivern^any years but had never seen the red scumbefore. A similar occurrence at some earliertime probably gave the river its name.

Ostracods (small zooplankters belonging to

the Crustacea) swarmed in the PamunkeyRiver, Va.,^ in April 1940. They formed a browncoating on the surface of the water and cloggedfine-meshed collecting nets fished near thebottom. The Chief of the Pamunkey Indians,who lived nearby, had never before seen sucha swarming.

Blooms of filamentous algae form densegreen rafts on bodies of enriched fresh waterin stagnant pools, small lakes, and protectedplaces in larger bodies of water during thesummer. Nearly everyone has seen them. Theysonnetimes interfere with boating and swim-ming at resorts, where the bloonns are anuisance. The bloonris usually last only a fewdays, for the life span of filamentous algae is

short.Most such rafts of filamentous algae are

formed of Spirogyra, an alga that has two

methods of reproduction-- vegetative (asexual)and sexual.By the vegetative method, Spirogyra rapidly

forms long strands of cells while the environ-ment is most favorable. The strands grow bythe elongation and division of all cells in thefilannent. Division usually takes place at night.

After elongation of the cell, the nucleusdivides by nnitosis, and then the cell is cut intwo by a ring of cellulose which grows inwardfrom the outer wall of the cell between thetwo nuclei to form two identical cells whichusually remain attached to each other.

Later, when the environment has changed,perhaps by the mere presence of the Spirogyrain it (food consumed, wastes released) or byexternal factors such as drought or extremesof temperature, the Spirogyra reproduce sex-ually. Conjugation usually takes place betweenthe cells of two vegetative strands, but it maytake place between adjacent cells on the samestrand. The contents of the cells of one strandpass into corresponding cells of the otherstrand, thus leaving the cells of one strandempty, or, if the cells are adjacent in the samestrand, every other cell is left empty. Althoughthe contents of both participating cells aremorphologically alike, the fact that those ofone strand remain passive and those in theother strand are motile indicates a slight

physiological differentiation of the contents ofthe cells that at this time become sex organscalled gametes. The organisnn resulting fromtheir union is a zygote. The zygote forms athick three-layered wall about itseli. It is thencalled a zygospore and is the resting stage ofthe Spyrogyra . The zygospore is highly resist-ant to extreme cold and to drought. It falls tothe bottom of the water on which the greenraft had rested a short time before. The cellwalls that formed the raft disintegrate andalso sink to the bottom.

The zygotes germinate after an indeter-minate period of rest. The time of germinationis entirely dependent upon environmental con-ditions required for the development of thevegetative and sexual reproductive cycles. Thelength of these cycles also depends on theenvironment. They will be longer in someplaces and times than others, but never longerthan a few weeks.Some species of salt-water plankton also

flower or swarm occasionally. The most pub-licized example is the "redtide, " which occursmost often in subtropical marine waters, suchas the Gulf of Mexico and the Pacific Ocean offsouthern California. The red tide has occurredin the Gulf of Mexico at least 20 times sinceits first recorded appearance in 1844; 17 ofthese events were off the west coast of Floridaand 3 off Texas and Mexico.

The red tide appears as a dense concentra-tion of dinoflagellates of the genera Gymno-dinium or Gonyaulax . These organisms meas-ure about 1/1,270 to 1/726 inch. The great

nunnbers of dinoflagellates often impart areddish amber color to the water, but shadesof green interlaced with yellow and brown arealso characteristic of the blooms. They maycover hundreds of square miles, and somespecies produce sufficient toxin to kill mil-lions of fish. Death comes suddenly after thefish enter the area of the bloom. Dead fish ofall species and sizes drift ashore, occasionallyto the amount of 100 pounds per linear foot ofshoreline, causing unpleasant odors and seri-ous disposal problems for cities and resortareas. The deeply colored water sometinneshas an oily appearance; when dipped up andallowed to stand a few minutes, it has a thick,slimy feeling.

Flowerings and swarmings of plankton arespectacular events, for the clumping of vastnumbers of organisms (as many as 15,982,560cells of the dinoflagellate, Ceratium furca ,

were counted per quart of water off the westcoast of Florida in 1955) makes them visibleto the human eye. Between population explo-sions the animals reproduce at a greatlyreduced rate. Even then, local plankton popu-lations often are dominated by one speciesalmost to the exclusion of others, as shownby the contents of collecting nets.

SURVIVAL

Ostracods, cladocerans, copepods, brineshrimp, and many other, but not all, smallaquatic animals and plants survive linfavorableseasons, severe droughts, and critically highor low temperatures in a quiescent state knownas a resting spore or, in some cases, a winteregg. Resting spores and winter eggs remainviable for long periods, sometimes for manyyears, and still develop a vigorous new gen-eration of individuals when suitable livingconditions return. Because organisms thatmake up the plankton are able to survive inthis manner they appear in temporary pondsformed after rain, although no water may havebeen there for months or years. This mode ofsurvival also explains why it is possible to

obtain many tiny organisms within a few daysby the simple nnethodof placing a bit of meadowhay in a shallow dish of water. Windblownspores and eggs that have settled upon andadhered to the vegetation develop rapidly in

water with proper light and temperature.

YIELD

Rough estimates of the annual yield of phyto-plankton in all the seas approximate 165million tons of organically bound carbon, andestimates of live weight run from 6 billion to

6 trillion tons. No reliable method has beendeveloped for measuring the total yield ofplankton. The number of organisms in the

standing crop (the number of individuals living

at one instant) in any area is limited by theamount and combination of nutrients in thewater; by temperature; by the quality, dura-tion, and penetration of light; and by the total

mortality of the organisms. The standing crop,therefore, varies sharply from one place to

another at a given time and from time to

time in the same place.Among the smaller and more abundant

forms of algae in the phytoplankton are thediatoms. Areas where diatoms occur in heavyconcentrations often are referred to as "pas-tures of the sea"; here diatoms may contrib-ute as much as 98 percent of the standing cropof organic matter. The fish and even the greatwhales depend ultinnately on them for sus-tenance. Fossil remains of diatoms indicatethat in eons past, as at present, billions,

possibly trillions, of tons of them must havebeen produced annually in excess of the enor-mous amounts required to feed the animals of

the sea.Diatoms surround themselves with walls of

silicon dioxide in the form of two valves, oneof which overlaps the other. These'walls areornamented by characteristic patterns-- someof exceptional beauty-- which taxonomists useto identify species. After death of the diatom,bacteria dispose of the soft body, but the wallsrennain intact and sink to the bottom. Theaccumulation of shells may reach a consider-able thickness over a long period of time.One deposit at Lompoc, Calif., formed on thebottom of a prehistoric sea but now a part ofthe land area as a result of geological changesin the earth's crust, extends over many squaremiles and is more than 700 feet thick in places.One scarcely can conceive the myriads of in-dividuals required to produce such immensebulk.

Bacteria, too, are very small andare pres-ent almost everywhere in the aquatic andterrestrial worlds. Bacteria are much likealgae but lack chlorophyll and must securetheir food ready made from the bodies ofother organisms or their products. Vegetativecells of bacteria grow to a maximum size andthen divide by fission into two bacteria ofequal size. Some surround themselves witha thick wall and thus become spores or rest-ing cells that are resistant to far moreunfavorable conditions than are the vegetativecells. No estimate of the abundance of bacteriain the plankton has been made, but many in-vestigators believe that the total bulk ofbacteria would be considerably more than thatof the diatoms.

Together with yeasts and molds, bacteriacause the decay of plant and animal tissues.Through this process, bacteria release thecarbon, oxygen, and phosphorus that are locked

^1/50,000 to 1/12,500 Inch long and 1/125,000 to

1/50,000 Inch wide.

into the tissues and reduce them to simplecompounds such as carbon dioxide, water, ni-

trates, sulphates, and phosphates that can beused again as food by living phytoplankters.

USES OF PLANKTON

Manufacture of Basic Nutriment

Extensive investigations have shown that a

great preponderance of the basic or primarynutriment in the aquatic environment is man-ufactured by the unicellular microscopic algaein the phytoplankton. These tiny plants containchloroplasts that can produce carbohydratesfrom carbon dioxide and water in the presenceof light (a process called photosynthesis). Theplant cells then synthesize complex organiccompounds from suitable salts of essentialinorganic substances--chiefly carbon, phos-phorus, and nitrogen. The plants that performthis miracle of chemical conversion then be-come the food of the zooplankton, which, bythemselves, are incapable of gaining nourish-ment from inorganic substances in the water.Whereas most primary producers are minutesingle-celled plants from the microplankton,the consumers are comparatively large single-or many-celled animals from the macroplank-ton.

Food for Aquatic Animals

The zooplankton that browse on diatomsbecome the food of the larval young of nearlyall species of fish, and of adult fish thatremain plankton feeders throughout life (e.g.,

minnows, anchovies, and menhaden). These in

turn, are food for large, carnivorous (flesh-

eating) fish and the whalebone (baleen) whales.Fish that have floating eggs must spawn

either on the feeding grounds for the youngor in places where the winds and water cur-rents will take the eggs to the feeding groundsby the end of the incubation period. The tiny,

newly hatched fish (less than 1/3 inch long)feed on small plankters and will perish unlessfood of appropriate size and variety is avail-able to them a few hours to a few days after

they hatch. As the young fish grow, they eat

proportionately larger forms of plankton.Mackerel are voracious feeders. They fre-

quently cram their stomachs until they becomedistended when certain types of plankton areabundant. The young eat chiefly immaturecopepods and ostracods, larvae of shrimp,crabs, and some small fish. At times duringsummer and fall, adult mackerel fill theirstomachs with Sagitta , an arrow- shaped worm,and mollusks known as pteropods, in localities

where these animals are plentiful. Duringspring in the North Atlantic, mackerel conn-monly eat large quantities of copepods of thegenus Calanus , which are known as "red feed"

because they are turned reddish-orange bystomach enzynnes. Fishermen report that pain-ful sores develop on their hands after handlingmackerel containing red feed, which is knownto them as "red pepper." The presence of this

food in the stomachs of mackerel causesrapid and extensive breakdown of the surround-ing flesh within 24 hours after the fish havebeen caught and packed in ice. Fishermenoccasionally experience heavy losses fromsuch spoilage.

The herring, one of the most abundant fish

in the world, occurs on both sides of the Atlan-tic and the Pacific Oceans, where it feedswhile young on small planktonic forms--dia-toms, Peridinium , Crustacea, larvae of worms,pelecypods (bivalve mollusks: e.g., oystersand clams), and gastropods (univalve n-iollusks:

e.g., snails). Among the crustaceans eaten byherring, the Calanus , red feed, has a verygreat influence on the economy of the herringindustry of the United States and Canada. In

these two countries small herring are cannedas sardines. When a catch of herring is to becanned, it must be inspected for red feed, andif Calanus was injested recently enough to bepresent in the alimentary tract, the fish mustbe held until both stomach and intestine arecleared of the red feed.

Menhaden are among the few fishes that

throughout life feed chiefly on diatoms andPeridiniuni (two of the most common plank-tonic forms). They also feed on the mostminute crustaceans.Many fishes prefer one or more groups of

plankters to the exclusion of others. Thestomachs of fish often contain only one or afew species, even when other organisms ofsimilar size are known to be in the particularlocality where the fish were feeding. Whalesthat feed on plankton also are selective. Theyroam the seas to locate massive bloonns oftheir favorite organisms. The reasons for thesefood preferences and the bases of selection(sight, taste, odor) are not fully understood.

Food for Man

The value of plankton as food for fish andother aquatic fauna has long been recognized,but the value of phytoplankton as a primarysource of food for man, and the tremendouspotential economic importance of its industrialculture, have only begun to be appreciated. Asthe human population grows, the need for addi-tional foods will increase. Even now, manypeoples of the world are underfed while anenormous aquatic resource remains undevel-oped and is wasted.

Large deposits of the remains of diatomslike the one at Lompoc, Calif., are mute evi-

dence that long ago greater quantities wereproduced annually than were consunned. Al-though excess production of other connponentsof the plankton has not been demonstrated so

dran-iatically, their numbers also surpass theneeds of their natural predators. Here inAmerica little consideration has been givento the possibility of using this surplus forhuman food. Fortunately we are capable ofproducing more land-grown foods than are re-quired to supply the needs of the presentpopulation.

In some European and Asian countries suchas Germany, England, Japan, China, and India,

however, scientists have given much seriousthought to the use of plankton for food. Asearly as 1939, the German State BiologicalInstitute of Helgoland was "investigating thepossibility of harvesting plankton of the sea asa new food source to make Germany moreindependent of foreign imports." The Insti-

tute found the nutritive value of zooplanktonequivalent to that of the best meats, and thenutritive value of phytoplankton equal to that of

rye flour. An English scientist, William A.Herdman, who became interested in the flavorof zooplankton, reported in 1891 that he hadeaten copepods boiled in butter; he liked thepreparation and stated that the flavor wassimilar to that of lobster. H. Tamiya, who hasdone extensive work in Japan on man's useof planktonic green algae, found that blanchedalgae are palatable and that man can convert30 to 50 percent of the algal material to his

bodily needs. During World War II, the UnitedStates made intensive studies of plankton asfood and recommended its use as food for

downed aviators or shipwrecked persons.Plankton nets were made part of survival kits.

An unprecedented increase in the world pop-ulation during the past century has causedscientists to estimate that by the year 2000J;he total will rise from the present 2.7 billion

to 7 billion people. Agriculture and knownnatural resources may be developed ade-quately to sustain a population of that size,

but segments of this horde no doubt will sxiffer

protein and fat deficiencies as they do evennow. Looking to the future, one can envisagea world with 50 billion or more people. Some-time during this tremendous expansion, a

critical worldwide food shortage is certainto occur. Then, or before- -depending uponcurrent technical knowledge--harvest or cul-

ture of phytoplankton must be undertaken to

ensure survival of the populace.Man is not likely to compete soon with fish

for the plankton of the sea. Collection of

plankton there is impractical now because thetiny creatures rarely are sufficiently con-centrated to support a commercial enterprise.On the west coast of Scotland, where the growthof plankton is particularly rich in the lochs andestuaries, a total of 525 pounds (dry weight)of plankton was procured with 10 nets hung

* The nets were necessarily of fine mesh cloth in orderto catch plankton but the exact size of mesh and dimen-sions of the net were not given in the article published.

The amount of water filtered was not measured.

collecting 12 hours each through a strongflood and ebb tide sequence. The planktontaken was considered sufficient to feed 357people a meal. It is not known whether equiva-lent amounts could be obtained anywhere alongthe American coast. Heavy concentrations of

plankton exist in polar regions, but harvestingthese would be hazardous owing to adverseweather and would entail the added expense of

transporting the catches long distances for usein the populous areas of the world, althoughthe bulk could be reduced to a minimum bydehydrating the catch aboard factory ships.

Cropping plankton on a large scale for humanfood might critically reduce the food supplyof fish, lobsters, clanns, whales, and otherfishery resources which now produce a world-wide annual yield of 45 to 60 n-iillion tons of

choice foods. Yet some authorities estimatethat only about 10 percent of the ocean'sannual production is now being used, that thepresent harvest could be increased from 1- 1/2to 10 times by the use of more effectual fish-

ing gear, and that production could be increasedeven more by cultivation and fertilization of thewater masses.Man scarcely can afford to jeopardize the

continuance and improvennent of this foodsupply from the seas, lakes, and rivers bycompeting directly with the aquatic aninnals fortheir food. He may, more wisely, supply hisgrowing needs by cultivating the planktonashore in automated factories establishednear markets, thus eliminating the problem of

collecting under adverse weather and seaconditions.

Phytoplankton can be cultured in vats wher-ever water and proper light, temperature, andnutrients are available, and the organisms canthen be floated off the nutrient into handycontainers. The single-celled alga, Chlorella ,

which has the capacity for rapid growth, is

particularly well suited to artificial culture.With suitable media and an appropriate ap-paratus, a bloom can be generated as often asnine times daily and these blooms can be re-peated indefinitely. When algal food for humanconsumption is produced under controlled con-ditions, yields will be high and crops can beharvested continuously by mechanical meansrequiring a minimum of hunnan labor. Culture ofalgae in the future may become a big business.

At present, great strides are being madetoward producing, in a closed ecological sys-tem with only a small amount of electricalenergy, sufficient algae to satisfy the foodrequirements of one man in space travel andto convert his wastes into nutrients for thealgae.

Purification of Water Supplies

The health of the people in a community isinfluenced by the purity of the water theydrink; moderate numbers of algae help purify

lake and stream waters. Algae use as nutrientsnitrogen and phosphorus compounds that havebeen washed frona the land, and convert into

oxygen the carbon dioxide dissolved in thewater from the atmosphere and from the decayof submerged organic matter. Blooming plank-ton, because they feed on the inorganic solutes,actually change the chemical composition of

the water. Nitrogen and phosphorus connpoundsnormally are not abundant in most surfacewaters, and a real scarcity of either compoundslows the growth of algae, thus graduallydiminishing their value for purification as theseason progresses.

Excessive enrichment (pollution) of watersupplies, and consequent blooms of algae, hasemerged as a major problem in the purifica-tion of water for human consumption in recenttimes. The rate of removal of nutrient mate-rials by biological means is dependent uponthe kind of planktonic organisms present andupon the environnnental conditions; conse-quently, the actual performances have beenerratic and unpredictable. Light intensity is

one of the critical factors. The minimumrequirement to produce rapid biological ex-traction of phosphate appears to be about 100to 200 foot-candles. Under normal conditionsadequate light intensities seldom are attainedin algal cultures in excess of a foot below thesurface; if the water is deeper than that, theillumination decreases sharply . For thesereasons, in the treatment of wastes fronn urbanareas the purest water and the greatest returnof nutrients are obtained in industrial plantswhere the best environmental conditions for thealgae and the most active species can be main-tained.

High fertility of the water need not neces-sarily generate noxious blooms. On the Eni-wetok coral reefs, where community produc-tion was well balanced, E. P. Odum wasimpressed not only by the importance ofwater movement, but by the intimate asso-ciation of algae with the corals and with manyother animals. This association was a highlydeveloped symbiosis (living together) of or-ganisms, some (i.e., green plants, some bac-teria, and true fungi) able to feed on simpleinorganic substances and others (i.e., animals,some bacteria, and true fungi) dependent oncomplex organic food materials which haveoriginated in other plants and animals. In this

environment lived, in addition, a large standingcrop of consumers including great numbersof herbivorous fish, which, Odum believed,"were capable of consuming algae as fast asproduced." This is an ideal situation with nooutside pollution that could not be duplicatedin the effluent from a modern city.

Odum suggested that man "get into the foodchain" at the primary level not only to alle-

viate his crying need for additional foods but,

at the same time, to, "make use of the in-

creased productivity created by cities rather

10

than attempting to destroy it." Man, then, wouldbe an important factor in the purification ofhis own drinking water. Appropriate plank-tonic organisms would consume objectionableinorganic solutes in the water, use them in themanufacture of proteins, and then be eaten byman. The purified water could also be con-sunned safely by man.

Industrial Uses

The importance of planktonic organisms to

mankind does not end with their death. Theshells of certain groups of these organismshave sunk to the bottom of the sea for millionsof years. In some localities, these shellsbecame fossilized and were eventually raisedabove the surface of the water by movementsof the earth's crust. The uses made of someof these materials are essential to our modernway of life.

Diatoms- -diatomaceous earth .- -Deposits offossil diatoms, called diatomaceous earth,have nnany industrial uses. The oldest use is

as a powder for polishing metals and cleaningkitchen utensils. Because of its porosity,diatomaceous earth is used as an absorbentfor nitroglycerine in the manufacture of dyna-mite, and as a filter for liquids, especially inthe refining of sugar and in the manufactureof rubber. Diatomaceous earth is also usedto insulate blast furnaces and to strengthenconcrete.

Foraminifera--chalk and limestone . --An-other well-known commodity that owes its

origin to the plankton of ancient seas is thechalk so widely used by teachers and students.Huge chalk deposits, formed by shells of deadForaminifera (especially Globigerina and its

allies), are the famous Cliffs of Dover, Eng-land; Fort Hayes Chalk in Kansas; NiobraraChalk in Nebraska; and other deposits in Ala-bama, Mississippi, and Tennessee.

The shells of Foraminifera also contributedmuch to the formation of calcareous rock orlimestone. Limestone has many commercialuses, including the making of the most impor-tant building materials of our time- -directlyas stone blocks and marble, and indirectly in

steel, cement, and plaster. It is also used in

building roads and for reducing the acidity ofsoils in agriculture.

The Foraminifera that contribute to the for-mation of limestone are strange little one-celled animals that secrete calcareous shellsaround tnemselves. As they grow larger, theybuild and move into progressively larger cham-bers which usually are arranged in a spiral.The name Foraminifera, from the Latin fora-men (a hole) and fero (to bear), was given theorganism because the shells are perforated

by a large number of small holes throughwhich are extended slender strands of proto-plasm called pseudopodia. Outside the shell,these protoplasmic strands branch and inter-weave to form a living network which resem-bles a spider's web but operates very differ-ently; it is both the spider and the web. Whena victim is caught in this sticky web thestrands of the net pour out digestive juicesthat convert the prey into a solution or emul-sion which passes into the protoplasnn of theforaminiferan.

Not all Foraminifera have been tiny. TheCamerina . which reached its peak of abundancein rather recent geologic time but is now ex-tinct, attained a diameter of 7-1/2 inches. Its

shells formed limestone in Europe, Asia, andnorthern Africa.

All plankton--petroleum .-- The origin of pe-troleum (rock oil) is still a mystery to au-thorities in geology, chemistry, and astronomywho have spent many years studying it. Twoopposing theories have been advanced: (1) that

the oil was formed from inorganic substancesduring volcanic action and later seeped into

sedimentary rocks, and (2) that it was formedfrom organic substances leached from decay-ing plants and animals. The latter theory wasadvanced first and is still held by mostscientists. If this is the true origin of oil,

then microscopic algae may have been animportant, if not the most important, sourceof petroleum in sedinnents from paleozoic to

tertiary time. Tne shells of radiolarians,foraminifers, and diatoms are present in sedi-ments closely associated with oil.

Petroleum is of prime importance in theworld today. A tremendous variety of impor-tant products are derived from crude petro-leum, many of which are essential for develop-ment of the activities of modern civilization.

Natural gas, gasoline, diesel oil, fuel oil, andlubricating oils and greases are used to heatbuildings in cold climates, to provide heat forcooking, and to power and lubricate highspeedmotors that nnake possible modern rapidtransportation on land and sea, and in the air.

They also supply heat and power for the opera-tion of most industries. Other important prod-ucts are: asphalt to build smooth roads;synthetic rubber to provide tires for automo-biles that travel these roads; antifreeze prep-arations to protect the cooling systems of thecars in freezing weather; soaps and antisep-tics for sanitation and cleanliness; paints,paint driers, a turpentine substitute; auto,

furniture, and metal oolishes to protect sur-faces and enhance beauty; inks for writing;and fertilizers to improve yields of foodcrops. In addition there are medicines, ex-plosives, solvents, acids, carbon bricks, andmany other products too nunrierous to mentionhere.

11

Aid to Science

Geologists have spent much time attemptingto learn the age of the world and to date eventsthat have led to the development of the presentland naasses. Some recent advances in this

knowledge depended on determination of theage of fossil shells of planktonic organismsby the radiocarbon technique. This methodmeasures the amount of radiocarbon remain-ing in a sample of the shells. Studies of fossildiatoms in deposits such as the one at Lompoc,Calif., have yielded much valuable information.A complete time scale, determined by radio-

carbon study of cores bored from deep-seasediments, dates the beginning of the ice ageat about 1-1/2 million years ago. Well-definedchanges in the abundance of the shells of cer-tain species of Foraminifera in cores fronnthe equatorial Atlantic and around the worldgive a legible record of major climatic eventsduring the ice age.

Intensive oceanographic studies now beingorganized cooperatively by many nations andthe international expeditions of recent years^are expected to add much new information aboutthe sea and its inhabitants. No doubt, newuses for plankton will be developed as aresult of this greater knowledge.

LUMINESCENCE

A boat ride after dark at sea is pure delightwhen the bow wave and the wake behind the boatsparkle with tiny points of light known asluminescence. If the boat happens to be small,reach into the water; your hand will come outwith some of the points of light clinging to it.

Rub your hands gently together and feel smallprickles. Put the bits of light into a drop ofwater under a nnicroscope, and the wonderfulworld of dinoflagellates comes to life for you.Think then, as many others have done, howlight is produced by these small creatures.The chemical nature of their photogenic cellswas still unknown as recently as 1962. Thedinoflagellates, minute animals or plants (ex-perts disagree), are characterized by thepresence of two flagella in grooves (seePeridinium and Ceratium , fig. 1). Usually thebody is covered by a cellulose shell. Many ofthese strange little creatures possess photo-synthetic pigment but cannot exist withoutorganic food; they are able to survive indefi-nitely without light if all required food ele-ments are present.

The most common luminescent flagellate is

Noctiluca scintillans , which is 12 percent drynnatter in the form of granules that are be-lieved to be the source of luminescence upon

Examples are the International Indian Ocean Expedition

and the International Cooperative Investigations of the

Tropical Atlantic.

mechanical or chemical stimulation. A numberof other dinoflagellates-

-

Gymnodinium , Cera-tium, and Gonyaulax - -also emit light in re-sponse to similar stimuli. These luminescentflagellates are widely distributed in saltwater.

HARMFUL EFFECTS OF PLANKTON

Waters that receive domestic and industrialwastes containing large amounts of nitrogenand phosphorus compounds often nourish heavygrowths of algae. The algae may interfere at

such times in manufacturing processes andin the operation of city water plants by clog-ging filters, and also may decrease recrea-tional and esthetic values of shore propertyby producing unsightly accumulations in thewater at bathing beaches and boating areas.Although algae use carbon dioxide and produceoxygen in photosynthesis during their shortlife span, the decay of large concentrations of

their dead cells frequently depletes the oxygenin the water. Massive fish-kills may result.

The decay of algal masses occasionally givesdisagreeable tastes and odors to city watersupplies and sometimes releases sufficient

hydrogen sulfide into the air to discolor painton boats and on nearby houses.Some species of algae produce toxins in-

jurious or fatal to animals. One of these,Gonyaulax catenalla, when eaten by sea mus-sels and clams, produces an alkaloid substancethat is harmless to the bivalves but is poison-ous to the people who eat them. Many casesof illness and some deaths have been reportedfrom this so-called mussel-poisoning.

REFERENCES

ABRAMOVA, V. D,1956. Plankton as an indicator of waters of

different origin in the North Atlanticseas, Tr. Polyarn. Nauch.-issled. Inst.

Morsk. Rybn. Khoz. i Okeanogr., No.9:69-92. In Russian. Transl. avail, in

U.S. Fish. Wildl. Serv., Spec. Sci. Rep.Fish. 327: 77-103.

ALFIMOV, N. N., and O. G. MIRONOV.1958. The effect of diatomaceous plankton

of rivers on certain chemical indicesof water contamination. Bot. Zhur. 43-

(12): 1763-1765.AL'TOVSKII, M. E., Z. I. KUZNETSOVA, and

V. M, SHVETS.1961 . Origin of oil and oil deposits. Russian

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12

BIGELOW, HENRY B.1924. Plankton of the offshore waters of the

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40(2), 1027 p.BROWN, HARRISON.

1958. The challenge of man's future. TheViking Press, New York, xii + 290 p.

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DEEVEY, EDWARD S., Jr.1952. Radio-carbon dating. Sci. Amer. 186-

(2): 24-28.GALTSOFF, PAUL S.

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1948. Catastrophic mass mortality of ma-rine animals and coincident phytoplank-ton bloom on the west coast of Florida,November 1946 to August 1947. Ecol.Monogr. 18(3): 309-324.

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ture 44(1 134): 273-274.HUTTON, ROBERT F.

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STANSBY, MAURICE E., and JAMES M.LEMON.

1941. Studies on the handling of fresh nnac-kerel (Scomber scombrus ). U.S. FishWildl. Serv., Res. Rep. 1, 46 p.

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